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- Posts: 3475
- Joined: Mon Jan 07, 2013 8:54 pm
- Location: Western Kentucky
I started last week to set up to run the main Anion list by 300.1 Fluoride, Chloride, Nitrite, Bromide, Nitrate, Phosphate, and Sulfate (listed in elution order) using the same Supp7 column as for the other 300.1 analytes. The first injections gave very very broad peak for Fluoride, massive tailing, Chloride, Nitrite, had only a tiny amount of fronting, Bromide was perfect, Nitrate had a tiny amount of tailing, and Phosphate was so broad it was barely detectable as a peak and bleed over into Sulfate which was also tailing very badly and very broad round top peak.
I did all of the suppressor cleaning procedures twice and it helped with peak shapes somewhat. I also ran the oxalic acid and acetone through the MCS and that also improved peak shapes. The peaks are now only a little misshapen and could be usable except I have an undulating baseline which has been present for a long time even when doing the Chlorate, Bromate, Chlorite analysis. This hump in the baseline did interfere with the Chlorate and DCAA surrogate before but makes finding low level peaks for Phosphate and Nitrate very difficult now. The top of the hump seems to stay at about 24 minutes. I switched to a Supp5 column and also found the hump at the end of the run which was 18 minutes and sometimes carried over into the next run with a drop at the beginning of the run.
From bottom to top is three blanks and a second level calibration standard, the next in that series showed that the shape of the humps follows the suppressor segments as it also had the double hump, but I didn't include that one.
Could this be related to a problem in the suppressor? If it is prior to the suppressor it would have to be in the injection valve, but it is odd that the retention time of the hump doesn't change when changing column and eluent mixture. I have been trying to get rid of this for a long time now, just wondering if anyone else has seen this problem.
Thanks.