Elemental recoveries for clay minerals analysed by inductively coupled plasma atomic emission spectrometry using slurry nebulisation

Abstract

Research was undertaken to determine the effects of particle size and matrix solution composition on matrix interferences for slurry nebulisation analysis of clay minerals by inductively coupled plasma atomic emission spectrometry. Four size fractions of Grundite illite and Georgia kaolinite 3 were used for these analyses. The spectrometer was calibrated with multi-element solution standards. Elemental recoveries were determined by comparing the results obtained using slurry nebulisation with results for elemental determination from hydrofluoric acid digests of the samples. A differential effect of particle size on elemental recoveries was observed for samples prepared in HNO₃ and NaCl matrix solutions. For the Grundite illite, Si and Al recoveries significantly decreased with increases in particle size, Mg and Fe recoveries decreased to a lesser extent and Ca recoveries were independent of particle size. These differences were attributed to the displacement of various amounts of Fe, Mg and Ca from clay particles into the matrix solutions by matrix solution cations and the more efficient transport of the matrix solutions than the particles to the plasma. In addition, Al recoveries were from 2 to 21% lower than Si recoveries for samples prepared in the HNO₃ matrix solutions. Aluminium recoveries significantly increased with increases in observation height, which indicates that Al recoveries were limited by the incomplete dissociation -excitation of clay particles within the plasma. Furthermore, Al recoveries were significantly greater for samples prepared in 0.1 M NaCl than for samples prepared in 1 M HNO₃. This effect is tentatively attributed to the enhanced collisional dissociation of clay particles. Matrix interferences may introduce substantial bias in results of slurry nebulisation analyses. This bias, however, can be minimised by restricting slurry nebulisation analyses to samples with particle sizes less than 2 µm and by using 0.1 M NaCl matrix solutions.