Том 73, № 13 (2018)
- Жылы: 2018
- Мақалалар: 12
- URL: https://journals.rcsi.science/1061-9348/issue/view/11427
Articles
Determination of Thiodiglycol and Its Oxide in Biomedical Samples by Gas Chromatography–Mass Spectrometry
Аннотация
A unified procedure is proposed for the determination of thiodiglycol (TDG) and its oxide (TDGO) as markers of exposure to sulfur mustard in biomedical samples (urine, blood plasma, hairs) by gas chromatography–electron ionization mass spectrometry. The limit of detection of the procedure is comparable with the lowest level of endogenous TDG in biosamples (1 ng mL–1). Solid-phase microextraction of the derivatized analytes from the reaction mixture decreases the matrix effect. The procedure was tested in the analysis of rat biosamples obtained after in vivo exposure to sulfur mustard. The procedure was found to offer a higher potential in the retrospective determination of the total TDG and TDGO level in rat urine (within 7 days after exposure to 2 mg kg–1 of sulfur mustard) compared to the determination of the same markers in blood plasma. Blood plasma can be used for confirmatory analysis, provided the samples are taken within 2 days after exposure. Hair was found to be the least suitable biomatrix in view of the variability of the TDG background level in these samples and the possibility of contamination with TGD from other sources.
A Comparison of “Low-Molecular” and Conventional Approaches to the Species Identification of Bacteria by MALDI Mass Spectrometry
Аннотация
A new approach to bacteria identification that uses the standard software for building mass spectral libraries of low-molecular compounds and for corresponding library searches is compared with the conventional approach based on the commercial Biotyper software and database. The results are obtained for a random sample of 100 mass spectra of 25 strains of S. pyogenes, S. dysgalactiae subsp. equisimilis, and S. anginosus. The spectra were sampled from the database of 728 mass spectra of 182 strains for some Streptococcus species. Both approaches were proved to result in the similar identification as 80–88% of the true outcomes. For similar reference mass spectra and the same identification criteria, the results of identification were very close to each other as 24 agreements for 25 strains. This is because different estimations of mass spectral similarity included in the programs under comparison lead to a correlation of similarity indicators. The difference in usual identification results is mainly due to different reference databases and also different identification criteria.
Study of the Products of Oxidation of 1,1-Dimethylhydrazine by Nitrogen Dioxide in an Aqueous Solution by High-Resolution Mass Spectrometry
Аннотация
Products of the interaction of 1,1-dimethylhydrazine with nitrogen dioxide in an aqueous solution are characterized by high-resolution mass spectrometry with electrospray ionization. It was found that more than 200 compounds of CHO, CHN, and CHNO classes formed in the reaction; the main component is extremely dangerous N-nitrosodimethylamine. Among the products of the transformation of 1,1-dimethylhydrazine, N-nitrosodibutylamine is identified for the first time. The results obtained are of importance for understanding processes of the transformation of rocket fuel in surface and ground waters at the places of impact of spent rocket stages containing both the propellant and the oxidant.
Methodological Problems in the Replacement of Discrete Mass Spectrometric Models by Continuum Models
Аннотация
Two problems of mass spectrometry, namely, involving the model of chemical kinetics of cluster formation and the model of the pseudopotential of stroboscopic samples of coordinates and ion velocities in quadrupole radio frequency fields, are considered as the examples in investigating the relationship between discrete models with finite-difference equations and continuum models with point derivatives. In developing continuum models, integer indices are replaced by real parameters, and finite-difference relations are replaced by approximate differential relations involving derivatives. It is shown that this procedure is not reliable: the discrete model and the continuum model can diverge globally, even if for intuitive reasons it is expected that the models should be close. As a result, the transfer of the conclusions obtained for the approximate continuum model to the exact physical model can lead to conceptually significant errors and requires the investigator to be careful. In particular, the continuum model of the chemical kinetics of cluster formation and the continuum model of the pseudopotential of stroboscopic samples of coordinates and ion velocities in quadrupole radio frequency fields, considered as an example, are both insolvent.
