MEMBRANE INLET ION MOBILITY SPECTROMETRY FOR ONLINE MEASUREMENT OF ETHANOL IN BEER AND IN YEAST FERMENTATION

A membrane inlet ion mobility spectrometric method was developed for o n-line measurement of ethanol concentration in beer and in yeast ferme ntation. Main parts of the measurement system are an ion mobility spec trometer, M90, and a custom built membrane inlet. The M90 ion mobility spectrometer is unique in the sense that positive and negative ions a re simultaneously measured at 6 different detection channels, 3 for po sitive ions and 3 for negative ions. The custom built membrane inlet u tilized a microporous polypropylene membrane for sample introduction i nto the M90 instrument. The developed measurement system allowed analy sis of ethanol at 0.05% (v/v) levels, clearly sufficient for the appli cations reported here. Good signal linearity was observed at positive ion channels 1 and 3 in ethanol concentration range 0.2-10% (v/v), cal culated correlation coefficients were 0.989 and 0.999, respectively. A greement between the ethanol concentration measured by membrane inlet ion mobility spectrometry and the values declared on the beer bottle l abels was good. Reproducibility of signals of the detection channels w hich gave the best response for ethanol was excellent in ethanol conce ntration measurement of beer samples, coefficient of variation was 1% for all these channels. Membrane inlet ion mobility spectrometry was a lso shown to be capable of on-line ethanol measurement, confirmed by m embrane inlet mass spectrometry, during yeast fermentations.