Vol 71, No 14 (2016)

Preliminary conversion of nonpolar organic sulfides into sulfonium salts was proposed for their study and analysis by laser desorption/ionization (MALDI and SALDI) and electrospray/ionization (ESI) mass spectrometry. General possibilities of the methodology proposed were demonstrated on examples of dialkyl sulfides, substituted thiacyclanes, dibenzothiophene, and methionine methyl ester. Various alkyl and aralkyl halides, as well as trimethyl- and triethyloxonium salts were tested as alkylating agents. S-alkylation was shown to proceed quantitatively under mild conditions. MALDI and SALDI mass spectra (a matrix-free nanostructurized target was used in SALDI experiments) displayed only ion peaks corresponding to sulfonium cations whose mass numbers were equal to the sum of molecular weights of sulfides and weight increments of the introduced alkyl and aralkyl groups. Trans-alkylation was observed for benzyl-substituted sulfides. Tandem mass spectrometry provided preliminary data on the fragmentation of ESI-generated sulfonium cations and demonstrated differences in the MS/MS spectra of regioisomers.

The potentials of different chromatography–mass spectrometry methods for the determination of alkyl methylphosphonic acids (AMPAs)—the chemical markers of nerve agents in urine—are compared. The gas chromatography–mass spectrometry (GC–MS) characteristics of various volatile AMPA derivatives are studied. The preference of perfluorobenzyl derivatives over methyl, trimethylsilyl and tert-butyldimethylsilyl esters for the GC–MS determination of AMPAs in urine is demonstrated. An optimal technique for the determination of AMPAs in urine is HPLC combined with high-resolution MS² mass spectrometry with the isotope–labeled forms of target compounds as internal standards. The detection limits of AMPAs in the proposed analytical procedures vary from 0.1 to 1.0 ng/mL.

A novel derivatization method for the analysis of primary amines by MALDI mass spectrometry is proposed. Tris(2,6-dimethoxyphenyl) methyl carbenium cation reacts smoothly with primary amines, forming permanently charged adducts with the mass increment +359 Da and absorbance in the UV region. The approach was tested on a number of amines, including biologically active compounds and therapeutic agents.

It is shown that the use of dimethylformamide dimethylacetal for the derivatization of analytes in gas chromatography/mass spectrometry cannot be restricted by the known conversion of carboxylic acids, phenols, and thiols into their methyl esters (ethers), as well as by the conversion of non-volatile amino acids (and C-amino compounds of other classes) into their dimethylaminomethylene derivatives. The application of this reagent to the derivatization of hydrazine derivatives and volatile carbonyl-containing analytes is considered. In the last case, the reaction proceeds selectively via CH₂ and/or CH₃ groups in the α-position to the carbonyl fragment. The principal predestination of the derivatization of such analytes is their characterization by differences of gas-chromatographic retention indices (ΔRI) of reaction products and initial substrates. The ranges of variation of such increments, ΔRI, appeared to be different for different subgroups of carbonyl compounds; this allowed us to determine their structures more precisely. The mass spectra of C-dimethylaminomethylene derivatives of some carbonyl compounds, preferably 2-substituted 1-methyl- and 1-aryl-3-(dimethylamino) prop-2-en-1-ones, revealed intense [M–17] peaks. The appearance of these signals can be explained by the migration of a hydrogen atom and the formation of [М–ОН]⁺ ions.

An approach to the creation of corpuscular-optical devices for transforming charged particle beams is discussed. These devices are useful for the optimization and creation of the most convenient configuration of the ion path. The approach relies on an inverse dynamics problem formulated on the basis of the Hamilton–Jacobi equation. Motion in the symmetry plane of a three-dimensional field is considered. The problem is solved by analytical methods. An algorithm for the construction electric fields ensuring particle motion along the desired trajectories is described. It is based on the method of physical analogies. The procedure is illustrated by an example. The calculated two-dimensional potential is extended to the 3D-space by a power series on the transverse coordinate. A device embodiment example is demonstrated on the basis of the calculated field structure.

Electron ionization mass spectra and gas chromatographic retention indices of a series of newly synthesized N-monosubstituted (alkyl, aryl, allyl) hydrazones of glyoxylic acid ethyl ester RNHN=CHCO₂C₂H₅ were considered. It was shown the hydrazones were partially converted into isomeric (ethoxycarbonyl)methyl diimides during their GC separation (mostly in the heated injector port of the gas chromatograph). The retention indices of these diimides are lower than those of initial hydrazones by 268 ± 26 i.u. The most remarkable feature of these isomers appeared to be the high identity of their mass spectra because of similar rearrangements in molecular ions.

The use of Euler’s homogeneous electric and magnetic fields can be a good basis for designing static mass spectrometers capable of operating in a spectrographic mode and enabling recording of mass spectra with a wide mass range in one measurement. It is proved mathematically that, when combined Euler’s homogeneous electric and magnetic fields are used to design a single-cascade mass-spectrometer, the double focusing mode cannot be achieved practically along the entire focal line. It is demonstrated that the use of mass spectrographic schemes in which the electric stage and the magnetic stage are separated is an inevitable solution in the creating of a mass spectrograph with high analytical performance.