Samples Containing Chromium

Overview

Chromium (Cr) is the seventh most abundant element, but minerals containing chromium are not wide spread, with most of the high Cr ores deposits being found in Africa. Chromite is the most common ore containing Chromium, with an empirical formula of FeCr₂O₄. The Cr and Fe are present in Chromite in the +3 and +2 oxidation states respectively, which is why it is best written and thought of as Cr₂O₃FeO. Cr is present in soil at concentrations ranging from 5 to 1000 ppm.

Chromium is most commonly used in alloys, steels, pigments, and chrome plating. Chromium is often described as having slow kinetics. Many of its forms are difficult to dissolve and it reacts slowly with ligands like EDTA making it's wet analytical chemistry challenging.

The most common oxidation states for Cr are 0, +3 and +6. Chromium is most commonly found in the +3 state, which is fortunate since the +3 state is considered benign as opposed to the +6 that is toxic.

At Inorganic Ventures we note the oxidation state of chromium in a given CRM by writing Cr⁺³ or Cr⁺⁶. We are not quite sure how this got started since it appears to be most confusing to the user that wants the "form of chromium present after sample preparation". The most common form after most sample preparations is +3, much the same as it is +3 for Fe, with the difference that we do not write Fe as Fe⁺³ , but just Fe when describing aqueous CRMs containing the element. Unless the analyst is in need of a CRM containing Cr⁺⁶ it is best if the Cr⁺³ is used, however, there are specific methods for the determination of 'hexavalent chrome' where the Cr⁺⁶ state is need.

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