An enzymic bicarbonate reagent that is free of pyruvate interference.

single Sep-Pak has been used for as many as 10 serum samples with no noticeable loss in efficiency. For analysis of clinical samples, I compared the above sample pretreatment procedure to the acetonitrile extraction of Kabra et al. (1). The chromatographic conditions were similar to those of Kabra et al. (1), except for our use of ambient temperature and a 3.5 mL/min flow rate. The Sep-Pak pretreatment procedure resulted in samples that were significantly “cleaner” than the acetonitnile extracts when chromatographed. The height and duration of the extraneous peaks eluting near the solvent front were greatly reduced and the baseline was re-established before the anticonvulsants emerged. Hexobarbital can be used as an internal standard for this procedure. This sample pretreatment procedure allows for reproducibility and sensitivity with less column degradation.