Removal of SDS from samples for analysis by LC/MS

[MarkFG]

I am currently analyzing an ophthalmic drug product that has been photodegraded in order to generate an impurities profile. I'd like to collect fractions of several of the observed peaks for LC/MS analysis. However, my diluent and mobile phase is a 58% aqueous solution of sodium dodecyl sulfate with 0.6% H3PO4 mixed with 42% acetonitrile. Is there any extraction technique available to removed the SDS in order to make the samples more LC/MS friendly?

[tom jupille]

Depends a bit on how big your fractions are and how many samples you want to run.

If you don't have many samples and the fractions are small, you might try a simple diverter valve and only run into the MS when your fractions of interest are eluting. You'd have to worry about ionization suppression and cleaning your interface frequently.

If you don't have many samples and the fractions are big enough, then SPE with an anion-exchanger might work. You would obviously have to do the usual checks for junk leached from the cartridge, recovery of analytes, etc.

If you have a lot of samples, but the fractions are fairly big, you might be able to do something similar with a switching valve and an appropriate guard cartridge. It would take some effort to work out the timing.

Finally, if you have a lot of samples and small fractions, it may be easiest to simply re-develop the separation with an MS-friendly mobile phase (HFBA?).