I. A. Revelsky

Electron Ionization and Atmospheric Pressure Photochemical Ionization in Gas Chromatography-Mass Spectrometry Analysis of Amino Acids

The mass spectra of tert-butyldimethylsilyl (TBDMS) derivatives of 17 amino acids were obtained using electron ionization (EI) and atmospheric pressure photochemical ionization (APPhCI) mass spectrometry. The APPhCI mass spectra for all of the derivatives except arginine were shown to consist of only molecular [M]+. and quasimolecular [MH]+ ions whereas, in the case o EI, the compounds in question underwent a drastic fragmentation. The application of APPhCI to gas chromatography-mass spectrometry enables a reliable identification of the TBDMS derivatives of amino acids in a mixture, even if its components are only partially resolved, due to the unique molecular masses for each compound. Comparison of the respective positive-ion chemical ionization (PICI) mass spectra available in the literature with APPhCI spectra has shown that, in the case of PICI, unlike APPhCI, noticeable fragmentation occurs.

New approach to complex organic compounds mixtures analysis based on gas chromatography-atmospheric pressure photoionization-mass-spectrometry.

The mass-spectra of a number of different hydrocarbons were obtained using atmospheric pressure photoionization (APPhI) and photochemical ionization (APPhCI) mass-spectrometry. The respective mass-spectra consisted mainly of molecular (M(+)) or quasimolecular (MH(+)) ion peaks or both. The composition of aromatic hydrocarbons in straight-run gasoline was investigated using standard PIONA method, based on capillary GC and retention time indexes, and GC/MS (APPhI). 56 aromatic hydrocarbons were identified using GC/MS (APPhI) and 43-using standard PIONA method. The opportunities of MS (APPHCI) for determination of impurities in pure hydrocarbons and for direct analysis of complex mixtures without separation were demonstrated when MS (APPhCI) analysis for GC standards of benzene and toluene was carried out (main component vapor was reagent gas). The targeted PAHs and phtalates were registered selectively in 44 component model mixture of semivolatiles with partial or without separation of the components, using GC/MS (APPhI).

Distinguishing by principal component analysis of o-xylene, m-xylene, p-xylene and ethylbenzene using electron ionization mass spectrometry.

The possibility of distinguishing between o-xylene, m-xylene, p-xylene and ethylbenzene on the basis of only their 70 eV electron ionization (EI) mass spectra has been investigated. These four isomers were distinguished by principal component analysis of respective EI mass spectra (recorded under identical conditions). The mass spectra considered contained either eleven or five m/z values, which had intensities greater than 5% or 10% of base peak, respectively.

Combination of supercritical fluid extraction and gas chromatography-mass spectrometry : Determination of impurities extracted from tablet preparations of the benzodiazepine series

A method is proposed for the determination of moderately volatile organic impurities in pharmaceutical tablet preparations based on a combination of solvent-free supercritical fluid extraction (SFE) and gas chromatography-mass spectrometry. The composition of moderately volatile impurities is determined in pharmaceutical tablet preparations of the benzodiazepine series (diazepam, phenazepam, nitrazepam, and clonazepam).

Electron ionization mass spectra and their reproducibility for trialkylsilylated derivatives of organic acids, sugars and alcohols.

Mass spectra of trialkylsilyl derivatives of fatty acids, dicarboxylic acids, hydroxyacids, oxoacids, sugars, amino acids and alcohols were obtained. Amino acids were analyzed as tert-butyldimethylsilyl derivatives; all other model compounds were analyzed as trimethylsilyl derivatives. Reproducibility of the electron ionization (EI) mass spectra for the derivatives obtained was discussed. It was shown that, for many investigated derivatives, composition of the respective mass spectra depended greatly on ion source contamination. The trimethylsilylated α-tocopherol mass spectrum composition was most significantly influenced by ion source contamination. This compound can be used to test ion source contamination.

Electron Ionization Mass Spectra of N(O,S)-Isobutoxycarbonyl Isobutyl Esters of Amino Acids:

Mass spectra of N(O,S)-isobutoxycarbonyl isobutyl esters of 17 amino acids (L-alanine, glycine, L-valine, L-norvaline, L-leucine, L-isoleucine, L-norleucine, L-proline, L-asparagine, L-methionine, L-threonine, L-serine, L-phenylalanine, L-lysine, L-tryptophan, L-tyrosine and L-cystine) were obtained in the electron ionization mode. These derivatives were found suitable for the analysis of amino acids in aqueous media allowing proper identification and quantitation from the mass spectral characteristics.

Fast Detection of Polycyclic Aromatic Hydrocarbons in Complex Mixtures of Organic Compounds Based on Gas Chromatography–Mass Spectrometry with Atmospheric Pressure Photoionization:

The research is devoted to the investigation of the selectivity detection of 16 polycyclic aromatic hydrocarbons (PAHs) using gas chromatography–mass spectrometry (GC-MS), electron ionization (EI) GC-MS with atmospheric pressure photoionization (APPhI) and GC-MS atmospheric pressure photochemical ionization (APPhCI) when vapors of different substances (benzene, toluene and naphthalene) were used as gas reagents. Capillary columns of different lengths were used for the separation of the components of the mixture of 44 semi-volatile organic compounds. It was shown that the most-selective detection of 16 PAHs in a 44-component mixture was possible when GC-MS APPhCI was used. Only 16 PAHs were registered on the respective mass chromatograms and a fast detection of them was possible. The respective APPhI and APPhCI mass spectra consisted of only peak of the respective molecular ion, M+• – the radical cation. Detection limits were 3 pg μL−1 to 15 pg μL.

Supercritical fluid chromatography and its application to analysis and preparation of high-purity compounds

The principles of supercritical fluid chromatography (SFC) and its application in various fields are reviewed. A comparison of high-performance liquid chromatography (HPLC) and SFC is performed. In discussing the applications, emphasis is placed on the possibility of using SFC in analysis of impurities in pharmaceuticals and biologically important substances and in preparation of high-purity substances. In describing detectors for SFC, special attention is paid to mass-spectrometric detectors.

Comparison of multidimensional impurity profiles for pharmaceuticals containing the same active compound using thermodesorption and gas chromatography coupled with mass spectrometry

The possibility of comparing pharmaceutical products containing the same active compound based on the comparison of multidimensional profiles of impurities isolated from the examined samples by thermodesorption in a carrier gas flow was studied by GC/MS with electron ionization. A substantially higher number of impurities can be detected using the analytical method based on thermodesorption of impurities and GC/MS analysis of the whole desorbate of impurities free of the active compound. The proposed approach makes it possible to compare the studied pharmaceutical products containing the same active compound taking into account information on the number of the found impurities, their retention times, and electron ionization mass spectra.

Reliable Comparison of Electron Ionization Mass Spectra Recorded Under Identical Experimental Conditions

ABSTRACT For the most reliable identification by means of electron ionization mass spectrometry, the full mass spectra of unknown compound and possible candidate should be recorded under identical experimental conditions and compared. The main problem is how to compare full mass spectra, which may contain a lot of peaks. We have proposed a new approach (based on using principal component analysis) for the reliable comparison of electron ionization mass spectra recorded under identical experimental conditions. Applicability of the approach has been demonstrated on the example of xylenol isomers.