Membrane inlet ion mobility spectrometry for on-line measurement of ethanol in beer and in yeast fermentation

Abstract

A membrane inlet ion mobility spectrometric method was developed for on-line measurement of ethanol concentration in beer and in yeast fermentation. Main parts of the measurement system are an ion mobility spectrometer, M90, and a custom built membrane inlet. The M90 ion mobility spectrometer is unique in the sense that positive and negative ions are simultaneously measured at 6 different detection channels, 3 for positive ions and 3 for negative ions. The custom built membrane inlet utilized a microporous polypropylene membrane for sample introduction into the M90 instrument. The developed measurement system allowed analysis of ethanol at 0.05% ( v v ) levels, clearly sufficient for the applications reported here. Good signal linearity was observed at positive ion channels 1 and 3 in ethanol concentration range 0.2−10% ( v v ), calculated correlation coefficients were 0.989 and 0.999, respectively. Agreement between the ethanol concentration measured by membrane inlet ion mobility spectrometry and the values declared on the beer bottle labels was good. Reproducibility of signals of the detection channels which gave the best response for ethanol was excellent in ethanol concentration measurement of beer samples, coefficient of variation was 1% for all these channels. Membrane inlet ion mobility spectrometry was also shown to be capable of on-line ethanol measurement, confirmed by membrane inlet mass spectrometry, during yeast fermentations.