Metals: Analytical Methodology for RoHS/WEEE Compliance Testing
Once the sample dissolution is complete, the final phase of the analysis is normally fairly simple, but does require careful evaluation by experienced atomic spectroscopists. As mentioned, ALS Environmental has an array of tools available to satisfy virtually any trace metals application.
As mentioned, a portion of the digestate from the bomb dissolution is normally split off for Mercury analysis. Since the action limits for Mercury are high compared to many of the ultra-trace applications at ALS Environmental, a simple Cold Vapor Atomic Absorption Spectroscopy (CVAAS) determination is generally satisfactory. The digestate is taken through an additional oxidizing process prior to performing the final reduction of mercuric ions to elemental mercury and detection by atomic absorption.
If the sample requires a lower limit of detection than can be accomplished with CVAAS, or if the sample is so small that a lower solution concentration is needed, ALS Environmental has the option to analyze the sample by Purge and Trap Atomic Fluorescence Spectroscopy (P&T-AFS). This produces results two to three orders of magnitude lower than conventional CVAAS. To date, ALS Environmental has not needed to use P&T-AFS for RoHS applications.
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Lead, Cadmium, Chromium (Total)
Lead and Cadmium are generally analyzed by Inductively Coupled Plasma/Mass Spectrometry (ICP/MS), which provides sufficient sensitivity for all applications and selectivity for the majority of applications. Care must be taken to monitor sufficient target and non-target isotopes to address potential isobaric interferences. Standard procedure at ALS Environmental is to monitor all potential interferences. Corrective action can be as simple as choosing an alternative isotope or performing arithmetic corrections. However, in some cases an alternative procedure is used to confirm ICP/MS results.
Chromium is measured by Inductively Coupled Plasma/Atomic Emission Spectroscopy (ICP/AES) due to uncorrectable interference from the hydrochloric acid present in the digestate. Both of the primary Chromium isotopes generally used for quantitation by ICP/MS are overlapped with polyatomic ions derived from the chloride (i.e. aqua regia is used for most digestions). Nonetheless, ICP/AES offers a satisfactory alternative. Depending on the level of Total Chromium present, future testing to speciate it is sometimes necessary.
When the total chromium approaches or exceeds the action level, speciation is necessary. Since the action level is relatively high compared to many other applications at ALS Environmental, a colorimetric procedure can be used. The technique is essentially identical to EPA Methods 3060A (alkaline digestion) and 7196A (colorimetric determination).
Learn more about Hexavalent Chromium Testing...