The combustion procedure was as follow: (1) 1000 W at 80°C for 5 min,(2) 1000 W at 50°C for 5 min, (3) 1000 W at 190 °C for 20 min,and (4) 0 W for 30 min for cooling. The contents of the tubes were then transferred to 50 mL self standing polypropylene volumetric tubes with plug seal caps. These volumes were then diluted to 25.0 g with ultrapure deionised water,labelled accurately and used for analysis of Pd, Cd and As,by ICP-MS and for Al by ICP-OES analysis.