An Experimental Method for Diffusion and Extraction Studies across the Liquid–Liquid Interface

Abstract

THE prototype apparatus shown schematically in Fig. 1 offers a promising experimental approach for diffusion and extraction studies across the interface between certain aqueous–organic systems uncomplicated by diffusion control in the adjacent bulk phases. It may also prove an effective probe of factors which influence the behaviour and ‘structure’ of the interface. The apparatus is operated in the following way. The substance being extracted (with tracer) is dissolved in 1 cm.³ of static aqueous phase placed so the aqueous surface formed at the bottom of the ‘Teflon’ slit (0.25 in. × 0.001 in.) is oriented lengthwise across the width of the rim, and about 0.006 in. above the wheel. Individual organic drops, at 1–5 drops/sec., are dropped on the ‘Teflon’ rim spinning at 10–200 r.p.m. Each drop is squeezed past the slit where it makes brief ‘contact’ with the aqueous phase before being almost entirely dragged away from the slit, wiped off, and collected at the bottom of the wheel. The activity/cm.³ of substance in the extract multiplied by the rate of production of drops is a measure of the ‘apparent extraction rate’, a parameter sensitive to the concentration of constituents involved in the extraction process.