Multi-element analysis of Tinishu Akaki River sediment, Ethiopia, by ICP-MS after microwave assisted digestion

This work describes a method for multi-element analysis of cadmium, cobalt, chromium, copper, manganese, nickel, lead and zinc in Tinishu Akaki River sediment, Ethiopia, by inductively coupled plasma mass spectrometry. River sediment samples were collected between November 2002 and January 2003 for the first campaign, and between November 2003 and January 2004 for the second campaign. The samples were kept frozen until they were lyophilized, grounded in a mortar and pestle and sieved. A fraction less than 63 mu m was taken for the analysis. Different acid combinations were investigated for the digestion of sediment samples: HCl/HNO3, HClO4/HNO3 and HF/HCl/HNO3/ H3BO(3) in a microwave digestion system. Complete dissolution of materials was achieved with the latter. Optimum values for instrumental parameters of the ICP-MS were sought and set up. Multi-element standard solutions were used for the calibration of the procedure. The methodology and accuracy was evaluated by the analysis of certified reference materials of sedimental origin. Very low limits of detection were obtained for all elements, which were less than 0.65 mu g g(-1), except for Zn, which was 2.8 mu g g(-1). Good precision, with relative standard deviations better than 7% for most of the elements, was found.