RoHS and WEEE Compliance Testing
What is RoHS/WEEE?
In 2003 legislation was introduced in the European Union (EU) to promote the collection, treatment, recycling, and recovery of waste from electrical and electronic equipment. This legislation is known as the Waste Electrical and Electronic Equipment (WEEE) act and is formally dictated by directive 2002/96/EC of the European Parliament. A complimentary directive, the Restriction of Hazardous Substances (RoHS), was also introduced in 2003 given by 2002/95/EC of the European Parliament. Beginning July 1, 2006, RoHS legislation restricts the amounts of lead, cadmium, mercury, chromium (VI), Polybrominated Diphenylethers (PBDEs), and Polybrominated Biphenyls (PBBs) in electronic and electrical equipment. These chemicals are known to present a risk to human health and the environment. Thus, restrictions are in place that limit the concentration of these constituents in electrical and electronic products and/or components.
Analytical Chemistry – PBDEs & PBBs
Traditional approaches to the analysis of PBBs and PBDEs have used high-resolution mass spectrometers. While this technique generally has very low detection limits, it is also very costly. As evidence continues to mount regarding the bioaccumulative and toxic effects of PBBs and PBDEs, the need for a sensitive, rugged, cost-effective methods exists.
In response to this need, Columbia Analytical has developed special analytical procedures for the determination of PBDEs and PBBs based upon EPA method 8270C with Selective Ion Monitoring (SIM). The method has been optimized by the addition of Large Volume Injection (LVI), which dramatically increases the sensitivity of the analytical procedure. The procedure provides adequate sensitivity so detection limits significantly lower than the compliance limits set by the European Union (EU) can be met in samples with as little as 10 mg of material available for testing. The standard target list of PBBs and PBDEs at CAS is based upon the environmentally significant and lipophilic congeners. The target list is derived from the primary components of the major products.
The first challenge to producing valid analytical results for electrical and electronic equipment samples is obtaining a representative aliquot for analysis. Samples can range from relatively simple materials (e.g. graphite, gold wire, silicon, etc.) to more complex examples of multi-component assemblies that can include plastics, metal circuitry, solder, etc.
A number of homogenization techniques are employed at CAS. These include ball mills, shatter box, mortar & pestle, Wiley mill, and manual particle size reduction with snips, clippers, etc. In addition to the standard use of these various techniques, cryogenic techniques can be combined to aid the milling process.
The general type of material(s) dictates the homogenization most appropriate for a particular sample. For example, carbon-filled silica is readily ground to a homogenous powder in a ball mill or shatter box. On the other hand, a metallic component is not amenable to milling. A manual approach is generally required to sufficiently reduce the particle size to allow representative sub-sampling, and to provide adequate surface area for efficient digestion and extraction. Generally speaking, brittle materials are processed through one of the mills or mortar & pestle. In cases where a component is pliable, it might be able to be made brittle for milling by freezing in liquid nitrogen, and then carried through the process accompanied by liquid nitrogen. As mentioned, metallic components present the most difficult challenge to homogenization because of their resistance to becoming brittle.
Once a sample is in a homogenous state, it is ready for extraction.
Extraction – PBDEs and PBBs
The solvent extraction procedure for PBDEs and PBBs is relatively simple. Hexane is the extraction solvent. Since fairly small sample masses are common, micro-extractions are generally required. In some cases, as little as 1-2 mg of sample is available, so the extraction is done in an auto-sampler vial prior to instrumental analysis. In all cases, isotopic labeled surrogates and internal standards are added. Two labeled PBDEs are used as surrogates (i.e. C13-Congeners 47 and 49). The internal standard is C13-Congener 118. The same surrogates and internal standards are used for both PBDE and PBB determinations.
Instrumental Analysis – PBDEs and PBBs
Although the level of concern for PBDEs and PBBs is relatively high (i.e. as high as 0.1%), sensitive instrumental techniques are required to compensate for small sample masses often encountered, and to provide adequate sensitivity to get at least ten times lower than the action level. The buffer between the reported detection limit and the action level is important so false positives or negatives can be avoided. From an analytical chemistry standpoint, values reported near the detection limit are subject to considerable variability. Thus, CAS has designed an analytical approach that assures a high level of accuracy and precision at the action level.
The Gas Chromatography-Mass Spectrometry (GC-MS) procedures employed at CAS include Selective Ion Monitoring (SIM) and Large Volume Injection (LVI). The SIM mode allows dwelling on a particular ion so additional signal can be accumulated. The LVI allows a larger volume of sample extract to be delivered to the GC column.
Together, the two techniques improve sensitivity significantly. Selectivity comes from the use of the MS.
