Gas chromatographic analysis of dialkylbarbituric acids

A variety of procedures for the derivatization of barbituric acids for gas-liquid chromatography (GLC) are described and a convenient procedure for n-alkylation of barbiturates is reported. The gas chromatographic behavior of derivatives(methyl, ethyl, propyl, butyl, pentyl and hexyl) is discussed on the basis of the retention index. For the identification and quatitation of 23 barbiturates in biological fluids, use of the propyl derivatives allows a clear gas chromatogram to be obtained by using only one stationary phase. Alkylation with n-alkylating reagents gives only the N,N'-derivative, as confirmed by nuclear magnetic resonance (NMR) and infrared spectroscopy and gas chromatography-mass spectrometry (GC-MS). The fragmentation pattern by electron-impact mass spectrometry is discussed. Alkylation with branched alkylating reagents gives up to three peaks, the major peak being the N,N'-derivative; the other peaks identified by NMR and GC, correspond to the isomeric N,O-derivatives.