DIRECT DETERMINATION OF THEOPHYLLINE IN HUMAN SERUM BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY USING ZWITTERIONIC MICELLAR MOBILE-PHASE - COMPARISON WITH AN ENZYME-MULTIPLIED IMMUNOASSAY TECHNIQUE

A liquid chromatographic procedure is reported for the direct determination of theophylline in human serum. It includes the use of a micellar zwitterionic mobile phase [10(-3) mol l(-1) 3-(dimethyldodecylammonio) propanesulfonate (also known as C-12 DAPS)-propanol (97 + 3, v/v) and a mu Bondapak phenyl column. Detection is based on ultraviolet absorption at a wavelength of 273 nm. After dilution with the mobile phase, the serum is injected into the chromatography; no solvent extraction or deproteinization is performed. The linearity of the method described was excellent over the range 0.5-20 mg l(-1). The within-run precision was better than 2%, and the recovery of the theophylline approached 98%. Two hundred direct injections of serum samples did not affect the column life. The total analysis time, including chromatography, was approximately 15 min. As little as 0.5 mg l(-1) of theophylline could be detected, and the results were in good agreement with those of an enzyme multiplied immunoassay technique.