Sample Preparation - Hexavalent chromium (Cr+6) analysis in stainless steel alloys
We need to perform a determination of hexavalent chromium in stainless steel alloys. Do you know of any standardized method to purchase that covers this analysis please? One method I looked at was the colorimetric method using diphenylcarbazide, but it stated that vanadium & molybdenum at concentrations >25 ppm can interfere with the colour development process. These elements are present in the % range in our alloys. One thought I had was to use an XRF calibrated for total Cr, and if that result was less than the spec of 0.1% max, then, by deduction the Cr6+ would be less. Any thoughts?
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admin
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The concern for measuring Cr(VI) in steel alloy samples would be the sample preparation; colorimetric methods such as the one you reference require liquid samples, and the final oxidation state of Cr in solution can be a function of the sample preparation, and not the sample itself. As your samples are alloys, the valence state of any chromium present should be zero, and it is reasonable that if total Cr present is below a threshold, then Cr(VI) must be as well. While this approach may not be as satisfactory as directly measuring Cr(VI) in the alloys, it might be the most appropriate and suitable. |