VAPOR-PHASE ACID DECOMPOSITION OF HIGHLY PURE SILICAS IN A SEALED PTFE BOMB AND DETERMINATION OF IMPURITIES BY ONE-DROP ATOMIC SPECTROMETRY

Using a sealed double PTFE vessel with a stainless-steel jacket, the purification of acids used in the vapour phase for the decomposition of highly pure silicas was carried out simultaneously in the same vessel at an elevated temperature. A significant decrease in the metal blank level, even from artificially contaminated acids containing 1 mg of each metal (Al, Ti, Cu, Fe, Mn, Ca, Mg and Na), was observed. By "one-drop" flame atomic absorption and "one-drop" inductively coupled plasma atomic emission spectrometry, Na, Ca, Mg, Cu, Fe, Mn and Ti in silicas were successfully determined owing to the very low blank level. This decomposition method made the determination of trace metals except aluminium in highly pure silicas possible without any other preconcentration step. Aluminium was determined only with the use of a small sample mass, owing to the poor decomposition by acid vapours.