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The previously described derivatization approach based on the interaction of compounds with the primary amino group and the tris(2,6-dimethoxyphenyl)methyl cation is tested and proposed for increasing the efficiency (desorption) of the ionization of low-molecular-weight oligopeptides under MALDI conditions. The results obtained showed that the use of the method ensures the achievement of an increase in the yield of ion, and a large increment of the introduced group outputs the target signals from the noisy low-molecular-weight region of the mass spectrum. The study of the main fragmentation pathways of the derivatives under collision-induced dissociation ensure the identification of a series of ions suitable for establishing the amino acid sequence of peptides., Author(s): N. Yu. Polovkov [sup.1] , A. P. Topolyan [sup.2] , V. V. Ilyushenkova [sup.1] , A. D. Danilov [sup.3] , M. E. Zimens [sup.1] , R. S. Borisov [sup.1] [...]

Preliminary transformation into sulfonium salts by an electrophilic reaction with alkyl formates in the presence of trifluoromethanesulfonic acid is proposed for the study and analysis of non-polar organic sulfides by matrix-assisted laser desorption/ionization (MALDI). The test samples are thiabicyclanes with different positions of the sulfur atom and methyl substituents (2- and 3-thiabicyclo[4.4.0] decanes, 7- and 8-thiabicyclo [4.3.0] nonanes). The reaction used provide quantitative S-alkylation under mild conditions. In MALDI mass spectra of sulfonium salts, only peaks of corresponding sulfonium cations were observed, the masses of which corresponded to the sum of molecular weights of the sulfide and the increment of the introduced alkyl group. Drastic qualitative and quantitative differences were found and interpreted in the mass spectra recorded in the collision-induced dissociation mode for regio-isomeric sulfonium cations., Author(s): Zh. E. Starkova [sup.1] , N. Yu. Polovkov [sup.1] , A. Yu. Kanateva [sup.1] , R. S. Borisov [sup.1] [sup.2] , V. G. Zaikin [sup.1] Author Affiliations: (1) grid.423490.8, [...]

We studied the interaction of acyl derivatives of carbocyclic alcohols of steroid structure with nitrogenous bases in the ion source of a 'direct analysis in real time' (DART) mass spectrometer. The protonation of esters in the DART plasma is accompanied by the elimination of a corresponding acid (acyl derivatives of cholesterol, [beta]-sitosterol, and estradiol), interaction of the formed cation with a nitrogenous base to yield a derivative with a bound charge. This effect was not observed for cortisone acetate and betamethasone dipropionate, which is consistent with the absence of ions of deacyl derivatives in their DART mass spectra., Author(s): S. V. Goriainov [sup.1] [sup.2], C. Esparza [sup.2], D. I. Zhilyaev [sup.1] [sup.2], N. Yu. Polovkov [sup.1], R. S. Borisov [sup.1] [sup.2], V. G. Zaikin [sup.1] Author Affiliations: (1) [...]

We studied a possibility of using direct analysis in real time (DART) mass spectrometry in combination with in situ derivatization by nitrogenous heterocyclic compounds for the rapid profiling of sterols in sweetened condensed milk. The data obtained are consistent with the detection of plant sterols by gas chromatography-mass spectrometry (GC-MS). The proposed approach can be used to detect vegetable fats in condensed milk, and the time required for the analysis of one sample, including sample preparation, is several times shorter than that in GC-MS., Author(s): S. V. Goryainov [sup.1] [sup.2], C. Esparza [sup.2], A. R. Borisova [sup.2], K. Fadi [sup.2], E. O. Rystsova [sup.2], N. Yu. Polovkov [sup.1], R. S. Borisov [sup.1] [sup.2], V. [...]

A comparative analysis of the results of using the method described in GOST (State Standard) 33490-2015, and an original method for the detection and quantification of markers of diary product adulteration with vegetable oils, 4-desmethylsterols, by gas chromatography/electron ionization mass spectrometry was performed. It was shown that, using the original procedure, one can avoid false positive results and reduce the time of analysis., Author(s): S. V. Goriainov [sup.1] [sup.2], C. Esparza [sup.2], A. R. Borisova [sup.2], L. N. Kulikova [sup.2], N. Yu. Polovkov [sup.1] Author Affiliations: (1) grid.423490.8, 0000 0000 9321 0752, Topchiev [...]

A new method of the derivatization of alcohols for their analysis by matrix-assisted laser desorption/ionization (MALDI) and surface-assisted laser desorption/ionization (SALDI) is proposed. The approach is based on the silylation of the analytes with bromomethylchlorodimethylsilane in the presence of tertiary amines to yield fixed-charge containing derivatives. The proposed method was tested using aliphatic alcohols, terpenols, and sterols. MALDI and SALDI mass spectra of all derivatives contain intense ion peaks corresponding to their cationic parts., Author(s): D. I. Zhilyaev [sup.1] , L. G. Voskresensky [sup.1] , N. Yu. Polovkov [sup.2] , R. S. Borisov [sup.1] [sup.2] Author Affiliations: (Aff1) 0000 0004 0645 517X, grid.77642.30, People's [...]

