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  • 1990-1994  (1,600)
  • 1925-1929
  • 1993  (1,600)
  • Analytical Chemistry and Spectroscopy  (1,600)
  • 1
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
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    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 7 (1993), S. 243-253 
    ISSN: 0886-9383
    Keywords: Orthogonal expansion ; Mapping ; Modelling ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this paper we discuss the orthogonal expansion of data matrices and its application to mapping and modelling. Two new methods, modified optimal discriminant plane (MODP) for mapping and order Gram-Schmidt orthogonalization (OGSO) for modelling, are proposed and examples are given.
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  • 3
    Electronic Resource
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    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 7 (1993) 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 4
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    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 7 (1993), S. 381-392 
    ISSN: 0886-9383
    Keywords: Factor analysis ; Kolmogorov-Smirnov test ; Non-parametric tests in factor analysis ; Non-parametric test for principal components ; Principal component analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Each eigenvector of the dispersion matrix [X]T [X] was shown to be a partial predictor of the original data matrix [X], the sum of the predictions from the individual principal components being equal to the expectance of [X]. By comparing the distributions of the members of two neighbouring predicted matrices, [X̃]1…i and [X̃]1…i+1 (i.e. the sums of the first i and i + 1 individual predictions respectively), it was shown that they should be indistinguishable provided that i is equal to or greater than the effective rank of [X], and significantly different otherwise. This was confirmed by analysing the visible absorption spectra of methyl orange and methyl red solutions as well as the Raman spectra of Na2SO4 and MgSO4 solutions. On the grounds of these findings, a non-parametric goodness-of-fit test for assessing the effective rank of [X] was proposed which proved to be comparatively conservative and more robust than most currently used tests.
    Additional Material: 6 Ill.
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  • 5
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    Journal of Chemometrics 7 (1993), S. 447-452 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
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  • 6
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    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 7 (1993), S. 477-494 
    ISSN: 0886-9383
    Keywords: Three-way principal components analysis ; Core matrix ; Body diagonalization ; Lower and upper bounds ; Simulation ; Soil contamination ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In contrast with conventional PCA, a direct superposition and joint interpretation of loading plots is not possible in three-way PCA, since there may be data variance which is described by unequal components of different modes. The contributions to variance of all possible combinations of components are described in the core matrix. Body diagonalization, which is achieved by appropriate rotation of component matrices, is an essential tool for simplifying the core matrix structure. The maximum degree of body diagonality which may be obtained from such transformations is analysed from both the mathematical and simulation viewpoints. It is shown that, at least in the average case, high degrees can be expected, which makes the procedure reasonable for many practical applications. Furthermore, simulation as well as theoretical derivation show that the success of body diagonality depends on the so-called polarity of the core array. The methodology is illustrated by a three-way data example from environmental chemistry.
    Additional Material: 4 Ill.
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  • 7
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    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 7 (1993) 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 8
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    Journal of Chemometrics 7 (1993), S. 495-526 
    ISSN: 0886-9383
    Keywords: Standard errors ; Eigenvalues ; PCA ; MLR ; GRAM ; Rank estimation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New expressions are derived for the standard errors in the eigenvalues of a cross-product matrix by the method of error propagation. Cross-product matrices frequently arise in multivariate data analysis, especially in principal component analysis (PCA). The derived standard errors account for the variability in the data as a result of measurement noise and are therefore essentially different from the standard errors developed in multivariate statistics. Those standard errors were derived in order to account for the finite number of observations on a fixed number of variables, the so-called sampling error. They can be used for making inferences about the population eigenvalues. Making inferences about the population eigenvalues is often not the purposes of PCA in physical sciences. This is particularly true if the measurements are performed on an analytical instrument that produces two-dimensional arrays for one chemical sample: the rows and columns of such a data matrix cannot be identified with observations on variables at all. However, PCA can still be used as a general data reduction technique, but now the effect of measurement noise on the standard errors in the eigenvalues has to be considered. The consequences for significance testing of the eigenvalues as well as the usefulness for error estimates for scores and loadings of PCA, multiple linear regression (MLR) and the generalized rank annihilation method (GRAM) are discussed. The adequacy of the derived expressions is tested by Monte Carlo simulations.
    Additional Material: 8 Ill.
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  • 9
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    Journal of Chemometrics 7 (1993), S. 559-566 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
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  • 10
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    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 7 (1993) 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 11
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    Journal of Chemometrics 7 (1993), S. 61-73 
    ISSN: 0886-9383
    Keywords: Compression ; Multivariate analysis ; B-splines ; Maximum entropy ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: For efficient handling of very large data arrays, pretreatment by compression is mandatory. In the present paper B-spline methods are described as good candidates for such data array compression. The mathematical relation between the maximum entropy method for compression of data tables and the B-spline of zeroth degree is described together with the generalization of B-spline compression to nth-order data array tables in matrix and tensor algebra.
    Additional Material: 7 Ill.
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  • 12
    ISSN: 0886-9383
    Keywords: Factor analysis ; Window factor analysis ; Multicomponent analysis ; Ultraviolet spectroscopy ; Cu(II) complexes ; Ethylenediaminetetraacetic acid ; EDTA ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Window factor analysis (WFA) is a self-modeling chemometric technique for obtaining the concentration profiles of components from evolutionary processes such as chromotography, titration and reaction kinetics. By specifying the ‘window’, i.e. the region along the evolutionary axis indigenous to a component, the concentration profile of the component can be obtained without recourse to any information concerning the other components. Mathematical expressions required to perform such computations are derived. The method is applied to the investigation of copper(II) complexation with ethylenediaminetetraacetate (EDTA) by recording and factor analyzing the ultraviolet spectra of aqueous solutions containing a fixed amount of the disodium salt of EDTA and varying amounts of CuCl2. Evidence for four different species of EDTA is obtained. Clues concerning the stoichiometry of the species are garnered from the concentration profiles.
    Additional Material: 5 Ill.
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  • 13
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    Journal of Chemometrics 7 (1993), S. 131-142 
    ISSN: 0886-9383
    Keywords: Classification ; Discriminant analysis ; Class modeling ; Specification limits ; Cross-validation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: There are many chemical products where product conformity is decided upon by qualitative human judgements of overall product quality. Nowadays, quantitative instrumentally determined quality parameters become available which are intended to replace such qualitative judgements by means of automatic decision rules using multivariate specification limits. Six classification methods to derive such limits are compared in terms of their power to predict corresponding human judgemets on overall color conformity of 17 dyestuffs based on historical quality data. Standard statistical classification methods turned out to be unacceptable for the routine generation of decision rules because of the frequent distinct suboptimality of their predictive power. Instead, a simple non-statistical classification method utilizing a priori knowledge about the underlying data structure yielded uniformly satisfactory decision rules.
    Additional Material: 2 Ill.
