Fixed-charge generation derivatization for analysis of thiols by «soft» ionization mass spectrometry methods

T16N1

A.V. Kozlov, R.S. Borisov, V.G. Zaikin

A new method for the fixed-charge generation derivatization of thiols of different structures by reaction with haloalkanes and dibromides was suggested. It was shown that 1,4-dibromobutane and 1,2-xylylene dibromide are the most effective alkylating agents, that provided the formation of stable five-membered ring with a positively charged sulfur atom. Such cations are readily detected by electrospray ionization and matrix-assisted laser desorption/ionization mass spectrometry methods. Sulfonium cations were further studied by tandem mass spectrometry using collision-induced dissociation (CID). Typical and specific directions of CID for cyclic cations formed from thiols of different structures were established. They can be used to identify and quantify the thiol analytes by the selected reaction monitoring method.

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Quadrupole ion trap time-of-flight MALDI mass spectrometry: hydration of the ions of hydroxyl-containing compounds

T16N1

D.S. Kosyakov, O. Yu. Khoroshev, E.A. Anikeenko, N.V. Ul’yanovskii

On the example of a number of natural hydroxyl-containing compounds of various classes the possibility of artifact formation, associated with ion hydration, in the quadrupole ion trap MALDI mass spectra is shown for the first time. It was established that when using tandem mass spectrometry, both precursor ions and product ions are involved in the formation of water adducts. The main source of water for ion-molecular interactions in the ion trap are buffer and collision gases. The role of metal cations in the formation of analytes adducts with water is noted. For the majority of studied hydroxyl-containing compounds, hydration proceeds most actively during cationization with lithium ions, with the peak of the [M+H2O+Li]+ ion dominating in the mass spectra.

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On the tryptic peptide features providing their detection and identification by MALDI mass spectrometry

T15N3

B.L. Milman1, А.V. Solov’eva, N.V. Lugovkina, I.K. Zhurkovich

The tryptic peptide features providing detection and identification of these bio compounds and corresponding proteins by matrix-assisted laser desorption/ionization mass spectrometry (MALDI) with the α-cyano-4-hydroxycinnamic acid matrix, are determined and discussed. Twenty five proteins were identified; the features of reliably identified peptides are compared to those of peptides which might be produced by tryptic cleavage and were not detected. Two key factors enhancing a detection possibility of tryptic peptides, were determined. The first one refers to the gas-phase peptide basicity, which is the highest for the C-terminal end arginine peptides; this reason for the emergence of big analytical signals is well-known. The second factor providing ionization of peptides under consideration in the MALDI conditions is their hydrophility. This result does not correlate with the most conclusions of earlier relevant researches and discussed in the article.

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Novel reactive matrices for analysis of alcohols by matrix-assisted laser desorption/ioization mass spectrometry

T15N2

M.S. Slyundina, R.S. Borisov, V.G. Zaikin

The possibility of using a number of aromatic and heteroaromatic carboxylic acids and their halogen anhydrides as reactive matrix compounds for the analysis of alcohols of different structures by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry has been studied. It is shown that acylation of alcohols with nicotinic and quinoline-6-carboxylic acid chlorides makes it possible to obtain derivatives having a high desorption/ionization efficiency under MALDI conditions, and the free acids formed as a result of the hydrolysis of anhydrides act as matrix compounds. The proposed approach is tested on a number of aliphatic, alicyclic and aromatic alcohols.

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A new post-chromatographic derivatization approach to identification of alcohols and phenols in complex mixtures by a combination of planar chromatography and matrix-assisted laser desorption/ionization mass spectrometry

T14N4

C.A. Esparza, N.Yu. Polovkov, R.S. Borisov, A.V. Varlamov, V.G. Zaikin

Simple and suitable approach for post-chromatographic derivatization in the analysis of mixtures of alcohols and phenols by combination of thin-layer chromatography and MALDI mass spectrometry was suggested for the first time. Chemical modification of analytes was accomplished by the treatment of eluted zones on thin-layer chromatograms by 3-bromopropionyl chloride in the presence of excess of a base (pyridine or triethylamine). The resulting derivatives contained a residue with fixed charge (ammonium fragment) that provided an efficient desorption of derivatized analytes from the sorbent layer during MALDI. It was shown that the suggested approach allows the recording of mass spectra with high signal/noise ratio and the detection of alcohols and phenols of different structures. Reproducibility of such MALDI mass spectra is rather high which predetermines a possibility to build the chromatogram curves using total or selected ion current and, hence, their visualization and treatment on quantitative level.

