Simultaneous sub-picogram speciation of methylmercury and ethylmercury in caustic nuclear tank waste using direct aqueous propylation

Abstract

Monoalkylmercury species have been discovered in nuclear waste tanks at the Savannah River Site, a superfund nuclear waste storage site in South Carolina. Common and standard methods for organomercury speciation could not be implemented within the context of the radioanalytical facilities in Savannah River National Laboratory (SRNL) in a safe, cost-efficient manner to facilitate data-driven regulatory action. SRNL conducted development, optimization, and validation work focused primarily on combining monomethylmercury and monoethylmercury speciation into one analysis to reduce, limit analyst radiation exposure, and improve the instrumental footprint area. Sodium tetra-n-propylborate was used as a derivatizing agent to enable chromatographic resolution of monomethylmercury and monoethylmercury without serial analyses. Linear calibration of monomethylmercury and monoethylmercury ranged five orders of magnitude, producing detection limits of 0.033 pg and 7.50 pg, respectively.Calibration verifications maintained 101% and 99.1% accuracy, respectively, with mean recoveries spiked in waste sample of 98.8% and 98.4%. Dilution volume was optimized to eliminate sample distillation, reduce sample radioactivity by 100% and 99.99992% for alpha and beta/gamma radiation, improve method runtime by 337%, and decrease total instrumentation footprint by 60.4%, compared with current standard methods. This method was validated internally against certified standards and externally via interlaboratory comparison. Compared with standard methods, this work potentially represents a significant improvement in safety, efficiency, and sensitivity of industrial organomercury speciation, particularly in nuclear analysis.

Separation and Speciation of Mercury from Hanford 241-AP-107 Tank Waste Supernatant

“…Historically, total mercury measurements have been made and speciation usually inferred from thermodynamic considerations. Only recently have speciation measurements been made at SRS (Boggess et al 2018). A review of analytical capabilities at SRS, PNNL, and the Hanford 222-S Laboratory was completed in the context of fulfilling the need to inform the mercury feed inventory, distribution, and speciation in Hanford tank waste liquids.…”

“…Most recently, SRNL has established new in-house total and mercury speciation technology for the determination of sub-picogram level determinations of total mercury, methylmercury, and ethylmercury in caustic tank waste (Boggess et al 2018). The method development is based on the EPA methods for the determination of total and methylmercury (U.S. EPA 1998(U.S. EPA , 2002.…”

Analysis of Ionic Mercury Species in SRR Samples Measured by SRNL and Eurofins FGS

“…Novel methods have been developed and optimized at SRNL to separate and quantify inorganic and organic mercury species of interest in High-Level Waste using modular analytical systems housed within radiochemical hoods. [4][5] The work presented here focused on the development of in-house methods for the analysis of ionic mercury species (Hg(I) and Hg(II)), in the liquid tank waste streams. 3 This work built heavily upon prior method development on the analysis of purgeable mercury in liquid tank waste solutions.…”

“…SRNL undertook work on the development, optimization, validation, and application of a fully-contained, modular method for the separation and analysis of ionic mercury in SRR samples. 4,[12][13][14] For this method, it was proposed that samples could be first purged with inert gas to remove any purgeable mercury species (e.g., elemental mercury, colloidal mercury, dense separate phase mercury, etc.). Then, with treatment by stannous chloride, ionic mercury could be volatilized and trapped on gold prior to analysis by thermal desorption and atomic fluorescence spectroscopy.…”

Development and Comparison of Purgeable Mercury Values in SRR Samples Measured by SRNL and Eurofins FGS

“…2 Novel methods have been developed and optimized at SRNL to separate and quantify organomercury species of interest in high-level liquid waste using direct aqueous alkyl derivatization, gas chromatography, and fluorescence spectroscopy. [5][6] This work focused on the development of in-house methods for the analysis of particulate and dissolved elemental mercury (deemed "purgeable mercury) in the liquid tank waste streams. 4 Given the high concentrations of mercury in the tanks at SRS, it was anticipated that all elemental mercury within the tanks should exist in equilibrium at its solubility point in aqueous solution.…”