PH04 Advances in Analysis and Measurements
Exhibit Hall
8:00 AM - Thursday
(PH017) Chemical Separation Using Reductive Precipitation.
Christian, J1, Coronado, J1, Bailey, J1, 1 Columbia Analytical Services, Kelso, WA, USA
ABSTRACT- A procedure for analyzing a relatively wide range of trace metals in samples containing elevated levels of dissolved solids is discussed. The procedure incorporates a chemical separation to remove interfering matrix components so final analysis can be performed using inductively coupled plasma-mass spectroscopy (ICP-MS). The separation utilizes reduction of certain target analytes to the elemental state and precipitation of others as the boride, depending on reduction potentials and/or boride solubility. The precipitation is facilitated using elemental palladium plus iron boride as carriers. Once separated from the seawater matrix, the precipitate is dissolved and analyzed using ICP-MS. A number of modifications to the procedure have been made over the past eleven years to improve performance. The method meets general U.S.E.P.A. performance criteria. A general outline of the procedure is included in the most recent version of EPA Method 1640. However, variations are presented that allow a wider range of elements to be tested. Additional modification eliminates filtration and filter manipulation, which is a source of significant potential contamination. Isotope dilution is incorporated to demonstrate a relatively simple and inexpensive mechanism to enhance recovery of nickel. Considerations are given to the introduction of excessive chloride via the acid mixture used for dissolution of the precipitate. Thus, arsenic and chromium are validated as part of the multi-element suite of target analytes. Recovery data for low level determinations is reported and demonstrates elements suitable for this procedure, as well as elements that do not conform to the reaction mechanism(s). Detection limits are presented that show this technique is a viable approach for many elements when a procedure is needed to measure trace metal concentrations at or near ambient levels in various sample types, including open-ocean seawater. The procedure has also been adapted to the analysis of industrial chemicals such as concentrated sodium hydroxide used by municipal drinking water suppliers for pH adjustment. Thus, the procedure is also applicable for extremely complex matrices occasionally encountered during environmental investigations.
Key words: seawater, reductive precipitation, trace metals, borohydride