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  • 14
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    Journal of Chemometrics 7 (1993), S. 153-163 
    ISSN: 0886-9383
    Keywords: Generalized inverse ; K-matrix analysis ; P-matrix analysis ; Least squares ; Principal component regression ; Partial least squares ; Continuum regression ; Beer's law ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This paper consists of two distinct but related parts. In the first part a geometric theory of generalized inverses is presented and a methodology based on this theory is developed and applied to solve the K-matrix and P-matrix forms of Beer's law. It is shown that most currently accepted and practiced methods for solving these forms of Beer's law are just special cases of this geometric theory of generalized inverses. In addition, this geometric theory is used to explain why the current methods work and why they fail.In the second part a general methodology that includes as special cases least squares, principal component regression, partial least squares 1 and 2, continuum regression plus a variety of other described and undescribed methodologies is presented and then applied to solve the P-matrix formulation of Beer's law. This general methodology, like the first, is also geometric in nature and relies on an understanding of projections.The main emphasis of this paper is one of perspective, which, if understood, provides the proper foundation for answering the general but extremely hard and possibly unanswerable question “what is the best method?”.
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  • 15
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    Journal of Chemometrics 7 (1993), S. 195-212 
    ISSN: 0886-9383
    Keywords: Calibration ; Non-linearity ; Principal components ; Stein estimate ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new regression method for non-linear near-infrared spectroscopic data is proposed. The technique is based on a model which is linear in the principal components and simple functions (squares and products) of them. Added variable plots are used to determine which squares and products to incorporate into the model. The regression coefficients are estimated by a Stein estimate which shrinks towards the estimate determined by the first several principal components and the selected non-linear terms. The technique is not computationally intensive and is appropriate for routine predictions of chemical concentrations. The method is tested on three data sets and in all cases gives more accurate predictions than does linear principal components regression.
    Additional Material: 8 Ill.
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  • 16
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    Journal of Chemometrics 7 (1993), S. 227-242 
    ISSN: 0886-9383
    Keywords: Non-linear mapping ; Graphical methods ; SAR ; SPR ; Quality of representation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: From a review of the theoretical aspects of non-linear mapping and the different algorithms available in the literature, the methodological and practical problems linked to the use of this multivariate method in structure-activity and structure-property relationship studies are underlined. Useful tools for the graphical display of the outputs and the interpretation of the obtained clusters are presented. Statistical parameters estimating the quality of the graphical representation of each individual are also introduced. An example of application on a data matrix of 37 acaricides described by four physicochemical descriptors (π, F, R, MR) is presented.
    Additional Material: 11 Ill.
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  • 17
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    Journal of Chemometrics 7 (1993), S. 291-304 
    ISSN: 0886-9383
    Keywords: Partial least squares ; Monte Carlo methods ; Cross validation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Partial least squares (PLS) regression is a commonly used statistical technique for performing multivariate calibration, especially in situations where there are more variables than samples. Choosing the number of factors to include in a model is a decision that all users of PLS must make, but is complicated by the large number of empirical tests available. In most instances predictive ability is the most desired property of a PLS model and so interest has centred on making this choice based on an internal validation process. A popular approach is the calculation of a cross-validated r2 to gauge how much variance in the dependent variable can be explained from leave-one-out predictions. Using Monte Carlo simulations for different sizes of data set, the influence of chance effects on the cross-validation process is investigated. The results are presented as tables of critical values which are compared against the values of cross-validated r2 obtained from the user's own data set. This gives a formal test for predictive ability of a PLS model with a given number of dimensions.
    Additional Material: 5 Ill.
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  • 18
    ISSN: 0886-9383
    Keywords: Reaction kinetics ; Initial rate ; Kinetic order ; Response surface modelling ; Canonical analysis ; Organic synthesis ; Optimization ; Reaction mechanisms ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method is presented by which it is possible to estimate the initial rate of chemical reactions when the experimental conditions are varied according to a response surface design. The method is intended as a complementary method for analysing data obtained from experiments in synthetic chemistry when the objective is to optimize the yield of the reaction.Data obtained by simulations have been used to develop the method. From the simulated reactions it is shown that sequential analysis of the chemical yield of the reaction makes it possible to estimate models which describe how the parameters of the response surface of the yield vary over time. The derivatives of these time functions of the response surface parameters can be used to define a rate function which describes how the variations in the experimental conditions influence the rate of the reaction.It is shown how such rate functions can be used to afford reasonable estimates of the initial rates of the reaction. The initial reaction rates thus estimated can be used to determine the kinetic order of the reactants and also to provide estimates of the activation energy of the reaction.A thorough discussion of how canonical analysis of the rate function may assist in the elucidation of reaction mechanisms is given.
    Additional Material: 4 Ill.
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  • 19
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    Journal of Chemometrics 7 (1993), S. 427-438 
    ISSN: 0886-9383
    Keywords: Quality control ; Kerosene ; Variable reduction ; Cross-validation ; Variable selection ; Procrustes rotation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This paper deals with a typical question encountered in all industrial analytical laboratories: are all the tests performed in the laboratory to characterize the final product really necessary? In this work the cross-validation technique, Procrustes rotation techniques and statistical variable selection have been used to reduce the 26 initial British Petroleum and ASTM kerosene specification test to ten ‘essential’ ones. Statistical as well as chemical considerations were used to select the optimum subset of original variables to be retained from all the possible ones.
    Additional Material: 3 Ill.
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  • 20
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    Journal of Chemometrics 7 (1993), S. 453-454 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 21
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    Journal of Chemometrics 7 (1993), S. 527-541 
    ISSN: 0886-9383
    Keywords: Principal component analysis ; Projection pursuit ; Simulated annealing algorithm ; Robust statistics ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Principal component analysis (PCA) is a widely used technique in chemometrics. The classical PCA method is, unfortunately, non-robust, since the variance is adopted as the objective function. In this paper, projection pursuit (PP) is used to carry out PCA with a criterion which is more robust than the variance. In addition, the generalized simulated annealing (GSA) algorithm is introduced as an optimization procedure in the process of PP calculation to guarantee the global optimum. The results for simulated data sets show that PCA via PP is resistant to the deviation of the error distribution from the normal one. The method is especially recommended for use in cases with possible outlier(s) existing in the data.
    Additional Material: 7 Ill.
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  • 22
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    Journal of Chemometrics 7 (1993), S. 45-59 
    ISSN: 0886-9383
    Keywords: Partial least squares ; PLS algorithm ; Kernel ; Multivariate image analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A fast and memory-saving PLS regression algorithm for matrices with large numbers of objects is presented. It is called the kernel algorithm for PLS. Long (meaning having many objects, N) matrices X (N × K) and Y (N × M) are condensed into a small (K × K) square ‘kernel’ matrix XTYYTX of size equal to the number of X-variables. Using this kernel matrix XTYYTX together with the small covariance matrices XTX (K × K), XTY (K × M) and YTY (M × M), it is possible to estimate all necessary parameters for a complete PLS regression solution with some statistical diagnostics. The new developments are presented in equation form. A comparison of consumed floating point operations is given for the kernel and the classical PLS algorithm. As appendices, a condensed matrix algebra version of the kernel algorithm is given together with the MATLAB code.
    Additional Material: 6 Ill.
