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A simple method to determine the water activity of ethanol‐containing samples
Author(s) -
Hallsworth J. E.,
Nomura Y.
Publication year - 1999
Publication title -
biotechnology and bioengineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.136
H-Index - 189
eISSN - 1097-0290
pISSN - 0006-3592
DOI - 10.1002/(sici)1097-0290(19990120)62:2<242::aid-bit15>3.0.co;2-r
Subject(s) - ethanol , chemistry , water activity , humidity , alcohol , relative humidity , filter paper , analytical chemistry (journal) , ethanol content , chromatography , water content , thermodynamics , organic chemistry , physics , geotechnical engineering , engineering
The water activity ( a w ) of microbial substrates, biological samples, and foods and drinks is usually determined by direct measurement of the equilibrium relative humidity above a sample. However, these materials can contain ethanol, which disrupts the operation of humidity sensors. Previously, an indirect and problematic technique based on freezing‐point depression measurements was needed to calculate the a w when ethanol was present. We now describe a rapid and accurate method to determine the a w of ethanol‐containing samples at ambient temperatures. Disruption of sensor measurements was minimized by using a newly developed, alcohol‐resistant humidity sensor fitted with an alcohol filter. Linear equations were derived from a w measurements of standard ethanol–water mixtures, and from Norrish's equation, to correct sensor measurements. To our knowledge, this is the first time that electronic sensors have been used to determine the a w of ethanol‐containing samples. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 62: 242–245, 1999.