Revealing compounds unstable during gas chromatographic separation. Non-substituted hydrazones of carbonyl compounds

Abstract

Evaluating the content of contemporary GC-MS databases (including the NIST database) allows revealing compounds not enough characterized both mass spectra, and GC retention indices ( RI ). Among relatively simple objects of this type there are the products of carbonyl compounds interaction with hydrazine – non-sub­sti­tu­ted hydrazones and azines. Revealing the reasons for the lack of reference information for these compo­unds indicates that non-substituted hydrazones are thermally unstable and converts into azines inside chromatographic column during separation. It is resulted in the appearance of specific profiles of chromatograms and leads to irreproducibility of relative peak areas of these compounds, strong variations of retention times and, hence, low reproducibi­lity of their retention indices. Nevertheless, more then do­zen of non-substituted hydrazones and the same number of corresponding azines were characterized first time by stan­dard EI mass spectra and RI values on stan­dard non-polar polydimethyl siloxane stationary phases. On the example of reaction mixtures of alkyl aryl ketones with hydrazine (un­der medium conversion of substrates into derivatives) the new effect in chroma­to­graphy is revealed. The chromatograms of these samples contain the diffused zo­nes of hydrazones with retention times less then retention times of such hydra­zones from reaction mixtures. The explanation of this anomaly is the for­ma­tion of volati­le hydrazine during hydrazone decomposition, followed by its secon­dary interac­tion with initial carbonyl compound taking place in another part of chromato­gra­phic column. Keywords: Gas chromatography, instability of analytes during separation, non-substituted hydrazones, thermal conversion into azines, mass spectra, retention indices, secondary reactions in gas chromatographic column DOI: http://dx.doi.org/10.15826/analitika.2017.21.2.002 Igor G. Zenkevich, Nikita E. Podol’skii St. Petersburg State University, Universitetskii prosp., 26, St. Petersburg, 198504, Russian Federation