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  • 1
    ISSN: 1612-1112
    Keywords: Ion-pair liquid chromatography ; Peak splitting ; Sympathominetic drugs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary In the determination of ephedrine using reversed-phase, ion-pair liquid chromatography, a chromatographically pure sample was observed to give three peaks under certain mobile phase conditions. The mobile phases which produced maximum peak splitting were determined for ephedrine and a number of other sympathomimetic drugs. A proposal that peak splitting was the result of the composite interplay of two discrete chromatographic mechanisms, was investigated. The results of analysis by GC/MS confirmed that each peak was due to ephedrine, however, only one of the three split peaks was found to contain ion pairs. It is postulated that peak splitting is a physical phenomenon on reversed-phase columns and the separation of these drugs by ion-pair HPLC is based on a mixed rather than a single mechanism. This study has also shown that errors can arise in ion-pair HPLC when multiple peaks are assumed to indicate heterogeneity. Interconvertible species of the same solute can give rise to these peaks.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1612-1112
    Keywords: Liquid Chromatography ; Nickel dithiocarbamate complexes ; Sympathomimetic drugs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Nickel dithiocarbamate complexes derived from some sympathomimetic drugs are examined on silica Radial-Pak columns using binary solvents containing a small percentage of an organic polar modifier. Both the type and concentration of this modifier was found to influence the separation of the ternary from the parent binary complexes. When the two ligands in a ternary complex are racemic to each other, separation of the ternary complex is only possible when certain structural requirements of the molecule are fulfilled. Ternary complexes which contain structurally similar, but nonracemic ligands, are shown to be readily separated from binary complexes. When two such complexes differ only in that one of the ligands in one is enantiomeric to a ligand in the second complex, then it can be shown that the ternary complex with the (+) enantiomer ligand elutes faster from the silica column than the one with the (−) enantiomer ligand. An example of the use of ternary complexes for the identification of optical and structurally related impurities in pharmaceutical products is also given.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1612-1112
    Keywords: Liquid chromatography detectors ; Noise suppression ; Electronic filters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Four electronic filters suitable for baseline noise suppression in HPLC detectors were compared for their response and peak distortion characteristics under conventional HPLC conditions. The filters were designed to be white noise equivalent and the types of filter used were lag, lag-lag, critically damped lag and chain, these being representative of common, simple filter configurations. These filters were evaluated for speed of response to an optical step input signal and also for the effects of their level of noise suppression on peak height, retention time, peak asymmetry and apparent column efficiency. The critically damped lag filter was superior to the other filters in almost all respects and its use considerably enhanced detector performance.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Chromatographia 22 (1986), S. 292-298 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ion chromatography ; Arsenic speciation ; Chloride interference ; Urine-seawater samples
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The presence of high concentrations of chloride in urine and seawater samples interferes with the separation of arsenic species by ion chromatography; single peaks may be split into two or more discrete peaks, as a result of the large differences in the ionic strengths of the mobile and injection solvents. A simple model is proposed to explain this phenomenon.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 11 (1984), S. 177-181 
    ISSN: 0306-042X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This study reports a rearrangement process observed in electron capture negative ion chemical ionization mass spectrometry of pentafluoropropionate and heptafluorobutyrate derivatives of some β-hydroxylated amines. The pentafluoropropionate derivatives of a number of these substituted amines yield a prominent anion of mass 145 (195 in the corresponding heptafluorobutyrate derivatives). In the pentafluoropropionate derivatives of ethanolamine and β-hydroxyphenethylamine this anion was quantitatively displaced to m/z 146 when the γ-hydrogen (relative to the derivatized hydroxyl group) was substituted by deuterium. We postulate an initial 6-membered transition state to produce a pentafluoropropionic acid anion (not observed) which then eliminates either a hydrogen atom to give m/z 163 or a fluorine atom to give m/z 145. The former remains at mass 163 in the γ-deuterated compounds examined. The proposed rearrangement is the negative ion analogue of the McLafferty rearrangement process of positive ion electron impact mass spectrometry. However, the negative ion rearrangement is not as general as its positive ion electron impact counterpart because the former is critically dependent upon the substitution present on the α and β carbon and nitrogen atoms, respectively, of the β-hydroxyamine-PFP (or HFB) derivatives. In this regard we examined the effects on m/z 145 anion formation of methyl substitution on the nitrogen and α and β carbon atoms of these pentafluoropropionate derivatives. The results suggest that electron capture methane negative ion chemical ionization mass spectra of β-hydroxylated PFP derivatives could be used as diagnostic tool for structural assignments within this group of compounds.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 11 (1984), S. 223-229 