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  • 23
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    Journal of Chemometrics 7 (1993), S. 77-88 
    ISSN: 0886-9383
    Keywords: Direct trilinear decomposition method ; Curve resolution ; Trilinear data ; Similarity transformation ; Generalized rank annihilation method ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The direct trilinear decomposition method (DTDM) is an algorithm for performing quantitative curve resolution of three-dimensional data that follow the so-called trilinear model, e.g. chromatography-spectroscopy or emission-excitation fluorescence. Under certain coditions complex eigenvalues and eigenvectors emerge when the generalized eigenproblem is solved in DTDM. Previous publications never treated those cases. In this paper we show how similarity transformations can be used to eliminate the imaginary part of the complex eigenvalues and eigenvectors, thereby increasing the usefulness of DTDM in practical applications. The similarity transformation technique was first used by our laboratory to solve the similar problem in the generalized rank annihilation method (GRAM). Because unique elution profiles and spectra can be derived by using data matrices from three or more samples simultaneously, DTDM with similarity transformations is more efficient than GRAM in the case where there are many samples to be investigated.
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  • 24
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    Journal of Chemometrics 7 (1993), S. 143-148 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
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  • 25
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    Journal of Chemometrics 7 (1993), S. 151-151 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 26
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    Journal of Chemometrics 7 (1993), S. 213-222 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
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  • 27
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 28
    ISSN: 0886-9383
    Keywords: Kalman filter ; Multivariate calibration ; Condition number ; Prediction error ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The usefulness of the Kalman filter as an algorithm for calibration in a real system is shown. Results are compared with classical least squares and pure component calibration. The prediction of four priority pollutant chlorophenols in binary, ternary and quaternary mixtures was also carried out by Kalman filtering. The condition number, standard deviation and prediction error have been employed to choose the most suitable wavelength range. Comparison of the standard error of prediction in the validation set shows significant differences between the evaluated chlorophenols, the best results being obtained with Kalman multivariate calibration.
    Additional Material: 1 Ill.
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  • 29
    ISSN: 0886-9383
    Keywords: Multicomponent analysis ; Factor analysis ; Detection limit ; Local rank ; Zero-component region ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this paper we redefine the term detection limit to embrace the inherent multivariate nature of samples, instrumental measurements and chemometrics resolution procedures. The so-called zero-component regions, i.e. parts with no chemical components eluting, are used as repeated analytical blanks to estimate a statistical multivariate detection limit for determining the number of chemical species in local regions of a single two-way chromatogram or a collection of synchronized one-way chromatograms. For two-way chromatography the detection limit is determined from the distribution of the first eigenvalues obtained from all possible combinations of spectra in the zero-component regions. The number of spectra in each calculation should correspond to the number included in the later examination of the local retention time regions. For one-way chromatography on a collection of samples with similar chemical components at varying concentrations the same procedure is used, with the samples taking the role of the spectra in two-way chromatography. The detection limit can be chosen at various confidence levels depending on whether false positive or negative detection of minor components is most critical. The results obtained from the zero-eigenvalue distribution are more robust than those obtained by a previously developed F-test.
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  • 30
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    Journal of Chemometrics 7 (1993), S. 369-379 
    ISSN: 0886-9383
    Keywords: Simulated annealing ; Constrained background bilinearization ; Calibration ; Two-way bilinear data ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Generalized simulated annealing (GSA) is an optimization technique for locating the global optimum. In this paper GSA was used as the optimization procedure in the constrained background bilinearization (CBBL) of two-way bilinear data in order to reduce the possibility of sinking into local optima. The behaviour of the algorithm and its comparison with the modified Powell algorithm were studied by simulations and real fluorescence excitation-emission data for organic dye mixtures.
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  • 31
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    Journal of Chemometrics 7 (1993), S. 1-14 
    ISSN: 0886-9383
    Keywords: Continuum regression ; Dynamic model identification ; Principal component regression ; Partial least squares regression ; Finite impulse response ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The use of continuum regression (CR) for the identification of finite impulse response (FIR) dynamic models is investigated. CR encompasses the methods of principal component regression (PCR), partial least squares (PLS) and multiple linear regression (MLR). PCR and MLR are at the two extremes of the continuum. In PCR and PLS, cross-validation is used to determine the optimum number of factors or ‘latent variables’ to retain in the regression model. CR allows one to vary the method in addition. Cross-validation then determines both the optimum method and the number of latent variables. The CR ‘prediction error surface’ - a function of the method and number of latent variables - is elucidated. The optimal model is defined as the minimum of this surface. Among the cases studied, the optimal model usually comes from the region of the continuum between PCR and PLS. Few derive from the region between PLS and MLR. It is also demonstrated that FIR models identified by CR have frequency domain properties similar to those identified by PCR.
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  • 32
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    Journal of Chemometrics 7 (1993) 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 33
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    Journal of Chemometrics 7 (1993), S. 75-76 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 34
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    Journal of Chemometrics 7 (1993), S. 117-130 
    ISSN: 0886-9383
    Keywords: Calibration ; Rank annihilation ; Three-way ; Trilinear ; Bilinear ; Non-bilinear ; Net analyte signal ; MS/MS ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several multivariate methods are now available for the calibration of second-order or hyphenated instruments (e.g. GC/MS). When applied to bilinear data, it has been shown that calibration can be performed in the presence of unknown interferences - a significant advantage over first-order calibration. In this paper, non-bilinear rank annihilation (NBRA), a method which has the potential of handling, second-order non-bi-linear data, is studied through theoretical analysis and computer simulation. It is found that the second-order advantage can be carried over to non-bilinear data if a property defined as net analyte rank (NAR) holds for the analyte of interest. The net analyte signal (NAS) is defined accordingly for second-order calibration and the analogy to and difference from lower-order calibration are discussed. With NAS, some analytical figures of merit such as signal-to noise ratio, selectivity, sensitivity and limit of determination can be calculated for second order calibration. An application to MS/MS data is also given.
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  • 35
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    Journal of Chemometrics 7 (1993) 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 36
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    Journal of Chemometrics 7 (1993), S. 177-193 
    ISSN: 0886-9383
    Keywords: Multivariate analysis ; Function space ; Coefficient space ; B-splines ; Compression ; PCA ; PLS ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A general framework for manipulating spectra as functions in traditional multivariate methods such as PCA and PLS is described. The functional representation is very convenient for compression, ensuring smoothness and continuity. There are two fundamentally different types of representations: (a) by functions and (b) by function coefficients. The use of coefficients is the most practical way of analysis.
    Additional Material: 9 Ill.
