Comparison of the Binding Constant of Decanesulfonate with β-Cyclodextrin as Determined by Liquid Chromatography with a Water Mobile Phase and Flow Injection Analysis Coupled with Dynamic Surface Tension Detection

Abstract

This paper compares two independent methods for the determination of the inclusion complex binding constant between β-cyclodextrin (β-CD) and decanesulfonate. First, reverse-phase liquid chromatography (RP-LC) separations of four surfactants are examined under two conditions for the binding constant determination. The first separation relies on RP-LC using a 100% water mobile phase and a cyanopropyl stationary phase. Hexanesulfonate, octyl sulfate, and decanesulfonate were separated in under 10 min. With the addition of only 1 mM β-CD to the water mobile phase, the same three surfactants, in addition to dodecyl sulfate, were separated in 6 min. Limits of detection were in the parts-per-billion range using conductivity detection but did not require a mobile phase conductivity suppressor. The binding constant for decanesulfonate with β-CD using RP-LC with a water mobile phase was found to be (3.13 ± 0.38) × 103M−1. Second, flow injection analysis (FIA) is coupled with dynamic surface tension detection (DSTD) to provide an independent method to determine the binding constant of β-CD with decanesulfonate. Using FIA with DSTD, a decanesulfonate binding constant with β-CD of (4.75 ± 1.25) × 103M−1was obtained. The two binding constant values were in close agreement, suggesting that secondary equilibria were minimal in RP-LC with a water mobile phase. The combination of FIA with DSTD is shown to be an excellent method to help study reverse-phase retention mechanisms involving complexation equilibria.