All chemicals used in this work were of analytical reagent grade
and all solutions were prepared with ultra-pure water (18.2 MV cm,
Milli-Q system). The certified standard stock solutions of mercury
(998
2 mg/L) and cadmium (1001
1 mg/L) nitrate, and the nitric
acid 65% were purchased from Merck. Sodium hydroxide solution
(0.1 mol/L) was used for pH adjustments and nitric acid 65% was
used to acidify the sample solutions.