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  • 11
    Electronic Resource
    Electronic Resource
    Statistical evaluation of the validity of a method for characterizing stationary phases for reversed-phase liquid chromatography based on retention of homologous series (1994)
    Springer
    Chromatographia 38 (1994), S. 137-146 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Characterization of reversed phases ; Column hydrophobicity ; Column hydrophylicity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The validity of a method for characterizing stationary phases for reversed-phase, liquid chromatography, based on the use of homologous series, has been evaluated. The method is based on a retention model which describes the dependence of the logarithm of the capacity factor on mobile phase composition and the carbon number of specific homologous series. A first-order as well as a second-order version of this model was investigated. The second-order model proved to be a significant improvement on the first-order model, even for smaller mobile-phase ranges. Nevertheless both models showed a significant lack of fit, reflecting the incompleteness of these models. Therefore, it is very questionable whether this method is suitable to describe HPLC-column characteristics like hydrophobicity and hydrophylicity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02290326
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  • 12
    Electronic Resource
    Electronic Resource
    The influence of surface treatments on the electroosmotic flow in micellar electrokinetic capillary chromatography (1992)
    Springer
    Chromatographia 33 (1992), S. 303-308 
    Details
    ISSN: 1612-1112
    Keywords: Micellar electrochromatography ; Electroosmotic flow ; Column coatings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An investigation was carried out to study the electroosmotic flow (EOF) in micellar electrokinetic capillary chromatography (MECC). Fused silica capillaries were treated with various reagents to investigate the parameters influencing the magnitude and reproducibility of the EOF. The results for untreated and treated columns were collected and compared under the same experimental conditions. Furthermore, experiments with and without sodium dodecylsulfate (SDS) addition to the buffer were carried out to elucidate the influence of this surfactant on the EOF. The mechanisms behind the effects of these modifications on the EOF and the stability of the coatings on the column wall are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02275906
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  • 13
    Electronic Resource
    Electronic Resource
    Permeability and preparation of micropacked columns (1975)
    Springer
    Chromatographia 8 (1975), S. 482-485 
    Details
    ISSN: 1612-1112
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A simple procedure for preparing packed columns with an internal diameter of 0.6–0.8 mm and up to 15 m long is described. Theoretical plate numbers of the order 40,000 at capacity ratios 〉4 can be obtained at moderate inlet pressures. Special attention is given to the permeability of packed capillaries and micropacked columns. Some examples are given of separations obtained with micropacked columns.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02267588
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  • 14
    Electronic Resource
    Electronic Resource
    Direct sample introduction of high boiling compounds onto glass capillary columns. Comparison of manual and automatic sampling (1975)
    Springer
    Chromatographia 8 (1975), S. 479-481 
    Details
    ISSN: 1612-1112
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The performances of two systems for the direct introduction of high boiling compounds onto glass capillary columns are compared. Samples investigated consisted of hydrocarbons and steroids. The “Moving Needle” system (a manual version) developed in our laboratory is extensively described in the literature [1]. The standard deviation for quantitative measurements is approximately 2.5% rel. Recently a Pye Auto Solids Injector has been modified so as to meet the requirements set by capillary gas chromatography. The very large dead volume of this sampling system, due to the use of sample holders prevents the direct coupling of this system to a capillary column. After introduction of a sample holder the solid sample evaporates slowly and the sample compounds are spread throughout a large volume of carrier gas, this badly affects the resolution obtainable. To overcome this problem the oven of the chromatograph contains a capillary precolumn (of some 50 cm length), which during a short period after sample introduction is cooled by a flow of air. During this cooling period the sample compounds are effectively trapped in the pre-column. After one minute the cooling medium is turned off, the pre-column rapidly heats in the column oven and a sharp reinjection of the sample occurs. A complete description of the system is given. The repeatability of quantitative measurements {σrel} is better than 1.5%. There is no loss of resolution by using this sampling technique. Both systems described are compatible with isothermal and programmed operation. Also in both versions the solvent does not enter the capillary column to an appreciable extent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02267587
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  • 15
    Electronic Resource
    Electronic Resource
    Ageing processes of alkyl bonded phases in HPLC; a chromatographic and spectroscopic approach (1985)
    Springer
    Chromatographia 20 (1985), S. 582-586 
    Details
    ISSN: 1612-1112