A New Post-Chromatographic Derivatization Approach to the Identification of Alcohols and Phenols in Complex Mixtures by a Combination of Planar Chromatography and Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry
Аннотация
A simple and suitable approach to the post-chromatographic derivatization in the analysis of alcohol and phenols mixtures by a combination of thin-layer chromatography and MALDI mass spectrometry was proposed for the first time. The chemical modification of analytes was accomplished by the treatment of eluted zones on thin-layer chromatograms by 3-bromopropionyl chloride in the presence of an excess of a base (pyridine or triethylamine). The resulting derivatives contained a residue with a constant charge (ammonium fragment) that ensures the efficient desorption of the derivatized analytes from the sorbent layer during MALDI. It was shown that the proposed approach allows the recording of mass spectra with a high signal/noise ratio and the detection of alcohols and phenols of different structures. The reproducibility of such MALDI mass spectra is rather high, which predetermines a possibility of building chromatogram curves using total or selected ion current and, hence, their visualization and treatment on the quantitative level.
Products of the Intermediate Oxidation of Flavonoids in Aqueous Solutions and the Determination of Their Composition by High-Performance Liquid Chromatography–Mass Spectrometry
Аннотация
Using high-performance liquid chromatography in combination with electrospray ionization mass spectrometry [HPLC–MS-ESI(NEG)], quercetin [Q] and luteolin [L] intermediate oxidation products were investigated. It was found that, in aqueous solutions at pH 8.0 under aerobic conditions, quercetin forms double and triple donor-acceptor complexes of the composition {[Q][Q–H2]} and {[Q][Q–H2]2}, which can be separated by HPLC, but are rapidly converted to deeper oxidation products. In the presence of another flavonoid, luteolin (L), the oxidized form of quercetin also forms mixed complexes of {[L][Q–H2]} and {[L][Q–H2]2} types. Luteolin in the oxidation does not form donor-acceptor {[L][L–H2]} complexes. Quercetin in complexes with luteolin is always present in an oxidized form. It can be assumed that these complexes form as a result of the recombination of two radicals of flavonoids, which formed initially as a result of manifestation of the antioxidant properties (one-electron transfer). These transformations of flavonoids are possible if strict anaerobic conditions in their quantitative determination are not implemented.
Group Identification of O-Alkyl Alkylphosphonothionofluoridates by Electron Ionization Mass Spectra Using Generalized Spectral Images of Taxonomic Groups
Аннотация
A method is proposed for the group identification of poorly studied highly toxic O-alkyl alkylphosphonothionofluoridates by electron ionization mass spectra. The method is based on the use of generalized spectral images of four taxonomic groups of this class, subjected to control under the Chemical Weapon Convention. The generalized spectral images were obtained by analyzing the revealed regularities of the fragmentation of these compounds. An advantage of the proposed method is that the assignment of a test substance to one of the class groups and to a class as a whole is a rapid automated standard procedure used in the NIST information retrieval system.
Characterization of Disinfection By-Products in Arkhangelsk Tap Water by Liquid Chromatography/High-Resolution Mass Spectrometry
Аннотация
Disinfection of drinking water with chlorine-containing reagents leads to the formation of a large number of disinfection by-products, resulting from the chlorination of natural dissolved organic matter. High-performance liquid chromatography/high-resolution mass spectrometry with solid-phase preconcentration on a polymeric sorbent was used to study the component composition of halogen-containing disinfection by-products in Arkhangelsk tap water. Fourteen chlorinated and brominated organic compounds, which belong to the classes of halophenols, aromatic acids, carbonyl compounds, and chlorine-substituted nitrogen-containing heterocyclic compounds, have been found. Based on the analysis of MS/MS spectral data, possible structures of the detected disinfection by-products are proposed.
