Clear a Needle or Needle Seat Clog Without Using Lab Advisor

Answer

This Information Applies To: Agilent LC Samplers except dual needle multisamplers

Issue

High pressure in the LC sampler is sometimes due to a clog in the needle seat assembly, the needle, or the sample loop. The needle can pick up sample particulates or plugs from the vial caps when the sampler is drawing the sample. When the valve switches back to mainpass, they are forced into the seat capillary and cause an obstruction and high pressure.

Tips: There is a procedure to back flush the needle seat using Lab Advisor (see Backflushing the Needle Seat of the Agilent Vialsampler). If you do not have Lab Advisor available, follow this procedure.

Steps to Follow

Caution: This procedure is not applicable to dual needle samplers

Preparing the system

1. Turn on the pump. In the acquisition software, right click the pump icon and from the contextual menu, select Method. Under Pressure Limits section, set the Max pressure to the maximum allowable. Under Flow, set the usual flow rate. If the current method uses an organic solvent, switch to water. Take note of the pressure value.
2. In the Acquisition software, right-click the autosampler icon and from the contextual menu, select the Bypass option.
3. Observe the pressure.
   • If it’s the expected pressure (200 bar as described above), then the issue is within the autosampler, between ports 2 to 5 on the injection valve. 
   • If the observed pressure is unexpected (350 bar), then the issue is past port 6 on the injection valve, after the autosampler, and you will need to methodically remove capillaries and column while monitoring the pressure to determine the source.
4. Set the pump flow to zero.
5. Lift the needle out of the needle seat
   • For Vialsamplers, Standard, and HIgh Performance autosamplers: Make sure that the autosampler door is closed, then right-click the autosampler icon and from the contextual menu, select Reset.
     Once the needle is lifted out of the needle seat, power off the autosampler module.
   • For Multisamplers: Make an injection, then after the needle is picked up by the sample handler, but before the needle is inserted into the vial, power off the multisampler
6. Remove the capillary from port 6 of the injection valve (to analytical column). Use Figure 1 as reference for the capillary connections to the injection valve.

   
   
   Figure 1. Injection valve ports,
   1. From pump, 2. To metering device, 3. Plug, 4. To waste, 5. From needle seat, 6. To analytical column
   

Backflushing the needle seat

1. Remove the capillary from port 5 of the injection valve (from needle seat) and connect it into the vacant port 6.
2. Place some absorbing paper or tissue on the needle seat.
3. Set the pump flow to 1 ml/min while monitoring the pressure. 
   • It may rise, then suddenly drop indicating that the clog was removed. On the other hand, it may continue to rise causing the pump to shut off. 
   • You may need to turn on the pump and get the flow going again several times until the pressure is relatively low (~ 10 to 15 bar). If repeated attempts do not clear the clog, then it will be necessary to replace the needle seat capillary.
4. Increase the flow to 5 ml/min for about 1 minute then turn off the pump.
5. Return the needle seat capillary from port 6, to port 5 of the injection valve

Flushing the Needle and/or Sample Loop Capillary

1. Remove the capillary in port 2 (to metering device) and connect it into port 6 of the injection valve.
   
   • Sometimes, the capillary in port 2 is too short to reach into port 6; in that case, connect line 1 (from pump) into port 6, and the capillary in port 2 to port 1.
2. Place some absorbing paper or tissue at the bottom on the raised needle.
3. Set the pump flow to 1 ml/min while monitoring the pressure.
   • It may rise, then suddenly drop indicating the clog was removed. On the other hand, it may continue to rise causing the pump to shut off. 
   • You may need to turn on the pump and get the flow going again several times until such time the pressure is relatively low (~ 10 to 15 bar). If repeated attempts do not clear the blockage, then it will be necessary to replace the needle and/or sample loop.
4. Return the capillary to metering device to port 2, and if necessary, reconnect the line from the pump to port 1 of the injection valve.

Restoring the system

1. Remove any absorbing paper or tissues from the autosampler, and dry any wet surfaces if necessary.
2. Connect line 6 (to analytical column) into port 6 of the injection valve
3. Make sure that the Autosampler door is closed, turn on the module, and wait until the initialization process is finished.
4. Turn on the pump, set the flow from the usual analytical method, and monitor the pressure.

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