Pressure maximum exceeded on RI detector - baseline unstable - flow cell possibly damaged?

We have a system with the following parts. 

  • Tray with THF Bottle as solvent A/no solvent B and Waters in Line Degasser
  • 1200 Series G1312A Binary Pump
  • 1100 Series G1313A Autosampler
  • 1100Series G1316A Column Compartment with guard column and analytical column in sequence
  • 1200 Series G1362A RI Detector

It has a baseline issue, was sitting for a long time unused and fixing and replacing the following things did not improve it:

  • Both solvent lines are drawing solvent from the same bottle
  • replaced solvent filters
  • hooked the system up properly (channel B was not hooked up at all and the capillaries were connected wrong)
  • changed the pump seals and did a pump-wear in procedure
  • cleaned the pistons and the inside of the pump
  • exchanged the active inlet valve and the outlet valve on both pump heads
  • exchanged the cartridge in the purge valve
  • primed degasser and pumps with IPA

I am currently bypassing columns for testing and the baseline shows a lot of noise. I am currently trying to clean the flow cell as I was told that this may be the issue. I would like to open the flow cell, but cannot find a description of how to do this in the manual. 

It says that the maximum pressure of 5 bar should not be exceeded for the flow cell, but since I did not know that when I initially tested the instrument, I exceeded that pressure for sure based on the pressure reading of the pump. What happens to the flow cell when it is overpressurized. If I am running the system at 1 mL/min (typical flow rate for previous samples), pressure is already at 6 bar. I thought I can go up to 5 mL/min and be fine, but maybe 5mL/min is just for purging. 

  • The pressure limit of the quartz cell refers to back pressure, not system pressure.

  • How do I know what the pressure of the Quartz cell is?

  • The back pressure on an RID cell cannot be measured directly, but as the limit is fairly low, you'd try to keep it as low as possible. This can be achieved by using the correct waste tubing and avoiding any kinks, knots or blockages on that line. No device (another detector, fraction collector etc.) should be installed after the RID. Still the waste and recycle container should be placed above the detector, so we maintain a minimal back pressure, which helps stabilizing the signal.

    With regards to the cell: All you can do is flushing it with water or IPA and keep switching the valves. The cell itself cannot be accessed, as it is inside the optical unit, which is not to be opened.

    Possible sources of noise could be contaminated degasser channels (try a different one), also poor solvent quality could be a reason for that. I would also take a look at the pump ripple. You said that you're using a binary pump with channel A only. That's not what we recommend. Binary pumps should always use premixed solvent, pumped from channels A and B 50:50

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