SOLVENT MICROEXTRACTION AS A SPECIATION TOOL - DETERMINATION OF FREE PROGESTERONE IN A PROTEIN SOLUTION

A 1-mu L drop of n-octane suspended from the tip of a microsyringe nee dle in 500 mi of stirred aqueous solution is used to extract unbound p rogesterone in the presence of 1% (w/v) bovine serum albumin (BSA) for analysis by gas chromatography (GC). The observed extraction kinetics are in good agreement with a proposed convective-diffusive mass trans fer model which accounts for diffusion of both free and bound species in the aqueous Nernst diffusion film adjacent to the interface. The eq uilibrium binding constant, which can be measured both at equilibrium and at nonequilibrium extraction times, is in good agreement with lite rature values. The very small phase ratio employed (i.e., 2 x 10(-6) m i of organic/mL of water) avoids perturbation of the aqueous solution equilibria.