Comparison of the binding constant of decanesulfonate with beta-cyclodextrin as determined by liquid chromatography with a water mobile phase and flow injection analysis coupled with dynamic surface tension detection

This paper compares two independent methods for the determination of the in clusion complex binding constant between beta-cyclodextrin (beta-CD) and de canesulfonate. First, reverse-phase liquid chromatography (RP-LC) separatio ns of four surfactants are examined under two conditions for the binding co nstant determination. The first separation relies on RP-LC using a 100% wat er mobile phase and a cyanopropyl stationary phase. Hexanesulfonate, octyl sulfate. and decanesulfonate were separated in under 10 min. With the addit ion of only 1 mM beta-CD to the water mobile phase, the same three surfacta nts, in addition to dodecyl sulfate, were separated in 6 min. Limits of det ection were in the parts-per-billion range using conductivity detection but did not require a mobile phase conductivity suppressor. The binding consta nt for decanesulfonate with beta-CD using RP-LC with a water mobile phase w as found to be (3.13 +/- 0.38) x 10(3) M-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 beta-CD with dec anesulfonate. Using FIA with DSTD, a decanesulfonate binding constant with beta-CD of (4.75 +/- 1.25) x 10(3) M-1 was obtained. The two binding consta nt values were in close agreement, suggesting that secondary equilibria wer e minimal in RP-LC with a water mobile phase. The combination of FIA with D STD is shown to be an excellent method to help study reverse-phase retentio n mechanisms involving complexation equilibria. (C) 1999 Academic Press.