90 Agilent 8453 Dissolution Testing System Installing and Operating Manual
4 Using the Valve Unit and Valve-pump Controller
Troubleshooting Your Valve System
Contamination Between Ports
This may be caused by too low flow rate or flow restrictions, that is, the
previous sample has not been flushed entirely from the tubing or flow cell, and
by a defective valve.
To check for Flow Restrictions—Too Low Flow:
1 Check for flow restrictions, for example blocked filter tips, or for bends in
the tubing which may restrict flow.
2 Set the flow control to a higher rate or longer pumping time if necessary.
3 Check for dirty tubing. If the tubing is dirty, see “Cleaning Tubing and
Valve” on page 91.
To check for a Defective Valve:
This check uses pure solvent in the odd-numbered channels (1, 3, 5, and 7) and
a sample solution of about 1 AU in the even-numbered channels (2, 4, 6, and
8). You measure the absorbance in the odd-numbered channels where the pure
solvent should give no difference in absorbance compared to the solvent
reference, if there is no cross-contamination between two adjacent valve ports.
You then repeat the check using sample solution in the odd-numbered
channels and pure solvent in the even-numbered channels.
1 Measure a blank on air, that is no flow cell in the sample area, for an
instrument zero.
2 Measure the absorbance of solvent directly in your flow cell, that is without
passing through the valve. Use this measurement as a solvent reference
during the next steps.
3 Prepare a sample solution, that consists of an absorbing substance
dissolved in the same solvent to give an absorbance of about 1.0 AU.
4 Place the tubing for valve positions 1, 3, 5, and 7 in the solvent you
previously used for the reference.
5 Place the tubing for valve positions 2, 4, 6, and 8 in the sample solution.
6 Pump the solvent and sample solution into the flow cell from each valve
position and measure the absorbance of channels 1, 3, 5, and 7 (solvent
reference). Make sure the solvent and sample solution reach the flow cell
for your selected pumping time. The pumping time depends on the length of
tubing.
7 Compare the results with the solvent reference. An absorbance of not more
than 0.005 AU for the solvent indicates less than 0.5% cross contamination.
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