[Solid phase clean up and determination of theophylline in plasma by reversed phase high performance liquid...

Theophylline is the drug of choice in the prevention and treatment of asthmatic symptoms. A plasma sample clean up procedure using alumina solid phase to eliminate the interference of plasma impurities and some other drugs and a RP-HPLC method to determine plasma theophylline concentration were developed. The system used a Zorbax-C18 (5 microns) column. The mobile phase consists of a mixture of methanol and sodium acetate (50:50) buffer (pH 3.0). Detection at a wavelength of 254 nm showed no interfering peaks. Caffeine was used as an internal standard. The clean up procedure is simple, rapid and satisfactory. The detection limit of theophylline is 0.2 ng (R/N, 3:1), the minimal detectable concentration of theophylline in plasma is 20 ng/ml. Calibration curve is linear (r = 0.9995) in the concentration range of 4 micrograms/ml to 30/micrograms/ml. Within-day precision and day-to-day precision (CV) were 1.89% and 2.41% respectively. The average recovery of the method is 98.44 +/- 0.89%.