This Information Applies To: Agilent LC pumps
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.
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 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).
For this step, it is recommended to remove the column and bypass the flow cell.
2. Binary Pumps
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.
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
If you cannot resolve the issue, contact your local Agilent Support representative for more help.
Learn how to effectively operate your Agilent 1290 LC System:
Agilent 1290 Infinity LC Systems with OpenLab CDS ChemStation e-learning path available from Agilent education