Chromatography Forum

Good morning,
I am developing a method using an ion pair on a C18 column.
The mobile phase: phosphate buffer 50mM pH 3.5 + Sodium dodecansulfate and CH3CN (850: 15).
I get a good retention of the peak, but it is split and asymmetric.
I read that this could be due to:
" if the rate of interconversion between the free and paired analyte is slow compared to the chromatographic retention time scale".
How can I solve it?
Thank you.
Gianna

Good evening,

To test if this is the case, try making the kinetics more favorable by manipulating the temperature of the separation, most likely by increasing the temperature.

MattM is right about raising the temperature. That will tell you if slow interconversion is, in fact, the problem. There *are* also other possible causes of peak splitting:
- "inlet flow anomaly" (a partially-plugged column frit or a headspace). The tipoff on that is that, if you have several peaks on the chromatogram, they will all show the same problem.
- "the strong diluent effect" (more generally, an incompatibility between the diluent and the mobile phase). This is particularly common where the sample diluent contains more organic solvent than does the mobile phase. To diagnose, try dissolving your sample in the mobile phase, or else inject a much smaller sample.