I am trying to quantify tri-ethylphosphate (TEP) in water by either HPLC or GC-MS and I was not successful. I can not directly inject into the GC. We use SPME and TEP either does not have enough vapor pressure (high solubility) or I am not using the correct SPME fibber. I would prefer HPLC or size exclusion chromatography. Any suggestion would be appreciated.

Try one of the low-capacity anion exchange columns designed for ion chromatography. Check with Alltech or Dionex (there are other suppliers, but those two come to mind) and see if they have any applications notes.