Passive Dosing to Determine the Speciation of Hydrophobic Organic Chemicals in Aqueous Samples

Abstract

A new analytical approach to determine the speciation of hydrophobic organic analytes is presented. The freely dissolved concentration in a sample is controlled by passive dosing from silicone (poly(dimethylsiloxane)), and the total sample concentration at equilibrium is measured. The free fraction is determined as the ratio between measured concentrations in pure water and sample. (14)C-labeled fluoranthene served as model analyte, and total sample concentrations were easily measured by liquid scintillation counting. The method was applied to surface water, stormwater runoff, and wastewater. In the untreated wastewater, 61% of the fluoranthene was bound to suspended solids, 28% was associated to dissolved organic matter, and 11% was freely dissolved, while in treated wastewater, the speciation was 16% bound to suspended solids, 4% bound to dissolved organic matter, and 80% freely dissolved. The free fraction in roof runoff (85%) and surface water (91%) was markedly higher than in runoff from paved areas, which ranged from 27 to 36%. A log K(DOC) value of 5.26 was determined for Aldrich humic acid, which agrees well with reported values obtained by fluorescence quenching and solid phase microextraction (SPME). This analytical approach combines simplicity with high precision, and it does not require any phase separation steps.

Measuring the toxicity of alkyl‐phenanthrenes to early life stages of medaka (Oryzias latipes) using partition‐controlled delivery

“…Because spectra were not different for compounds from the test vials and from the stock solution, test compounds were not modified by the polymerization. To ensure that the polymer is clean, a clean-up step following a different method of PAH loading in the polymer could also be added as an improvement to our method [22].…”

Solid Phase Microextraction for Sensing Freely Dissolved Analytes in Complex Water Sample

“…Calibration is done by comparing the ratio of the analytes signals to the internal standard with a known concentration [18,26,31,55,59,64]. However, it is worth noting that the calibration concentration obtained by internal standard method is the total concentration in the sample not the freely dissolved concentration.…”

“…Furthermore, with the SPME extraction method, either negligible depletion sampling [23,45] or equilibrium sampling [70] process should be fulfilled to minimize the disruption of partition equilibrium in the sample. On the contrary, fiber depletion method (also called solid-phase dosing method) can be employed to overcome the limitations of extraction strategy [64,[72][73][74]. In SPME depletion procedure (as shown in Fig.…”

“…This technique has been applied to determine the sorption coefficients of OCs in a variety of samples [3,54,64,65]. In comparison with fiber dosing method, which achieves the speciation by the depletion of analytes concentration in the fiber coating under a complete mass balance assumption, the coated vial passive dosing method applies a much larger and thicker polymer phase to dominate the partitioning between polymer and sample.…”

“…In literatures, the sorption coefficients of a variety of organic contaminants to binding matrixes including commercial humic acid [25,58,65], surfactant [4], protein [17,57], liposome [54], and DOM from pore water/wastewater [18,30,31,34,55,56,64] have been investigated and determined. Sorption coefficients of suspended particles including the C60 [29], latex [66], and particles with different sizes separated from sediment [55] were also measured with similar procedure described above.…”