A simple method to determine the water activity of ethanol-containing samples

✍ Scribed by J. E. Hallsworth; Y. Nomura

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 82 KB
• Volume: 62
• Category: Article
• ISSN: 0006-3592
• DOI: 10.1002/(sici)1097-0290(19990120)62:2<242::aid-bit15>3.0.co;2-r

✦ Synopsis

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 ethanolcontaining samples.