Alternatively, for direct energy coupling devices, such as a microwave, digest samples for analysis by GFAA or ICP-MS by adding 10 mL of 1:1 HNO , mixing the slurry and 3 then covering with a vapor recovery device. Heat the sample to 95EC ± 5EC and reflux for 5 minutes at 95EC ± 5EC without boiling. Allow the sample to cool for 5 minutes, add 5 mL of concentrated HNO , heat the sample to 95EC ± 5EC and reflux for 5 minutes at 95EC ± 3 5EC. If brown fumes are generated, indicating oxidation of the sample by HNO , repeat this 3 step (addition of 5 mL concentrated HNO ) until no brown fumes are given off by the sample 3 indicating the complete reaction with HNO . 3 Using a vapor recovery system, heat the sample to 95EC ± 5EC and reflux for 10 minutes at 95EC ± 5EC without boiling.