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Cadmium (Cd) analysis for RoHS/WEEE


In today's global marketplace, the regulation of hazardous substances (recognized by RoHS/WEEE as Cr, Cd, Hg, Pb, and Br) in everyday products has become increasingly important to manufacturers and governments.

Current legislation has the maximum allowable level for mercury (Hg), lead (Pb), chrome (Cr), and bromine (Br) at 1000 ppm, while cadmium (Cd) alone is set at no more than 100 ppm permitted in manufactured goods. Cadmium is one of the more difficult contaminants to analyze in the hazardous element suite via XRF. This analysis is difficult for many XRF spectrometers due to the overlap of this particular element with lines from the common rhodium or palladium targets used in most X-ray tubes. Cadmium analysis by WDXRF is made possible through the use of a primary beam filter made of zirconium (Zr) . The Zr acts as an absorber that does not allow the interfering or overlapping palladium K-lines (in the case of the Rigaku Supermini200) from the X-ray tube to overshadow the low level cadmium K-lines.

Historically, this analysis technique has only been available on higher-power WDXRF spectrometers, and usually at a premium price for the instrumentation. Now, Rigaku has brought this necessary analysis into the realm of possibility at a benchtop level with the Rigaku Supermini200 WDXRF spectrometer (Figure 1). Rigaku pioneered the benchtop WDXRF technology and now successfully maintains dominance in this arena through capability of hazardous materials analysis by offering our newest 200 watt benchtop model WDXRF with Zr primary beam filter as a standard component.

Figure 1 shows the typical XRF spectral footprint from the Supermini200 WDXRF Spectrometer with the Pd Kβ Compton line from the X-ray tube occurring at about 15.8° 2θ.

qualitative scan

Figure 1

Figure 2 shows a Qualitative scan done implementing the Zr filter. The image shows where the Cd K-line occurs at 15.3° 2θ. The obvious overlap is effectively removed by the zirconium filter thereby allowing a more accurate and reliable analysis to be achieved for cadmium.

qualitative scan

Figure 2

Using the filter, two polymer samples were analyzed through a quantitative analysis 10x producing the following results (Table 1).

Cd results table
Table 1: Units in ppm

The ability to do Cd analyses in the RoHS/WEEE hazardous element suite has proven to be fast and easy with the benchtop WDXRF Supermini200 system using the standard Zr primary beam filter.