![]() To remove this volatile As species, it is recommended to employ a boiling procedure for hydrofluoric acid prior to the conventional subboiling purification procedure ( Hu et al., 2005). This limit may be related to the presence of volatile As species such as AsF 3 (boiling point of 63 ☌). Notably, the conventional subboiling purification procedure is not effective at removing As impurities in HF. A clear advantage of NH 4F-assisted acid digestion is that it does not require handling the very corrosive and toxic HF. Recently, NH 4F has been proposed to replace HF for the acid digestion of geologic and environmental samples ( Hu et al., 2010 Mariet et al., 2008). HF will cause irreparable damage to the skin and eyes and should never be used without full safety precautions. Contact with HF does not cause an immediate burning sensation or pain but readily penetrates deep tissue and causes intense pain after an hour or more. Any HF spills on the skin should be immediately washed with copious cold water, and the affected area should be treated with a gel containing monosodium glutamate ( Potts, 1987). It should also be noted that HF is one of the most hazardous mineral acids used in the laboratory, and it is both highly corrosive and toxic. Even diluted HF solutions will etch glass, so plastic labware (preferably PTFE or Teflon) is essential. HF is almost always mixed with other oxidizing acids such as HNO 3 and/or HClO 4 to ensure complete dissolution and to produce uniformly high oxidation states in the final solutions. However, HF is rarely used as the sole reagent because some salts are poorly soluble in this acid ( Potts, 1987). HF by itself is more effective in the digestion of silicate rock minerals than when mixed with another acid. ![]() Silicates are converted to volatile SiF 4, which will be lost in open vessel digestion procedures. Hydrofluoric acid (HF) is the most effective mineral acid for breaking up strong Si–O bonds to form SiF 6 − 2 ions in acidic solution. Qi, in Treatise on Geochemistry (Second Edition), 2014 15.5.2.1.1 Hydrofluoric acid
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