Hello Everyone.

I am doing a normal Capillary Zone Electrophoresis method development project. One of my analytes, pyridine (pKa= 5.23) is neutral. I am using 100mM Phosphate Buffer (pH 6.5 to pH 7.8) as my background electrolyte (BGE).

At pH 6.5 to pH 6.9 there is co-elution between sample plug and pyridine as they are both neutral. However, above pH 7.1, the pyridine peak separates and comes out 0.2 mins later after the sample plug. I am trying to find reasons for this.

Any ideas would be helpful. By chance is there any attraction between water and BGE? Or between pyridine and BGE?

I am sorry for the approach, and I know I should shift to MEKC or acidic pH instead.