Fourier transform infrared determination of caffeine in roasted coffee samples.
A new procedure has been developed for the FT-IR determination of caffeine in roasted coffee samples. The method involves wetting the coffee samples with a 0.25 M aqueous NH3 solution, extracting the caffeine with CHCl3, and measuring absorbance at 1,659 cm(-1) using a baseline established between 1,900 and 830 cm(-1). The procedure proposed is fast, only requiring a total extraction time of 16 min for each sample, and provides a drastic reduction of the organic solvent consumed, from the 200 mL diethyl ether and 50 mL CHCl3, required for each sample by the reference chromatographic UV-spectrometric determination to only 5 mL CHCl3. The method provides a limit of detection of the order of 3 mg L(-1) caffeine and a relative standard deviation of 0.4% for 3 independent analyses of a sample containing 18.6%mg/g caffeine. The accuracy of the FT-IR procedure was evaluated from recovery experiments on spiked samples providing values from 94.4 to 100.1% and from the comparison of results found for a series of commercial samples, by both FT-IR and the official reference procedure.
Department of Analytical Chemistry, University of Valencia, Spain.
J M
JM
Garrigues
Z
Z
Bouhsain
S
S
Garrigues
M
M
de la Guardia
D000641:Ammonia; D002110:Caffeine / Q000032:analysis*; D003069:Coffee / Q000737:chemistry*; D005511:Food Handling; D007202:Indicators and Reagents; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012997:Solvents; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods
D003069:Coffee; D007202:Indicators and Reagents; D012997:Solvents; D002110:Caffeine; D000641:Ammonia