PERFLUORINATED ACID ALTERNATIVES TO TRIFLUOROACETIC-ACID FOR REVERSED-PHASE HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

Over the past decade trifluoroacetic acid (TFA) has become the ion-pai ring agent (IPA) of choice for reversed-phase high-performance liquid chromatography (RP-HPLC) of peptides and proteins. Reagent grade TFA i s highly pure, water soluble, transparent at 220 nm and readily volati le. A drawback of this universal appeal is that several alternative pe rfluorinated carboxylic acids tend to be overlooked when TFA does not work in a particular separation. Examples are given comparing TFA sele ctivity with those of pentafluoropropionic acid, heptafluorobutyric ac id, perfluoropentanoic acid, perfluorohexanoic acid and perfluorohepta noic acid. We have found that increasing the IPA n-alkyl chain length can resolve sample components that otherwise co-elute in the void volu me of TFA-based RP-HPLC. Examples are given for the resolution of an o ligoglycine series and enhanced selectivity for a bovine hypothalamic extract.