Comparison of gas chromatographic and spectrophotometric methods of determination for caffeine in coffees and teas.

Caffeine (CAF) levels in instant regular coffees, instant decaffeinated coffees, and instant teas are determined and compared using spectrophotometric and gas chromatographic methods of determination. Modification of a previously reported spectrophotometric assay for CAF in biological fluids is necessary to reduce interference from theophylline (THP) and theobromine (THB). Readjustment of the buffer pH and the introduction of an intermediate buffer wash were found to effectively limit interference from THB arid THP. The gas chromatographic assay involves extraction of CAF into benzene followed by evaporation of the benzene and redissolution of the CAF into chloroform for injection into the gas chromatograph. The spectrophotometric method consistently gave higher levels of CAF than were found by the gas chromatographic method for the decaffeinated and regular coffees. However, these differences were not observed for the teas. Using the results from the gas chromatographic assay, two decaffeinated coffees were found to be greater than 97% CAF free. CAF levels in regular coffees were found to vary as much as 32% within the group of five brands studied.