Microwave digestion of sludge, soil and sediment samples for metal analysis by inductively coupled plasma-atomic emission spectrometry

Three digestion programs for the Anton Paar multiwave microwave were investigated to obtain a simple, rapid method for the determination of metals in sludge, soil and sediment samples. The digests were subsequently analysed for metal content by inductively coupled plasma-atomic emission spectrometry (ICP-AES). The trace metals determined were Mn, Ni, Zn, Pb, Cr, Cd, Cu and V, and the major elements determined were Mg, Ca, Fe and Al. In addition to the heating programs used, different combinations and volumes of hydrofluoric, nitric and hydrochloric acids were evaluated for digestion efficiency. Three standard reference materials (SRMs) were used in the comparison. From the results obtained, the fastest microwave program (36 min) provided the most consistent recovery data for all three SRMs. Six millilitres of HNO3 was the optimum acid mixture for the digestion of LGC6136 sewage sludge (with the exception of Al) and for LGC6138 coal carbonisation site soil. For PACS-1 marine sediment (and for the determination of Al in LGC6136), a mixture of 3 ml of HNO3+2 ml of HF produced the best analytical results. The experimental results were in agreement with the certified values and demonstrated that the proposed method was precise and accurate