Having an issue with my PRP-X100

[rkrebo]

I am trying to figure out if I can run a KOH mobile phase with a gradient of 10 mM - 45 mM, ten minutes on the 10 mM then slowly ramping to 45 mM over fifteen minutes. The detection method is suppressed conductivity. I was running parahydroxybenzioc acid in 2.5% meOH originally and I was trying to determine if this new mobile phase was viable. Currently I am just seeing if I can get a fluoride standard to elute at a normal time. For some reason when I equilibrated my column to the new mobile phase the fluoride went from eluting at around five minutes with my old method to 25 minutes with my new method.

This doesn't make sense to me because I am using a much higher concentration of KOH than I was pHBA and I would think that a hydroxide anion would kick other anions off the column much faster than the comparably weak pHBA anion.

I can give more details if needed obviously, but this just doesn't add up to me.

Any ideas?

[Markus Laeubli, Metrohm]

p-hydroxibonzoate is a much stronger eluting ion then hydroxide. Therefore your result sounds OK to me.