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?
