Two cephalosporin antibiotic derivatives, ceftriaxone (CFRX) and cefoperazone (CFPZ), have been studied by direct current, differential pulse polarography (DPP), and cyclic voltammetry. Both give rise to two irreversible two-electron reduction steps. The characteristics of the corresponding electrode reactions are discussed. The electrooxidation of both drugs was also studied at the carbon paste electrode (CPE). Both drugs give rise to one oxidation peak at about 1-1.05 V vs. SCE (pH 1.6, phosphate buffer solution). Optimum pH ranges for the determination of these drugs at the CPE are also given. Linear calibration plots were obtained over the concentration ranges 0.49 to 99 pg/mL and 0.66 to 534 pg/mL for CFRX and CFPZ, respectively. Detection limits of 2.5 ng/mL and 0.13 pg/mL for CFRX and CFPZ, respectively, were readily achieved.

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Lipid-modified carbon paste electrodes were electrochemically characterized and their potential for drug analysis was compared with conventional carbon paste electrodes. The presence of lipids (phospholipids, fatty acids) in the paste matrix provided enhanced current responses with improved reproducibility. With 5 miputes of accumulation, phenothiazines exhibit a 40-fold enhancement of the response compared to that obtained without accumulation. As a result, a detection limit of 1 X attained. The response was characterized with respect to pH, preconcentraiion potential, accumulation time, paste composition, possible interferences, and other variables. The determination of the tranquilizer in serum and urine required no preliminary treatment other than dilution with phosphate buffer and medium exchange, Detection limits are 5 x M was ' M in urine and 2 X lo-' M in serum.