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An improved micromethod for theophylline determination by reversed-phase liquid chromatography.

We describe an improved micro-scale method for determining serum theophylline by reversed-phase liquid chromatography. Samples are deproteinized with two volumes of methanol containing beta-hydroxyethyltheophylline as an internal standard. The supernate is chromatographed with a methanol/sodium acetate buffer (15/85 by vol) mobile phase, and the amount of theophylline is calculated from the ratio between peak heights for theophylline and the internal standard at 273 nm. We also monitor for chemical interferences at 254 nm. We found no interferences from ampicillin, methicillin, cephalosporin, and cephalothin. None of the drugs tested or metabolites and compounds related to theophylline have been found to interfere. The method is rapid, accurate, sensitive, and specific for theophylline.