CONCENTRATIONS OF L-DOPA IN PLASMA AND PLASMA ULTRAFILTRATES

A sensitive and specific procedure is described for the determination of therapeutically relevant concentrations of L-dopa in plasma and pla sma ultrafiltrates (free fraction) by high performance liquid chromato graphy with electrochemical detection. In plasma samples from healthy adult subjects (n = 15) spiked with L-dopa (500 mu g l(-1)) the free f raction averaged 76 +/- 8% (range 61-84%). Free fraction values increa sed by 38% with increasing plasma concentrations of L-dopa from 100-50 00 mu g l(-1), L-dopa free fraction was not affected by the presence o f 3-o-methyl-dopa at concentrations up to 10 000 mu g l(-1).