Low Control Values Dionex ICS5000 Anions Analysis

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Hi all,

I’m fairly new to ion chromatography and am hoping I can get some troubleshooting advice on an issue I’m having with our Dionex ICS-5000. We test for several anions using an IonPac AS5A-5u column with guard column and use KOH as eluent from eluent generator cartridges. My problem is that I’m getting consistently low values with the first control standard injection for each of 10 analytes being tested for that will gradually increase upon subsequent injections of standard until they get to within limits many injections later. I’m only seeing this on one side of our instrument, the other side with identical hardware and modules does not have this issue.

My initial thought was that there wasn’t enough sample being injected on to the column due to some kind of blockage in the line. The back pressure wasn’t abnormally high but I changed the sample transfer line and tubing up to the suppressor/detector anyways. Immediately after this the control values were consistently 2-3 ppm above the expected and just above our accepted range. I figured a recalibration was necessary and the first control values immediately after calibration were all within 1 ppm of target, but the next few dropped by a couple ppm and are now all just outside of accepted range. After turning off the pump, EG, etc. and going through standard pump and column conditioning the next day I’m now seeing control values 10 ppm lower than target.

With my limited experience I am unsure of what the issue might be. If anyone has suggestions or advice that would be greatly appreciated. Not sure if I gave enough info on hardware components or run method, I can provide more info if needed.

Thanks in advance,
John
you may not be injecting enough volume to fill the sample loop completely.

You could try increasing injection volume or reducing your sample loop size.
jmurray2 wrote:
I’m getting consistently low values with the first control standard injection for each of 10 analytes being tested for that will gradually increase upon subsequent injections of standard until they get to within limits many injections later

I had this exact same thing happen, but with a different column and eluent. If you're still having issues you could try what worked for me - cleaning the column/guard column and suppressor according to their manuals, then do a chemical regeneration of the suppressor.

If you have an older working column/suppressor you can swap them out and quickly confirm (or eliminate) if the issue is coming from there.
Thanks for the advice guys. After performing a complete annual PM on the instrument I'm seeing consistent values again so it appears the problem has been fixed for now.
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