New sensitive method for chromium speciation analysis: No hexavalent chromium in dairy and cereal products

Chromium is released to the environment mainly as a result of its widespread industrial use. Chromium exists in a variety of oxidation states, the trivalent (Cr(III)) and hexavalent (Cr(VI)) states being relatively stable and largely predominant. These two states differ markedly with respect to chromium bioavailability, absorption, mode of action and toxicity.

Since hexavalent chromium is classified as genotoxic and carcinogenic, its presence in food cannot be tolerated. However, since Cr(VI) is a strong oxidant, it is well accepted that due to the presence of organic matter, foodstuffs of plant and animal origin cannot contain significant amounts of Cr(VI). Despite such general agreement, several researchers have reported the presence of Cr(VI) in biological materials including food such as tea and bread (see the EVISA News below).

However, the results of these studies have recently been the object of controversy. Indeed, a group of researchers from the Jozef Stefan Institute in Ljubljana (Slovenia) found that former studies indicating the presence of hexavalent chromium in foodstuffs such as tea or bread based solely on the alkaline extraction of chromium are biased. Using a highly selective approach of the hyphenated technique of LC-ICP-MS for chromium speciation analysis they proved that the reported hexavalent chromium is just an artifact of a technique not sufficiently selective to differentiate between trivalent and hexavalent chromium (see the EVISA news below). More recently, using an on-line speciation technique by ion chromatography–inductively coupled plasma mass spectrometry (IC–ICPMS), a group of French and Spanish researchers could not find Cr(VI) in any of the samples investigated. However, their method lacked sensitivity (LOQ of 3 µg/L in dairy products and 30 µg/kg in other foodstuffs).

A group of French researchers now optimised their methodology for chromium speciation analysis of food samples with respect to extraction efficiency and detection power. The method was optimised by using an experimental design and validated for the determination of Cr(VI) in different food materials such as dairy products and cereal products. The method developed was free from interferences possibly associated with chloride and organic or inorganic carbon and proved satisfactory with respect to linearity, specificity, sensitivity, accuracy, repeatability and intermediate precision. Using on-line hyphenation between  high-performance ionic chromatography with inductively coupled plasma mass spectrometry limits of quantification could be significantly improved compared to former approaches and ranged from 0.6 µg/kg in dairy products to 0.8 µg/kg in cereal products. Despite the method’s very high sensitivity, Cr(VI) was not found in any of the studied samples including those of high chromium content. The authors believe that their results confirm the results of the most recent studies using an on-line speciation method, and invalidates older studies that found traces of Cr(VI) in food by using a less specific off-line speciation method.