    Keywords: Reversed-phase HPLC ; Ageing processes ; Solid state NMR ; FTIR ; Chain dynamics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Laboratory use of HPLC columns packed with C8 and C18 bonded phases leads to changes in selectivities and retention volumes. FTIR,1H NMR of hydrolysed bonded phases and solid state13C- and29Si NMR were applied to characterize the materials. The results of the various techniques are in fair agreement except solid state NMR. Loss of silane and hydrolysis of surface siloxane groups have been observed for the C8 bondes phase, while for the C18 material the latter process seems to dominate. The solid state NMR results have been tentatively explained in terms of changing chain arrangements and mobilities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02263215
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  • 16
    Electronic Resource
    Electronic Resource
    The separation of herbicides by micellar electrokinetic capillary chromatography (1992)
    Springer
    Chromatographia 34 (1992), S. 25-30 
    Details
    ISSN: 1612-1112
    Keywords: Electrokinetic capillary chromatography ; Micellar agents ; Chlorophenoxy acids ; Herbicides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A method for the separation of a number of herbicides consisting of chlorophenoxy acids by micellar electrokinetic capillary chromatography (MECC) was developed. Sodium dodecyl sulphate (SDS), Brij 35, cetyltrimethylammonium bromide (CTAB) and methanol were introduced into the buffers to investigate their effects on the separation of the herbicides. SDS combined with Brij 35 as the micellar agent was found to provide the best overall separation of these components.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02290454
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  • 17
    Electronic Resource
    Electronic Resource
    Monitoring of nicotine in air using sorptive enrichment on polydimethylsiloxane and TD-CGC-NPD (1999)
    Springer
    Chromatographia 49 (1999), S. 520-524 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Sorptive preconcentration ; Air monitoring ; Nicotine ; Hospital air
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A novel method for the enrichment of nicotine from gaseous samples is presented. It is based on the sampling of 6 liters of air onto a cartridge packed with 100% polydimethylsiloxane (PDMS) particles. The analytes are dissolved (partitioned) into the PDMS phase which results in much better recoveries and reproducibilities compared to those obtained on common adsorbents. The PDMS tube is then placed in a thermal desorption (TD) unit connected to a CGC-NPD or CGC-MS system. The procedure was employed for routinely monitoring air in a hospital. Nicotine was typically found at levels ranging from 5 to 250 μg m−3 (ppb) depending on the location and number of smokers present. Additionally, the efficiency of nicotine filters was determined by sampling simultaneously at the filter in- and outlet and was found to be 46%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02467752
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  • 18
    Electronic Resource
    Electronic Resource
    High precision capillary gas chromatography of hydrocarbons (1974)
    Springer
    Chromatographia 7 (1974), S. 99-106 
    Details
    ISSN: 1612-1112
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A low cost home-made gas chromatographic system is described. With this system a precision of retention data is attained corresponding to a standard deviation of less than 0.03 index units for all types of hydrocarbons. A method has been found of preparing high resolution steel capillary columns in a reproducible way and with a homogeneous film. Adsorption of hydrocarbons on the column wall is negligible. With different instruments and different columns and operators, the reproducibility of retention data is in most cases considerably better than 0.1 index units. A list of retention indices of some 170 hydrocarbons (C4–C9) on squalane (nonpolar) and acetyltributylcitrate (polar) at 50 and 70°C is given. It is shown that the temperature coefficient of the retention index, which is now available with a higher precision, yields important structural information (e. g. cis-alkenes have a consistently higher dl/dT than trans-alkenes).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02269819
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  • 19
    Electronic Resource
    Electronic Resource
    Direct measurement of the “dead time” in gas chromatography with a flame-lonisation detector (1970)
    Springer
    Chromatographia 3 (1970), S. 441-442 
    Details
    ISSN: 1612-1112
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The elution of an inert gas peak from capillary columns is directly measured with a flame-ionisation detector operating at reduced hydrogen and air flow rates. Under the conditions tested the inert gases give negative signals. No significant diferences in “dead times” obtained from different inert gases are found. Experimental values deviate from the measured methane elution time and even more from “dead times” calculated from the logplot of n-alkanes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02279449
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    Paper (German National Licenses)
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  • 20
    Electronic Resource
    Electronic Resource
    Factors determining flow rate in chromatographic columns (1981)
    Springer
    Chromatographia 14 (1981), S. 439-444 
    Details
    ISSN: 1612-1112
    Keywords: Flow rate ; Packed columns ; Open tubular columns ; Chromatographic permeability ; Column resistance factor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary It is shown that the flow in chromatography is nearly always laminar in nature. Starting from the Darcy equation, expressions are given for the flow rate in both gas and liquid chromatography columns. The concepts of specific permeability, chromatographic permeability and column resistance factor are discussed for packed as well as open tubular columns. The experimental determination of all these factoers is demonstrated. The influence of the shape and pore volume of porous and non-porous supports on the column resistance factor and the chromatographic permeability is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02262882
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