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  • 37
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    Journal of Chemometrics 7 (1993) 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 38
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    Journal of Chemometrics 7 (1993), S. 255-265 
    ISSN: 0886-9383
    Keywords: Multicomponent calibration ; Non-linearity ; Selectivity ; Wavelength selection ; Graphical diagnostics ; Outliers ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Modern scanning infrared reflectance/absorption spectroscopes measure absorptions or reflectance at a sequence of around 1000 wavelengths. Training data may consist of 10-100 carefully designed sample mixtures whose true compositions are either known by formulation or accurately determined by wet chemistry. In future, one wishes to predict the true composition of a newly presented sample from its spectrum. Varying compositions of a mixture of three sugars in water are used for illustration of several different graphical techniques; the spectral measurements here are near-infrared (NIR) absorbances, but there is nothing exclusively infrared about the methodology. Graphs display the adequacy of a linear explanation of absorbance variability at each wavelength by wavelength linearity plots. These highlight regions of the spectrum where non-linearities and interaction effects are substantial. By selecting out these substantially non-linear regions, one can concentrate on linear formulae for prediction with resultant robust linear modelling. Such selections are further aided by plots which identify the component sugar for which each wavelength is most selective. Such plots offer rather natural pre-screening as an alternative or supplement to the wavelength selection method of Brown.We also display prediction diagnostics (R, Rx) which on a sample-by-sample basis may diagnose a particularly unusual presented spectrum. These diagnostics are shown to have predictive import for a validation data set.
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  • 39
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    Journal of Chemometrics 7 (1993), S. 439-445 
    ISSN: 0886-9383
    Keywords: Calibration ; Rank annihilation ; Residual bilinearization ; Three-way ; Trilinear ; Net analyte rank ; Second-order ; Generalized rank annihilation method (GRAM) ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Through theoretical analysis and computer simulation, this short communication comments on the residual bilinearization (RBL) method and compares it with non-bilinear rank annihilation (NBRA) for the treatment of second-order calibration with non-bilinear data. It is found that these two methods are mathematically equivalent but have different noise propagation properties. The second-order advantage, namely quantitation in the presence of unknown interferences, can be carried over to non-bilinear data only if there exists a net analyte rank (NAR) for the analyte of interest.
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  • 40
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    Journal of Chemometrics 7 (1993), S. 455-475 
    ISSN: 0886-9383
    Keywords: Biological activity ; Cross-validation ; Exchangeability ; Molecular descriptors ; Prediction ; Relationship ; Structure ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The two parts of this paper form a critique of a variety of statistical techniques of actual or potential use in quantitative structure-activity relationship (QSAR) studies and related fields. Part I explores the statistical thinking that is needed to underpin those techniques. Emphasis as placed on (a) the role of ‘exchangeability’ as an alternative to unrealistic statistical modelling and (b) the use of cross-validation to limit self-deception in the use of any particular technique. The problem of the almost unlimited range of molecular descriptors is seriously addressed. (Part II provides a concise critical review of methods-some well-established and some new.)
    Additional Material: 4 Ill.
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  • 41
    ISSN: 0886-9383
    Keywords: Curve resolution ; Multicomponent analysis ; Latent projections ; Local factor analysis ; Chlorophyll degradation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: High-performance liquid chromatography with diode array detection (HPLC--DAD) is used to characterize mixtures from chlorophyll a degradation experiments. Overlapping chromatographic peaks are resolved by means of the heuristic evolving latent projections (HELP) method. The HELP method is a self-modelling curve resolution method. No assumptions are made about spectral and/or chromatographic peak shape. In the first step the method establishes the real noise level in the data by use of the so-called zero-component regions. This information is used to reveal selective chromatographic information and the number of chemical species at every retention time in unresolved chromatographic peaks. Utilising the selective chromatographic regions in combination with the zero-concentration windows, unique resolution into concentration profiles and spectra of the pure chemical species is accomplished. HPLC-DAD data from six chlorophyll a degradation experiments were analysed. Consistent results were obtained even with very similar spectra for six or seven overlapping chemical components.
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  • 42
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    Journal of Chemometrics 7 (1993), S. 99-115 
    ISSN: 0886-9383
    Keywords: Classification ; Appreciation function ; Regularized discriminant analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Regularized discriminant analysis has proven to be a most effective classifier for problems where traditional classifiers fail because of a lack of sufficient training samples, as is often the case in highdimensional settings. However, it has been shown that the model selection procedure of regularized discriminant analysis, determining the degree of regularization, has some deficiencies associated with it. We propose a modified model selection procedure base on a new appreciation function. By means of an extensive simulation it was shown that the new model selection procedure performs better than the original one. We also propose that one of the control parameters of regularized discriminant analysis be allowed to take on negative values. This extension leads to an improved performance in certain situations. The results are confirmed using two chemical data sets.
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  • 43
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    Journal of Chemometrics 7 (1993), S. 149-150 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 44
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    Journal of Chemometrics 7 (1993), S. 165-176 
    ISSN: 0886-9383
    Keywords: Measurement error ; Outliers ; Environmental ; Quality control ; Multivariate kurtosis ; Generalized distance ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Environmental data are usually multivariate, with the variables conforming to some correlation structure. Occasionally, measurements which do not conform in structure or magnitude may occur in one or more variables. It is important (1) to characterize these discordancies in terms of the disturbed variables and the direction and magnitude of the anomalous error and (2) to associate each discordant observation with a specific cause of measurement error in order to prevent further mismeasurement. We describe a procedure for identifying suspected causes of discordant observations in otherwise multinormal data sets. Variables are assigned to groups, each of which is associated with a specific cause of measurement error. Discordant observations are identified with the generalized distance test or the multivariate kurtosis test. Suspected causes of measurement error are identified by repeating the tests with one of the groups of variables omitted in each analysis. The procedures are evaluated with simulated data sets having a correlation structure similar to that of a large environmental data set.
    Additional Material: 4 Ill.
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  • 45
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    Journal of Chemometrics 7 (1993), S. 305-340 
    ISSN: 0886-9383
    Keywords: Stem & leaf display ; Histogram ; Boxplot ; Quantile plot ; Scatterplot ; Regression ; Smoothing ; 3D rotation ; Scatterplot matrix ; OMEGA strategy ; Dimension reduction ; Stability of structure ; Resampling ; Interpretation of structure ; Prediction models ; Variables selection ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Exploratory data analysis (EDA) is a toolbox of data manipulation methods for looking at data to see what they seem to say, i.e. one tries to let the data speak for themselves. In this way there is hope that the data will lead to indications about ‘models’ of relationships not expected a priori. In this respect EDA is a pre-step to confirmatory data analysis which delivers measures of how adequate a model is. In this tutorial the focus is on multivariate exploratory data analysis for quantitative data using linear methods for dimension reduction and prediction. Purely graphical multivariate tools such as 3D rotation and scatterplot matrices are discussed after having introduced the univariate and bivariate tools on which they are based. The main tasks of multivariate exploratory data analysis are identified as ‘search for structure’ by dimension reduction and ‘model selection’ by comparing predictive power. Resampling is used to support validity, and variables selection to improve interpretability.
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  • 46
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    Journal of Chemometrics 7 (1993), S. 393-425 
    ISSN: 0886-9383
    Keywords: Preprocessing ; Closure ; Normalization ; Ratioing ; Constant sum transformation ; Constant length transformation ; Maximum value transformation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The geometric properties of three common object-preprocessing transformations (constant sum, or closure; constant length, or normalization; and maximum value, or ratioing) are investigated. An argument is made for using absolute values in the constant sum and maximum value transformations. In general, each transformation distorts the shape and dimensionality of patterns in the data: transformed data lie on (C-1)-dimensional surfaces in the original C-dimensional space. A data set that has been closed by one of these transformations can be reopened if a vector containing the constant sums, constant lengths or maximum values of the original objects was retained. Transformed data sets may be freely interconverted among these three transformations without the loss of information.
