A 0.1 g amount of Ni–Cr-based dental alloy Wiron 99 (Bego, Germany) was dissolved using aqua regia (5 ml), concentrated (60% w/w) HClO4 (2 ml), and aqua regia (5 ml) in this order, evapo- rated to a small volume (2 ml) and diluted to 100 ml with distilled water. A 5 ml aliquot of this solution was taken, evaporated to dryness, and dissolved in 5 ml of 5 M HCl. Chromium was reduced to Cr(III) by adding 2 ml of 35% H2O2 and evaporating to dryness to remove the excess of hydrogen peroxide. This operation was re- peated twice, and the residue was dissolved in 100 ml of 0.05 M HCl. A 0.3 ml aliquot was drawn from this final solution, and the standard proce- dure was followed to analyze Ni. This solution (containing 9.6 mg Ni) was also spiked with 0.2– 0.5 ml volumes of 2.0×10−4 M Co so as to produce synthetic mixtures for simultaneous analysis.