Sample preparation of polymers for halogen determination requires special attention because they are difficult to bring into solution and due to the risk of analyte losses when using acid digestion. A method using microwave-induced combustion (MIC) was optimized for accurate determination of halogens in polymeric parts obtained in waste of electrical and electronic equipment. Results were compared with those by using microwave-assisted extraction (MAE) with alkaline solution and microwave-assisted wet digestion (MAWD) using concentrated nitric acid, which are common choices for sample preparation. In this particular case, the MAE method was not suitable and underestimated results were obtained, showing the necessity for the complete digestion. Even with the use of MAWD under high temperature and pressure, incomplete digestion and high acid content were obtained, which were unsuitable for analysis and resulted in poor recovery. Only by using MIC (diluted ammonia as absorbing solution) acceptable recoveries (95 to 104%) and agreement with certified values for the certified reference materials (CRMs) of polymers were obtained. Thus, a suitable method for all halogen to be determined by ion chromatography (IC) or inductively coupled plasma mass spectrometry (ICP-MS), with the exception of F, was obtained in agreement with the requirements by the Restriction of the Use of Certain Hazardous Substances (RoHS) European directive.

In this work, solutions of oxidant salts were evaluated as alternative to nitrate solution for the ignition step in microwave-induced combustion (MIC) method. Aqueous solutions of KClO4, K2Cr2O7, KMnO4 and K2S2O8 in several concentrations were evaluated and it was observed that the ignition was dependent on the concentration and type of igniter solution. Moreover, it was possible to observe that ignition and combustion times are not related with sample mass, which was confirmed by evaluating sample masses ranging from 100 to 500 mg of whole milk powder. Certified reference materials were digested using K2Cr2O7 as igniter solution and digests analyzed by inductively coupled plasma optical emission spectrometry (ICP OES), with good agreement to certified values. The obtained results suggest that MIC can be performed using solutions of oxidants salts. In addition, the proposed study contributed to a better undestanding and explaining the ignition with microwaves.