Bestimmung von refraktärmetallen in pflanzlichem material durch röntgenfluoreszenzanalyse nach anreicherung

Abstract

An x-ray fluorescence spectrometric method is described for determining molybdenum, tungsten, niobium and tantalum in plant material. The sample is decomposed with nitric acid, hydrogen peroxide and hydrofluoric acid, and the refractory metals are collected on an anion-exchange paper and quantified by wavelength-dispersive x-ray fluorescence spectrometry. The decomposition of the sample and the enrichment of the elements on the ion-exchange paper including the mutual interference of the elements were investigated by using the radiotracer technique. In all cases, recoveries exceeded 95%. For about 1 g of sample material, limits of detection between 0.3 μg g −1 (Mo) and 0.6 μg g −1 (Ta) are achieved. After the same decomposition procedure, molybdenum was also determined by flame atomic absorption spectrometry; the sensitivity was 0.7 μg ml −1 for 1% absorption. The results for molybdenum and tungsten obtained on different grass samples are discussed in detail. The accuracy of the technique was checked for molybdenum and tungsten by instrumental neutron activation analysis; the results agreed within 5–11%.