Determination of Caffeine in Human Plasma and Urine by Gas Chromatography Using a Nitrogen Phosphorus- Detector

Abstract

A simple method for the determination of caffeine (1, 3, 7-trimethylxanthine) in plasma and urine is described. Caffeine was extracted by diethyl ether, together with spiked N-methylphenothiazine (NMPZ) as an internal standard. The amount was measured with gas chromatography (GC) using a nitrogen phosphorus-detector (NP-D). Almost 96% of the caffeine was recovered by diethyl ether. The detection limits of this assay were 1ng/ml of both in plasma and urine. Moreover, good linear relationships between peak height ratios and the concentrations of caffeine were found in the range 0 to 10μg/ml of plasma and 0 to 40μg/ml of urine, and reproducibility was kept within 3%. This method is rapid, sensitive and suitable as a routine method in the clinic.