6533b85bfe1ef96bd12bb5b5

RESEARCH PRODUCT

Flow injection Fourier transform infrared determination of caffeine in coffee

subject

description

Abstract A fully automatized procedure has been developed for the Fourier transform infrared (FT-IR) spectroscopic determination of caffeine in coffee samples. The method involves the on-line extraction of caffeine with CHCl3. Samples, weighed inside empty PTFE cartridges of 0.5 cm internal diameter (i.d.) and 1.5 ml volume, were humidified with four drops of 0.25 M NH3. The cartridge was installed in a flow manifold, in which samples were extracted in a closed-flow system with 1 ml CHCl3 during 6 min. Four hundred microliters of the extract were introduced in a microflow cell and absorbance measured as a function of time at 1659 cm−1, with a baseline established between 1900 and 830 cm−1, thus providing a fiagram. Peak height values of the FI recordings, obtained for samples, were interpolated in an external calibration line established from standard solutions of caffeine in CHCl3. The method provided a limit of detection (LOD) of 9 mg l−1 caffeine, a relative standard deviation of 0.6% for five independent measurements of a solution containing 1 mg ml−1 and a sampling frequency of the whole procedure of 6 h−1. Results obtained for market samples agree well with those found by the official chromatographic–spectrometric method, but involving a drastic reduction of solvents, from the 200 ml ether and 50 ml CHCl3 required for each sample preparation by the reference procedure to less than 30 ml CHCl3 necessaries for the whole determination of caffeine in a sample, also including standards and carrier solution.