Micromethod for the Determination of Diphenylhydantoin in Plasma and Cerebrospinal Fluid—A Comparison Between a Gas Chromatographic and a Spectrophotometric Method

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Abstract
Several methods are available for the determination of diphenylhydantoin in plasma, but so far no method has been published where capillary samples can be used. The gas Chromatographic procedure described is based upon an extraction method published by Mac Gee (11), requires only 100 μ1 plasma samples at therapeutic concentrations, and can be used with accuracy down to 0.8 μmol/1 (0.2 μg/ml) with 200 μl plasma samples. A comparison with the spectrophotometric method by Dill et al. (5) reveals that the precision is higher for the gas chromatographic method (S.D.=0.8 μmol/l or 0.2 μg/ml) than for the spectrophotometric method (S.D.=2.4 μmol/l or 0.6 μg/ml).