Microwave-assisted digestion of soils for the determination of 90Sr

A method is presented for the treatment of soil samples prior to the determination of 90Sr activity concentration. An open-focused microwave system – Prolabo Microdigest A301 – is used, and attention is paid to the microwave power, the time and the volume of the acids used in the digestion. The results of both microwave-assisted total attack and leaching extraction with 65% HNO3 did not differ significantly from those given by classical attacks on a hot-plate. A leaching procedure is thus proposed, consisting of the digestion of 2 g of sample for mineral soils and 1 g for organic soils at 50 W (25% of total power) for 20 min using 15 ml of 65% HNO3. The method was validated by using CRM IAEA-375. Digestion time was considerably reduced, and precision and accuracy were satisfactory.