Multi-element chemical analysis of printed circuit boards - challenges and pitfalls.

Printed circuit boards (PCB) are an essential component of electrical and electronic equipment (EEE) and account for roughly 5% of the mass of EEE. Knowledge about the chemical composition of PCB is crucial to enable an enhanced recycling, especially for elements considered critical regarding their economic importance and supply risk (e.g. precious metals or specialty metals such as tantalum, germanium, gallium). No standard reference methods exist for determining the chemical composition of PCB. Previously published element mass fractions cover a wide range and were produced with numerous methods for sample preparation, digestion, and measurement. This impedes comparability of PCB composition from different studies. To investigate sample- and element-specific effects of applied methods a PCB sample from desktop PC was analysed in two separate labs. One lab applied sample- and element-specific validated methods (aqua regia, HF, H2SO4 blend; ICP-OES, QQQ-ICP-MS), providing reference values, the other applied routine in-house methods (aqua regia; ICP-OES, ICP-MS) to assess the validity of in-house methods for chemical analysis of PCB. A t-test was used to identify elements depicting significant differences between validated and in-house methods. For base metals, in-house methods led to comparable results. For precious, specialty, and hazardous metals as well as REE investigated in this study, significant differences were detected. With respect to all results for in-house methods in this study, the combination of aqua regia and ICP-OES led to less significant differences than aqua regia and ICP-MS. The results show that sample- and element-specific quality assurance is crucial to prevent analytical bias.

Standardization of fluorescence excitation-emission-matrices in aquatic milieu.

Fluorescence excitation-emission-matrices (EEM) are a useful tool for water quality monitoring. Recent publications show the potential of the method for real time drinking water control. However, in fluorescence measurements there is still a need for standardization to make data interpretation comparable. In this work a standardization procedure based on excitation and emission correction as well as normalization and optional inner filter effect correction is presented. By measurements of humic acid and tryptophan standards with two different spectrometers (LS 50 and LS 55 by PerkinElmer) the procedure application leads to comparable fluorescence intensities with relative standard deviations (median) of 6.6-8.4% and 10.6-12.0%, respectively. These small differences are not avoidable even if all possible correction methods are implemented and constant measurement conditions are given. The used BAM kit for emission correction induced good agreement in peak shape not only for single wavelengths but also for the whole EEM. As a consequence it is necessary to use identical equipment and identical experimental conditions in order to apply this method in fields of water quality control if small changes of fluorescence intensities are relevant for data assessment.