The minimisation of aqua regia cross contamination in PFA and TFM microwave digestion vessels using silver as an indicator

An effective decontamination procedure was developed using thermogravimetri c data obtained from TFM and PFA vessels that were contaminated with aqua r egia. This procedure allows one set of vessels to be used without contamina tion of subsequent samples. The vessels are decontaminated at 140 degrees C in a vacuum oven at a pressure of 6 mmHg. It has been demonstrated that if the decontamination procedure is carried out, 100% recoveries of silver ar e possible in TFM [a copolymer of tetrafluoroethylene and a small amount of the perfluoro(propyl vinyl ether)] and PFA (a perfluoroalkoxy resin) micro wave digestion vessels that have been previously used in conjunction with a qua regia. This study illustrated how chlorine-based species present in aqu a regia can enter microwave digestion vessels constructed from TFM and PFA due to permeation processes. It was demonstrated using thermogravimetric an alysis that this process is reversible and that chlorine-containing species can later leave PFA and TFM when the vessels are re-heated in a microwave oven and thus contaminate subsequent digests. The study used silver to indi cate the release of chlorine-containing species from previously contaminate d vessels. In this study sufficient chlorine-containing species were releas ed back into a vessel to precipitate completely 0.1 mg of silver in a nitri c acid digest.