DETERMINATION OF HOMOVANILLIC-ACID IN HUMAN PLASMA USING HPLC WITH ELECTROCHEMICAL DETECTION AND AUTOMATED SOLID-PHASE EXTRACTION

An isocratic HPLC method with electrochemical detection for the quanti fication of homovanillic acid (HVA) is described. The method included automated solid phase extraction on C18-reversed phase material, follo wed by separation on a 3-mum Nucleosil 100 C18 column (250 mm x 4.6 mm I.D.) with a 100 mM citric acid solution (pH 6.6) containing 4% aceto nitrile (v/v) as eluent at a flow rate of 0.6 ml/min. Isovanillinic ac id served as internal standard. Extractability of both analytes was ca . 80 %. After extraction of 1 ml of plasma, coefficients of variation of replicate analyses were below 10 % in the naturally occuring concen tration range.