Feasibility of microwave-assisted ultraviolet digestion of polymeric waste electrical and electronic equipment for the determination of bromine and metals (Cd, Cr, Hg, Pb and Sb) by ICP-MS

Abstract

A method for the digestion of polymeric waste electrical and electronic equipment (WEEE) by microwave-assisted ultraviolet wet digestion (MAWD-UV) was proposed for the first time allowing us to obtain a single digest for the further determination of Br, Cd, Cr, Hg, Pb and Sb according to the Restriction of the Use of Certain Hazardous Substances (RoHS) directive. The determination of bromine and metals was carried out by inductively coupled plasma mass spectrometry (ICP-MS). The efficiency of MAWD-UV was compared with that obtained without the UV lamp, using 1 to 7 mol L⁻¹ HNO₃ and HNO₃ plus HCl (5 + 1) mixtures. A wet acid digestion method combined with ICP-MS, as well as neutron activation analysis (NAA), was used to obtain reference values. Although the UV lamp improved the digestion, thus allowing for the use of diluted solutions, possible losses of bromine were observed using a 3 mol L⁻¹ HNO₃ solution. After a careful optimisation, a diluted solution containing 0.5 mol L⁻¹ HNO₃ + 0.5 mol L⁻¹ HCl + 5.3 mol L⁻¹ H₂O₂ provided results that were in agreement with the reference values for bromine and metals in the same digest solution. Spike recoveries ranged from 90 to 113% for all the analytes. The results were compared with the values of certified reference materials (ERM 680k and ERM 681k, low-density polyethylene) digested by MAWD-UV and no statistical difference was observed, except for Cr. Limits of quantification using ICP-MS ranged from 0.010 μg g⁻¹ (Cd) to 4.5 μg g⁻¹ (Br) that were suitable according to the RoHS directive. The MAWD-UV method allowed for the single digestion method using diluted acids and did not require different digestion solutions for bromine and metals, thus providing suitable digestion efficiency without bromine losses.