A high-pressure liquid chromatographic method for plasma phenylacetic acid, a putative marker for depressive disorders.

An HPLC procedure for the determination of total phenylacetic acid (PAA) in human plasma is described. After precipitation of plasma proteins with 0.4 N HClO4, the supernatant was hydrolyzed with 1.5 N HCl at 100 degrees C for 5 h, and PAA was extracted with benzene. From the organic layer PAA was back-extracted into 0.5 ml of 0.1 N NaOH. After neutralization with HCl the sample was directly injected onto the HPLC column (C18). An ultraviolet detector at 210 nm was used to monitor PAA. The plasma PAA values for a control population (536.18 +/- 54.99 ng/ml, N = 10) (X +/- SE) obtained by the described method are in agreement with values reported using GC/MS methods. Depressed subjects showed significantly lower values (327.64 +/- 45.44 ng/ml, N = 10), supporting the view that PAA may be a marker for depressive disorders.