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Phospholipid composition of human blood plasma as detected by matrix-assisted laser desorption/ionization mass spectrometry: new observations

T14N2

B.L. Milman, N.V. Lugovkina, I.K. Zhurkovich

The dependence of matrix-assisted laser desorption/ionization (MALDI) mass spectra of lipids extracted from human blood plasma and corresponding lipid compositions on different experimental conditions was studied. Not only numerous compounds from groups of lysophosphatidylcholines (LPC) and phosphatidylcholines (PC) but also lipid oxidation products including six oxidized LPC, were detected. They were available in the original samples and also produced by the reaction with air oxygen molecules resulted in their accumulation in samples under analysis. A higher sensitivity of MALDI detection was observed for less hydrophobic LPC as compared to more hydrophobic PC and was explained. The hydrophobicity/lipophilicity factor was possibly revealed when the matrix of 2,5-dihydroxybenzoic acid has been replaced by α-cyano-4-hydroxycinnamic acid. The latter was rarely used in MALDI of lipids and may be suitable for the selective determination of LPC and oxidized LPC.

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The comparison between «low-molecular» and conventional approaches to species identification of bacteria by MALDI mass spectrometry

T13N4

B.L. Milman, V.V. Gostev, A.V. Dmitriev

 

The new approach to bacteria identification which uses the standard software for building mass spectral libraries of low-molecular compounds and for corresponding library searches, is compared to the conventional approach based on the commercial Biotyper software and database. The results are obtained for the 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 true outcomes. For similar reference mass spectra and the same identification criteria, the identification results were very close to each other as 24 agreements for 25 strains. This is the result from that different estimations of the mass spectral similarity included in programs under the comparison lead to the correlation of similarity indicators. A difference of identification results is mainly due to not the same reference databases and also different identification criteria.

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The «low-molecular» approach to identification of microorganisms by MALDI mass spectrometry

T13N3

B.L. Milman, Yu.Yu. Ilyasov, N.V. Lugovkina, A.A. Golovina1, A.V. Dmitriev

The new approach to microorganism identification is presented which includes the transformation of their MALDI mass spectra directed to decreasing mass scale by the order of magnitude and the use of the standard software for building mass spectral libraries of low-molecular compounds and library searches. The library of 728 transformed mass spectra of 182 strains for some Streptococcus species was built. With this library, the rate of true identification was estimated by cross-comparison between library mass spectra. The true identification rate is 84 % for three Streptococcus species that corresponds to the average trueness of species identification by MALDI as found in the literature. The proposed approach to identification can be considered as the method of choice for solving problems of bacteria identification.

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Application of microbial alkaloid prodigiosin as a potent matrix for analysis of low molecular mass plant antioxidants by maldi mass spectrometry

T12N3

A.B. Duzhak, T.D. Williams, Z.I. Panfilova, Y.P. Tsentalovich, T.G. Duzhak

Microbal alkaloid prodigiozin (PG) is introduced as a new efficient matrix for negative mode matrix assisted laser desorption/ionization (MALDI) mass spectrometry analysis of low molecular mass plant antioxidants. Physicochemical properties demonstrated by PG such as efficient ionization/desorbtion of the analytes, strong absorbtion at the applied laser wavelength, high solubility in the same organic solvents as analyte, uniform crystallization on the target, stability at working conditions, devoid of matrix fragment and cluster ions in the low m/z region, are in a good agreement with the requirements for the effective matrix. PG as a potent matrix facilitates effective ionization of plant antioxidants from multicomponent preparations. Characteristic features of flavonoid aglycones mass spectra recorded in the presence of PG as a matrix are high quality (signal to noise ratio more than 103) and good reproducibility. Application of PG for MALDI MS analysis of complex plant antioxidants mixtures permit the simultaneous detection and confident interpretation of the large set of ions corresponding to more than twenty different antioxidants in the low m/z range of 100 – 500.

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Влияние органических добавок на увеличение интенсивности сигналов протонированных пептидов в масс-спектрах матрично-активированной лазерной десорбции/ионизации

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