This mixture was sonicated for 10 min centrifuged for 5 min at 2000 rpm
After filtration
using sample digestion with a digester block Approximately 5.0 g of each sample was weighed into the digestion vessels
The digestions adding 3.0 mL sulphuric acid and 4.0 mL nitric acid
heated to a maximum temperature of 200 C
When the maximum temperature reached 15.0 mL of H2O2 30% added in 1.0 mL aliquots.
The mixture was heated until the volume was reduced to approximately 3 mL
The digests were diluted with water to 20.0 mL
After the digestion procedure analytes were determined by ICP OES