I have recently been analyzing some biological samples for chromium using a standard Cr(VI) solution for external calibration.

Cr standards are typically supplied in a 2% nitric acid matrix. That concentration corresponds to a pH of 0.44. Under that pH, most species of Cr would have oxidized into the form of $\ce{Cr2O7-}$ or $\ce{CrO4-}$; yet in literature, all measurements carried out on ICP-MS for Cr have been in the +1 oxidation state.

Could this be from the rapid reduction from the free electrons in the argon plasma?


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