A. I. Revelsky

Some new features of Direct Analysis in Real Time mass spectrometry utilizing the desorption at an angle option

The present study is a first step towards the unexplored capabilities of Direct Analysis in Real Time (DART) mass spectrometry (MS) arising from the possibility of the desorption at an angle: scanning analysis of surfaces, including the coupling of thin-layer chromatography (TLC) with DART-MS, and a more sensitive analysis due to the preliminary concentration of analytes dissolved in large volumes of liquids on glass surfaces. In order to select the most favorable conditions for DART-MS analysis, proper positioning of samples is important. Therefore, a simple and cheap technique for the visualization of the impact region of the DART gas stream onto a substrate was developed. A filter paper or TLC plate, previously loaded with the analyte, was immersed in a derivatization solution. On this substrate, owing to the impact of the hot DART gas, reaction of the analyte to a colored product occurred. An improved capability of detection of DART-MS for the analysis of liquids was demonstrated by applying large volumes of model solutions of coumaphos into small glass vessels and drying these solutions prior to DART-MS analysis under ambient conditions. This allowed the introduction of, by up to more than two orders of magnitude, increased quantities of analyte compared with the conventional DART-MS analysis of liquids. Through this improved detectability, the capabilities of DART-MS in trace analysis could be strengthened.

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.

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.

Sorption concentration of phenylcarboxylic acids (biomarkers of sepsis) from standard test solutions on hyper-cross-linked polystyrene

Sorption conditions (on hyper-cross-linked polystyrene) have been developed for six phenylcarboxylic acids (PCA), which are biomarkers of sepsis, from aqueous standard test solutions and conditions of elution of these acids for subsequent derivatization and analysis by gas chromatography-mass spectrometry (GC-MS). The conditions facilitate detection of PCA in solution at the level (and below) of content of these compounds in blood serum of normal patients. Group extraction of different in polarity required acids from aqueous solutions has been performed selectively with regard to cholesterol adopted as peculiar marker of high boiling interfering compounds. Application of the developed experimental procedure will make it possible to increase significantly the rate of express analysis for diagnostics of sepsis at early stages of development.

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.

Optimization of the conditions for preparation of silyl derivatives of phenylcarboxylic acids in diethyl and methyl tert-butyl ethers

In this work, the optimum conditions of derivatization of six phenylcarboxylic acids (sepsis biom-arkers) in diethyl ether and methyl tert-butyl ether were selected. N,O-Bis(trimethylsilyl)trifluoroacetamide (BSTFA) was used as a silylating agent. The following conditions were chosen as optimum in terms of sensitivity of the silylating agent and its amount: 300 µL of ether and 80 µL of BSTFA, at which the derivatization yield of the studied compounds in model solutions was more than 70% in diethyl ether and more than 85% in methyl tert-butyl ether. The developed conditions will make it possible to increase the derivatization yield at various sample preparation procedures (liquid–liquid or solid-phase extraction) compared to the currently used conditions.

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.

Study of the influence of derivatization conditions on the structure and stability of nucleoside derivatives using gas chromatography-mass spectrometry

Conditions of the derivatization of nucleosides are studied using various reagents. Single trimethylsilyl derivatives of uridine, 5-methyluridine, cytidine, 5-methylcytidine, inosine, xanthosine, N2,N2-dimethylguanosine were obtained by reaction with N,O-bis(trimethylsilyl)trifluoroacetamide. A mixture of trimethylsilyl derivatives of adenosine and guanosine formed under these conditions. N-trifluoroacetyl-O-trimethylsilyl derivatives of cytidine, 5-methylcytidine, adenosine (in mixture with trimethylsilyl derivative) were prepared using N,O-bis(trimethylsilyl)trifluoroacetamide and N-methyl-bis(trifluoroacetamide) (mixed derivatization). Derivatives of cytidine and 5-methylcytidine obtained by mixed derivatization possessed better chromatographic characteristics compared to trimethylsilyl derivatives. The formation of a trifluoroacetyl derivatives of adenosine by the action of N-methyl-bis(trifluoroacetamide) is shown. The possibility of the replacement of the reagent and pyridine by an inert solvent is studied.

Development of Conditions for the Derivatization of Phenyl Carboxylic Acids Isolated from Blood Using Gas-Chromatography/Mass Spectrometry

A method is described for increasing the sensitivity and selectivity of determination of phenyl carboxylic acids (low molecular sepsis markers) in blood using gas chromatography/mass spectrometry. Mass spectra of trimethylsilyl and tert-butyldimethylsilyl derivatives of the target compounds are studied, their structures and molecular ion fragmentation to characteristic m/z values are determined. To prevent the ingress of derivatization agents into the chromatograph-mass spectrometer, the possibility of reagent substitution with inert solvents after the derivatization reaction is studied. The loss of analytes derivatives in the process is estimated. The time dependence of the degree of derivatization of phenyl carboxylic acids in a wide concentration range is investigates using blood serum samples. The chosen optimum conditions are universal for the entire range of analytes over a wide concentration range.