Mass transfer characteristics of solvent extraction into a single drop at the tip of a syringe needle

The amount of a sample compound extracted into a 1-mu L drop of n-octane suspended in a stirred aqueous solution from the tip of a microsyringe needle is measured by gas chromatography (GC) as a function of time, The observed extraction rate curve is first order and yields the overall mass transfer coefficient for the sample compound, <(beta)over bar (o)>. For a given compound, <(beta)over bar (o)> varies linearly with stirring rate, Among the four compounds malathion, 4-methylacetophenone, 4-nitrotoluene, and progesterone, at a given stirring rate, <(beta)over bar (o)> is linearly proportional to the diffusion coefficient of the compound (D-aq), This supports the film theory of convective-diffusive mass transfer, as opposed to the penetration theory. The relative standard deviation of the GC signal for 4-methylacetophenone after a 1.00 min extraction at 1500 rpm is 1.5%, which suggests that the system exhibits excellent potential as a tool for rapid analysis by solvent extraction/GC.