Extraction of silver from soils and its determination by atomic absorption spectrometry

A simple, sensitive and reliable method for determining silver in soils by atomic absorption spectrometry with a graphite furnace is described which involves direct analysis of acid digests and avoids pre-concentration of the analyte. Chemical extracts have been investigated as a means of fractionating soil silver and results are reported for a range of soils, from areas of differing geology in Wales, U.K. Background concentrations are compared with areas contaminated by spoil from derelict mines. Uncontaminated soils contained silver in the range 0.01–1 μg Ag/g. The proportion of total silver extracted from a soil spiked and equilibrated with 110m AgNO₃ and unspiked field samples gave good agreement for the extractants 0.1 M and 1.0 M nitric acid, 0.005 M DTPA (diethylenetriaminepentaacetic acid), 0.05 M acetic acid, 1 M ammonium acetate and deionised water, although some extractants did not meet their predicted extraction efficiency. In the field samples soluble plus exchangeable silver was present between 0.4–40 ng Ag/g (< 1% of total), whereas biologically-available silver measured in 0.005 M DTPA was in the range 3–540 ng Ag/g (< 5% of total).