For PBDEs, the entire range of bromine substitution is covered by the calibration curve. Although the number of congeners that were historically produced is limited (i.e. less than the 209 theoretically possible congeners), the calibration and identification scheme employed at CAS allows detection of any PBDEs present in the sample. The detection limit reported is calculated directly from the concentration of the lowest standard in the calibration curve. Note that a theoretical detection limit is also determined via precision measurements at the low end of the curve. These values are significantly lower than the limit derived from the low calibration point and serve as validation of the sensitivity of the procedure.
The analysis for PBBs is a bit more complex due to limited availability of PBB congeners. Currently, only the di- through hexa- and the deca- are commercially available for use as calibration standards. (Note: CAS is currently having octa- synthesized). For detections of PBBs with those levels of substitution, fully quantitative results are possible. To provide identification and semi-quantitative information about hepta- and octa- substituted PBBs, commercial fire retardant mixes are analyzed. The commercial mixes have octa- present, as well as small amounts of hepta- and nona-. Semi-quantitative results for those congeners are derived from the response factor for hexa- substituted PBBs.
Metals Analytical methods are also well developed for measuring metals once in solution. The challenge with electronic and electrical equipment is related to sample preparation, both homogenization and digestion (i.e. getting the target metals in solution ready for instrumental measurement). CAS has numerous homogenization and digestion procedures on line so the appropriate techniques can be applied to each sample on an individual basis. Once satisfactory dissolution of the sample is achieved, the appropriate instrumental technique can be applied. CAS has the capability to select from numerous instrumental techniques to match the correct procedure with a particular sample type. These include Flame Atomic Absorption Spectroscopy (FAAS), Graphite Furnace Atomic Absorption Spectroscopy (GFAAS), Hydride – Atomic Absorption Spectroscopy (Hydride-AAS), Purge & Trap – Cold Vapor Atomic Fluorescence Spectroscopy (P&TCVAFS), Cold Vapor Atomic Absorption Spectroscopy (CVAAS), Inductively Coupled Plasma – Argon Emission Spectroscopy (ICPAES), and Inductively Coupled Plasma – Mass Spectrometry (ICP-MS). As with PBBs and PBDEs, this array of options allows for meeting compliance levels in very small electrical component samples (i.e. as small as 1 or 2 mg). The following sections provide more detailed information about the CAS procedure. Note that EPA procedures can be cited for the various techniques employed for digestion and analysis of samples. For some sample types, modification is required to accommodate the material because the scope of the EPA procedures does not cover more advanced applications.
Digestion for Metals
The choice of acid digestions for metals is dictated by the sample type. For non-metallic samples, total dissolution is generally not achieved. This is the result for many samples consisting of materials relatively inert to nitric and hydrochloric acids, or aqua regia (combination of the two). These materials include most plastics, silicon, and carbon based samples. However, by achieving a reasonably fine particle size on these samples, a significant amount of surface area is exposed. Hot, concentrated acids then provide an aggressive leach of the material so the results generated meet the purpose of the regulation. Of particular importance is that the inert materials generally are not the components that would be expected to potentially contain Lead, Cadmium, Mercury, and Hexavalent Chromium.
Samples that contain metallic components or are themselves a metallic material can usually be completely dissolved. Silver and gold components are sometimes present, which require special treatment to achieve dissolution (e.g. dilute nitric for silver; aqua regia for gold). Other metallic components (e.g. solder, micro circuitry, etc.) are readily attacked using aqua regia digestions. For most samples, an aqua regia digestion performed under elevated temperature and pressure in a sealed Teflon bomb is appropriate.
If the sample is digested using the closed vessel approach, Mercury is included through that point. A portion of the digestate is then split and sent for separate handling and further digestion prior to instrumental analysis for Mercury. The other portion of the digestate is ready for Lead, Cadmium, and Total Chromium analysis using the appropriate instrumental approach.
Note: The standard approach at CAS is to analyze for Total Chromium first. If the Total Chromium concentration is below the action limit, then no further determination is necessary (i.e. Hexavalent Chromium cannot be greater than Total Chromium). If Total Chromium is detected near the action limit or above it, then a re-analysis of the sample is performed using an alkaline digestion followed by a colorimetric determination for Hexavalent Chromium.
Instrumental Analysis – Metals
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. CAS has an array of tools available to satisfy virtually any trace metals application.
Mercury – 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 CAS, 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 a lower limit of detection is needed in the original sample than can be accomplished with CVAAS or the sample is so small that a lower solution concentration is needed, then CAS has the option to analyze the sample by Purge and Trap Atomic Fluorescence Spectroscopy (P&T-AFS), which produces results two to three orders of magnitude lower than conventional CVAAS. To date, CAS has not needed to use P&T-AFS for RoHS applications.
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. The standard procedure at CAS 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.
Hexavalent Chromium – 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 CAS, a colorimetric procedure can be used. The technique is essentially identical to EPA Methods 3060A (alkaline digestion) and 7196A (colorimetric determination).