Untitled

Abstract

The most stable oxidation states of chromium, e.g. Cr(III) and Cr(VI), exhibit significantly different biological and toxicological properties. Cr(III) is considered as an essential element for the proper functioning of living organisms, particularly in glucose metabolism, while Cr(VI) shows mutagenic effects. It is regarded as carcinogenic owing to its oxidizing potential and easy permeation of biological membranes. Unfortunately, Cr(VI) compounds have a large application in industry, and soils and sediments can become contaminated with this species. Because of the dangerous effects of hexavalent chromium and its high mobility in the environment, several directives have been adopted by the European Commission to limit the release of Cr(VI) into the environment. The maximum concentration of total chromium and Cr(VI) in drinking water was set as 50 µg/L and 20 µg/L, respectively, according to European Council Directive 98/83/EC. For this reason, the selective determination of Cr(VI) in different food samples is of particular importance. Thor et al. [1] evaluated the availability and reliability of analytical data on the total chromium composition of foods reported in the literature [1].The proposed in literature analytical procedures for speciation of chromium can be divided onto two groups. In the first of them hyphenated techniques such as high performance liquid chromatography or capillary electrophoresis have been utilized [2,3]. In the second group, selective liquid-liquid extraction procedures, co-precipitation, separation of one or two chromium species onto a solid phase extraction column or complexation reactions have been proposed [4][5][6]. Such approaches enable also preconcentration of given species. The content of the second species is then calculated by the difference after determination of total chromium preceded reduction of Cr(VI) or oxidation of Cr(III).The analytical procedure for chromium speciation in food samples depends on the nature of the sample matrix. Additionally, exposure to light, the type of storage container and high storage temperature may affect the stability of chromium species [4,5]. The lower the pH of solution, the more likely it is for the species of chromium to be Cr(III) or be converted to Cr(III). Thus, the main difficulty is to preserve the initial distribution of both redox chromium species in a sample as well as to obtain the high extraction efficiency [7]. From solid food samples chromium species have to be extracted. Na 2 CO 3 solution at elevated temperature was used for extraction of Cr(VI) from several species of plants collected in South Africa and Russia [8], tea leaves [9,10] and tomato and corn leaves [9]. This alkaline digestion procedure was recommended for Cr(VI) extraction from soils, sediments and similar materials as US EPA 3060A method. The accuracy of selective extraction of Cr(VI) was verified by the analysis of CRM 545 with good agreement between the certified and determined value [8]. However, that reference material (Cr (VI) in welding dust) has c...