Flow Injection Fourier Transform Infrared Determination of Caffeine in Soft Drinks

A fully automated procedure has been developed for FT-IR determination of caffeine in soft drinks. Samples are first degasified by filtration and then directly injected into a flow manifold and passed through a 100 mg C18 SPE cartridge, conditioned with methanol and water. After the cartridge has been cleaned with water, the caffeine is eluted with CHCl3 and stabilized with ethanol. The flow injection (FI) recording is obtained by measuring the absorbance at 1658 cm-1 with a baseline established at 1800 cm-1. Area values for the FI recording obtained between 0.4 and 1.4 min after sample injection are interpolated in the calibration graph of a series of aqueous standards of caffeine, which w…