I am having an ongoing issue with my anion chromatography where the baseline is rising with my concentration gradient. System is an ICS-5000, AS17C column, 0.25 ml/min, KOH gradient from 0.85 to 51.5 mM, 32 mA current on suppressor. Analyzing ultrapure water for anions in the 5-20 ppb range.

The increase in background conductivity is reminiscent of GC column bleed. Here, however, the analyte signal is not riding on top of the baseline, it appears that the increase in background conductivity is rather sitting "on top" of the analyte, masking the analyte response.

Photo of chromats comparing a standard from a month ago to the same standard today:


I have tried replacing the suppressor, guard, gradient mixer, and CR-TC trap thus far. None of these components have resolved the issue.