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

Abstract

The extraction of two methylated anilines and three chlorinated phenols by solid-phase microextraction (SPME) fibers coated with polyacrylate was investigated as a function of pH. Only the neutral species of the acids and bases partitioned into the polymer. Extraction kinetics were accelerated for the hydrophobic phenols at pH values around their acidity constant. This is presumably due to a reconstitution of the neutral species in the unstirred aqueous layer adjacent to the polymer surface by the charged species through the fast acid-base equilibrium. Although the charged species is not taken up into the polymer, liposome/water distribution ratios could be measured up to a pH value, where 99% of the compounds were present as charged species. The partition coefficients of the neutral and charged species were extrapolated from the pH profiles of the liposome/water distribution ratios. The resulting values were slightly lower than those measured with equilibrium dialysis. The discrepancies are discussed with respect to differences in the experimental conditions and the possibility of matrix effects during SPME measurements.

Measurement of the free concentration of octylphenol in biological samples with negligible depletion-solid phase microextraction (nd-SPME): Analysis of matrix effects

“…With a molecular weight of human albumin of 65 kDa [19], this corresponds to 1.0 ± 0.1 pmol of HSA per fibre. Thus, fouling of the fibre by protein adsorption does take place, as reported by Poon et al [20,21] and suggested by Escher et al [22]. According to Heringa et al [9], fouling could have two types of effects on the uptake of compounds into the fibre coating: either the fouling blocks uptake or the adsorbed protein adds to the measured amount of compound by its bound ligands.…”

Combined effects of aqueous suspensions of fullerene and humic acid on the availability of polycyclic aromatic hydrocarbons: Evaluated with negligible depletion solid-phase microextraction

“…The PAH sorption coefficient between matrix and aqueous solution (K matrix ) at each matrix concentration can be calculated from Eq. (3), which was modified from Escher et al (2002),…”

Evaluating the impacts of some environmentally relevant factors on the availability of bisphenol A with negligible-depletion SPME

“…As can be seen, the normalization to neutral BPA has no significant change to the profiles. In SPME it is generally assumed that only the neutral species is partitioning into the fiber (Escher et al, 2002) or at least the portioning of the charged species is less than 10% of the neutral species (Lutzhoft et al, 2000). Therefore, the D value of BPA should be constant as BPA (a weak acid with reported pK a = 9.60-10.2) should be present mainly as nondissociated form in the studied pH range of 5.0-8.5.…”

“…Schwarzenbach and co-workers investigated the partition in liposome-water system of a series of substituted phenols and anilines with pH dependent results (Escher and Schwarzenbach, 1996;Escher et al, 2002) and Arnold et al also found that the association of triorganotin compounds with dissolved humic acids was strongly pH dependent (Arnold et al, 1998). A few studies on the association of chlorophenols with various DOM were reported.…”