Advanced

A calorimetric method to determine water activity

Björklund, Sebastian LU and Wadsö, Lars LU (2011) In Review of Scientific Instruments 82(11).
Abstract
A calorimetric method to determine water activity covering the full range of the water activity scale is presented. A dry stream of nitrogen gas is passed either over the solution whose activity should be determined or left dry before it is saturated by bubbling through water in an isothermal calorimeter. The unknown activity is in principle determined by comparing the thermal power of vaporization related to the gas stream with unknown activity to that with zero activity. Except for three minor corrections (for pressure drop, non-perfect humidification, and evaporative cooling) the unknown water activity is calculated solely based on the water activity end-points zero and unity. Thus, there is no need for calibration with references with... (More)
A calorimetric method to determine water activity covering the full range of the water activity scale is presented. A dry stream of nitrogen gas is passed either over the solution whose activity should be determined or left dry before it is saturated by bubbling through water in an isothermal calorimeter. The unknown activity is in principle determined by comparing the thermal power of vaporization related to the gas stream with unknown activity to that with zero activity. Except for three minor corrections (for pressure drop, non-perfect humidification, and evaporative cooling) the unknown water activity is calculated solely based on the water activity end-points zero and unity. Thus, there is no need for calibration with references with known water activities. The method has been evaluated at 30 °C by measuring the water activity of seven aqueous sodium chloride solutions ranging from 0.1 mol kg−1 to 3 mol kg−1 and seven saturated aqueous salt solutions (LiCl, MgCl2, NaBr, NaCl, KCl, KNO3, and K2SO4) with known water activities. The performance of the method was adequate over the complete water activity scale. At high water activities the performance was excellent, which is encouraging as many other methods used for water activity determination have limited performance at high water activities. (Less)
Please use this url to cite or link to this publication:
author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
vaporisation, nitrogen, sodium compounds, solutions, thermal variables measurement, calorimetry, chemical variables measurement, calorimeters
in
Review of Scientific Instruments
volume
82
issue
11
publisher
American Institute of Physics
external identifiers
  • wos:000297941100043
  • scopus:82555173665
ISSN
1089-7623
DOI
10.1063/1.3660815
language
English
LU publication?
yes
id
e7e07377-fc04-4fa9-95eb-a8886e53741b (old id 2222151)
date added to LUP
2011-12-01 11:09:41
date last changed
2017-01-01 05:20:51
@article{e7e07377-fc04-4fa9-95eb-a8886e53741b,
  abstract     = {A calorimetric method to determine water activity covering the full range of the water activity scale is presented. A dry stream of nitrogen gas is passed either over the solution whose activity should be determined or left dry before it is saturated by bubbling through water in an isothermal calorimeter. The unknown activity is in principle determined by comparing the thermal power of vaporization related to the gas stream with unknown activity to that with zero activity. Except for three minor corrections (for pressure drop, non-perfect humidification, and evaporative cooling) the unknown water activity is calculated solely based on the water activity end-points zero and unity. Thus, there is no need for calibration with references with known water activities. The method has been evaluated at 30 °C by measuring the water activity of seven aqueous sodium chloride solutions ranging from 0.1 mol kg−1 to 3 mol kg−1 and seven saturated aqueous salt solutions (LiCl, MgCl2, NaBr, NaCl, KCl, KNO3, and K2SO4) with known water activities. The performance of the method was adequate over the complete water activity scale. At high water activities the performance was excellent, which is encouraging as many other methods used for water activity determination have limited performance at high water activities.},
  articleno    = {114903},
  author       = {Björklund, Sebastian and Wadsö, Lars},
  issn         = {1089-7623},
  keyword      = {vaporisation,nitrogen,sodium compounds,solutions,thermal variables measurement,calorimetry,chemical variables measurement,calorimeters},
  language     = {eng},
  number       = {11},
  publisher    = {American Institute of Physics},
  series       = {Review of Scientific Instruments},
  title        = {A calorimetric method to determine water activity},
  url          = {http://dx.doi.org/10.1063/1.3660815},
  volume       = {82},
  year         = {2011},
}