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Regulations on hazardous substances in consumer products aim to prevent human health risks, reduce the environmental impact of end-of-life products, and simplify waste management. Many jurisdictions worldwide have issued laws restricting the use of hazardous substances in those products. One of the most important regulations in this field is the European Union’s Restriction of Hazardous Substances (RoHS) Directive (2002/95/EC), which initially applies to consumer electrical and electronic equipment.

RoHS directive 2002/95/EC prohibits manufacturers from using materials, parts, and subassemblies that contain more than 1000 ppm each of mercury (Hg), lead (Pb), hexavalent chromium (Cr VI), polybrominated biphenyls (PBB), polybrominated diphenyl ethers (PBDE), or more than 100 ppm of cadmium (Cd). The RoHS II directive (2011/65/EU) extended the regulation to include additional products such as medical devices and monitoring and control instruments. The RoHS II directive was later amended (2015/863/EU) to prohibit four common phthalate plasticizers: bis(2-Ethylhexyl) phthalate (DEHP), benzyl butyl phthalate (BBP), dibutyl phthalate (DBP) and di-isobutyl phthalate (DIBP) at levels above 1000 ppm. The RoHS directive also regulates the recycling of all types of electrical goods related to the Waste Electrical and Electronic Equipment Directive (2012/19/EU).

Similar regulations have been promulgated in many countries outside of the European Union, including the Chinese Measures for Administration of the Pollution Control of Electronic Information Products (Chinese RoHS), the Japanese standard JIS C 0950 (Japanese RoHS) or the Korean Act for Resource Recycling of Electrical and Electronic Equipment and Vehicles (Korean RoHS). In the U.S., several states, including California, New Jersey, Illinois, Indiana, Minnesota, New York, Rhode Island, and Wisconsin, have enacted laws prohibiting the sale of non-RoHS-compliant targeted electronic products (e.g., LCD displays).

Need for screening technologies

For electrical consumer product manufacturers, importers, and retailers, the demand to meet strict regulations on allowable levels of heavy metals, brominated flame retardants, and phthalates plasticizers represents a considerable challenge due to the high cost of compliance testing. External laboratories typically conduct this, which often results in a small number of test samples, which puts their business at risk of placing unsafe products on the market.

Hence, all electronic consumer goods value chain stakeholders must have easy-to-use screening technologies at their disposal to maximize the number of items analyzed, and electronic consumer goods value chain stakeholders must have easy-to-use screening technologies at their disposal to maximize the number of items analyzed and limit the risk of non-compliance. Handheld X-ray fluorescence spectrometry (XRF) (Figure 1a) and Fourier Transform Infrared spectroscopy (FT-IR) (Figure 1b) are two easy-to-use, nondestructive, and cost-effective technologies that can be used for screening purposes of heavy metals, brominated flame retardants, and phthalates.

Handheld XRF spectrometry

Modern handheld XRF analyzers can detect and measure the total concentration of elements regardless of their oxidation state, with atomic numbers ranging from magnesium (12) to uranium (92) in diverse types of materials such as metals and alloys, ceramics, glass, minerals, or plastics. Therefore, the technology is adequate to determine the concentration of heavy metals, including Pb, Hg, and Cd, and to provide the total concentrations of Cr and Br, which are excellent indicators for the presence of respectively hexavalent chromium and brominated flame retardants such as PBB and PBDE. The screening workflow for handheld XRF according to the international standard IEC 62321 [1] is shown in Figure 2. Depending on the Cd, Pb, Hg, Cr, and Br levels, the specimens are classified into three categories: RoHS-compliant (pass), RoHS-non-compliant (fail), or inconclusive. Samples with inconclusive results should be further analyzed using laboratory techniques.

One key benefit of the technology is the ability to work in point-and-shoot mode and generate results in seconds. Furthermore, the instruments are fully portable and can be brought to receiving docks, warehouses, product assembly, or retail stores for on-site screening. Modern handheld XRF analyzers are also easy to operate by non-experts: the instruments are delivered pre-calibrated and ready to use for the analysis of different types of materials (metals, ceramics, inorganic, plastics), and an algorithm automatically recognizes the type of material and selects the adequate measurement parameters and calibrations. Figure 2 shows some examples of analyses: the handheld XRF analyzer accurately identifies a first specimen as PVC-plastic. It does not detect any regulated element above the threshold and displays “Pass.” In contrast, it identifies a second specimen as metal (solder SAC 305) containing Cd above the threshold (± uncertainty) and therefore displays “Fail.”

Although the analysis itself is fully nondestructive, the operator may require disassembling the product when a homogeneous unit cannot be isolated using the standard (diameter 8 mm) or the small (diameter 3 mm) measurement spot. For better ergonomics, small-sized samples or electronic parts such as printed circuit boards (PCBs) can also be analyzed using a test stand, which converts the analyzer into a small benchtop unit and provides laboratory-like conditions.

