The application of Flow Injection Technology to automating cold vapor MERCURY analyses

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Courtesy of PerkinElmer, Inc.

This document describes the application of flow injection technology to cold vapor mercury analyses. It can be obtained from PerkinElmer by requesting method number ENVA-100. Appendices 1 and 2 show letters from the US EPA indicating acceptability through the Alternate Test Program for both drinking water and wastewater sample analysis.

1.0 Scope and Application

1.1 This method measures total mercury (organic plus inorganic) (CAS Registry No. 7439-97-6) and is applicable to waters regulated under the National Primary Drinking Water Regulation (NPDWR) and National Pollutant Discharge Elimination System (NPDES) monitoring. These waters include drinking waters, effluents, indirect discharges, and effluent samples containing high chlorides.

1.2 This method is suitable for the determination of total mercury content in the concentration range between 0.01 and 20 μg/L Hg, depending on the instrument configuration and sample loop size used. Table I shows the method detection limits achievable for different configurations of the flow injection system. The range may be extended above or below the normal range by increasing or decreasing sample aliquot size taken for digestion, but changes cannot be made without first demonstrating the performance requirements (i.e., accuracy, precision, and MDL) may be achieved. The actual method detection limit and linear dynamic range will be dependent on the sample matrix, type of instrument configuration, and selected operating conditions.

2.0 Summary of Method

2.1 A known portion of a water sample is transferred to a BOD bottle, equivalent ground glass stoppered flask or other suitable closable container. It is digested in diluted potassium permanganate - potassium persulfate solutions and oxidized for 2 hours at 95 oC. Mercury in the digested water sample is reduced with stannous chloride to elemental mercury and measured by the conventional cold vapor atomic absorption (CVAA) technique.

The CVAA procedure is a physical method based on the absorption of radiation at 253.7 nm by mercury vapor. The analyst may use a Flow Injection Mercury Analysis System (FIAS) in conjunction with an atomic absorption spectrometer or a stand-alone Flow Injection Mercury System (FIMS). Organic mercury compounds are oxidized and the mercury is reduced to the elemental state and aerated from solution in a closed system. The mercury vapor passes through a cell positioned in the light path of an atomic absorption spectrometer. Alternatively, the stand-alone mercury analyzer can be used which contains a light source and detector specific for mercury and does not require the use of a separate atomic absorption spectrometer. Figure 1 shows a general schematic of the technique. Absorbance (peak height) is measured as a function of mercury concentration and recorded in the usual manner.

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