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METHOD 200.5 - DETERMINATION OF TRACE ELEMENTS IN DRINKING WATER BY AXIALLY VIEWED INDUCTIVELY COUPLED PLASMA-ATOMIC EMISSION SPECTROMETRY
Martin, T D. METHOD 200.5 - DETERMINATION OF TRACE ELEMENTS IN DRINKING WATER BY AXIALLY VIEWED INDUCTIVELY COUPLED PLASMA-ATOMIC EMISSION SPECTROMETRY. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-06/115, 2003.
Under this task a low cost multi-analyte method will be developed for the determination of the following analytes: Ag, Al, As, B, Ba, Be, Ca, Cd, Cr, Cu, Fe, Hg, Mg, Mn, Na, Ni, Pb, Sb, Se, Sn, V, Zn, and silica in drinking water and raw water drinking supplies. This list of analytes can be subdivided into groups of primary contaminants: As, Ba, Be, Cd, Cr, Cu, Hg, Pb, Sb, and Se; secondary contaminants: Ag, Al, Fe, Mn, and Zn; elements on the drinking water Contaminant Candidate List: B, Sn and V; elements without a maximum contaminant level (MCL), but require routine monitoring: Mg, Na, and Ni; and finally, analytes that must be measured when an action level is exceeded: Ca and silica. The objective of this work is to provide an alternate multi-analyte procedure to the slower and more costly single analyte graphite furnace atomic absorption technique. This work will provide precision and recovery data at critical analyte concentrations such as the established or proposed MCLs, < the MCL, and 10X the method detection limit (MDL) or 100X the MDL, whichever is most appropriate.
2.0 SUMMARY OF METHOD
2.1. A 50 mL aliquot of a well-mixed, non-filtered, acid preserved aqueous sample is accurately transferred to clean 50-mL plastic disposable digestion tube containing a mixture of nitric and hydrochloric acids. The aliquot is heated to 95 degrees C (+ or - 2 degrees C), evaporated to approximately 25 mL, covered with a ribbed plastic watch glass and subjected to total recoverable solubilization with gentle refluxing for 30 minutes. The sample is allowed to cool and diluted to 25 mL with reagent water to effect a 2X preconcentration. The sample is capped, mixed and now ready for analysis. (The time requried to complete the sample preparation step is approximately 2.5 hours.)
2.2. The analytical determinative step described in this method involves multi-elemental determinations by AVICP-AES using sequential or simultaneous instruments. The instruments measure characteristic atomic-line emission spectra by optical spectrometry. Standard and sample solutions are nebulized by pneumatic nebulization and the resulting aerosol is transported by argon carrier-gas to the plasma torch. Element specific emission spectra are produced by a radio-frequency inductively coupled plasma. The spectra are dispersed by a grating spectrometer, and the intensities of the line spectra are monitored at specific wavelengths by a photosensitive device. Photo currents from the photosensitive device are processed and controlled by a computer system. A background correction technique is required to compensate for variable background contribution to the determination of the analytes. Background must be measured adjacent to the analyte wavelength during analysis. Possible interferences that can occur must be considered and addressed appropriately as discussed in Section 4.