Presumably this is a run of the analysis you mentioned previously: Folic acid and pangamic acid, yes? It would help if you included the text in your question, so people doing Google searches find this forum.
I'd also help if you were as specific as possible about your separation: column type, manufacturer, eluent composition, and what you've tried.
I'd also like to direct you to
http://www.chromforum.com/ , they're a great group of professionals, who specialize in these sort of questions. Don't get me wrong -- I love talking about separation science, and could do this all day. They're just better at it than I am, that all.
Now, for my specific help:
Folic acid tails badly. It just does. If you look at some of the promotional literature for the more advanced, and expensive columns, from such companies like FMC, Waters, etc., you see pretty high tailing, like 1.7. And that's with ion pair reagents, which, as I recall, you prefer not to use, right?
Now, some simple HPLC tips, that you may already know. You want to analyze folic acid, presumably by reverse phase. An acid is by definition, charged at high pH. If your eluent pH is close to the pKa of folic acid, you are analyzing two things -- folate, and folic acid, so you will get bad tailing. To analyze just one on reverse phase, you will have to lower the pH, so the folate is protonated, and behaves more like a non-polar molecule and less like an acid.
Now as for pangamic acid, as I recall from your other post, it's structure is more than a little different than folic acid, so improving one separation may harm the other separation. Heh. I'd need to look up the pKa to see for sure. However, I think an ion pair reagent may be just what your separation needs, if you're not using it already.
And another tip. I don't much care for Word documents as attachments. They can carry viruses, and I don't care to scan so carefully. The plain graphics, as attachments, are easier to handle.