We are looking for a volatile component to replace EDTA in the mobile phase in order to allow us to perform an identification analysis by LC-MS. The current mobile phase also contains a phosphate buffer in addition to EDTA. Our attempts to use acetic acid or similar volatile acids have not provided a satisfactory separation. Any suggestions for possible replacements for EDTA in the mobile phase without resorting to other changes of chromatographic conditions?

Why is EDTA in the mobile phase in the first place? We'll need to know that before we can make suggestions. Isn't the phosphate buffer a problem to the MS?

The EDTA is used in the mobile phase as a complexation agent asssisting in the separation of numerous related compounds to the active ingredient. In our first few attempts to produce an LC-MS modified method,we prepared a mobile phase using acetic acid and I believe ammonium acetate to replace the phophate buffer and the EDTA but unfortunately the peaks will either elute near the void volume or presumably they would not elute at the designated run time. Hence the need to find to fin a volatile replacement for EDTA. A couple of possible candidates (eg. oxyquinoline) suggested in-house were not suitable because they were non-volatile just like EDTA.
Thanks for taking the time to answer my question.

If I understood your problem right, you want to transfer an existing, validated method to your LC-MS system. You only want to replace EDTA and your phosphate buffer, but you still want to get the same elution profile and retention times for your compounds. This might be perhaps impossible, just to "modify" an existing method. What chromatographic parameters are you able to change? I would highly recommend to all colleagues, doing method development, to bear in mind, that later this new method should be also usable with LC-MS.

I haven't ever used it in chromatography applications but one candidate which is a fairly good chelator and volatile is: acetylacetone.