Agilent Technologies 8453 User Manual, Installing And Operating Manual page 90

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
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
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
2 Measure the absorbance of solvent directly in your flow cell, that is without
3 Prepare a sample solution, that consists of an absorbing substance
4 Place the tubing for valve positions 1, 3, 5, and 7 in the solvent you
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
7 Compare the results with the solvent reference. An absorbance of not more
90
the tubing which may restrict flow.
Valve" on page 91.
instrument zero.
passing through the valve. Use this measurement as a solvent reference
during the next steps.
dissolved in the same solvent to give an absorbance of about 1.0 AU.
previously used for the reference.
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.
than 0.005 AU for the solvent indicates less than 0.5% cross contamination.
Agilent 8453 Dissolution Testing System Installing and Operating Manual
"Cleaning Tubing and