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Water activity
instrument tests

Details for salt
solutions and slurries




Salt solutions used for testing

The samples were saturated salt slurries, Decagon calibration
with used aw = 0.25, isotonic salt solution and water.
For simplicity, these samples as a group are called "salt slurries".

Salts of high purity (pro analysi) were used. Water and Isotonic
salt solution were according to European Pharmacopoeia.

The LiCl solution, aw = 0.25 at 22.5 °C was obtained from ADAB.
As the sample was used in the Decagon calibration samples,
this sample was omitted in the tests of desktop instruments.

Preparation of salt slurries

The salt slurries were prepared by adding water to salt during
stirring until the slurry flew and showed liquid at the surface.

Lithium Chloride slurry prepared at the first testing period,
i.e. 2004, did not form a slurry but became hard upon hydration.
The substance was crushed into smaller pieces and was
checked for presence of liquid.

During preparation of the slurry in 2005, it was chilled and
stirred while adding water to the salt. The alternated mixing
eliminated problems with solidification of the slurry.

Water activity of the samples were interpolated between
literature values at 20 and 25 °C (Greenspan, L. 1977,
Humidity fixed points of binary saturated aqueous solutions,
J. Res. Nat. Bur. Stand. 81A:89-96).

The samples were analysed in the order according to
the table at right.

sample aw
NaCl 0.754
LiCl solution 0.25
K2CO3 0.432
Water 1.00
MgCl2 0.3295
K2SO4 0.9745
LiCl 0.113
0,9% NaCl soln. 0.996

       aw at 22.5 °C for salt solutions

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