Determination of Trace Elements in Fluoropolymers after Microwave-Induced Combustion Erico M. M. Flores,* ,† Edson I. Muller, † Fabio A. Duarte, ‡ Patricia Grinberg, § and Ralph E. Sturgeon § † Departamento de Química, Universidade Federal de Santa Maria, 97105-900 Santa Maria, RS, Brazil ‡ Escola de Química e Alimentos, Universidade Federal do Rio Grande, 96201-900 Rio Grande, RS, Brazil § National Research Council Canada, Ottawa, Ontario, CAN K1A 0R6, Canada ABSTRACT: An effective approach to the digestion of fluoropolymers for the determination of Ag, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, and Ni impurities has been developed using microwave-induced combustion (MIC) in closed quartz vessels pressurized with oxygen. Samples that were examined included the following: polytetrafluorethylene (PTFE); poly- tetrafluoroethylene with an additional modifier, perfluoropro- pylvinylether (PTFE-TFM); and fluorinated ethylene propy- lene (FEP). A quartz device was used as a sample holder, and the influence of the absorber solution was evaluated. Determination of trace elements was performed by inductively coupled plasma-optical emission and mass spectrometry. Neutron activation analysis (NAA) was used for validation purposes. Results were also compared to those obtained using microwave-assisted acid extraction in high-pressure closed systems. Dilute nitric acid (5 mol L -1 ), which was selected as the absorbing medium, was used to reflux the sample for 5 min after the combustion. Using these conditions, agreement for all analytes was better than 98% when compared to values determined by NAA. The residual carbon content in the digests was lower than 1%, illustrating the high efficiency of the method. Up to 8 samples could be digested within 30 min using MIC, providing a suitable throughput, taking into account the inertness of such samples. F luoropolymers represent a rather specialized group of polymeric materials with large numbers of new types being continuously developed. Some are derivatives of the original polytetrafluoroethylene (PTFE), such as fluorinated ethylene propylene (FEP) and polytetrafluoroethylene with additional modifier, perfluoropropylvinylether (PTFE-TFM), etc. 1,2 These compounds are used in numerous industrial applications, because of their favorable properties of high resistance to corrosive reagents, thermal stability, inertness, resistance to aging and low coefficient of friction. 3 Fluoropolymers are widely used in chemical, automotive, aerospace, electrical, and electronic industries, medical devices, special packaging, communications, protective garments, and a variety of other industrial and consumer products. 2 For some of these applications, i.e., the production of semiconductors, fluoropol- ymers must present high purity in order to ensure their performance, especially with respect to their trace element content. 2,4,5 The expanded use of fluoropolymers as raw materials in industrial processes requires the development of rapid and accurate methods of analysis having limits of detection (LOD) suitable for the determination of contaminants at low levels, several of which have been described for the determination of trace elements in polyethylene, 6 acrylonitrile butadiene styrene, 6 polyethyleneterephthalate, 7 polystyrene, 8 and poly- (vinyl chloride). 8 However, despite numerous quality control requirements, only a few studies have appeared related to trace elements in fluoropolymers. 9-13 These materials are exception- ally inert, extremely difficult to solubilize, and generally require complex and time-consuming sample preparation procedures. Previous research efforts for the determination of metallic contaminants in fluoropolymers have been based on extrac- tion 9,10 and combustion methods. 11 Combustion systems operating at atmospheric pressure using oxygen and quartz tubes heated to 600 °C have been used for digestion of PTFE with subsequent determination of metallic impurities by electrothermal atomic absorption spectrometry. 12 However, only a portion of ∼200 mg of such test samples was used and the residue on the quartz boat had to be digested with nitric acid after the combustion step. Moreover, to avoid contami- nation, each boat was used only once. 12 To obviate the di fficulties involved in digestion of fluoropolymers, solid sampling-electrothermal vaporization- inductively coupled plasma mass spectrometry has been used for multielement analysis of these materials. This method exhibits useful features, such as low detection limits (ng g -1 range) with calibration performed using aqueous standard solutions for at least seven analytes (Cr, Cu, Fe, K, Mn, Pb, and Zn). However, it is clear that this technique is not readily available in many laboratories and requires careful optimization Received: October 8, 2012 Accepted: November 21, 2012 Published: November 21, 2012 Article pubs.acs.org/ac © 2012 American Chemical Society 374 dx.doi.org/10.1021/ac3029213 | Anal. Chem. 2013, 85, 374-380