Element determination by total-reflection X-ray fluorescence spectrometry at the initial step of element speciation in biological matrices

Total-reflection X-ray fluorescence spectrometry (TXRF) is used for the simultaneous determination of Ca, Cu, Fe, K, Mn, Rb, Sr and Zn in 12 different vegetable foodstuffs and their cell fractions after mechanical cell breakdown. The vegetables are homogenized by liquid shearing (ultra-turrax treatment) in the presence of buffer. The homogenates are separated into cytosols (liquid fractions) and pellets (solid fractions) by centrifugation. The distribution of the elements between the fractions is determined. Before analyses all samples were digested with HNO3. The quick and simple method of cell breakdown as an initial step for speciation transfers Zn, Cu, Mn, Rb and K in significant percentages into the soluble form. Consequently, a large fraction of each of these elements is directly accessible to further analytical separation procedures. On average Sr, Ca and especially Fe are mainly bound to pellet components. TXRF proved to be an excellent analytical tool in these investigations. It requires only one internal standard and minute samples with simple preparation.