Chromatography Forum

Please help!

Our lab is running EPA 300.1 and we have been experiencing issues with our baseline pressure for MONTHS. We ran the IC for about 9 months with a very consistent 16.1 MPa background pressure. We started to see a 0.1-0.3 MPa increase every time we turned the IC on.

A Metrohm service tech assured us this was normal, so we kept running the IC. We eventually replaced the guard column (which helped a bit) and then ended up replacing the entire column after we started to see peak splitting (and the pressure was regularly hitting 20.0 MPa). We are seeing the same slow, but continual baseline pressure increase on our new column (jumping from 15.3 to 16.5 with under 150 injections). This increase happens even when we are just running eluent through the system. We were using ASTM Type II water (to save costs, as we are in Alaska) in our eluent but since having issues we have switched back and still we are having these baseline problems.

We use Metrohm reagents for everything, save some oxalic acid (Ricca) and sulfuric acid that we add to the pre-diluted regenerant solution for our dosino. We also use the concentrated Hach nitrate and nitrite standards for our method, but like I said, the pressure increase happens even with just eluent!

We are a drinking water lab, so the samples aren't too horrible (some high calcium carbonate and iron, because of the high well usage in AK) and I am just baffled as to what could be causing the issues. Our eluent is 8.0 mM Na2CO3 and 0.25 mM NaHCO3. It could be bacterial but I'm not sure how to troubleshoot that and I'm not sure how likely that is. I've done column regeneration with DI water and 10x concentrated eluent, as well as ACN.

Please help me, this IC haunts me. Any and all suggestions are welcome at this point as my next step will be to throw it out the lab window.

I just had that problem with my Integrion. It was running at 4600 psi. I replaced the guard column and the pressure dropped 200 psi which was not enough. I then replaced the check valves and got the pressure under 4000 psi.

It sounds like you might be having a particulate build-up problem. I would strongly urge you to keep using Type I water. I found my baseline drifts a lot when I use anything less pure. I have some follow up questions:

-Are you filtering the water with a 0.2um filter before using it in the instrument?
- Are you using Metrohm Sample Ultrafiltration?
- Are you using the white eluent filter that connects to the capillary in your eluent bottle?
- Have you tried replacing the inline eluent filter? It is a PEEK cylinder located just above your injection valve. It unscrews to expose a frit that can be replaced. You likely received extras when the instrument was installed.

As a side note, it sounds like you are using an A Supp 19 column. I'm curious as to what you're using as a surrogate. I found that dichloroacetate coelutes with chlorate on that column. Chlorate elutes right before bromide using the column standard conditions. You might have lower background chlorate than we do, so it might not be an issue, but we were unable to use this column due to that coelution.