A Dual Column pH Switchable Water Stationary Phase System for Separation Control in Supercritical Fluid Chromatography.

A dual column system comprised of a pH switchable water stationary phase column and a conventional non‐polar capillary column is introduced for use in Supercritical Fluid Chromatography (SFC). By removing or adding NH4OH to the system hydration source, the water stationary phase pH can be rapidly switched between acidic (measured at pH∼3) and basic (measured at pH∼9) in seconds, while the operating character of the conventional column is unchanged. This switch modulates the velocity of ionizable analytes about 20‐fold in the system, whereas non‐ionizable analytes are not affected. In this way, the retention time of acids and/or bases can be reproducibly altered (<1% RSD; n = 3) in SFC separations. As a result, analyte selectivity and resolution can be readily controlled during analyses. For example, a selectivity reversal (alpha from 0.4 to 1.6) and a resolution increase (from 0 to 13) are demonstrated. Rapid stationary phase pH switching also allows multiple acids, bases, and/or neutral analytes to be determined simultaneously. Applications demonstrate that this method can greatly simplify complex mixture analysis in SFC by helping to separate target analytes from interfering matrix components. [ABSTRACT FROM AUTHOR]