SI-Traceable Determination of Mass Fractions of Technology Critical Elements in Electronic Waste

Within the European metrology project “MetroCycleEU”, fourteen partners from eleven countries around Europe joined forces to develop — among other aims — new methods for the SI-traceable determination of technology critical elements (TCEs) in urban waste and other environmental relevant matrices, giving industry and authorities a more robust framework for the sustainable usage of these elements as well as decision making in waste management, future pollution control and early environmental protection. To establish new protocols for digestion and mass-spectrometric quantifications of representative waste electrical and electronic equipment (WEEEs), a novel standard addition approach was developed for mass spectrometry. The novel approach — while maintaining the advantages of standard addition — allowed to clearly distinguish between the measurement uncertainty due to the mass spectrometric measurement itself and the contributions arising from the inhomogeneity of the sample and the reproducibility of its digestion. It was first applied to printed circuit boards (PCBs), which are known to contain important TCEs in varying amounts up to the μg/g level. Crucial for the determination of SI-traceable mass fractions of TCEs within the PCB matrix was the calibration within the matrix itself, eliminating biases that otherwise would have been arisen from the different sensitivities of the analytes in the sample matrix and external calibration standards. The use of a suitable internal standard element and therefore the measurement of signal intensity ratios instead of absolute signal intensities rendered the measurements virtually invariant against drift effects. The determination of cobalt, lanthanum, and lithium in PCBs and the associated measurement uncertainties estimated according to the GUM demonstrate the advantages of the novel approach compared to the original standard addition.