Determination of caffeine in tea samples by Fourier transform infrared spectrometry

Abstract.

A sustainable and environmentally friendly procedure has been developed for the FTIR determination of caffeine in tea leaf samples. The method is based on the extraction with ammonia and CHCl₃ and direct determination of caffeine on the chloroform extracts using peak height absorbance measurements at 1658.5 cm^–1 and external calibration. The method provides a sensitivity of 0.2142 absorbance units mg^–1 mL and a limit of detection of 1 mg L^–1, corresponding to 0.002% m/m caffeine in tea leaves. As compared with a reference procedure, based on UV absorbance measurement at 276 nm after low pressure column chromatography, the developed procedure reduces the consume of CHCl₃ by a factor of 10, that of NH₄OH by a factor of 20 and avoids the use of diethyl ether and Celite. The time required to do the analysis of a sample is 15 minutes as compared with the 6 hours for the reference one.