Development of a simple and low cost device for vapour phase Fourier Transform Infrared spectrometry determination of ethanol in mouthwashes

A new vapour phase manifold coupled with Fourier Transform Infrared (FTIR) spectroscopy was developed for ethanol determination in mouthwashes. Two microliters of samples were injected, without any previous pre-treatment into a reactor heated at 70 °C, and the vapour phase generated transported to the FTIR spectrometer using a carrier nitrogen flow of 6 ml min−1. FTIR spectra were continuously recorded, as a function of time, by accumulating two scans and employing 8 cm−1 nominal resolution. Analytical measurements for ethanol were made in the range from 1130 to 992 cm−1 with a baseline defined between 1158 and 957 cm−1. After ethanol measurement the carrier flow was increased to 300 ml min−1 in order to put out of the manifold the water evolved from samples. Several commercial mouthwash samples were analysed by reference methods as titrimetry and headspace gas chromatography and results were comparable with those obtained by vapour phase FTIR. The proposed procedure is a simple, fast and environmentally friendly alternative to the reference methods providing accurate results, with a limit of detection of 0.15% (v/v) and a total analysis time of 2 min.