    ISSN: 0306-042X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The positive and negative chemical ionization mass spectra of 29 amino acid carboxy-n-butyl ester N-(O,S)-Pentafluoropropionate derivatives hae been determined. The positive ion (PI) mass spectra conform to the expected fragmentation patterns for this amino acid derivative but their methane negative ion chemical ionization (NICI) mass spectra displayed marked differences between various amino acid classes and bvetween positional isomers within the same class. Isomeric butyric acid (α, β and γ) and tyrosine (o, m amd p-hydroxylation) derivatives all had remarkably difterent NICI mass spectra. Aliphatic amino acid CO2-n-butyl-N-PFP derivatives (except glycine) can be readily recognized by a characteristic fragmentation process corresponding to [M-H-C4CO2H]-. Deuterium labellung studies were used to delineate some of the major NICI fragmentation processes. While the PICI mass spectra all gave comparable detection responses differences were observed with various amino acids when operating in the NICI mode. The order of sensitivity of detection for six representative amino acid-carboxy-n-butyl-N-PFP derivatives were: hydroxyproline 〉 lysine 〉 cysteine 〉 glycine=leucine=methionine in the ratio of 100:20:7:1. In PICI mass spectrometry derivatized leucine yielded a response 25 times less than its NICI mass spectrometric value.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Further studies have demonstrated that the site-specific hydrogen transfer process involved in the formation of the m/z 145 anion of β-hydroxyamine pentafluoropropionate (PFP) derivatives observed under electron capture negative ion chemical ionization conditions occurs when the two functional groups are separated by up to five carbon atoms. Deuterium labelling has established that the site specificity, transfer of a hydrogen atom from the carbon adjacent to nitrogen to the OPFP group, is maintained in 4-amino-butan-1-ol-N, O-(PFP)2. The corresponding PFP derivatives of the N-methylaminoalkanol-(PFP)2 derivatives lack the m/z 145 species with m/z 163, [OPFP]- being the base anion. Substitution of alkyl groups on the carbon adjacent to oxygen results in a diminution of the ion intensity at m/z 145. with a marked increase in the intensity of m/z 144. The formation of the m/z 145 and 144 anions to proposed to proceed through the intervention of a fluoride ion-molecule complex as outlined in Scheme 1 with the product ion distribution dependent on which of the two pathways is preferred.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Methane chemical ionization mass spectrometry has been used to investigate the components of kava resin prepared by solvent extraction of commercial Piper methysticum Forst. All the known constitutents of this resin were identified together with several new compounds which of formally result from decarboxylation of the 4-methoxy-2-pyrone ring system in the known compounds. Chemical ionization mass spectrometry is a useful probe for the identification of these compounds because all gave easily recognized protonated molecular ions and the fragmentation patterns were related to molecular structure. Using this technique, the steam distillation products of commercial P. methysticum were identified, as was the product distribution from base hydrolysis of the known kava pyrone, yangonin.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This study reports studies using electron capture negative ion chemical ionization gas chromatography/mass spectrometry (EC-NICI GC/MS) of 21 polycyclic aromatic hydrocaroon (PAH) compounds. The selectivity and sensitivity of these compounds are shown here to be highly dependent on ion source temperature and pressure. Changes in selectivity arise from variations in instrumental and can be largely explained by the competitive formation processes of [M]-. and [M—H]- ions. The formation of the adduct ion, [M + 15]-, previously attributed to [M + CH3]-, is shown here by using perdeuterated PAH analogues to be a [M + O — H]- ion. For fluorene and acenaphthene, abundant [M + 14]- and [M + 13]- ions can be similarly rationalized to be [M + O — 2H]- and [M + O — 3H]-. The NICI mass spectrum of (2H10)acenaphthene demonstrates that ring proton losses most likely occur. This study also indicates that there is a strong correlation between the NICI response factor and the reported carcinogenic activity of PAHs in the literature. In addition, this work assesses the viability of NICI GC/MS as an analytical technique for determining PAHs in fly ash with minimum sample pretreatment.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 12 (1985), S. 348-354 
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Amino acid methyl esters were condensed with 1,3-dichloro-1,1,3,3-tetrafluoroacetone to yield the corresponding oxazolidinone derivatives whose electron capture negative ion methane chemical ionization mass spectra were studied. Anions corresponding to [M + CI]-, (HCI2)- and (CF2CI)2CO)- are discussed in relation to their appearance in the amino acid oxazolidinone spectra. Other common fragmentation modes were the elimination of stable neutral molecules (HCI, HF, CO2) in various combinations from the molecular anion. Aliphatic amino acids having a γ-hydrogen atom relative to the oxazolidinone ring carbonyl group gave an anionic fragment formally equivalent to the McLafferty rearrangement product of positive ion electron impact mass spectrometry.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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