    Additional Material: 24 Ill.
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  • 47
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    Journal of Chemometrics 7 (1993), S. 551-557 
    ISSN: 0886-9383
    Keywords: Krylov sequence ; Partial least squares ; Polynomial regression ; Principal component regression ; R2 ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: PLS1 regression is generally viewed as lying in between PCR and OLS regression. Proof is given that the coefficient of determination, R2, for a PLS multivariate calibration model is at least as high as that for a PCR model with the same number of components. It appears that PLS can be linked to a correlation-weighted polynomial regression of a constant response on the eigenvalues of the covariance matrix of the predictor variables.
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  • 48
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    Journal of Chemometrics 7 (1993), S. 543-550 
    ISSN: 0886-9383
    Keywords: Fragment occurrence data ; Molecular similarity ; Similarity searching ; Standardization ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Substructural fragment occurrence data are widely used as the basis for measures of inter-molecular structural similarity. This paper investigates the effect of standardization on the effectiveness of such measures using eight data sets for which both structural and biological activity data are available. Eight different standardization methods are studied and it is shown that there is no significant difference in the effectivenesses of the various methods; accordingly, any of them can be used for the calculation of intermolecular structural similarity.
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  • 49
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    Journal of High Resolution Chromatography 16 (1993), S. 379-380 
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Natural gas ; Tetrahydrothiophene (THT) ; Odorant ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
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  • 50
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    Journal of High Resolution Chromatography 16 (1993), S. 393-393 
    ISSN: 0935-6304
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 51
    ISSN: 0935-6304
    Keywords: Coupled LC-GC-MS ; Aqueous sample ; s-Triazine Herbicides ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Liquid chromatographic (LC) type trace enrichment is coupled online with capillary gas chromatography (GC) with mass spectrometric (MS) detection for the analysis of aqueous samples. A volume of 1-10 ml of an aqueous sample is preconcentrated on a trace-enrichment column packed with a polymeric stationary phase. After cleanup with HPLC-grade water the precolumn is dried with nitrogen and subsequently desorbed with ethyl acetate. A fraction of 60 μl is introduced on-line into a diphenyltetramethyldisilazane-deactivated retention gap under partially concurrent solvent evaporation conditions and using an early solvent vapor exit. The analytes are separated and detected by means of GC-MS. The potential of the LC-GC-MS system for monitoring organic pollutants in river and drinking water is studied. Target analysis is carried out with atrazine and simazine as model compounds; the detection limits achieved under full-scan and multiple ion detection conditions are 30 pg and 5 pg, respectively. Identification of unknown compounds (non-target analysis), is demonstrated using a river water sample spiked with 168 pollutants varying in polarity and volatility.
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  • 52
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    Journal of High Resolution Chromatography 16 (1993), S. 450-450 
    ISSN: 0935-6304
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 53
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    Journal of High Resolution Chromatography 16 (1993), S. 453-454 
    ISSN: 0935-6304
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 54
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    Journal of High Resolution Chromatography 16 (1993) 
    ISSN: 0935-6304
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 55
    ISSN: 0935-6304
    Keywords: Gas chromatography, GC ; Sample introduction ; At-column sample transfer ; On-line liquid backflush ; Nonvolatile material ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Deteriorated performance in capillary GC is often caused by the deposition of nonvolatile components in capillary GC inlets. In many cases this is a limiting factor in trace analysis of complex samples. Volatile solutes of the sample interact with the high boiling material, which leads to broadened and unsymmetrical peaks. This paper describes a novel technique which utilizes independent temperature programs of a retention gap and the column as well as a liquid backflush of the retention gap. Samples that normally contaminate the retention gap after a few injections can be repeatedly injected over extended periods of time, while the chromatographic resolution is retained.
    Additional Material: 6 Ill.
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  • 56
    ISSN: 0935-6304
    Keywords: GC-FTIR ; GC-MS-FTIR ; Hyphenated techniques ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: As part of a detailed investigation into the application of GC-FTIR in industrial and environmental analysis, representative sets of samples have been analyzed in parallel using commercial high-sensitivity instruments. Two of the instruments utilize low temperature storage of the GC eluate to extend the time available for FTIR analysis, yielding greater sensitivity than that possible by conventional ‘light-pipe’ GC-FTIR. In certain circumstances, instruments using both types of sample storage give rise to spectra exhibiting features characteristic of the interface used. Chromatographic resolution was found not to be significantly degraded by use of either sample storage interface. Particular advantages were found in having parallel flame ionization detection and mass spectrometry; this enabled the location of smaller components and gave greater certainty of identification.
    Additional Material: 5 Ill.
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  • 57
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    Journal of High Resolution Chromatography 16 (1993), S. 525-529 
    ISSN: 0935-6304
    Keywords: Capillary electrophoresis ; Cyclodextrin derivatives ; Separation of enantiomers ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The use of cyclodextrin derivatives for the efficient separation of enantiomeric drugs is described. Hydroxypropylation, methylation or carboxymethylation of the cyclodextrin not only result in a better solubility of the cyclodextrin in aqueous solutions, but also favor, via additional hydrogen bonding, the stabilization of one of the cyclodextrin-analyte complexes. The influence of the background electrolyte on peak shape is also described here. Carboxymethylated cyclodextrin can be used in similar manner to uncharged cyclodextrins at low pH values (below 4). At pH values above 5, however, its charge also allows the separation of uncharged enantiomers as in a micellar-like system.
    Additional Material: 7 Ill.
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  • 58
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    Journal of High Resolution Chromatography 16 (1993), S. 536-538 
    ISSN: 0935-6304
    Keywords: Coupled LC-GC ; Tocopherols ; Margarine ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Tocopherol analysis in margarine is usually carried out by HPLC after saponification of the sample and extraction of the vitamin compounds; these steps consume both time and solvents. In this paper we propose an on-line HPLC-HRGC coupling method, which allows us to simplify the preparation of the analytical sample. The sample of margarine is solubilized in hexane in an ultrasonic bath in the dark; the filtered solution is then injected into the liquid chromatograph using a normal phase microbore column eluted with hexane-isopropanol 99.8:0.2. The α-tocopherol, which is eluted with some wax esters, is transferred on-line to the gas chromatograph, using a loop-type interface with the concurrent eluent evaporation and solvent vapor exit, thus it is separated from interfering compounds and determined using an Alltech RSL 300 column (22 m × 0.25 μm i.d., 0.2 μm film thickness). The β, γ, and δ-tocopherols are determined in the same LC run, using fluorimetric detection. The analysis was carried out in 50 min.
    Additional Material: 5 Ill.
