analysis of the quaternary metabolite , n-methylpyridinium ion , was carried out by selective ion-pair extraction and cation-exchange high-performance liquid chromatography ( h.p.l.c . ) using a u.v . detector , and also by direct cation-exchange h.p.l.c . of incubates containing s-adenosyl-l- [ methyl-3h ] methionine using a flow-through radioactivity detector .
C0022023
ion
C0007447
cation