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

Abstract

An effective decontamination procedure was developed using thermogravimetric data obtained from TFM and PFA vessels that were contaminated with aqua regia. This procedure allows one set of vessels to be used without contamination of subsequent samples. The vessels are decontaminated at 140 °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 are possible in TFM [a copolymer of tetrafluoroethylene and a small amount of the perfluoro(propyl vinyl ether)] and PFA (a perfluoroalkoxy resin) microwave digestion vessels that have been previously used in conjunction with aqua regia. This study illustrated how chlorine-based species present in aqua regia can enter microwave digestion vessels constructed from TFM and PFA due to permeation processes. It was demonstrated using thermogravimetric analysis 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 indicate the release of chlorine-containing species from previously contaminated vessels. In this study sufficient chlorine-containing species were released back into a vessel to precipitate completely 0.1 mg of silver in a nitric acid digest.