Anzor I. Mikaia

Mass spectrometry of analytical derivatives. 1. Cyanide cations in the spectra of N- alkyl-N-perfluoroacyl- α-amino acids and their methyl esters.

The central mission for the development of the National Institute of Standards and Technology/National Institutes of Health/Environmental Protection Agency Mass Spectral Library is the acquisition of reference gas chromatography–mass spectrometry data for important compounds and their chemical modification products. The addition of reliable reference data of various derivatives of amino acids to The Library, and the study of their behavior under electron ionization conditions may be useful for their identification, structure elucidation, and a better understanding of the data obtained when the same derivatives are subjected to other ionization methods. N-Alkyl-N-perfluoroacyl derivatives of amino acids readily produce previously unreported alkylnitrilium cations of composition [HC≡N-alkyl]+. Homologous [HC≡N-aryl]+ cations are typical for corresponding N-aryl analogs. The formation of other ions characteristic for these derivatives involves oxygen rearrangement giving rise to ions [C n F2n+1–C≡N+–C n H2n+1] and [C n F2n+1-C≡N+-aryl]. The introduction of an N-benzyl substituent in a molecule favors a process producing benzylidene iminium cations. L-Threonine and L-cysteine derivatives exhibit more fragmentation pathways not typical for other α-amino acids; additionally, the Nω-amino group in L-lysine directs the dissociation process and provides structural information on the substitution at the amino functions in the molecule.

Gas chromatographic-mass spectrometric characterization of thebaol,an opium constituent, and its structural analogs

HIGHLIGHTSA highly efficient GCMS method is developed for reliable detection of thebaol, a constituent of opium poppy.A unique behavior for trialkylsilyl derivatives of thebaol derivatives under mass spectrometry conditions is established.Loss of two radicals via violation of the ‘even electron rule’ is specific for trialkylsilyl and perfluoroacyl derivatives of thebaol. ABSTRACT A GC–MS method is described for the characterization of thebaol, a component of opium poppy. The method includes preliminary sample derivatization to TMS, TBDMS, TFA, PFP and HFB substituted products. Fragmentation of resulting derivatives is unique under electron ionization, and proceeds via consecutive loss of two radicals that violate the “even‐electron rule”. Peaks of [M‐2CH3]+. and [M‐C4H9‐CH3]+. ions show maximum intensities in the spectra of trimethyl‐ and tert‐butyldimethylsilyl‐thebaols. Elimination of perfluoroalkyl and methyl radicals from M+. is characteristic for TFA, PFP and HFB thebaols. The same fragmentation peculiarity is characteristic for derivatives prepared from related natural compounds containing vicinal 2‐methoxyphenol moieties. The unique fragmentation of trialkylsilyl and perfluoroacyl derivatives of thebaol can be successfully used for thebaol determination within complex mixtures. This is part 4 from the series “Analytical derivatives in mass spectrometry”, parts 1, 2 and 3 see [1–3].