No Pressure, No Flow, RT shift Issues: Cleaning Acetonitrile (ACN) Aggregations in Agilent Pumps

Answer

This Information Applies To: Agilent LC pumps

Issue:

Stuck or obstructed check valves (Active Inlet Valve (AIV), Passive Inlet Valve (PIV), Outlet Ball Valve (OBV)) can cause issues such as no-flow or no-pressure, moderate to strong drops in pressure or retention time shifts. You can see the article How to Troubleshoot no flow or no pressure issues: Binary/Quaternary/Isocratic Pumps - G131XX, and G711XX to troubleshoot the issue. If one of the valves is the source of the blockage, and acetonitrile (ACN) is one the solvents used in the LC, this guide may help you recover the system.

ACN is a by-product from the polymer industry, and therefore has a strong tendency to self-polymerize. It may form or contain polymer blocks that can accumulate and form a sticky layer on the ball valves (see Figure 1), which can prevent them from opening or closing correctly. Heat, light, oxygen, and acids promote the polymerization. Use of ACN in HPLC and UHPLC can therefore be unproblematic over years and then suddenly cause issues. When sequences using ACN in the mobile phase are run overnight and in the morning no pressure or no flow is found, one of the causes is ACN polymerization.

Short-chained polymers are, however, partly dissoluble in water.

Resolution: 

Perform a warm water (60 to 70 °C, HPLC grade) flush for 20 to 30 minutes at 2 mL/min against a restriction capillary to have some backpressure. Doing this procedure on a monthly basis, or more often depending on use, is a general recommendation when working with ACN.

Caution: Bypass any equipment further ahead in the flow path to not contaminate or obstruct these parts (InfinityLab Max-Light Cartridge Cell, for example) in the initial purging or cleaning procedure steps.

Caution: Do not flush your column with inappropriate solvents.

The following recommendations go into more detail:

1. Quaternary Pumps and Multichannel Gradient Valves (MCGV)
2. Binary Pumps
3. Passive Inlet Valves (PIVs) and passive Outlet Ball Valves (OBV)
4. Active Inlet Valve (AIV) cartridges
5. Other recommendations for ACN use and good practices

1. Quaternary Pumps and MCGVs

Never leave the Multichannel Gradient Valve (MCGV) in water, buffer, or ACN for a long time. Unused channels should be stored in, e.g., methanol (MeOH) or isopropanol (IPA) and closed off.

If the retention time is shifting or jumping, oftentimes the MCGV is blocked (one or more channels do not open or close as planned and thus the composition is not correct).

• Blocked channels can often be released by purging with a high flow with warm water (60 to 70 °C, HPLC grade). You can purge all channels using a composition of 25 % for each channel, using warm water in all four channels. For more persistent blockages, you may try using a 85:5:5:5 composition with warm water for channels A/B/C/D to let the MCGV switch faster.

• For this step, it is recommended to remove the column and bypass the flow cell.

  Often it is unknown which component is causing a blockage, so the use of an HPLC flushing solvent such as G1969-85026 in your LC system may be helpful
  Note: If you are using buffer salts, make sure to flush them out before using this flushing solvent. Otherwise, they may precipitate and obstruct the flow in random parts of your instrument. Remove the analytical column before flushing the system with this solvent.
• As a general maintenance procedure, all channels should be flushed weekly with warm water and stored in IPA for long periods without use.

2. Binary Pumps

• As a preventive measure, you may regularly change the hydrophilic and the hydrophobic eluent channel (channel A = water / channel B = ACN to channel A = ACN / channel B = water,) after cleaning both channels from buffer salts or other additives.
  Note: If you do, make sure to let all personnel know of this change of the channels. Make sure to update all methods accordingly (e.g. by creating a second version with switched solvent channels).
• Use the preceding general flushing procedure for both pump heads / all solvent channels (i.e. warm water with a composition equally distributed across all channels).

3. PIVs and OBVs

Passive inlet valves used in quaternary pumps of the 1260-series and all pumps of the 1290-series are sensitive to particles (ACN polymers, buffer salts, and other solid residue). Because they experience higher pressure, OBVs are not as sensitive to this blockage, but the same issues can be observed. Often, defective PIVs and OBVs could be misdiagnosed as a defective pump head.

Figure 1. Schematic of Ball Valves for Agilent Reciprocating Piston Pumps: The flow of the solvent opens and closes the passive check valves; 1 - Gold seal, 2 - Sapphire insert, 3 - Ruby ball, 4 - Spring, 5 - Insert, A - PIV, B - AIV with cartridge, C - Flow direction.

• Regeneration of the PIV and/or OBV is possible: Se the following article for more details on how to sonicate the valves:How to Sonicate the Inlet and Outlet Valves of Agilent 1100, 1200 and 1260 Series Pump Heads. To evaluate the performance of the valves make a test run, or run the Pump Leak Rate Test in the Agilent Lab Advisor Software (see How to Install Lab Advisor).
  
  If this does not solve your issue, change the valve according to the following articles: How to Change the Outlet Valve on a 1260 Isocratic or Quaternary Pump and How to Change the Passive Inlet Valve (PIV) on a 1260 Isocratic or Quaternary Pump.

4. AIV cartridges

• Use appropriate PPE when dealing with special or hazardous solvents.

  If the conclusions from the article How to Troubleshoot no flow or no pressure issues: Binary/Quaternary/Isocratic Pumps - G131XX, and G711XX, and performing the Pump Leak Rate Test, points to a defective or clogged AIV, you may try the following procedure: How to Sonicate the Inlet and Outlet Valves of Agilent 1100, 1200 and 1260 Series Pumps. Use a new cartridge if the preceding procedure does not solve the problem.

5. General recommendations for proper use of ACN

• Always use fresh ACN (not older than 48 to 72 h).
• To prevent photochemical reactions and oxidations, use brown or amber bottles for CAN, and stick to minimal amounts. Use the amount that will be needed, including in-between-run time, plus a 20 to 30% allowance for time issues.
• If the application allows for it, mix your ACN with 5 to 10% HPLC grade water, especially for LC/MS applications where 0.1% formic acid (HCOOH) is used as mobile phase.
• Do not leave an unused system in water, buffer, or ACN.
• At least once per month, perform a warm water (60 to 70 °C, HPLC grade) flush at 2 mL/min for 20 to 30 min, to get rid of ACN reaction products.
• Filter ACN using a 0.45 µm nylon filter depending on initial solvent quality (unless you use High Sensitivity LC/MS).
• When the quality of the lot/batch is in doubt, change the lot/batch or the manufacturer/provider.
• You will also find useful information in your user manuals. Please follow the recommendations given there.
  
  

If you cannot resolve the issue, contact your local Agilent Support representative for more help.

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