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  • 59
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    Journal of High Resolution Chromatography 16 (1993), S. 601-604 
    ISSN: 0935-6304
    Keywords: Supercritical fluid chromatography ; On-line mixing ; Pressure programming ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A simple inexpensive system comprising a piston pump, switching valves, and capillary tubing has been developed for preparing mixed mobile phases for capillary supercritical fluid chromatography. The system enables the on-line preparation of mixed mobile phases without contamination of the pump with modifier. Modifier concentrations, which can be changed stepwise, were determined both experimentally and theoretically, the latter on the basis of density-viscosity relationships. Examples of both isobaric and pressure programmed separations are demonstrated.
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  • 60
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    Journal of High Resolution Chromatography 16 (1993), S. 605-608 
    ISSN: 0935-6304
    Keywords: Micropacked liquid chromatography ; ODS stationary phases ; Temperature optimization ; Polycyclic aromatic hydrocarbons ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of column temperature on the separation of the sixteen polycyclic aromatic hydrocarbons (PAHs) of mixture SRM 1647a of the US Environmental Protection Agency has been studied on different micropacked ODS columns. Isothermal temperature optimization was successfully used for complete separation of the PAHs on a polymeric ODS stationary phase, whereas temperature programmed conditions were selected for separation on a monomeric ODS stationary phase.
    Additional Material: 7 Ill.
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  • 61
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    Journal of High Resolution Chromatography 16 (1993), S. 619-620 
    ISSN: 0935-6304
    Keywords: Capillary gas chromatography ; Headspace gas chromatography ; Terpene analysis ; Picea abies K. ; Plant taxonomy ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The terpene composition of cortical tissue in five Italian populations of Picea abies K. has been analyzed by headspace gas chromatography. The results of analysis of variance showed significant differences in content of most terpenes between the populations. Because intensive sampling is required for description of the natural variability of forest trees, the application of headspace gas chromatography may provide many opportunities in genetic research.
    Additional Material: 1 Ill.
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  • 62
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    Journal of High Resolution Chromatography 16 (1993), S. 609-614 
    ISSN: 0935-6304
    Keywords: Capillary GC ; Expanded polystyrene ; Pyrolysis ; Volatiles ; Industrial hygiene ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This paper reports on the methodology to collect volatiles from the hot-wire cutting of expanded polystyrene. Analytical scale pyrolysis was used to model the conditions in the field. It appears that gas chromatographic profiles are little affected by the presence or absence of flame retardants. Pyrolysis in air or in an inert gas generates very similar pyrograms but the temperature at which pyrolysis takes place is the major factor affecting amount and distribution of volatiles. An experimental design is discussed that permits to model in the laboratory the production of volatiles generated in the field.
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  • 63
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    Journal of High Resolution Chromatography 16 (1993), S. 615-618 
    ISSN: 0935-6304
    Keywords: Supercritical fluid chromatography (SFC) ; Micropacked columns ; Quantitative analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The performance of a type of micropacked column for the quantitative SFC analysis of samples containing solutes at very different concentrations has been studied. The chromatographic characteristics of the column were compatible with high sample volume loadability, and at the same time adequate efficiency and low pressure drop. In order to increase both the separating power and sample capacity of the column, the percentage liquid phase loading was optimized. The accuracy, precision, and detection limit obtainable with the micropacked column are compared with the performance of a wall coated open tubular capillary column having the same phase ratio.
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  • 64
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    Journal of High Resolution Chromatography 16 (1993), S. 700-702 
    ISSN: 0935-6304
    Keywords: Packed column SFC ; Selectivity tuning ; Refsum's syndrome ; Phytanic acid ; Human blood serum ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new packed column SFC method has been developed for the determination of phytanic acid in human blood serum. Because of the low viscosity and high diffusion coefficient of supercritical carbon dioxide, several columns can be connected in series, significantly improving separation. Series connection of columns which differ in their selectivity enables the adjustment of the total selectivity towards the individual separation problem (‘selectivity tuning’). In this instance it was possible, after transesterification into their ethyl esters, to separate all the fatty acids in human blood serum, including phytanic acid, by coupling three columns (silica, amino-propyl, and RP8) in series.
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  • 65
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    Journal of High Resolution Chromatography 16 (1993), S. 713-716 
    ISSN: 0935-6304
    Keywords: SFE ; Supercritical carbon dioxide ; Sand ; Test mixture ; Solvent trapping ; Solvent mixtures ; Trapping efficiency ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A polarity test mix consisting of acetophenone, N, N-dimethylaniline, naphthalene, decanoic acid, 2-naphthol, and n-tetracosane was spiked onto sand, and extracted with supercritical carbon dioxide, to evaluate the collection efficiency of various solvents and solvent mixtures. Nine single collection solvent systems and four mixed collection solvent systems were studied. When one-component collection solvents were employed, quantitative (above 90%) recovery of all analytes was not possible. With mixed collection solvents, recoveries of 90% or better with all analytes studied were possible.
    Additional Material: 4 Tab.
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  • 66
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    Journal of High Resolution Chromatography 16 (1993), S. 188-191 
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Thermostable WCOT columns ; PLOT columns ; Stainless steel ; Silicon layer for deactivation ; Simulated distillation ; PNA analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A layer of elemental silicon has been deposited on the surface of stainless steel tubing by means of chemical vapor deposition (CVD). Two kinds of capillary column were prepared from the deactivated tubing: cross-linked, silanol-terminated polydime-thylsiloxane wall coated open tubular (WCOT) columns and molecular sieve 13X porous layer open tubular (PLOT) columns. Unlike fused silica capillary columns, stainless steel WCOT and PLOT columns can be operated at temperatures in excess of 400°C. High temperature simulated distillation has been performed successfully with a macro bore WCOT column and rapid PNA (paraffin, naphthene, and aromatic) analysis with a multidimensional gas solid chromatographic (GSC) system using PLOT columns.
    Additional Material: 10 Ill.
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  • 67
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    Journal of High Resolution Chromatography 16 (1993), S. 193-193 
    ISSN: 0935-6304
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 68
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    Journal of High Resolution Chromatography 16 (1993), S. 194-195 
    ISSN: 0935-6304
    Keywords: Open-tubular liquid chromatography ; Liquid-liquid chromatography ; Electrochemical detection ; Phenols ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
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  • 69
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    Journal of High Resolution Chromatography 16 (1993), S. 202-204 
    ISSN: 0935-6304
    Keywords: GC ; Open tubular column ; Chirasil-Dex ; Enantiomer separation ; Overloading phenomenon ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
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  • 70
    ISSN: 0935-6304
    Keywords: Free solution capillary electrophoresis, FSCE ; Cyclodextrins ; Inclusion constants ; Retinoic acid ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
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  • 71
    ISSN: 0935-6304
    Keywords: Supercritical fluid extraction (SFE) ; Modified supercritical fluid ; Methanol-supercritical carbon dioxide ; Solid-phase trapping ; Cryogenic trapping ; Sample matrix, effect of ; Recovery efficiency ; Herbicides ; Sulfonyl ureas ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Important considerations are discussed for analytical SFE method development employing methanol-modified carbon dioxide and solid-phase trapping. The focus of this study was to break the method development procedure into distinct steps so that the origins of low recoveries could be determined conclusively. Sulfonyl urea herbicides were used as probe analytes. Analyte solubility, analyte trapping, analyte trap removal (solid-phase), and extract analysis were all shown to be equally important in achieving quantitative SFE recoveries.
