We never had an issue with our MDLs not showing up until recently and I don't know why. Maybe the column is shot? Also the baseline seems to be lifting towards the end of sulfate and have no idea why as well. Any suggestions would be appreciated since we're trying to get our PT's done. Thank you. :)
Maybe you need to wash the column. Follow the manual of your column for wash/clean. Additionally, purge your system after wash the column. Another thing that affects it could be the pH of your movil phase, check it and try again to run the sample. Good luck!
Dear Araceli Martinez
Many thanks for your message and the chromatograms. Very telling! Comparing the peak shapes, we see that the fluoride and phosphate peaks are broad(er) and tail. This is very often an indication of metal contamination within the analytical flow path. With carb/bicarb eluents - such as the one you use - you might find the contamination either in the connecting line of the autosampler you use, the injection loop, (sometimes on) the column, and very often on the suppressor device (= cation exchanger).
I assume you are analyzing plenty of samples of different origins on this instrument. In that case, metal contamination - which is an accumulating thing over time - could be the reason. I would check the rinsing instructions of your packed bed suppressor to remove the metal contaminations. Assuming you are running a discontinuously operated three-chambered device, please ensure that every single chamber is exhaustingly regenerated - it may take a while on your specific instrument.
I would start with the packed bed suppressor columns, then - if that does not help -the guard and separator column (please rinse separately!), and then either exchange or clean the injection loop and connecting tubing (autosampler - injection valve).
Some users follow the slope of the calibration curves (and some even the peak-symmetry) of fluoride and phosphate as an indication of possible metal contamination. If metals accumulate, more fluoride and phosphate will be trapped (better complexed), the calibration slope will change, and the peaks of fluoride and phosphate will broaden. In contrast, the others remain "stable." As you know your samples better than anyone, you might even decide whether you need to remove metals before injection. Say, when you see that the metal contamination happens fast. In this case, check with your local application specialist for integrated metal removal options. Modern IC offers plenty of options. If you want to discuss it separately, please let me know, and I will provide you with my contact details.
If I may add two suggestions? 1) please increase the data acquisition time so that you can integrate sulfate - it looks to be cutoff 2) All peaks show an untypical peak tailing - not as much as fluoride and phosphate - which could indicate an additional dead volume (connection?). To allow optimized peak area integration, your peaks should show symmetrical peak characteristics (at least less tailing than they do). Hence, please check and optimize the connection from valve to guard to the separator, suppressor, and conductivity cell.
I am crossing my fingers! Good luck with your analytical determinations!
Cheers
Detlef.
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