STP1062: Evaluation of SW-846 Cold-Vapor Mercury Methods 7470 and 7471

    Beckert, WF
    research chemistresearch Scientists, U.S. EPA Environmental Monitoring Systems Laboratory, Las VegasColumbus, NevadaOhio

    Messman, JD
    research chemistresearch Scientists, U.S. EPA Environmental Monitoring Systems Laboratory, Las VegasColumbus, NevadaOhio

    Churchwell, ME
    research chemistresearch Scientists, U.S. EPA Environmental Monitoring Systems Laboratory, Las VegasColumbus, NevadaOhio

    Livingston, RL
    research chemistresearch Scientists, U.S. EPA Environmental Monitoring Systems Laboratory, Las VegasColumbus, NevadaOhio

    Sgontz, DL
    research chemistresearch Scientists, U.S. EPA Environmental Monitoring Systems Laboratory, Las VegasColumbus, NevadaOhio

    Wallace, GF
    research chemistresearch Scientists, U.S. EPA Environmental Monitoring Systems Laboratory, Las VegasColumbus, NevadaOhio

    Pages: 12    Published: Jan 1990


    Abstract

    The protocols for Methods 7470 and 7471 in the SW-846 methods manual are designed for the cold-vapor atomic absorption spectrometric (CV-AAS) determination of total mercury in aqueous (extracts, wastewater, ground water, etc.) and solid (soils, sediments, sludges, etc.) materials, respectively. Aqueous samples are digested with a combination of nitric and sulfuric acid plus permanganate and persulfate solutions at elevated temperature; solid samples are heated either on a steam bath with aqua regia and permanganate, or in an autoclave with sulfuric acid, nitric acid and permanganate. The mercuric ions in the digests are then reduced with hydroxylamine, and the elemental mercury is aerated into the AAS cell, either in a closed (recirculating) or an open system, where the absorption at 253.7 nm is determined.

    The topics of this presentation are the results of a performance evaluation study of these methods conducted, without and with changes, by the Battelle Columbus Division Laboratory. The methods were evaluated using aqueous and solid environmental samples of homogeneous and known compositions in order to assess the accuracy and precision of the methods without introducing uncertainties due to sample inhomogeneities. The methods, as originally written, were satisfactory for the analyses of samples containing relatively high concentrations of mercury. However, the method quantification limits for the closed and open systems were inadequate for the determination of mercury in environmental samples such as ground-water samples, when low concentrations were encountered. Spectral interferences which are caused by nonspecific absorption of the analytical radiation degraded the accuracy of the recirculating CV-AAS method.

    The protocols in Methods 7470 and 7471 were modified to improve mercury detectability and to minimize the additive effect of nonspecific background absorption. The use of an amalgamation CV-AAS system operated in an open configuration resulted in an improvement of one order of magnitude in instrumental detection limit for mercury over the recirculating method. The results of the analyses of four reference sediment materials and a simulated aqueous waste sample by the amalgamation CV-AAS method indicated acceptable accuracy and precision for most of the environmental samples tested. As expected, the amalgamation CV-AAS method revealed no spectral interferences resulting from nonspecific absorption of the analytical radiation by organic vapors.

    The modified protocols are at present the subject of a multilaboratory evaluation with the Battelle Columbus Division Laboratory as the coordinating laboratory. Seven laboratories are participating in this study.

    Keywords:

    mercury determination, cold-vapor mercury method, SW-846 Methods 7470/7471, mercury amalgamation method, atomic absorption


    Paper ID: STP18967S

    Committee/Subcommittee: D34.02

    DOI: 10.1520/STP18967S


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