title: Two high-performance liquid chromatographic methods for quantitation of theophylline in plasma.
abstract: Two high-performance liquid chromatographic methods are described for the assay of theophylline in plasma. Both allowed the separation of theophylline from the caffeine metabolites, theobromine and 1,7-dimethylxanthine. Method A, using 8-chlorotheophylline as internal standard, involved back extraction of theophylline from organic extract with 0.1 M sodium hydroxide. Method B used generally accepted solvent extraction followed by evaporation and beta-hydroxyethyltheophylline as internal standard. High-performance liquid chromatographic analyses were performed on reversed-phase phenyl columns (25 X 0.46 and 25 X 0.41 cm) using 20% methanol in 20 mM phosphate buffer at pH 5.6 for Method A and 2% acetonitrile and 8% methanol in 20 mM phosphate buffer for Method B. The column effluent was monitored at UV 273 nm. Standard curves for both Methods A and B were fitted by linear regression (r greater than 0.999) in the concentration range of 0.05-50 micrograms/ml. Either method was selective, accurate and reproducible over the concentration range 0.08-26 micrograms/ml. However, compared with Method B, Method A provided significant advantages in terms of simplicity, speed and efficiency.
mesh_terms: D002110:Caffeine / Q000097:blood; D002851:Chromatography, High Pressure Liquid; D006801:Humans; D006863:Hydrogen-Ion Concentration; D013056:Spectrophotometry, Ultraviolet; D013805:Theobromine / Q000097:blood; D013806:Theophylline / Q000097:blood*
chemical_list: D002110:Caffeine; D013806:Theophylline; D013805:Theobromine; C021183:1,7-dimethylxanthine