Electrophore-labeling and alkylation of standards of nucleic acid pyrimidine bases for analysis by gas chromatography with electron-capture detection

Abstract The pyrimidine bases cytosine, uracil and thymine, along with some analogues, are electrophore-labeled either with pentafluorobenzoyl chloride ( PFBC ), pentafluorophenylsulfonyl chloride ( PPSC ), or heptafluorobutyric anhydride. Subsequent alkylation is most successful for PFB -cytosine, PFB -cytosine, PPS -uracil, and PPS -thymine. These same alkylated compounds also have the highest aqueous stability and respond most strongly by gas chromatography—electron-capture detection. One of these derivatives, determined to be N 4 - PFB -1,3-dimethylcytosine by authentic synthesis, and its 5-methyl analgue, can be detected with good precision down to the 100-fg level. Poor reprocucibility is encountered at the 10-fg level.