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Extraction of Total and Methyl Mercury from a DGT
Oral Presentation
Prepared by R. Shock
TestAmerica Laboratories Inc., 4101 Shuffel Street NW, North Canton, OH, 44720
Contact Information: ray.shock@testamericainc.com; 330-966-9396
ABSTRACT
Background/Objectives. Diffusive Gradients in Thin films (DGT) can be used to examine the bioavailability of mercury and methyl mercury in a variety of matrices. A 0.45mm filter allows labile mercury species to enter the sampling device to be captured on the resin gel. The DGT provides in-situ measurement of mean analyte concentrations. The goal of this study was to design an efficient sample extraction procedure to be used in a production laboratory that provides a reporting limit of 1ng methyl mercury and 10ng total mercury per DGT.
Approach/Activities. The DGT was disassembled and only the resin gel was used to evaluate extraction efficiency. DGT resins were spiked with commercially available methyl mercury chloride and divalent mercury. The first extraction solution used was 0.65 mM thiourea (TU) in 0.1 M HCl, which didn’t meet extraction efficiency requirements. A more aggressive solution (1.3 mM TU in 0.6M HCl) was prepared which yielded better recovery of methyl mercury. All mercury species were not effectively leached from the resin with the TU/HCl solution, so an aqua regia extraction was performed for measurement of total mercury. A four hour soak in aqua regia (8 mL HCl / 2 mL HNO3) proved to be more effective in leaching mercury from the DGT resin for total mercury analysis.
Results/Lessons Learned. This extraction process has been developed to support a pilot study and field study of a tidal estuary involved several hundred DGT sampling devices beginning summer 2012. Limited performance details were available in the literature. Current efforts have yielded 80-110% recovery for methyl mercury and 60-65% recovery for total mercury at their respective reporting limits. Completion of the tidal estuary studies will also yield statistical performance data for this process.
Oral Presentation
Prepared by R. Shock
TestAmerica Laboratories Inc., 4101 Shuffel Street NW, North Canton, OH, 44720
Contact Information: ray.shock@testamericainc.com; 330-966-9396
ABSTRACT
Background/Objectives. Diffusive Gradients in Thin films (DGT) can be used to examine the bioavailability of mercury and methyl mercury in a variety of matrices. A 0.45mm filter allows labile mercury species to enter the sampling device to be captured on the resin gel. The DGT provides in-situ measurement of mean analyte concentrations. The goal of this study was to design an efficient sample extraction procedure to be used in a production laboratory that provides a reporting limit of 1ng methyl mercury and 10ng total mercury per DGT.
Approach/Activities. The DGT was disassembled and only the resin gel was used to evaluate extraction efficiency. DGT resins were spiked with commercially available methyl mercury chloride and divalent mercury. The first extraction solution used was 0.65 mM thiourea (TU) in 0.1 M HCl, which didn’t meet extraction efficiency requirements. A more aggressive solution (1.3 mM TU in 0.6M HCl) was prepared which yielded better recovery of methyl mercury. All mercury species were not effectively leached from the resin with the TU/HCl solution, so an aqua regia extraction was performed for measurement of total mercury. A four hour soak in aqua regia (8 mL HCl / 2 mL HNO3) proved to be more effective in leaching mercury from the DGT resin for total mercury analysis.
Results/Lessons Learned. This extraction process has been developed to support a pilot study and field study of a tidal estuary involved several hundred DGT sampling devices beginning summer 2012. Limited performance details were available in the literature. Current efforts have yielded 80-110% recovery for methyl mercury and 60-65% recovery for total mercury at their respective reporting limits. Completion of the tidal estuary studies will also yield statistical performance data for this process.