Simultaneous vapour phase Fourier transform infrared spectrometric determination of butyl acetate, toluene and methyl ethyl ketone in paint solvents

Abstract

Two analytical procedures were evaluated for the direct and simultaneous determination of butyl acetate, toluene and methyl ethyl ketone (MEK) in paint solvents based on the use of vapour phase FTIR measurements. In both cases, a 0.2 µl volume of untreated sample was injected into an electrically heated Pyrex glass reactor maintained at 80 °C. The vapour phase generated was transported by means of a nitrogen carrier flow into an IR gas cell and the mid-IR spectra were recorded as a function of time. The first procedure was based on univariate regression, using calibration graphs obtained by injecting different volumes of the three pure sample components. It provided relative standard deviations lower than 1% for pure standard solutions, a limit of detection of the order of 1 µg for each compound and a sampling frequency of 71 h^–1. In the second procedure, partial least squares (PLS) regression was employed. Spectrometric data were used for PLS calibration, based on the characteristic absorption bands in the wavenumber range 2033–644 cm^–1 (a total of 360 absorbance data points). For calibration, a set of seven standard mixtures of the three compounds to be analysed, considered at different concentrations, was used. In the analysis of natural and synthetic samples using univariate and PLS regression, relative errors of the order of 1.5–3.3 and 0.2–4.0%, respectively, were found.