Gas-chromatographic determination of mexiletine with a nitrogen-selective detector.

The authors present a procedure for the determination of mexiletine in serum. The drugs are extracted under basic conditions into n-heptane/isobutanol (96/4 by vol) and then extracted again into 1 mol/L H2SO4. The acidic solution is made basic with sodium hydroxide, reextracted with diethyl ether, and the extract evaporated. The residue is redissolved in ethanol and analyzed by gas chromatography with a nitrogen-selective detector. By use of two internal standards, diphenhydramine and p- chlorodisopyramide , concentration and instrument response are related linearly from 500 micrograms/L to 4.0 mg/L. Interferences from other drugs also are eliminated by using two internal standards. Within-run precision (CV) was 5% at the 1 and 2 mg/L concentration: between-run precision was 10% and 5% at those respective concentrations. Interference studies indicate that most commonly prescribed basic drugs will not interfere with this procedure.