8 SAMPLE PREPARATION AquaLab
4. Make sure the rim and outside of the sample cup are
clean. Wipe any excess sample material from the rim of the
cup with a clean Kimwipe. Material left on the rim or the
outside of the cup can contaminate the sensor chamber and be
transferred to subsequent samples.
5. If a sample reads at some other time, put the dis-
posable sample cup lid on the cup to restrict water
transfer. For longterm storage, seal the lid by placing tape or
Parafilm
R
completely around the cup to lid junction.
6. Be consistent in sample preparation practices. If you
crush, grind, or slice your sample, be consistent in the method
you use in order to obtain reproducible results.
8.2 Samples Needing Special Preparation
The AquaLab reads most materials in five minutes or less. However,
the nature of some samples necessitates longer reading times. These
materials need additional preparation to ensure quick, accurate read-
ings. To find out whether special sample preparation is necessary,
take several readings to see if readings (a
w
and time) stabilize. If
continued readings take longer than six minutes, remove the sam-
ple and take a reading of a verification standard. This ensures the
sample itself is causing the long read time, and that there is not a
problem with your instrument. If the verification standard also takes
longer than six minutes to test, the chamber may be dirty. Refer to
Section 6 for cleaning procedures.
Coated and Dried Samples
Samples with high sugar or fat coatings often require multiple read-
ings, because it takes longer for them to equilibrate. If this is the
case for your samples, it is not a problem with your instrument; it
simply means that your particular sample takes longer than most to
equilibrate.
To reduce the time needed to take a water activity reading for coated
or dried samples, you can crush or slice the sample before sampling.
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