Volatile Samples - Decagon Devices AquaLab 4TE Operator's Manual

AquaLab
8. Sample Preparation
For faster reading, it is important to have the water activity of the
chamber at or below the water activity of these type of samples. Th is
causes the sample to release water to the vapor phase and equilibrate
with the chamber. If the water activity of the head-space is greater
than this type of sample, a long period of time will be required to
reach equilibrium and the water activity of the sample may be aff ected.

Volatile Samples

AquaLab will give accurate readings on most samples. However,
samples with certain volatiles in high enough concentrations may
give inaccurate water activity values. Th is is because the volatiles
condense on the mirror during the reading process, but do not
evaporate from the mirror as water does. As a result, the reading on
samples with volatiles will not be accurate. Th e concentration of vol-
atiles that will cause interference is variable and matrix dependent.
Th e most eff ective method to determine if volatiles are a problem is
to compare dewpoint readings to capacitance readings. If the dew-
point readings are more than 0.0153 higher than the capacitance
readings, volatiles are likely a problem.
Decagon's Series 4TEV is designed for measuring volatiles such as
propylene glycol and ethanol. Th e Series 4TEV contains both a
chilled-mirror dewpoint and a capacitance sensor. Simply choose
the sensor you want to use from the menu in the instrument. Th e
only diff erence in operation is a lower accuracy of ±0.015 a for
w
the capacitance sensor. All other operations and features will be the
same, including measurement times and adjusting for linear off set.
After measuring volatiles with the volatiles sensor, it is a good idea
to clean the chamber and run charcoal before switching to the dew
point sensor.
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