DIRECT ANALYSIS OF SOIL SUSPENSIONS BY INDUCTIVELY COUPLED PLASMA-ATOMIC EMISSION SPECTROMETRY FOR DETERMINATION OF TOTAL METALS

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Abstract
A rapid and efficient method is needed for determining total concentrations of multiple elements in soils. A procedure was developed whereby a soil was finely ground (25 min in a micronizing mill), suspended in water (2 g.L−1), and analyzed directly by inductively coupled plasmaemission spectrometry (ICP) to determine total concentrations of Al, Ba, Ca, Fe, Mg, Mn, and Sr. The average concentrations obtained for these elements in 10 soils agreed to within 2% of values obtained for the same soils analyzed after first solubilizing the samples by sodium carbonate fusion. The concentrations of the seven elements determined in the 10 soils analyzed ranged from a low of 44 mg Sr.kg−1 soil to over 7% of the soil sample as Al. The sensitivity of the direct analysis procedure could be increased by increasing the concentration of soil in suspension to 10g.L−1. Large variations in concentration due to particle size differences among soils were initially observed. Grinding the soil in a micronizing mill reduced the variation caused by the particle size differences. When two soils with sand compositions of 79 and 17% were ground for 25 min, particle size analysis showed that 81 and 90%, respectively, of the gound soil had a particle size of equivalent diameter less than 2 μM. The direct analysis of soil suspensions by ICP eliminates the time-consuming solubilization step required in other total analysis methods and allows for the simultaneous determination of the total concentration of multiple elements in soils.

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