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- Posts: 4
- Joined: Wed Mar 13, 2019 2:32 am
I've spent several years working with liquid chromatography, but have been struggling with an IC issue for several months now and I'm hoping someone here can offer a possible solution.
My lab has a Dionex ICS 1000 and a Thermo Scientific Aquion. Both instruments are used for inorganic anion analysis of drinking water and waste water by EPA Method 300.0. Both use the Dionex IonPac AS22 (4 x 25 mm) analytical column with an AG22 (4 x 50 mm) guard column and an eluent that is
4.5 mM Na2CO3/1.4 mM NaHCO3.
When I first started working with this method a couple of years ago on the ICS-1000, there were no issues. Then all of a sudden (after changing the columns), I started seeing what I assumed was a negative peak eluting approx. 0.5 min after the nitrate peak. A couple of months later, we purchased the Aquion and saw the exact same negative peak appear after nitrate. The Thermo tech who helped with the install did not know what was causing the negative peak as he had never seen it happen before. Since the negative peak was not interfering with nitrate, we decided to just let it be. However...
Recently , that negative peak has started to co-elute with the nitrate peak which is affecting my recovery. I'm seeing this on both of my ICs (different column lot #s), but it is a bigger problem on the Aquion.
I've been trying to work with Thermo to troubleshoot what is happening because I believe the issue was column-related. They are telling me that the negative peak is a carbonate dip. Here are the things I have tried at their suggestion with no success.
- Different water source
- New reagents for eluent prep.
- Weaken the concentration of Na2CO3
- Increase the ratio of Na2CO3 in the eluent to move retention times
I'm just about at my wit's end here. Any help would be appreciated!
Thanks in Advance