AquaLab 7 VERIFICATION AND CALIBRATION
Table 1: Verification Flowchart
Verification Standard @ 25
◦
C Water Activity
13.40 mol/kg LiCl 0.250 ±0.003
8.57 mol/kg LiCl 0.500 ±0.003
6.00 mol/kg NaCl 0.760 ±0.003
2.33 mol/kg NaCl 0.920 ±0.003
0.50 mol/kg KCl 0.984 ±0.003
USP Purified Water 1.000 ±0.003
Note: If you need to obtain a Material Safety Data Sheet (MSDS)
for any of these standards, a printable version is available on our
website at www.decagon.com/msds.
To use a verification standard, remove the twist top and pour the
contents into an AquaLab sample cup. Information about the stan-
dard value and molality can be found printed on the outside of the
plastic vial. If for some reason you cannot obtain Decagon’s ver-
ification standards and need to make a saturated salt solution for
verification, refer to Appendix A.
In TEV models, the capacitance sensor can hold a memory of high
water activity samples such as UPS Purified Water or the 0.984 a
w
standard. If you verify calibration with one of these high water activ-
ity standards, you will need to wait an hour to allow the capacitance
sensor to dry before testing samples of lower water activity or the
results may be slightly high.
7.2 Verification of Calibration
When to Verify for Linear Offset
Linear offset should be checked against two known verification stan-
dards daily, either once per shift or before each use. Linear offset
should never be verified solely against steam distilled water, since
it does not give an accurate representation of the linear offset. For
batch processing, the instrument should be checked regularly against
a known standard of similar water activity. It is also a good idea to
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