A focused microwave digestion system operated at atmospheric pressure was applied to the preparation of milk, total parenteral nutrition, tissues (mussel, kidney, oyster and bovine liver) and urine. Reagent combinations (HNO3, H2SO4 and H2O2) and power–time programmes were examined with respect to the residual carbon content (RCC) and element recovery. Inductively coupled plasma atomic emission spectrometry was used to determine the residual carbon and analytes (As, Ba, Ca, Cd, Cu, Fe, K, Mg, Mn, Na, P, Pb, Sr and Zn). Different reagents (HNO3, HCl and ethylenediaminetetraacetic acid) were investigated for the final digestion step in order to improve the accuracy in the determination of elements forming low-solubility sulfates. The RCC obtained with an open-focused microwave system was similar to that obtained with high-pressure digestion, but lower than with a closed, medium-pressure microwave system.