4
OPERATION
A larger sample surface area increases instrument efficiency by providing more
stable infrared sample temperatures. It also speeds up the reading by shortening
the time needed to reach vapor equilibrium.
b. Do not fill the sample cup more than half full.
Overfilled cups can contaminate the chamber and do not make the readings faster
or more accurate.
3. Wipe any excess sample material from the rim and outside of the sample cup with a
clean KIMWIPES
®
tissue prior to loading the sample into the instrument.
Material left on the rim or the outside of the cup can contaminate the chamber and can
be transferred to subsequent samples.
4. If a sample cannot be measured immediately, put the disposable sample cup lid on the
cup to restrict water transfer.
If waiting more than 20 min to measure the sample, seal the cup with Parafilm
®
wax or a
similar material. Properly sealed samples can be measured up to 4 h after sampling.
2.2.1 SAMPLE COMPOSITION
The nature of some samples results in longer reading times. These materials may need
additional preparation to ensure accurate readings. Contact
for questions
on sample composition.
Use the following steps to determine if further sample preparation is necessary:
1. Take several readings of the sample to see if the readings (
a
w
and time) stabilize
2. If the readings take less than 6 min to stabilize, the sample can be handled normally.
If the readings take longer than 6 min, remove the sample and take a reading of a
verification standard (
Section 4.1.1
).
3. If the verification standard takes less than 6 min to test, the sample itself is causing the
long read time. Refer to the following sections for pertinent sampling considerations.
If the verification standard also takes longer than 6 min to test, the chamber may be
dirty and will need to be cleaned (
). Retest the sample after cleaning and
verifying the instrument.
2.2.1.1 COATED AND DRIED SAMPLES
Samples with high sugar or fat coatings often require multiple readings because they
equilibrate very slowly with the sample chamber.
Crush or slice the sample before sampling to reduce the time needed to take a water
activity reading for coated or dried samples. This increases the surface area of the sample,
thus decreasing reading times. However, modifying some samples may alter their water
activity readings.
