Table of Contents
Advertisement
Blocked Proportioning Valve
Blocked Check Valve
Irreproducible Retention Times
Thermo Scientific
If flow from the degasser is normal, then the next area to check is the proportioning valve.
To check for blockage in a proportioning valve
1. Set the pump to deliver 100% of solvent A at a flow rate of 1000 L/min.
2. Measure the actual flow rate.
3. Repeat steps 1 and 2 for each channel.
If one or more of the values are low, clean the LDA by flushing it with the appropriate
solvents, as described in
"Cleaning the LDA Components without Disassembling the LDA"
on
page
38.
Occasionally a valve might freeze closed entirely if it hasn't been used for an extended period
of time. To open the valve, insert the valve tool (stainless steel wire) into the valve inlet and
push the floating piston away from the valve seat, as described in
Valves"
on
page
62.
Insufficient flow rate can also be a result of a blockage in one or both check valves. In this case,
clean the liquid displacement assembly by flushing it with the appropriate solvents, as
described in
"Cleaning the LDA Components without Disassembling the LDA"
There are many reasons for retention time problems. Some of the more common causes are:
• An old or damaged column
• Inconsistent stationary phase (Was a new column installed?)
• A validated method lacks robustness
• Changes in mobile phase composition
• Temperature fluctuations
• Pump problems
If you suspect the pump to be responsible, replace the column with a flow restrictor and run a
step gradient, as described in
Inaccuracy in the steps is most likely caused by contamination of the proportioning valves.
Clean the LDA by flushing it with the appropriate solvents, as described in
LDA Components without Disassembling the LDA"
"Testing the Pump Proportioning"
on
Surveyor MS Pump and Surveyor MS Pump Plus Hardware Manual
5
Troubleshooting
Irreproducible Retention Times
"Servicing the Proportioning
on
on
page
31.
"Cleaning the
page
38.
page
38.
73
Advertisement
Table of Contents
Troubleshooting
