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Determination of caffeine in coffee by means Fourier transform infrared spectrometry

Abstract:

Abstract In this work a flow analysis-Fourier transform infrared spectrometric (FA-FTIR) method for the determination of caffeine in coffee was developed. The method involves the extraction, in batch, of caffeine from solid samples of roasted coffee with hot water (80°C), on-line retro-extraction of caffeine in chloroform and direct analysis of the organic phase by FTIR spectrometry. The measurement criterion selected the quantification of caffeine was the absolute peak-valley value (1668-1649 cm-1) of the first orderderivate of the absorption spectrum, corresponding to the 1659 cm -1 band. The method provides a limit of detection (3σ) of 0.001% (w/v) caffeine, a relative standard deviation corresponding to the whole procedure, until the sample preparation, of 1.2% ([Caffeine] ≈ 0.05% (w/v), n = 5) andasample throuǵhput (triplicate) of approximately 12 samples h-1. The method was validated by means of standard addition, recovery and inter-day precision studies and by comparative analysis of real samples with the official chromatographic- spectrophotometric procedure. The method was applied to the analysis of commercial samples, obtaining a caffeine content ranging from 0.60 to 1.16% (w/w).