Determination of Trace Elements in Plant Material by Fluorescent X-Ray Analysis

A method is presented for the determination of trace elements in plant materials. The samples were composed of organic material, which was eliminated by wet ashing, large amounts of group I and II elements, and many trace elements of interest in the concentration range 0.1–100 ppm. An attempt to achieve preconcentration of the trace elements by absorption on cation-exchange membrane (which could have been used directly for analysis) was unsuccessful because of preferential absorption and saturation of the membrane by group I and II cations. Formation of complex-metal anions in acid solution and absorption on anion-exchange resin was more successful, but, because of a lack of precision and incomplete absorption, the technique was inadequate. In the most successful preconcentration scheme, an organo-metallic precipitation was used in a matrix suitable for X-ray analysis. In this precipitate the elements Fe, Mn, Cu, Zn, Co, Mo, Cr, Ni, Ti, V, Ca, Sn, Sc, Ba, and Pb could be quantitatively determined. In many cases the lower limit of detection was 0.01 ppm. The accuracy and precision of the technique were proved by comparison to chemically analyzed samples, recovery experiments, and replicate analyses. The method is generally applicable for the analysis of many organic materials.