I have been asked to develop a method to assay PETS in a polymeric formulation, which I intend to do by LC-MS/MS. Has anyone any ideas on solubility. Ideally I need a solvent that is miscible with water/MeOH mobile phase gradient? Has anyone been asked to look at this analyte before?

I can't speak to your compound specifically, except to say that it looks rather nonpolar. If you're getting the usual MS/MS sensitivity, then you only need it to be soluble at ng/mL levels. But, if solubility in methanol is poor, then dissolving it in a miscible solvent and injecting onto water / methanol (reverse phase) gradient might result in very long retention.

If it turns out that nonpolar solvents are necessary for your LC separation, this does not preclude LC/MS. There are papers published on normal phase and non-aqueous reverse phase coupled to MS. Mind you, I've never done this before, I've only read about it. Just take care not to create an explosive environment in your ion source, e.g. use N2 and not compressed air.

I am doing analysis of acrylic esters of pentaerythrol. In LC retention this is not comparable to your PETS, however, I would like to share our finding that we always see a large range of combinations, e.g. tetra-acrylate plus mono-hydroxy-tri-acrylate plus di-hydroxy-di-acrylate. You should keep this in mind when you are looking for a calibration compound.

Good Luck!