Concurrent measurement of theophylline and caffeine in neonates by an interference-free liquid-chromatographic method.

A sensitive liquid-chromatographic method was developed for the simultaneous measurement of theophylline and caffeine within 6 min. The excellent resolution of the method allows the complete separation of theophylline, internal standard, and caffeine from frequently encountered interfering drugs including acetaminophen, acetazolamide, acetylsalicylate, ampicillin, 8-chlorotheophylline, cefazolin, cephalosporin C, cephalothin, cephapirin, chloramphenicol, dyphylline, metronidazole, 3-methylxanthine, salicylate, sulfadiazine, sulfamerizine, sulfamethazine, sulfamethoxazole, sulfisoxazole, and theobromine. The chromatographic system involves a Waters' Radial-Pak C18 reversed-phase column and acetonitrile in 0.1 mol/L potassium phosphate buffer, pH 4.0, (9.5/90.5 by vol) as the mobile phase. The method can detect theophylline or caffeine concentrations as low as 0.5 mg/L in 50 microL of serum. Precision and accuracy are excellent.