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- Posts: 26
- Joined: Wed Jun 05, 2019 3:57 pm
I'm looking for some help from somebody far smarter than I am.
I am doing suppressed anion chromatography on a Metrohm 940. On the anion side, no matter what calibration range I do (small range or large range with orders of magnitude) my y-intercept is always negative.
This has been the case for 3 separately prepared 6-point calibrations with good precision and 96-103% accuracy.
My anion eluent is 3.2mmol sodium carbonate and 1mmol sodium bicarbonate. Suppressor is regenerated by 150mmol sulfuric acid and 100mmol oxalic acid.
My most recent calibration curve had the following y-intercepts for a calibration range of 0.5 - 6ppm.
Linear model: -0.0164440
Quadratic model: -0.0201090
Neither are forced through zero and have no weighting applied. I tried all weighting options and the y-intercept remains negative. Forcing through zero compromises result accuracy.
When analyzing cations (un-suppressed), this negative y-intercept is not observed and so I don't think it's a product of poorly made standards.
Could anybody offer some help as to why this is happening and some guidance on whether this is acceptable or not?
Thank you.