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  • 72
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    Journal of High Resolution Chromatography 16 (1993), S. 52-52 
    ISSN: 0935-6304
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 73
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    Journal of High Resolution Chromatography 16 (1993), S. 53-55 
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Plant extract ; Photochemical degradation ; Insecticides ; Volatile compounds ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
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  • 74
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    Journal of High Resolution Chromatography 16 (1993), S. 55-57 
    ISSN: 0935-6304
    Keywords: Liquid chromatography, HPLC ; Cyanopropyl phase ; Simple lipids ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
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  • 75
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    Journal of High Resolution Chromatography 16 (1993), S. 57-59 
    ISSN: 0935-6304
    Keywords: HPLC ; Fluorescence emission detection ; Specific dual detection ; Amperometric oxidation detection ; Polymeric reagent ; Derivatization ; Aliphatic amines ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
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  • 76
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    Journal of High Resolution Chromatography 16 (1993), S. 59-61 
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Glass capillary micropacked columns ; SPE sorbents ; Aliphatic hydrocarbons ; Aromatic hydrocarbons ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 4 Ill.
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  • 77
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    Journal of High Resolution Chromatography 16 (1993), S. 65-66 
    ISSN: 0935-6304
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 78
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    Journal of High Resolution Chromatography 16 (1993), S. 62-64 
    ISSN: 0935-6304
    Keywords: Capillary electrophoresis ; Hollow fiber ; Polypropylene ; Capillary dynamic coating ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
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  • 79
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    Journal of High Resolution Chromatography 16 (1993) 
    ISSN: 0935-6304
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 80
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    Journal of High Resolution Chromatography 16 (1993), S. 69-69 
    ISSN: 0935-6304
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 81
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    Journal of High Resolution Chromatography 16 (1993), S. 312-323 
    ISSN: 0935-6304
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 82
    ISSN: 0935-6304
    Keywords: Capillary electrophoresis ; Isotachophoresis preconcentration ; Nonaqueous buffer ; Metabolism ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
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  • 83
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    Journal of High Resolution Chromatography 16 (1993), S. 326-327 
    ISSN: 0935-6304
    Keywords: Capillary electrophoresis ; Laser-induced fluorescence ; 6-Thioguanine nucleotides ; 6-Mercaptopurine metabolites ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
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  • 84
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    Journal of High Resolution Chromatography 16 (1993) 
    ISSN: 0935-6304
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 85
    ISSN: 0935-6304
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 86
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    Journal of High Resolution Chromatography 16 (1993), S. 353-357 
    ISSN: 0935-6304
    Keywords: Capillary GC Curie point pyrolysis ; Multichannel autosampler ; Polymer analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new multichannel autosampler which can automatically analyze up to twenty samples in sequence has been developed for Curie point pyrolysis - capillary GC. Compared with a previous system [1] the transfer line between the pyroysis unit and chromatograph is shorter, and thus has less dead volume, and can be operated at a higher temperature (300 °C). The relative yields of higher boiling point, highly polar, and thermally labile pyrolysates generated from polymers, and the reproducibility, were better than those obtained from the previous autosampler. To facilitate rapid operation an additional flow controller is installed on the new device to shorten the time taken to purge air from the sampler.
    Additional Material: 6 Ill.
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  • 87
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    Journal of High Resolution Chromatography 16 (1993), S. 689-692 
    ISSN: 0935-6304
    Keywords: Solid phase microextraction (SPME) ; Headspace analysis ; Headspace solid phase microextraction ; Environmental analysis ; Water analysis ; Solid samples ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The analysis of samples contaminated by organic compounds is an important aspect of environmental monitoring. Because of the complex nature of these samples, isolating target organic compounds from their matrices is a major challenge. A new isolation technique, solid phase microextraction, or SPME, has recently been developed in our laboratory. This technique combines the extraction and concentration processes into one step; a fused silica fiber coated with a polymer is used to extract analytes and transfer them into a GC injector for thermal desorption and analysis. It is simple, rapid, inexpensive, completely solvent-free, and easily automated. To minimize matrix interferences in environmental samples, SPME can be used to extract analytes from the headspace above the sample. The combination of headspace sampling with SPME separates volatile and semi-volatile analytes from non-volatile compounds, thus greatly reducing the interferences from non-target compounds.This paper reports the use of headspace SPME to isolate volatile organic compounds from various matrices such as water, sand, clay, and sludge. By use of the technique, benzene, toluene, ethyl-benzene, and xylene isomers (commonly known as BTEX), and volatile chlorinated compounds can be efficiently isolated from various matrices with good precision and low limits of detection. This study has found that the sensitivity of the method can be greatly improved by the addition of salt to water samples, water to soil samples, or by heating. Headspace SPME can also be used to sample semi-volatile compounds, such as PAHs, from complex matrices.
    Additional Material: 5 Ill.
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  • 88
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    Journal of High Resolution Chromatography 16 (1993), S. 182-187 
    ISSN: 0935-6304
    Keywords: PTV injector ; Liner design ; On-line LC-GC interfacing ; Large volume sample introduction ; Programmed temperature injection ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Programmed temperature sample introduction is an attractive technique both for the introduction of large volumes of dilute samples in capillary gas chromatography and for LC-GC interfacing.In this study a new type of liner containing a porous bed of sintered glass is introduced and evaluated. Solute recoveries achieved with this liner are compared with those obtained from liners packed with Tenax TA and Thermotrap TA. An open liner containing baffles and a small plug of silanized glass wool in its upper section was used as a reference.The maximum speed of sample introduction allowable using the new liner is ca one order of magnitude higher than for the standard liner. For similar liner operating conditions the trapping efficiency is substantially improved: at a liner temperature of -30°C components with a volatility lower than or equal to that of n-tridecane are trapped quantitatively.Liners packed with trapping materials such as Tenax TA or Thermotrap TA also provide significantly improved trapping efficiencies, even when used at relatively high temperatures.
    Additional Material: 7 Ill.
