39
AQUALAB VSA
To use a verification standard, remove the twist top and puncture the foil cap. Pour the
contents into a sample cup.
NOTE: To avoid inaccurate water activity readings, verification standards should be used once immediately after
opening. Do not store standards in sample cups for repeated use.
6.1.2 VERIFICATION OF CALIBRATION
Verification of the calibration should be performed regularly to ensure the AQUALAB VSA
is operating within specification. Check the linear offset against two known verification
standards before running a new isotherm test. Never verify the linear offset solely against a
single standard, since it does not give an accurate representation of the linear offset. For best
results, conduct the VSA water activity verification using the 0.25 a
w
and 0.76 a
w
standards.
NOTE: The verification process is the same whether you set the volatiles to yes or no, except that the accuracy for the
capacitance sensor is ±0.020 a
w
.
Checking the water activity of a standard solution checks for the possibility of unit
contamination or shifts in the linear offset from other causes.
The following steps explain how to verify for linear offset of the AQUALAB VSA (Figure 29).
1. From the Isotherm Tab, navigate to the Measurement tab by pressing the Enter button.
NOTE: The AQUALAB VSA needs to warm up for approximately 15 min to make accurate readings.
2. Choose a 0.25 a
w
standard.
3. Remove the weighing pan.
4. Empty a vial of solution into the stainless steel sample cup.
5. Place it in the AQUALAB VSA testing chamber. Make sure that the standard is as close to
the instrument temperature as possible.
NOTE: Make sure the rim and outside of the sample cup are clean.
6. Carefully close the lid and move the lever to the READ position.
7. Take two readings.
The water activity readings should be within ±0.005 a
w
of the given value for the
verification standard. The standards will read at 25 °C. If other temperatures are
required, refer to Table5.
To Next Page
Loading...
Need help?
General
