Mass-spectrometric assay of tocainide in serum

This mass-spectrometric method for assaying tocainide in serum is specific, reproducible, and sensitive, and sample preparation is rapid. The drug is isolated from serum by liquid-solid extraction on a Baker C18 disposable column. Underivatized drug is separated by elution on a 0.20 mm X 25 m fused-silica capillary column coated with 5% phenylmethylsilicone, then quantified by mass-selective detection (selected ion monitoring). Sample size is 1 mL of serum, but smaller volumes may be used. Mean analytical recovery of the drug from the disposable columns is 75%. Commonly used antiarrhythmics, sedatives, or hypnotics do not interfere. The run-to-run CV at 3.7 mg/L is 4.0%, 3.0% at 10.5 mg/L.