Quality control in the simultaneous assay of anticonvulsants using an automated gas chromatographic system with a nitrogen detector.

An automated gas-liquid chromatographic technique for the routine determination of phenobarbitone, primidone and phenytoin using a nitrogen-detector is described. The high selectivity of the detector for nitrogen-containing compounds allows a direct extraction procedure and the use of a phenytoin analogue as an internal standard obviates the need for accurate aliquot measurement after extraction. The anticonvulsants are chromatographed as methyl derivatives produced by on-column methylation with trimethylphenyl ammonium hydroxide following automatic liquid injection. Quality control data from an internal quality control scheme is presented and the performance of the laboratory in an inter-laboratory control scheme is reported and discussed.