GLC determination of caffeine in plasma using alkali flame detection.

A rapid, specific, and sensitive GLC assay for caffeine in plasma was developed utilizing alkali flame-ionization detection. The procedure involves the addition of mepivacaine as an internal standard, alkalinization of the sample, and extraction with chloroform. Peak height ratio measurements produced linear standard curves in the 0.25-10.0-microgram/ml range. Absolute sensitivity from a 1.0-ml plasma sample was 0.1 microgram/ml. The relative standard deviation of a 2.0-microgram/ml pooled plasma standard run repeatedly over several months was 5.2%. The method is applicable to time-concentration studies in human and animal plasma following typical oral doses of caffeine.