Fourier transform-near infrared (FT-NIR) and FT-Raman spectrometries have been used to design partial least squares
(PLS) calibration models for the determination of the ethanol content of ethanol fuel and alcoholic beverages. In the
FT-NIR measurements the spectra were obtained using air as reference, and the spectral region for PLS modeling were
selected based on the spectral distribution of the relative standard deviation in concentration. In the FT-Raman measurements
hexachloro-1,3-butadiene (HCBD) has been used as an external standard. In the PLS/FT-NIR modeling for ethanol fuel analysis
50 ethanol fuel standards (84.9–100% (w/w)) were used (25 in the calibration, 25 in the validation). In the PLS/FT-Raman
modeling 25 standards were used (13 in the calibration, 12 in the validation). The PLS/FT-NIR and FT-Raman models for
beverage analysis made use of 24 standards (0–100% (v/v)). Twelve of them contained sugars (1–5% (w/w)), one-half was
used in the calibration and the other half in the validation. Different spectral pre-processing were used in the PLS modeling,
depending on the type of sample investigated. In the ethanol fuel analysis the FT-NIR pre-processingwas a 17 points smoothed
first derivative and for beverages no spectral pre-processing was used. The FT-Raman spectra were pre-processed by vector
normalization in the ethanol fuel analysis and by a second derivative (17 points smoothing) in the beverage analysis. The PLS
models were used in the analysis of real ethanol fuel and beverage samples. A t-test has shown that the FT-NIR model has
an accuracy equivalent to that of the reference method (ASTM D4052) in the analysis of ethanol fuel, while in the analysis
of beverages, the FT-Raman model presents an accuracy equivalent to the reference method. The limits of detection for NIR
and Raman calibration models were 0.05 and 0.2% (w/w), respectively. It has also been shown that both techniques, present
better results than gas chromatography (GC) in evaluating the ethanol content of beverages.
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