For the digestion of samples for analysis by GFAA or ICP-MS, add 10 mL of 1:1 HNO , mix the slurry, and cover with a watch glass or vapor recovery device. Heat the sample to 3 95EC ± 5EC and reflux for 10 to 15 minutes without boiling. Allow the sample to cool, add 5 mL of concentrated HNO , replace the cover, and reflux for 30 minutes. If brown fumes are generated, 3 indicating oxidation of the sample by HNO , repeat this step (addition of 5 mL of conc. HNO ) over 3 3 and over until no brown fumes are given off by the sample indicating the complete reaction with HNO . 3 Using a ribbed watch glass or vapor recovery system, either allow the solution to evaporate to approximately 5 mL without boiling or heat at 95EC ± 5EC without boiling for two hours. Maintain a covering of solution over the bottom of the vessel at all times