MOBILE-PHASE ADDITIVES VS BONDED PHASES FOR HPLC

It is likely that 90% of all small-molecule high-performance liquid ch romatography (HPLC) separations can be done with a hydrocarbon-bonded phase of C4, C8, or C18 length using various mobile phases. The remain ing 10% of the cases are more challenging. One solution is to follow t he historical path of gas-liquid chromatography and create more bonded phases. The second and more easily done is to add components to the m obile phase that interact selectively with the molecules of interest a nd change RPLC selectivity and retention. This paper begins with a gen eralized discussion of additive strategy and mechanism and then leads to a study of nonionic but coordinatively unsaturated (beta-diketonate s as additives which serves as an example of the connection between mo lecular chemistry and chromatographic selectivity and a review of othe r work done. A system of coordinatively unsaturated metal beta-diketon ates was investigated as mobile phase additives for HPLC. Unlike previ ous ionic, metal dopants, these neutral complexes combine reasonable e lution times, high chromatographic efficiency, and enhanced chromatogr aphic selectivity for polar compounds in normal and reversed-phase mod es. The influences of mobile-phase composition, stationary-phase subst rate, and metal on solute retention behavior were examined for the met al-dipivaloylmethane additive systems.