Amphiphilic homopolymers that self-assemble into reverse micelles in nonpolar solvents have been used by us in the context of a two-phase liquid-liquid extraction protocol to selectively extract peptides from aqueous solution for MALDI-MS detection. In this manuscript, we investigate the scope of these materials in terms of its extraction capabilities, using compounds with varying isoelectric points (pI) and pK(a) values over a range of aqueous solution pHs. We find that the aqueous solution pH and analyte pK(a) values are the major factors controlling extraction selectivity. We also find that the experimental extraction efficiencies correspond very well with the fractional compositions of species calculated using analyte pK(a) values, indicating that these extraction materials can be used to simultaneously generate titration-type curves for each individual peptide in a mixture. We predict that such titration curves, along with accurate mass measurements, could represent a new way of improving protein identification procedures.