MALDI mass spectra of 33 pharmacological substances recorded from standard metal targets using four different matrices (HABA, DHB, IAA and AT) have been obtained for the first time. They revealed only peaks for ions [[M + H].sup.+], [[M + Na].sup.+], and [[M + K].sup.+] with different intensities. It has been shown that MALDI spectra of the compounds can be obtained as a result of the desorption/ionization of analytes from spots on thin-layer chromatogram (TLC) (silica stationary phase) in the presence of the same tested matrices. It has been found that graphite can be efficiently used as a matrix in combination of TLC with MALDI mass spectrometry, as it eliminates the danger of the broadening of spots on TLC plates in the treatment with matrix solution and reduces the time of sample preparation. Keywords: MALDI mass spectrometry, combination of TLC with MALDI, pharmaceutical substances, graphite as a matrix DOI: 10.1134/S1061934815140038, INTRODUCTION Planar (thin-layer) chromatography (TLC) occupies an important place in the qualitative and semi-quantitative analysis of complex natural, pharmaceutical, medico-biological, and chemical samples. The main advantages of TLC are the [...]

A simple and convenient method for the derivatization of alcohols for their subsequent analysis by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry has been proposed. The method includes the acylation of alcohols by bromoacetyl chloride followed by treatment with a base (triethylamine in this work). If amine is used as a base, an excessive amount of it in the reaction mixture immediately reacts with bromoacetate and the process in fact consists of one stage. MALDI mass spectra of the formed quaternary salts recorded in the presence of non-acid matrices or using a target with a nanostructured surface demonstrated only peaks for cationic parts of the derivatives. Using a mixture of aliphatic primary alcohols from C2 to C18, it has been shown that the derivatization reaction proceeds completely and MALDI mass spectra can be used not only for the determination of their molecular masses, but also for their quantitative analysis and profiling. Keywords: MALDI mass spectrometry, alcohols, derivatization, covalently bound charge, ammonium salts DOI: 10.1134/S106193481513002X, INTRODUCTION At present soft ionization mass spectrometric methods, among which versions with electrospray ionization (ESI) and matrix-assisted laser desorptoion/ionization (MALDI) are particularly popular, are widely used in the analysis of [...]

The potentials of using a graphite matrix for laser desorption/ionization from a thin-layer chromatography (TLC) spot is studied. Using a series of pharmaceutical substances with various functional groups and synthetic N-heterocyclic compounds, it was shown that the simple application of graphite onto TLC spots (outlining contour of the spots and shading the spots with a pencil lead) ensured the efficient desorption/ionization of analytes. In most of cases, the recorded mass spectra revealed only [[M + Na].sup.+] and [[M + K].sup.+] ion peaks, doublets of which can be used to determine molecular masses. The appearance of [[M + H].sup.+] ion peaks in some mass spectra may be due to the presence of mineral acids in the samples. The described approach to the application of the 'matrix' onto analyte spots eliminates the danger of spot blurring by a solution or an organic matrix, simplifies the procedure, and shortens the time of sample preparation. Keywords: graphite-assisted laser desorption/ionization, GALDI mass spectrometry, thin-layer chromatography, graphite, pharmaceutical substances, N-heterocyclic compounds DOI: 10.1134/S1061934814140032, INTRODUCTION Matrix-assisted laser desorption/ionization mass spectrometry (MALDI) most often includes the use of various organic matrices. At the same time, the so called matrix-free versions, based on the activation of [...]

Humans are widely exposed to bisphenol-A (BPA) owing to the ubiquitous use of this chemical in consumer products. Increasing attention is paid to the effect of BPA, because it has the hormone-like structure and it can potentially adversely affect. A simple, efficient, cheap analytical procedure for quantitative determining the analyte is reported in this paper. The suggested method includes the sample preparation based on a double liquid-liquid microextraction combined with non-enzymatic acidic hydrolysis under the influence of microwave radiation of the BPA conjugates with glucuronic and phosphorous acids followed by trimethylsilylation and GC/MS detection. The detection and quantification limits of BPA in the human urine sample are 0.3 and 1 ng/mL respectively. The calibration curve for this analyte is linear with a correlation coefficient of > 0.99 in the range of 1-50 ng/ml. Method recoveries were between 86 % and 110 %, while repeatability was below 10 %. The method was satisfactorily applied to the determination of target compounds in human urine samples from 20 randomly selected individuals. The detection frequency in urines was 40 %. The maximum detected concentration of BPA was 479 ng/mL. The proposed non-enzymatic method is simple, fast, inexpensive and suitable for the determination of BPA in urine samples in the framework of biomonitoring studies and bioanalytical analyses., Competing Interests: Declaration of Competing Interest The authors declare that there are no conflicts of interest., (Copyright © 2020 Elsevier B.V. All rights reserved.)

On-spot fixed-charge derivatization has been suggested for the modification of α-amino acids for their analysis by thin layer chromatography/matrix-assisted laser desorption ionization (TLC/MALDI) mass spectrometry. The approach was based on post-chromatographic treatment of separated analytes by tris(2,6-dimethoxyphenyl)methenium salt and triethylamine. The reaction proceeded smoothly in mild conditions and gave rise to pink-red colored derivatives, containing permanent positive charge. Their MALDI mass spectra, recorded directly from TLC plates, revealed intense peaks corresponding to decarboxylated cationic parts. All derivatives are characterized by high ionization efficiency, which indicates the high sensitivity of the developed method for analyzing amino acids. Applicability of the method to analysis of amino acids was demonstrated on artificial mixtures and dietary supplement., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

The potential of preliminary silylation for the determination of numbers of hydroxyl groups in separate molecules of oligomeric silsesquioxanes by matrix-assisted laser desorption/ionisation mass spectrometry has been demonstrated for the first time. Derivatisations allowing the introduction of trimethylsilyl, tert-butyldimethylsilyl and pentafluorophenyldimethylsilyl groups were tested. It was shown that more reliable structure elucidation of individual oligomers can be achieved knowing the number of hydroxyl groups thus determined.