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SAMPLE PREPARATION
8. SAMPLE PREPARATION
Proper sample preparation is important to keep the AQUALAB VSA clean and achieve
repeatable results. A contaminated sample chamber can lead to unusually long read times
and water activity readings that drift over time.
Carefully prepare and load samples to lengthen time between cleanings and help avoid
downtime. Be consistent in sample preparation methods (e.g., crush, grind, slice the sample)
to obtain reproducible results. For more information on proper sample preparation for
different sample types, visit Six AQUALAB sample preparation best practices (metergroup.
com/food/articles/six-sample-preparation-best-practices).
More specific considerations regarding sample composition are discussed in Section8.1
through Section8.4.
Follow the steps listed below to prepare samples:
1. Tare a stainless steel cup
2. Make sure the sample to be measured is homogeneous.
Multicomponent samples (e.g., muffins with raisins) or samples that have outside
coatings (like deep-fried, breaded foods) can be measured, but they need to have
representative portions in the cup and may take longer than other sample types
toequilibrate.
3. Place the sample in a disposable sample cup.
a. Completely cover the bottom of the cup, if possible, to provide enough sample to get
an accurate reading.
The AQUALAB VSA is able to accurately measure a sample that does not (or cannot)
cover the bottom of the cup. For example, raisins only need to be placed in the cup
and do not need to be flattened to cover the bottom.
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. METER recommends a sample size of 1,000 to 1,500 mg (the VSA can accommodate
samples of 500 to 5,000 mg). This sample size gives a high resolution isotherm curve
without adding excessive time to the test.
c. Do not fill the sample cup.
Overfilled cups can contaminate the chamber and do not make the readings faster
or more accurate. Filling the sample cup can extend test time, create layering within
the sample and case-hardening, and can lead to contamination of the chamber. The
volume of sample versus weight of the sample has to be optimized for each material
to achieve the desired resolution and test times.
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