Microdetermination of caffeine in blood by gas chromatography--mass spectrometry

Rapid and sensitive gas-chromatographic determination of caffeine in blood plasma, saliva, and xanthine beverages

A gas chromatographic procedure is reported for the determination of caffeine in plasma, saliva, and xanthine beverages. Using a 75 cm column packed with OV-17, nitrogen-sensitive detection, and 1 ml samples, a suitable limit of analysis (coefficient of variation (CV) = 10.2%) of 50 ng/ml was obtained in plasma. Within-day CVs at caffeine concentrations of 0.1-0.5-2.0-7.5-15.0 micrograms/ml in plasma were 7.7-5.6-4.8-3.8-3.4%, respectively. The limit of detection, defined as the injected quantity of caffeine giving rise to a signal to noise ratio of 2, is 40 pg, corresponding to a plasma concentration of 1 ng/ml. The procedure involves addition of the internal standard 7-pentyl theophylline and alkaline extraction of the sample with dichloromethane. The method described rivals any gaschromatographic assay published so far in rapidness and accuracy. Plasma and saliva caffeine concentrations were determined in a healthy male volunteer after swallowing 400 ml of coffee. The calculated pharmacokinetic parameters, assuming complete absorption of caffeine from the G.I. tract, agree well with previously published values.

Rapid quantitative liquid chromatographic determination of caffeine levels in plasma after oral dosing

A simple method is described for the rapid, quantitative analysis of caffeine in human plasma. Caffeine levels present in plasma following drug administration were determined by high-performance liquid chromatography with UV detection at 273 nm after plasma protein precipitation. Caffeine was detectable at levels as low as 0.1 micrograms/mL. Mean recoveries of 98% with a coefficient of variation of 3% were obtained for plasma standards, in which concentrations ranged from 0.1 to 8 micrograms/mL. Interassay variability of the slope of the standard curve had a coefficient of variation of 3%. Application of this method during human bioavailability studies is described.

The simultaneous determination of theophylline, theobromine and caffeine in plasma by high performance liquid chromatography

A high performance liquid chromatographic procedure for the stimultaneous micro-scale determination of theophylline, theobromine and caffeine in plasma is described. After a single dichloromethane extraction of 0.5--0.2 ml of acidified plasma, the evaporated residue is chromatographed on a reverse-phase gC-18) column. With a mobile phase of acetate buffer (pH 4)--acetonitrile (88:12) at a flow-rate of 2.0 ml/min., the three methylxanthines are separated within six minutes. Detection at xanthines are separated within six minutes. Detection at 276-280 nm enables quantitation of 0.1 mg/1 of drug in a 0.1 ml sample. The method is reproducible, correlates well with EMIT for plasma theophylline, and is applicable to the routine monitoring of both paediatric and adult patients as well as to metabolic studies.