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  • 89
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    Journal of High Resolution Chromatography 16 (1993), S. 736-737 
    ISSN: 0935-6304
    Keywords: Aminophenols ; Ion-pair liquid chromatography ; Electrochemical detection ; Quinobenzoxazine ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
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  • 90
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    Journal of High Resolution Chromatography 16 (1993), S. 386-387 
    ISSN: 0935-6304
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 91
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    Journal of High Resolution Chromatography 16 (1993), S. 388-390 
    ISSN: 0935-6304
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 92
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    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 16 (1993) 
    ISSN: 0935-6304
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 93
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    Journal of High Resolution Chromatography 16 (1993), S. 404-406 
    ISSN: 0935-6304
    Keywords: tert-Butylcatechol ; Electrochemical detection ; Liquid chromatography ; 1,3-Butadiene purification ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Amperometric detection is shown to be highly selective and sensitive for the determination of tert-butylcatechol (TBC) added as an antioxidant in the circulating N-methyl-2-pyrrolidone (NMP) used for the purification of 1,3-butadiene by extractive distillation. The separation of TBC from numerous polar and nonpolar species present in the analyte is achieved on a 5-cm reversed-phase C-18 column using acetonitrile-water gradient conditions, both solvent components containing tetrabutyl ammonium dihydrogen phosphate as the amphiphilic modifier. The separation process is optimized for the resolution of TBC from nonpolar hydrocarbons as well as polar compounds, and a complete elution of all species from the column. An applied potential of 0.6 V relative to the Ag/AgCI electrode is found to provide an optimum sensitivity by the amperometric detector. It is also shown that the hydrocarbon content in NMP can be monitored simultaneously by coupling a spectrophotometric detector in series.
    Additional Material: 4 Ill.
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  • 94
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    Journal of High Resolution Chromatography 16 (1993), S. 413-418 
    ISSN: 0935-6304
    Keywords: On-line extraction-GC ; Phase-switching ; Open-tubular traps ; Stationary phase swelling ; Large volume injection ; PTV ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The applicability of open-tubular trapping columns for on-line extraction-capillary GC analysis is evaluated. The extraction step involves sorption of the analytes from water into the stationary phase of an open-tubular column, removal of the water by purging the trap with nitrogen, and desorption of the analytes with an organic solvent. The effect of swelling of the stationary phase with organic solvents on the retention power of the trap is studied. When using pentane or hexane as swelling agent breakthrough volumes of at least 10 ml can easily be obtained for non-polar compounds. For a number of medium polarity compounds breakthrough volumes of 5 ml can be achieved when chloroform is used as the swelling agent. The required drying time is less than 1 minute. Quantitative desorption requires only 75 μl of organic solvent. Solvent elimination prior to transfer to the GC column is carried out using a PTV injector and a multidimensional GC system. The system is applied for the analyses of river water, urine, and serum samples.
    Additional Material: 6 Ill.
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  • 95
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    Journal of High Resolution Chromatography 16 (1993), S. 422-424 
    ISSN: 0935-6304
    Keywords: Capillary gas chromatography ; Offset printing ; Residual solvent ; Solvent retention ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method was developed for measuring the residual solvent content in a dried offset print. The method is based on hexane extraction. The presence of additives and resins in the printing inks necessitated purification of the extract on an aluminum oxide column. In the study concerning the effect of the heatset web offset drying process on print quality, a distinct correlation was found between the residual solvent content of the print and the drying parameters.
    Additional Material: 6 Ill.
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  • 96
    ISSN: 0935-6304
    Keywords: On-line SFE-GC ; Split/splitless interface ; Quantitative aspects ; Discrimination ; Reproducibility ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The quantitative aspects of on-line supercritical fluid extractioncapillary gas chromatography (SFE-GC) with a split/splitless injector as interface were investigated. Special attention was paid to the discrimination behavior and the reproducibility of the split/splitless interface. A simple experimental set-up is proposed that allows accurate quantitation in on-line SFE-split GC. The results obtained in on-line SFE-GC compare favorably with those from conventional GC with split injection. Discrimination was found to be absent when working at sufficiently high interface temperatures. Finally, the effects of the carbon dioxide flow rate, interface temperature and split ratio on both discrimination and reproducibility were studied.
    Additional Material: 4 Ill.
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  • 97
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    Journal of High Resolution Chromatography 16 (1993), S. 429-432 
    ISSN: 0935-6304
    Keywords: Sample evaporation inside injector ; Injector liners ; Laminar cup splitter ; Glass wool in injector insert ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Completeness of sample evaporation in conventional vaporizing injection is a problem for many samples and calls for measures to arrest the sample liquid in the space between the needle exit and the column entrance. A visual testing procedure reveals that a small plug of loose glass or quartz wool ensures complete evaporation in all instances. Obstacles built into the liner also stop liquid, provided they force the sample to pass through narrow channels. Other important design characteristics concern access to the narrow channel. Evaporation in a packed insert usually occurs from a surface, whereas the sample hardly touches surfaces in the instance of an insert with obstacles. Evaporation from a packing is, in fact, more reliable, but creates more problems concerning inertness.
    Additional Material: 5 Ill.
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  • 98
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    Journal of High Resolution Chromatography 16 (1993), S. 433-436 
    ISSN: 0935-6304
    Keywords: Capillary electrophoresis ; Miniaturization ; Planar chip technology ; Silicon and glass microstructures ; Small volume optical detector cell ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Miniaturization of separation columns implies equally reduced vol- umes of injectors, detectors, and the connecting channels. Planar chip technology provides a powerful means for the fabrication of micron-sized structures such as channels. This is demonstrated by two examples. An optical absorbance detector chip exhibits the expected behavior of a 1 mm optical path length cell despite its volume of 1 nL. A capillary electrophoresis device allows integrated injections of 100 pL samples, efficiencies of 70,000 to 160,000 theoretical plates in 10 to 20 seconds, and external laser-induced fluorescence detection at any capillary length of choice between 5 and 50 mm.
    Additional Material: 4 Ill.
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  • 99
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    Journal of High Resolution Chromatography 16 (1993), S. 441-444 
    ISSN: 0935-6304
    Keywords: High resolution capillary gas chromatography ; High resolution gas chromatography-mass spectrometry ; Essential oil analysis ; Ylang-ylang oil composition ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Samples of essential oil from Colombian ylang-ylang trees were analyzed by means of HRGC, HRGC-MS, IR and 1H- and 13C-NMR. 57 components were detected, 51 of which were positively identified. Camphene and anethol were identified in ylang-ylang essential oil for the first time. Among the composition-determining variables studied (extraction time, part of the flower, and flower freshness), the extraction time and the flower condition (fresh versus dry) were found to have the largest incidence in the quality of the essential oil.
    Additional Material: 3 Ill.
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  • 100
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    Journal of High Resolution Chromatography 16 (1993), S. 437-440 
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Open tubular column ; n-Pentane ; Human breath analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new procedure, requiring expired sample volumes of approximately 2L, has been developed for the quantitative determination of n-pentane in human breath. The methodology capitalizes on the superior resolving power and separating efficiency of the open tubular capillary column and incorporates an effective prechromatographic cryofocusing technique. Molecular sieve is used to simultaneously remove moisture and carbon dioxide from breath samples which are “spiked” with an internal standard to optimize the validity of analysis. Reproducible data for both internal standard spiking (CV = 5.8%) and sample n-pentane level (CV = 3.2%) have been obtained, together with a mean recovery of 104%. Preliminary data show n-pentane levels in normal female subjects (n = 10) to range from 0.62 to 3.16 nmole/L (mean 1.76 nmole/L) and in males (n = 10) from 3.20 to 8.76 nmole/L (mean 5.66 nmole/L).
    Additional Material: 2 Ill.
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