Sample Preparation; Preparing The Sample - Decagon Devices AquaLab 4TE Operator's Manual

AquaLab

8. Sample Preparation

8. Sample Preparation
Proper sample preparation is an important step in keeping your
AquaLab clean and achieving repeatable results. Careful preparation
and loading of samples will lengthen time between cleanings and
help you avoid downtime.

Preparing the Sample

1. Make sure the sample to be measured is homogeneous. Multi-
component samples (e.g., muffi ns with raisins) or samples that have
outside coatings (like deep-fried, breaded foods) can be measured,
but may take longer to equilibrate. For samples like these, AquaLab
may take more than fi ve minutes to give an accurate reading, or may
require multiple readings of the same sample. Measuring the water
activity of these types of products is discussed in detail later in this
chapter (see Samples Needing Special Preparation).
2. Place the sample in a disposable sample cup, completely cov-
ering the bottom of the cup, if possible. AquaLab is able to accu-
rately 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 not fl attened to cover the bottom. A larger sample surface area
increases instrument effi ciency by providing more stable infrared
sample temperatures. It also speeds up the reading by shortening the
time needed to reach vapor equilibrium.
3. Do not fi ll the sample cup more than half full. Overfi lled cups
will contaminate the sensors in the sensor chamber. Filling the
sample cup will not make the readings faster or more accurate. Th ere
only needs to be enough sample in the cup to allow the water in
the sample to equilibrate with the water in the vapor phase and not
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