Prediction of gas chromatographic retention indices of 2,4-dinitrophenylhydrazones

Kovats retention indices (I) of C-1-C-8 aldehydes and ketones and their 2,4-dinitrophenylhydrazones (DNPHs) were determined. The temperature gradient of the retention indices of keto hydrazones is higher than that of aldehyde hydrazones, hence the separation of certain co-eluting hydrazones is possible by changing the elution temperature. The retention index difference between the E- and Z-isomers increases with increasing asymmetry in the groups attached to the hydrate carbon atom. The slope a in the equation I-DNPH = aI(oxo), + b is near unity for not heavily branched aldehyde DNPHs, whereas for keto E-isomers it is less than unity and changes with the structure