Troubleshooting High Pressure Issues in Agilent LC Systems

Created by Max Schütte over 1 year ago | Last modified by paubudge 2 months ago

This Information Applies To: All standard analytical scale Agilent 1100/1200/1260/1290 Infinity / Infinity II LC system configurations: Single Pump (Isocratic, Quaternary, or Binary) with Manual Purge Valve. Does not apply to systems with Agilent G7167A/B Multisampler or extra Switching Valves.

Issue:

When facing high pressure-related problems, like aborted runs, or high pressure error messages, it is important to identify the location of the blockage that is causing high pressure. This information will help you to solve the issue, or to provide the Agilent Service Representative with the necessary information to do so.

Even when part of your whole system configuration is not included in this article, you may still find helpful tips for checking other modules.

Steps to follow:

Be aware that even though it may be unlikely, more than one blockage can occur at the same time. A common example of simultaneous blockages, is the obstruction of the needle and the needle seat.

Warning: When disconnecting capillaries and starting flow, always have paper towels or tools ready to collect the mobile phase flow coming out of the open end of the flow path.

Warning: Avoid removing capillaries under high pressure, make sure to wear appropriate protective gear.

Check the column:
1. Disconnect the column outlet and check the pressure (Figure 1).
  
  Figure 1. Example of a column compartment.
  I - Heat exchanger inlet. II - Column inlet. III - Column outlet.
  A - From autosampler/injector. B - To detector.
2. If the pressure drops drastically (more than a few bar due to simple reduction of capillary backpressure), then the blockage is after the column: Go to step 6, and if it does not point to a solution, go through steps 2 to 5 also.
3. If the pressure remains high, disconnect the inlet to the column.
4. If the pressure is fine now (does not rise above the expected values) and you get a flow of solvent out the end of the capillary, the column is clogged. You may try to backflush the column or replace the column as required.
5. If the pressure remains high, the cause for high pressure is somewhere before the column. Go on to step 2.
Check the method parameters:
1. Ensure that the upper and lower pressure limits in the method are set to suitable values for the analysis and the system (be aware of the upper pressure limit for your system). In both ChemStation C.01.X and OpenLab 2.X in the system diagram, right-click the pump icon in the dashboard and select Method (see Figure 2).
  
  Figure 2. System Diagram - Pump module
2. Next, insert suitable values for the pressure limits according to your system (compare with Figure 3).
  
  Figure 3. Pressure Limits - Method parameters
Check the Pump / Purge Valve:
1. If the pressure limits are correct, open the purge valve and check the pressure (for a flow of 1 mL/min the pressure should be roughly below 2 bar under normal conditions).
2. If the pressure drops when opening the purge valve, the pump is not clogged (bear in mind that this article only applies to pumps with manual purge valve). Close the purge valve and go on to step 4.
3. If the pressure is still high, the problem is most likely due to a clogged PTFE frit that resides in the purge valve (see Figure 4). Replace the PTFE frit.
  
  Figure 4. Purge Valve Assembly: 1 - Valve body, 2 - PTFE frit with groove, 3 - Seal cap
4. If the preceding step does not solve the issue, remove the purge valve and start the pump. If the pressure does not rise, the purge valve needs to be replaced as it was the cause of high pressure. If the pressure is still high, the blockage is either in the pump head or between the pump head (or heads) and the purge valve.
Check the Autosampler:
1. Go to the sampler icon in your software. Switch the injection valve to bypass by right-clicking the sampler in the system diagram and selecting Switch Valve to Bypass and start the flow.
2. If in bypass mode the expected pressure values are obtained, the blockage is in the autosampler flow path (needle, needle seat capillary, sample loop, metering head, rotor seal, or associated capillaries). Go on with step 4.d.
3. If the pressure is still high in bypass mode, check the capillary that goes from the pump (purge valve outlet) to the autosampler:
  1. First, remove the capillary connected to the purge valve outlet (Figure 5) and - with the purge valve closed - see if the pressure still rises when starting flow.
    
    Figure 5. Purge valve outlet capillary
  2. If the pressure does not rise, and solvent comes out of the purge valve outlet, tighten the connection from Figure 5 again. Loosen the other end of the capillary on the injection valve (Figure 6). Start the flow.
  3. If solvent comes out of the capillary's end, the capillary is fine. The blockage is either in the rotor seal or somewhere after the autosampler in the flow path. Reconnect it and go on to step 4.h.
4. Disconnect the needle seat capillary tubing from its port of the switching valve (typically port 5, compare with Figure 6) and switch the valve back to main pass.
  
  Figure 6. Injection valve ports, standard configuration. Connections:
  1 - from pump
  2 - to metering device + needle
  3 - plug
  4 - to waste
  5 - from needle seat
  6 - to analytical column.
5. If high pressure is observed again, then there is a blockage before the entry port of the needle seat (typically port 5).
6. If the pressure is normal and liquid drops out of the capillary, the rotor seal is clogged between port 5 and 6.
7. Re-attach the needle seat capillary back into port 5.
  
  Tip: If the blockage is found to be in the needle seat assembly, sometimes it can be recovered by backflushing the needle seat.
8. Now remove the capillary going from the injection valve to the column or column compartment by removing the capillary fitting at the injection valve port (see Figure 7).
  
  Figure 7. Injection valve ports, standard configuration
9. If the pressure is normal, the blockage is located after the injection valve (capillary, column compartment, column, detector, or associated capillaries).
10. If high pressure is observed, the blockage is in the rotor seal within the injection valve. Replace the rotor seal.
Check the Thermostatted Column Compartment / Multicolumn Thermostat:
1. When the pressure in bypass is still high, disconnect the inlet to the column compartment / heat exchanger (Figure 1, Figure 8) and check the pressure. If you have not done step 1 already, do it first.
  
  Figure 8. Example of a Multicolumn Thermostat - Inlet and outlet of the heat exchanger (blue) are marked in red.
2. If the blockage is not in the heat exchanger, the capillary or the injection valve are blocked.
3. To check if the capillary or the rotor seal is causing the blockage, disconnect the end of the capillary at port 6 of the injection valve (see Figure 7).
If a blockage lies after the column:
1. If disconnecting the column outlet releases the high pressure, look for a blockage in the system beyond the column. Check the capillary to the detector, the flow cell, and the waste tubing.
2. If you cannot locate the source of high pressure after having been through steps 1 to 6, contact your local Agilent Support representative for further technical support.