Aqua Regia Digestion for Cd Analysis

For each sample, 15 mL of aqua regia was transferred to a conical 100 mL flask that had been infiltrated by aqua regia vapors. An additional 6 mL of aqua regia solution was added and a glass funnel was placed at the top. Each flask was heated on an electric hot plate to maintain the aqua regia at a slight boiling state for 2 h. Then, samples were cooled to room temperature and allowed to settle. The extract was then slowly filtered through quantitative filter paper into a 50 mL volumetric flask. The glass funnel, conical flask, and residue were rinsed with a small amount of nitric acid solution at least three times, with the reinstate collected in the volumetric flask. After filtration, the inductively coupled plasma mass spectrometry (ICP-MS 1600, Hexin Mass Spectrometry, China) was used to determine Cd concentrations in the digested sample solutions.