Measurement of the Free Concentration Using Solid-Phase Microextraction: Binding to Protein

Abstract

A method is described to measure freely dissolved compounds, using solid-phase microextraction (SPME) as sampling technique. Currently applied techniques, like solvent extraction, have the disadvantage of extracting the total amount of a compound that is present in a sample. For many applications, though, the freely dissolved fraction of a compound is of more interest than the overall amount. The procedure described in this work is based on the principle that only the freely dissolved compound is available for partitioning to the SPME fiber. By extracting only a small amount of the freely dissolved fraction, the equilibrium between the fraction of a compound bound to a matrix and the fraction dissolved in the aqueous phase is not perturbed. The procedure was applied to study the binding of four polar compounds, i.e., aniline, nitrobenzene, 4-chloro-3-methylphenol, and 4-n-pentylphenol, to bovine serum albumin to illustrate the possibilities of the method.