using HPLC for fish medicines

[Jealemy]

I'm using HPLC to determine the concentration of certain compounds on fish medicines. The medicines contain a mixture of the following compounds (in low concentrations) and between 80-95% dextrose:

Nifurpurinol
Acrinol
Malachite green oxalate
Metronidazole
Diflubenzuron
Cupric sulphate
Acriflavine
Citric Acid

Now, I've already used a polyamine II column (Acetonirtile/water 75/25) but some compounds coelute. A C18 column does not work at all. I'm now trying to optimize the gradient to see if I can resolve that problem. Does anybody have some experience with these compounds or suggestions????
Thanks a lot

[Einar Ponten]

You seems to have promising results by using HILIC conditions. While you still may need some other selectivity the ZIC®-HILIC column is an alternative.

Since you are using a gradient, I recommend that you initially run this from 5% to 50% buffer and then later tune the interval.

[Rafael Chust]

Usually you can try to separate complex mixtures of polar compounds with phenyl reversed phase columns, since it increases the retention of polar compounds and have a specific selectivity for molecules with pi orbitals.