Kynurenic acid (KA)is reportedly separated from kynurenine (KYN)using Dowex H+ resin equilibrated with 0.1N HCl and eluted with water. Detection of KA is by flourescence (EX: 344mn; EM: 388) after isocratic HPLC. However, in my hands KA & KYN are not well separated and both flouresce @ 388 nm. Any ideas to improve specificity for KA analysis?

If you're getting *some* separation, you might try getting an equivalent resin in a smaller particle size. As far as I know, the Dowex resins per se only ever came in fairly big particles (200 mesh would be down around 40 microns). If you know the percent crosslinking (the number after the "X" in the resin designation; e.g., 50WX8 is 8% crosslinked), you should be able to call someone like BioRad, Dionex, or Hamilton and get an equivalent in a 5 or 10 micron diameter.

I'm out of league here, but something to consider, since you aren't getting much help. Did you start with a new column?

The reason I ask is that for the analysis we do using ion exchange columns, other materials in the samples (Fe ions?? in our case) use up the exchange capacity of the column, with the results you have. In our case, the effect was shortening retention times, and less resolution, as the batch of samples ran. We were lucky to have plenty of resolution to start with. If you started with an old column, or one not properly activated, it might have the same effect.

If you haven't already done so, contact the folks who claim the separation. They probably have learned more about the analysis since the publication, and can hopefully update you.