DETERMINATION OF THE AQUA REGIA SOLUBLE CONTENT OF RARE-EARTH ELEMENTS IN FERTILIZER, ANIMAL FODDER PHOSPHATE AND MANURE SAMPLES USING INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY

The aqua regia soluble content of all rare earth elements (REE) was de termined in manure, animal fodder phosphate and mineral fertilizer sam ples using a quadrupole-based inductively coupled plasma (ICP) mass sp ectrometer. In order to obtain accurate results, spectral overlap due to oxide formation had to be taken into account. The influence of the instrumental operation conditions on the oxide ratio was investigated, permitting systematic optimization. In order to further decrease the amount of oxide formation, the aerosol was desolvated by cooling the s pray chamber to below 0 degrees C. To ascertain the accuracy of the re sults obtained, two reference materials, USGS AGV-1 Andesite and USGS GSP-1 Granodiorite, were used as quality control samples. The REE data obtained for these materials show a good agreement with the correspon ding reference values (within 10% for all REE in AGV-1, and for most o f the REE in GSP-1). All REE results obtained were also ''Chondrite-no rmalized'' and the smoothness of the curve obtained was used as an add itional indication for accuracy. The precision expressed as relative s tandard deviation for 3 independent measurements was observed to be be tter than 3%. Detection limits (3s-criterion) vary between 2 and 11 ng /l except for Sc, for which the detection limit is approximately 100 n g/l due to the occurrence of a spectral interference. Hence, when the Sc concentration was < 1 mu g/l, a magnetic sector ICP-mass spectromet er was used for its determination. The REE patterns of fertilizer and manure were found to be different and REE concentrations in the latter were lower. REE concentrations can therefore be used as an indication of the addition of fertilizer to manure, a practice which is speculat ed to be applied by some farmers to circumvent European regulations on manure disposal. (C) 1998 Elsevier Science B.V. All rights reserved.