Rapid Quantitative Analysis of Ethanol and Prediction of Methanol Content in Traditional Fruit Brandies from Romania, using FTIR Spectroscopy and Chemometrics

Fourier Transform Infrared (FTIR) spectroscopy in combination with chemometrics were applied for the quality control of 26 fruit brandies made by traditional technology in Romania. Firstly, for the identification and quantitative evaluation of methanol and ethanol in such samples, 4 mixtures of methanol and ethanol standard solutions and a spiked sample were fingerprinted in the 1200 - 950 cm-1 FTIR spectral range, identifying specific wavelength of 1020 and 1112 for methanol, 1047 and 1087 for ethanol. Then, the FTIR spectra of all brandy samples in the range 3500 - 750 cm-1 was registered and the methanol and ethanol concentrations were determined according to the previous calibration. By PCA (Principal component analysis) of FTIR areas (1170 -1000 cm-1), the variability and discrimination between samples was possible, discriminating between the biological and geographical origin of brandy samples. Based on peak areas and intensities, it was predicted the concentration of methanol in all samples, using Partial least squares regression (PLS). The correlation between FTIR and the reference method (GC-FID) was well correlated and significant (p<0.05). It was demostrated that FTIR technique offer a good prediction and statistical correlation with GC-FID technique for methanol quantification.