Conformity Magazine - June 2008 - (Page 14)

Protecting consumers and the environment from hazardous materials is nothing new for manufacturers and regulatory agencies. In July 2006, in response to the growing need for regulatory control over hazardous materials, the European Union initiated the restriction of hazardous substances (RoHS) directive. In order to meet RoHS and other impending regulations, as well as avoid the monetary fines associated with lead-contaminated products, appropriate, properly performed testing is a must. Many techniques can be used to identify and quantify lead so customers aren’t put in danger. However, in order to get accurate results, some of the most common methods result in destruction of the product, raising costs for the manufacturer, distributor and reseller. Currently, X-ray fluorescence is the only detection technique that offers high-precision, non-destructive analysis to detect lead in metals, powders, ceramics, rubber, plastics and liquids. This article looks at various methods of lead detection and will specifically analyze the advantages and applications of energy dispersive X-ray fluorescence (EDX), with an overview of recent environmental regulations. Locating the Contaminate There are two main areas of concern for contamination, the surface and substrate. The surface finish can be a variety of materials, paint, resin or metal. The surface is the first area of concern because this part has the most direct contact with the user. Contamination in the surface has the highest possibility of exposure or transfer to its user, with oral exposure being of particular concern. Not to be overlooked is the substrate surface. Over time, the surface will wear off, exposing the user to the substrate and any contamination therein. As an example, the outer surface of a pen may be completely lead-free and harmless. Below the surface, however, components of the pen may contain contaminated parts. Over time and use, the surface of the pen may wear off, exposing users to the contaminated portion. This could be the case with any product, from children’s toys to electrical wire coatings. Common Lead Detection Techniques Manufacturers can use many techniques to identify and quantify lead. Two very popular and commonly used methods are inductively coupled plasma (ICP) and atomic absorption (AA). ICP is primarily used to detect trace metals in environmental samples by measuring characteristic wavelength specific light emitted by the atoms of an element. The light is converted to an electrical signal to be measured quantitatively. To make quantitative measurements of samples, ICP must be used in conjunction with other analytical equipment such as mass spectrometers or atomic emission spectrometers. 14 Conformity JUnE 2008 For example, the light emitted by the sample in the ICP is converted to electrical signals by the photomultiplier in the spectrometer.1 AA uses the absorption of light to determine the concentration of a particular metal in a sample. The analyte concentration is determined from the amount of light it absorbs. A working curve is used to determine concentration measurements after calibrating the instrument with standards of known concentrations.2 Because these techniques require the sample to be in an aqueous or gaseous form, ICP and AA are both destructive measurements. In addition, intensive sample prep can be required. For samples containing plastics or metal, this can be a daunting task, requiring a lot of time and dangerous chemicals. Non-Destructive X-Ray Detection Methods X-ray is another commonly used technique because it is nondestructive and saves manufacturers time and cost in product damage for testing. There are three X-ray techniques: X-ray diffraction, wavelength dispersive X-ray and energy dispersive X-ray. X-ray diffraction (XRD) is based on observing the scattering pattern of X-rays from the sample in order to determine its structure, composition or other physical properties. XRD measurements provide routine identification and quantification of crystal phases in powder and polycrystalline samples. XRD is not suitable for the type of analysis discussed here as the structure of the molecules and other physical properties are not the issue. The wavelength dispersive X-ray (WDX) spectroscopy method counts the number of X-rays of a specific wavelength diffracted by a crystal. As shown in Figure 1, X-rays focused on a sample fixed on the axis of the spectrometer (goniometer) are diffracted by the sample. The changes in the diffracted X-ray intensities are measured, recorded and plotted against the rotation angles of the sample. The result is referred to as the X-ray diffraction pattern of the sample. Computer analysis of the peak position and intensities associated with this pattern enables qualitative analysis, lattice constant determination and stress determination of the sample. WDX only reads/counts the X-rays of a single wavelength, not producing a broad spectrum of wavelengths or energies. This can severely limit the amount of quantitative data garnered from the test. At times, WDX can produce better energy resolution and less background noise. However, such disadvantages as more analysis time, more sample damage and high cost outweigh the advantages for most manufacturers. Energy dispersive X-ray (EDX) is, by far, the easiest of the techniques and the most cost effective for screening consumer products. EDX permits non-destructive rapid measurement

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Conformity - June 2008 Contents Editor's Note 700 MHz Auction Raises a Record $20 Billion FCC Modifies PCS and AWS Power Limit Rules for Broadband Wireless Commission Designates Spectrum Test Bed FCC Releases Report on Wireless Competition Commission Proposes $5 Million Fine for Slamming Using EDX for Non-Destructive Detection of Lead in Consumer Products ESD Open Forum Challenges in Testing - Improving Election Security and Accuracy Part 1 Challenges in Testing - Human Body Model: The Hidden Challenges High-Speed Signal Integrity Considerations for ESD Components Focus On...EMC Components Buyer's Guide FCC Levies $2.6 Million Fine for Junk Faxes FDA Updates Guidance on its Product Review Process EU Issues Updated Energy Star Regulations EU Repeals Directive on Veterinary Electro-Medical Equipment New Product Announcements Updated Standards List for the EU's PPE Directive CPSC Announces New Effort to Keep Out Hazardous Products CPSC Actions in the News IEC Standards Update UL Standards Update Product Reviews Telcordia Standards Update From Our "You Can't Make This Stuff Up" Department Looking Back: Items from Past Issues of Conformity Advertisers

Conformity - June 2008

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