A. Perezponce et al., PARTIAL LEAST-SQUARES FOURIER-TRANSFORM INFRARED SPECTROMETRIC DETERMINATION OF METHANOL AND ETHANOL BY VAPOR-PHASE GENERATION, Analyst, 123(6), 1998, pp. 1253-1258
A partial least-squares (PLS)-FTIR procedure is proposed for the direc
t determination of methanol and ethanol in liquid samples, based on va
pour generation from small injected volumes of untreated samples, vola
tilized inside a Pyrex glass reactor, transported into a multi-pathlen
gth cell with nitrogen carrier gas and then continuously measured by F
TIR spectrometry, The spectra were processed using PLS regression, Sev
eral sets of standards and different wavenumber ranges were tested for
calibration. A calibration set integrated by aqueous solutions of eth
anol from 2.5 to 22.5% v/v and aqueous solutions of methanol from 0.5
to 3.5% v/v provided the lowest prediction errors. Average relative pr
ediction errors for the PLS model of about 3% for ethanol and 2% for m
ethanol were obtained for aqueous mixtures of the two compounds studie
d, with RSDs of 2.7 and 2,3%, respectively, calculated from four injec
tions of 1 mu l of sample, providing the method with a sampling freque
ncy of 69 h(-1). Results predicted by PLS-FTIR were compared with thos
e found using a proportional equations approach. The method was applie
d to the determination of methanol and ethanol in high-level alcoholic
beverages and cosmetic products, obtaining average recoveries of 107
+/- 6 and 98 +/- 2%, respectively.