Determination of distribution coefficients by stepwise flow ratiometry/spectrophotometric detection without phase separation

Abstract

A new system of flow ratiometry having UV detection without a phase separator was developed and applied to the determination of the chloroform/water distribution coefficients (KD) of phenol and its derivatives. An aqueous solution of analyte and chloroform was delivered independently and merged at various flow ratios (Rf). The ratio was changed stepwise. Both phases, segmented each other, passed through an extraction coil and were directly led to a flow cell, where the absorbance of each phase was monitored. A wide-bore tubing (2 mm, i.d., 20 cm long) was inserted between the extraction coil and the flow cell in order to coalesce the chloroform segments and/or aqueous segments. Thus formed bigger segments were easily measured. The KD was calculated from the slopes and the intersections of linear plots of A−1 vs. Rf, (ARf)−1 vs. Rf−1, and ARf vs. A, where A is Ao (absorbance of chloroform phase), Aa (absorbance of aqueous phase), ΔA (= Ao−Aa) or ΣA (= Ao + Aa). Among them, the plots using ΣA as A gave the best results, probably due to a cancellation of the intrinsic errors in the Ao and Aa measurements. The method was simple and efficient (< 5 min/determination) with satisfactory precision.