Determination of chromium in complex matrices is a notorious challenge, as interconversions between species may occur during sample preparation, making quantification very difficult. In a recent research study published in Journal of Agricultural and Food Chemistry, Rahman et al. performed speciated isotope dilution mass spectrometry (SIDMS), as described in EPA Method 6800 (update V) to determine chromium species in dietary supplements.
EPA Method 6800 was implemented with a Metrohm ion chromatograph coupled to an Agilent mass spectrometer with inductively couple plasma (IC-ICP-MS). A free abstract and the complete paper are available from pubs.acs.org
Although Cr(III) and Cr(VI) are chemical forms of the same element, the effects of the two species on human health could not be more different. While Cr(III) is considered an essential trace metal found in many foods, Cr(VI) is a known carcinogenic with very strict limits applying to its presence in foods and the environment. The authors of the study point to the potential risk to consumers resulting from the fact that manufacturers of dietary supplements may not be aware of or even neglect the effects of possible interconversions of chromium species on the quality of the final products.
The authors continue to present in detail the sample preparation/extraction methods required (EPA Method 3060A, EPA Method 3052) to make sure that subsequent determination of chromium species in solid samples is both accurate and reliable. As they state in their conclusion “SIDMS [as per EPA Method 6800] facilitates simultaneous accounting of both Cr species concentrations and correction for transformations by enabling isotopic tagging for the oxidation of Cr(III) and the reduction of Cr(VI) during analysis in aqueous samples. […] the combined extraction/SIDMS procedure is capable of correcting for bidirectional species transformations that may occur during analyses of Cr(VI) in solid samples.”
