Temperature-programmed gas chromatography linear retention indices of all C4-C30 monomethylalkanes on methylsilicone OV-1 stationary phase. Contribution towards a better understanding of volatile organic compounds in exhaled breath.

Monomethylated alkanes have been proposed to be contained in exhaled breath, their concentration pattern serving for identification of lung carcinoma, breast carcinoma and rejection of foreign tissue after heart transplant rejection. Improving the accuracy of identification for monomethylated alkanes will enhance work on their biochemical background which presently is unknown. The programmed temperature linear retention indices of all 196 C(4)-C(30) monomethylalkanes on OV-1 stationary phase were measured with an average repeatability of +/-0.07 index units (i.u.). The mixture of C(9)-C(30) monomethylalkanes was prepared by methylene insertion reaction to C(8)-C(29)n-alkanes mixture. The preliminary identification of monomethylalkanes was performed on the basis of the dependence of homomorphy factors on the number of carbon atoms of individual homologous series of monomethylalkanes (retention indices extrapolated with s=0.15 i.u.). The prediction of retention of isomers with new position of methyl group beginning at higher carbon atoms number, as well as for second, third, fourth, etc., member of homologous series allowed the dependence H(P)=f(C(n)) for first, second, third, etc., members of beginning homologous of monomethylalkane series (retention indices extrapolated with s=0.17 i.u.). The identification was confirmed by mass spectrometry. All gas chromatographic unseparated monomethylalkane isomers with methyl-group near the middle of molecule carbon chain were resoluted by mass spectrometric deconvolution. Obtained regular dependences H(P)=f(C(n)) allow precise retention prediction of monomethylalkanes C(30).