Decagon Devices AquaLab 4TE - Measuring Samples with Volatiles

AquaLab
8. Sample Preparation
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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.  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 a 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.  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.  e concentration of vol-
atiles that will cause interference is variable and matrix dependent.
 e most e 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.  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.  e
only di erence in operation is a lower accuracy of ±0.015 a
w
for
the capacitance sensor. All other operations and features will be the
same, including measurement times and adjusting for linear o 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.