Freshly prepared magnetic ferrite for the speciation of silver using dispersive micro-solid phase extraction and electrothermal atomic absorption spectrometry

A micro-solid phase extraction procedure based on the use of freshly prepared magnetic ferrite particles allows small amounts of silver in solution to be preconcentrated. Phase separation is carried out using a magnet. For a typical 10 mL water sample at a pH close to 8, the solid recovered phase (about 2 mg) is dissolved in 0.1 mL of a solution containing 8% v/v concentrated hydrofluoric acid and 4% v/v concentrated nitric acid and then introduced into an electrothermal atomizer to obtain the silver atomic absorption signal. The detection limit is 3 ng L-1 and the relative standard deviation for five measurements at the 50 ng L-1 silver level is 5.7%. Only silver(i) is retained. By repeating the procedure with another aliquot of sample after a suitable oxidation process, the discrimination between solid and dissolved silver can be achieved. The results are verified by analyzing reference water samples with a certified silver content. In addition to the application to water analysis, data for silver in items of clothing, sticking plasters and vegetables are given. The procedure is suitable for potable waters but not for seawater due to the interference caused by the high chloride concentration.