Determination of caffeine in coffee by means Fourier transform infrared spectrometry

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 for the quantification of caffeine was the absolute peak-valley value (1668-1649 cm-1) of the first order derivate of the absorption spectrum, corresponding to the 1659 cm-1 band. the method provides a limit of detection (3s) 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) and a sample throughput (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).