Stability of 3,4-dihydroxyphenylacetic acid in plasma extracts assayed by high-performance liquid chromatography with electrochemical detection.

3,4-Dihydroxyphenylacetic acid (DOPAC) can be easily assayed by high-performance liquid chromatography (HPLC) with electrochemical detection at the same time as norepinephrine (NE), epinephrine (E), and dopamine (DA). The latter catecholamines are stable in perchloric acid extracts for over 6 h at 4 degrees C in the dark whereas DOPAC levels drop rapidly by more than 50% in 6 h at 4 degrees C in the dark. This study investigated the effects of reducing agents [ascorbic acid, dithiothreitol (DTT), reduced glutathione with or without a metal chelating agent (diethylenetriaminepentaacetic acid or ethylenediaminetetraacetic acid)] on DOPAC. Extracted with alumina using 0.65 mmol/1 DTT prior to HPLC and electrochemical detection, DOPAC remained stable in the perchloric acid extract for 2 h at 4 degrees C in the dark.