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TECHNICAL REPORTS

Organic Compounds in the Environment

Use of Mixed Solvent Systems to Eliminate Sorption of Strongly Hydrophobic Organic Chemicals on Container Walls

^a Soil and Water Science Dep., Univ. of Florida, Gainesville FL 32611
^b Dep. of Chemistry, Univ. of Florida, Gainesville, FL 32611

^* Corresponding author (Kizza{at}ufl.edu).

Received for publication March 7, 2008. Strongly hydrophobic organic chemicals (SHOCs) can be defined as neutral organic chemicals that have soil organic carbon (OC) normalized sorption coefficient (K_OC) >10,000. Sorption isotherms of SHOCs are normally measured in aqueous systems to determine K_OC. Since SHOCs can adsorb on container walls leading to overestimation of K_OC, we used mixed solvent systems to characterize this potential error. Sorption coefficient (K^M) and percent recovery (%R^M) of anthracene, DDT, and dieldrin during sorption on centrifuge tubes made of polytetrafluoroethylene (PTFE), polycarbonate (PC), polypropylene copolymer (PPCO), and glass high pressure liquid chromatography vials (HPLCV) were measured in volume ratio-varied methanol-water mixtures until 100% recovery of the sorbate was achieved. The data were evaluated using the Solvophobic theory. The K^M values of the entire test SHOCs decreased exponentially with increasing fraction of methanol (f^c). For sorption on PTFE, 100% recovery of the three chemicals was at f^c > 0.45. However, 100% recovery of DDT and anthracene from PC and PPCO was at f^c > 0.90. The 100% recovery of dieldrin from HPLC vials was at f^c > 0.70. In water the calculated recoveries of DDT, dieldrin, and anthracene from PTFE were 32, 43, and 48%, respectively. However, the recoveries of dieldrin from HPLC vials and DDT and anthracene from PC and PPCO ranged from 2 to 14%. The data demonstrate that sorption on container walls is a source of error that can reduce the integrity of the analyte and might be one of the causes for the large variability in literature K_OC values for SHOCs.

Abbreviations: ^c, cosolvency power • ^c, empirical constant • % R, percent recovery • f^c, volume fraction of methanol • AUFs, absorbance units full scale • HPLCV, high pressure liquid chromatography vials • HSA, hydrocarbonaceous surface area of a molecule • K^M, sorption coefficient in mixed solvents • K_D, soil-water partition coefficient • K_OC, soil-water partition coefficient normalized with soil organic carbon content • K_OW, octanol water partition coefficient • K^W, sorption coefficient in water • LSC, liquid scintillation counting • OC, organic carbon • PC, polycarbonate • PPCO, polypropylene copolymer • POPs, persistent organic pollutants • PTFE, polytetrafluoroethylene (Teflon) • SHOCs, strongly hydrophobic organic chemicals • PSA, polar surface area of a molecule • S^M, solubility in mixed solvents • S^W, solubility in water • TSA, total surface area of a molecule