Evaluation Of Methods For Quantifying Cr (VI) And Cr (III) In Soils And Wastes: Research Project Summary



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Trenton, N.J. : New Jersey Department of Environmental Protection, Division of Science, Research and Technology


An interlaboratory study comparing the three quantitation methods EPA 7196A, 7199 and 6800 demonstrated a statistically significant 31.6% difference between method 6800 and the results from the other two quantification methods (7196A and 7199) using the same extraction protocol (3060A). Method 6800 uses a stable isotope spike to adjust for loss of Cr (VI) to reduction during the extraction process. Method 6800 had significantly higher values for soluble Cr (VI) than either of the two methods that do not compensate for reduction or loss of Cr (VI) measured with an external spike. It is however limited by the amount of stable isotope spiked into the matrix. The other methods of quantification (USEPA method 7196A, 7199, or others) can underestimate the amount of soluble Cr (VI) if reduction occurs during the extraction or analysis process. Determination of where in the analytical process the Cr (VI) spike loss occurs cannot be made without the ability to quantitate the Cr (III) species. Therefore, it cannot be assumed that a poor Cr (VI) measurement was caused only by reduction of the Cr (VI). For example,if the Cr (VI) in a sample was either precipitated or absorbed to the soil surface by the addition of the extraction solvent or formed a complex with an organic moiety, it may still be available for oxidation back to Cr (VI) or dissociation to soluble Cr (VI) if conditions in its environment change. While ICP/MS analysis should identify all soluble chromium, species, whether or not they had been complexed with an organic ligand, it cannot compensate for insoluble forms of Cr (VI) that may have been precipitated or absorbed to the soil surface. The process of making all Cr species soluable is key to an accurate determination of the amount of Cr (VI) present.


Prepared by NJDEP, Division of Science, Research and Technology, Rutgers, The State University of New Jersey, University of Medicine and Dentistry of New Jersey and Environmental and Occupational Health Science Institute.


New Jersey