UNUSUAL DEUTERIUM-ISOTOPE EFFECT ON THE RETENTION OF FORMAMIDES IN GAS-LIQUID-CHROMATOGRAPHY

The deuterium isotope effect on gas chromatographic retention of a ser ies of N,N-dimethylformamide, N-methylformamide and formamide isotopom ers was studied on methyl and phenyl methyl polysiloxane and polyethyl ene glycol stationary phases. The deuterium isotope effect was substan tially affected by the position of deuterium in the molecule. Whereas methyl-deuterated ((CH3)2NCHO)-H-2 and (CH3NHCHO)-H-2 eluted, as expec ted, earlier than their non-labelled analogues, elution of formyl-deut erated ((CH3)2NCHO)-H-2, (CH3NHCHO)-H-2 and (NH2CHO)-H-2 was always de layed. The presence of chemically inequivalent deuterium atoms in ((CH 3)2NCHO)-H-2-H-2 and (CH3NHCHO)-H-2-H-2 resulted in final deuterium is otope effects to which the contributions of the individual groups were additive. The elution order of the individual isotopomers was not aff ected by the polarity of the stationary phase. Interpretation of the d euterium isotope effect observed is provided by the theory of vapour p ressure isotope effects.