Using handheld XRF, manufacturers, importers, and retailers can implement a standardized screening protocol according to IEC 6232-3-1 [2] or ASTM F2617-15 [3] to verify compliance with electronic and electric devices and reduce the chances that non-compliant products will enter the manufacturing process or reach the store shelves.

Since handheld XRF is an elemental analysis method that does not excel at detecting organic molecules, it does not provide much useful information about the presence of phthalates or other plastics. Thus, materials like polyvinyl chlorides (PVC) and their counterparts should be confirmed via FT-IR spectrometry.

FT-IR spectroscopy

FT-IR spectroscopy is a nondestructive method capable of identifying and quantifying organic molecules and polymers. At a molecular level, the mass of the atoms in the molecule and the bond strength (consider a single, double, and triple bond) will define the ‘resonance frequency’ for a given molecule. The key point: when light of the same frequency as the molecular ‘resonance’ is passed through the sample, it will be somewhat absorbed. Thus, the absorption peak (often referred to as an absorption band) is directly related to the structure and dipole moment of the molecules. For example, phthalates typically have an IR signature as a doublet near 1600 cm^-1 because the wavenumber location of these absorption bands is dependent on the molecular type of functional group that is present. For the scope of RoHS regulation, FT-IR spectroscopy is mostly used to analyze PVC plastics utilized in wire insulation and cable jackets that can potentially contain elevated levels of phthalates. Raw PVC is hard and brittle. Therefore, phthalate plasticizers such as DEHP, BBP, DBP, or DIBP are added to improve properties such as flexibility, durability, and processing of the PVC.

FT-IR spectroscopy can utilize different sampling approaches depending on the type of sample (e.g., liquid, solids, and gas) or what an end user is trying to learn about their sample (e.g., material identification or additive concentration). The most common sampling technique for material identification is attenuated total reflection (ATR), which enables direct and nondestructive screening of plastics and the phthalates in plastics. This is accomplished by pressing the sample against an IR inactive crystal (typically diamond or germanium) via a pressure tower to ensure intimate contact and optimize the signal. Although FT-IR using ATR sampling is easy to implement, it does not have the sensitivity to detect those phthalates down to the regulated level of 1000 ppm. Therefore, it is only suitable for preliminary screening of their total concentration (sum of all phthalates) in plastics at levels above 50000 ppm according to the standard IEC 62321-3-4 [4].

To be more selective to the lower concentration of potential phthalates in a plastic sample, the IR beam can be physically transmitted through the sample to increase the sensitivity by a factor of about 50. This method is suitable for screening around the regulatory level of 1000ppm. To accomplish this, one needs to cut small quantities and collect small pieces of PVC or other thermoplastic polymers from the specimen and press those pieces using a dedicated tool called a universal filmmaker under a controlled temperature above the softening point of the material (Figure 3). Once pressed into a thin film (thickness of 500 µm), the IR beam can be transmitted through the prepared film to classify and quantify the amount of phthalates in a sample.

The general workflow for phthalate screening via FT-IR starts with an ATR measurement followed by a transmission-based measurement, if needed, for samples with lower concentrations of phthalates. First, the identification of the polymer type via ATR sampling is performed and in the example in Figure 3, it is found to be PVC. The second step, to follow the RoHS regulations, is to run a method to quantify the level of phthalates. When the concentration of total phthalate is high, generally at a single percent level and above, then the item/sample will be classified as non-RoHS-compliant. Alternatively, suppose no phthalates are detected via the ATR sampling method. In that case, the PVC sample is then pressed to about a 500 µm thick film and analyzed in transmission mode to increase the sensitivity (sub-one percent) for detecting and quantifying possible phthalates. If the measured concentration is below 1000 ppm, the result is a ‘negative’ or passing report, or if the concentration of the phthalate is above the 1000 ppm level, the result is ‘positive’ or a failing sample due to the RoHS compliant regulations. If the analysis remains inconclusive, further investigations in the laboratory using liquid chromatography with ultraviolet detector or thermal desorption mass spectrometry coupled will be necessary to obtain the result.

Conclusion

Many manufacturers, importers, and retailers of electric and electronic products have incorporated handheld XRF and FT-IR testing into their workflows as additional insurance and due diligence to ensure regulatory compliance. Regulation authorities worldwide also encourage using those technologies as screening tools to complement traditional lab analysis.

Handheld XRF and FT-IR analyzers are easy-to-operate analytical instruments that require no or little sample preparation compared to lab procedures involving acid dissolution or solvent extractions and subsequent analysis using inductively coupled plasma optical emission spectrometry, UV-visible spectrometry, and liquid or gas chromatography. The full analytical process using Handheld XRF or FT-IR is completed in seconds to a few minutes. Implementing those technologies not only enables a dramatic increase in the total number of samples analyzed and minimizes the cost of lab analysis, but it also greatly reduces the chances of placing non-compliant products and the associated risks, including fines, product recalls, and reputational damage.