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-npentylphenol, to bovine serum albumin to illustrate the possibilities of the method.

Predicting Bioavailability and Accumulation of Organochlorine Pesticides by Japanese Medaka in the Presence of Humic Acid and Natural Organic Matter Using Passive Sampling Membranes

“…Hence, a negligible depletion extraction method using TECAM (nd-TECAM) was developed to measure the free pesticide concentration in the test samples containing DOM (14). Negligible depletion extraction implies that only a very small amount is extracted from a solution, so that the existing equilibrium between the bound and free form of a chemical in the solution is not disturbed (15). Briefly, in a 1 L conical flask, a piece of TECAM was immersed in the 1 L of test solution for 1 h sampling.…”

Determination of liposome/water partition coefficients of organic acids and bases by solid-phase microextraction

“…If it is assumed that charged species do not partition to the PA polymer, then the pH dependence of D fw (pH,t) for organic acids and bases can be described by D fw (pH,t) = a n D fw,n (t) (6) where D fw,n (t) refers to the fiber/water distribution ratio of the neutral species and a n refers to the fraction of the neutral species in aqueous solution. …”

“…Drawn lines: models described by eqn. (6). B, Organic acids, PA fiber, extraction time 10 min (5 26DCP, : 246TriCP, -2346TeCP, / PCP, 1 non-ionogenic reference DIB).…”

“…Broken lines: models described by eqn. (6). The error bars correspond to the 95% confidence interval limits.…”

“…A similar experiment has been conducted for protein/ water partitioning and it was found that bovine serum albumin did not sorb to the SPME fiber to such an extent that it increased the concentration in the fiber. 6 In the equilibrium dialysis cell, the liposomes are physically retained in one half-cell but the equilibrium between the liposomes is maintained throughout both compartments. Therefore the aqueous concentrations in both half-cells are equal.…”