Volume 73, Nº 13 (2018)

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.

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.

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.

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.

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.

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.