A rapid ultraviolet spectrophotometric procedure for the microdetermination of theophylline (1,3-dimethylxanthine) in plasma or serum.

An ultraviolet spectrophotometric procedure for the microdetermination of theophylline in plasma is described. Theophylline is extracted at pH 5 with chloroform. An aliquot of the solvent is shaken with molar hydrochloric acid and the absorbance of the acid layer determined at 267 nm. The resulting procedure is rapid, reliable, sensitive and virtually specific. It requires 250 microliters sample for a single estimation and has a detection threshold of less than 5 mumol/l.