An Improved Procedure for the Gas Chromatography–Tandem Mass Spectrometry Detection of the Globin Adduct of Sulfur Mustard
Аннотация
Features of the electron and chemical ionization mass spectra of derivatives of N-[2-[(hydroxyethyl)thio]ethyl]-DL-valine (НЕТЕ-Val)—a biomarker of sulfur mustard—recorded by GC–MS and GC–MS/MS are studied. The retention indices of the studied derivatives were measured. An optimized procedure of the GC–MS/MS (MRM mode) identification of НЕТЕ-Val was tested in the analysis of donor blood samples in vitro exposed to sulfur mustard. The linear range of the detector was from 10 to 100 ng mL–1, and the limit of detection for sulfur mustard was 10 ng mL–1.
Determination of the Structure of Alkyl Radicals in a Series of Highly Toxic Organophosphorus Compounds Using Mass Spectrometry Databases and Library Search
Аннотация
We propose an approach to the identification of alkyl radicals attached to the ester oxygen atom in a series of highly toxic organophosphorus compounds, based on the revealed regularities in the formation of mass spectra of monofunctional RX compounds (R is alkyl radical and X is functional group). The method includes the extraction of the hydrocarbon subspectrum from the mass spectrum of the analyte and its comparison with the hydrocarbon subspectra of the known monofunctional compounds. Alkyl radicals are identified using simple metrics that characterize the coincidence of hydrocarbon subspectra. The results of the identification of alkyl (cycloalkyl) radicals in a series of O-alkyl (cycloalkyl) alkylphosphonofluoridates, and O-alkyl (cycloalkyl) N,N-dialkylphosphoramidocyanidates show that ≥95% of the structures of the radicals of these compounds are within 10 positions of the search result list.
Development of a System for Measuring and Recording Ion Currents for an MI-1201IG Mass Spectrometer
Аннотация
In the complex modernization of an MI-1201IG isotope mass spectrometer, a new system for measuring and recording ion currents was developed, including an electrometric amplifier based on a high-resistivity (1 TΩ) feedback resistor and a special chip located in the electrometer head. A recording circuit based on a high-precision analog-to-digital converter was included in the new unit for controlling the separating magnetic field and measuring the ion current. In designing the system circuit, the task was not only to increase the sensitivity and expand the dynamic range when measuring the intensity of peaks in mass spectra but also to decrease the time constant of the analog part of the measuring system for the undistorted transfer of the ion current distribution form to the input of the analog-to-digital converter in a dynamic mode. A shielding system was designed that distributes the electric field gradient on the surface of a high-resistivity feedback resistor, which made it possible to compensate its distributed capacitance and decrease the time constant of the electrometric amplifier to 0.2 s. To compensate for the distortion of the shape of the ion current pulses, caused by the in-to-out stray capacitance of the electrometer’s amplifier chip, a special circuit was developed. This results in that the end-to-end frequency response of the new system for measuring and detecting ion currents is determined only by the upper cut-off frequency of the low-pass filters of 10 Hz. The high-speed measuring system made it possible to improve the mass-spectrometric resolution and mass accuracy and to increase full-spectrum scan rate. The working range of the new system for measuring and recording ion currents is 1 × 10–15 to 3 × 10–12 A. The measured equivalent root-mean-square input noise is 0.86 fA at the sampling frequency of 10 Hz and the integration time of 1 s and 0.14 fA at the integration time of 10 s.
A Study of Novel Organic Optoelectronics Materials Based on Thiophene and Silicon by Time-of-Flight Laser Desorption/Ionization Mass Spectrometry
Аннотация
The results of investigation of a variety of new organic semiconductors for optoelectronics based on thiophene and silicon by time-of-flight direct laser desorption/ionization mass spectrometry are presented. The peculiarities of the behavior of these species are analyzed. The main ionization route for many of the compounds was found to be the only formation of a molecular radical cation. For a small group of species, protonation and deprotonation were observed rather than the above path. However, there are some molecules for which several competing routes were detected, namely, the formation of a molecular radical cation, protonation, and deprotonation