Chromatography Forum

We got a new Waters system in 2009 and run EPA 531 with it. Back then or starting pressure was about 2900 psi, now it's 3400. I do regular maintenance yesterday changing the inlet frit hoping that the sequence would run, no joy.
The column has not been installed for very long ( the initial pressure does not go down significantly with column swaps).
The only replaceable part that has been in use is the RX column. Could this be my problem? Running column effluent with 0.5% NAOH through it for close to 6 years?

What is the chemistry of the column material/particles?
Not least that of the RX column.

Best Regards

Since the pressure doesn't change much when you replace the column, that suggests a blockage upstream from there. So:
1. What pressure do you see when you run no column at all?
2. Have you looked for / changed any in-line filters (some Alliance systems have an inline filter at the pump head)?

If you are doing the post column reaction you can get precipitates in the reaction coil either in the heated one between the NaOH and OPA tees or in the room temperature one after the OPA tee. We use the Pickering post column system and over the years have had to replace the reaction coil in the heated zone and the final coil that is not heated because they become clogged. Since these are polymer if they become clogged and the pressure goes above 500psi they can and have ruptured causing leaks in the system.

If you are still getting flow through to the detector, try taking the detector out of the flow path and flushing the reagent paths with 5% Nitric acid to dissolve any precipitates that may have formed. I had to do the same for the Waters Carbamate System I had 20 years ago as well as the Pickering one we have now.