What is Potassium hexafluorophosphate used for in LC?

[MestizoJoe]

I'm curious and the only information I found so far was that potassium hexafluorophosphate is a chaotropic agent.

[Andy Alpert]

Actually it's the sodium salt that's used most often in HPLC. PF6 and BF4 are highly chaotropic anions. While I'm not aware of any applications where they're used in preference to more common additives, there are a couple of papers in the literature that systematically compare results with various chaotropic additives. In each case they increase retention in reversed-phase HPLC of analytes with a potential (+) charged group:

1) A. Jones et al., J. Chromatogr. A, 964 (2002) 179;
2) J. Flieger, J. Chromatogr. A, 1113 (2006) 37;
3) J. Flieger, J. Chromatogr. A, 1175 (2007) 207

Andy Alpert