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Flow Injection Fourier Transform Infrared Determination of Caffeine in Soft Drinks

1997; American Chemical Society; Volume: 69; Issue: 6 Linguagem: Inglês

10.1021/ac960693v

1520-6882

Yasmina Daghbouche, Salvador Garrigues, Maider Vidal, Miguel de la Guárdia,

Advanced Chemical Sensor Technologies

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 were loaded and eluted in the same way as the samples. Preliminary studies were carried out using off-line SPE and off-line elution and on-line extraction and on-line elution, and the parameters involved in both the retention and elution of caffeine in solid phase extraction cartridges were evaluated, together with the measurement conditions for FT-IR determination of caffeine in CHCl3 solutions and the flow injection parameters. The procedure developed provides a limit of detection of 10 μg mL-1 of caffeine for a sample injection of 1 mL, a sampling frequency of 30 h-1, and a relative standard deviation of 3.5% for eight independent measurements at a concentration level of 100 μg mL-1.