Voltammetric behaviour of salicylic acid at a glassy carbon electrode and its determination in serum using liquid chromatography with amperometric detection.

Cyclic voltammetry was used to investigate the oxidation of salicylic acid at a planar glassy carbon electrode. The electrode reaction was found to be dependent on the pH and ionic strength of the acetate buffer, which contained 35% methanol. Under these conditions the maximum electrochemical signal was obtained with a supporting electrolyte of 0.06 mol dm-3 acetate buffer in 35% methanol (pH 5.0). The peak current value (ip) increased by approximately 10% when the methanol concentration was decreased to 8%. The substance was found to undergo an irreversible reaction involving one electron and possibly two protons in the initial oxidation step with at least one possible quasi-reversible follow-up reaction. The optimum mobile phase for the liquid chromatography, with amperometric detection, of the serum extracts was found to be 0.06 mol dm-3 acetate buffer in 8% methanol (pH 5.0); the acidified serum was extracted with a mixture of chloroform and acetonitrile (60 + 40), prior to injection onto a reversed-phase column. The peak current was measured at +1.35 V and the calibration graph was found to be linear in the range 4-200 ng of sample injected. The average recovery from serum was found to be 60% with a relative standard deviation of 5.8%. A pharmacokinetic study was carried out and the results obtained were comparable to those found in the literature. It was concluded that the method developed had possible application for the measurement of trace levels of salicylic acid in clinical studies.