Energy-dispersive X-ray fluorescence spectrometry

The efficiency of X-ray fluorescence spectrometry as a fast screening method for RoHS related samples is demonstrated using the analysis of cadmium in Sicolen^® following the directive for restriction of the use of hazardous substances in electrical and electronics equipment. Red, orange and also green polymers can contain organic cadmium compounds as pigments or stabilizer. In particular, "older" materials can include cadmium concentrations up to the percent range. Cadmium and other hazardous substances according to RoHS, as well as all elements from ₆C/₁₁Na to ₉₂U can be determined quantitatively using energy-dispersive X-ray fluorescence spectrometers such as Shimadzu's EDX series (EDX-700HS/ -800HS/ -900HS) in a fast and reliable way, often without any sample preparation. For the determination of heavy metals in plastic components such as cases or cable insulations down to the ppm range the samples are positioned directly in the large sample compartment as shown in figure 1.

For experimental work, cadmium reference standard material has been used which has been prepared and certified by the Institute of Reference Materials and Measurements (IRMM), Geel, Belgium. These standards have been used for the cadmium calibration showing a very good linearity in the concentration range from 40.9 mg/kg up to 407 mg/kg. All measurements have been performed using a primary molybdenum filter (standard), 10 mm collimator and 300 seconds measurement time. In order to evaluate the calibration curve, another certified cadmium standard has been analysed using the same method. Sicolen^® orange (ref. no. 28/16494) containing 75.9 ± 2.1 mg/kg cadmium in Sicolen^® has been measured in the same way as the standards. The quantitative analysis results in a concentration of 76.5 mg/kg (ppm) cadmium. The result is therefore within the certified tolerance – without further sample preparation and after only 300 seconds of measurement time!

Energy-dispersive X-ray fluorescence spectrometry using the Shimadzu EDX-700HS is a fast and non-destructive method for quantitative determination of heavy metals in polymers. The experimental results of cadmium are also representative for other heavy elements such as lead, mercury, chromium and bromine. Depending on the system configuration, even measurement of the complete element range from ₆C/₁₁Na to ₉₂U is possible.