XRF is a well-established technology for screening and quantification of toxic metals and compounds regulated by global directives, like RoHS-3/WEEE/ELV, ‘Chinese RoHS’: Administration on the Control of Pollution Caused by Electronic Information Products and similar directives. All these directives have a slightly different scope but the commonalities are the restriction of lead, cadmium, mercury, hexavalent chromium and several brominated phenylic flame retardants. ASTM F2617 is a well-accepted test method to quantify the concentration of the restricted elements and compounds. This work demonstrates the capabilities of the Epsilon 1 to comply with ASTM F2617.
Measurements were performed using an Epsilon 1 EDXRF spectrometer, equipped with a 50 kV X-ray silver anode tube, 6 filters and a high-resolution silicon drift detector. The data was automatically processed by the Epsilon 1 software. Figure 1 shows an XRF spectrum of one of the RoHS Calibration Standards and illustrates the excellent detector resolution.
Figure 1. XRF spectrum of RoHS Calibration Standard
RoHS Calibration Standards
A set of reference materials for the analysis of RoHS elements in polyolefins has been developed in collaboration with DSM Resolve. The basic RoHS Calibration Standards set consists of two discs each of five different standards, including a blank. Additionally, commonly found additive and filler elements (As, Zn, Sn, Sb) have been added to provide users with unique and relevant reference materials.
Two disks of each of the five different standards were analyzed, using two measurement conditions (Table 1). The total measurement time was only 10 minutes per standard.
Table 1. Measurement conditions
Accurate calibration results
Detailed calibration results are shown in Table 2 where the RMS value equals 1 sigma standard deviation. The lower limits of detection (LLD; 3 sigma, 300 s) are also shown in Table 2.
Table 2. Calibration details (* RMS: Root Mean Square. The more accurate calibrations have the smaller RMS values). Elements in bold are restricted by RoHS or similar regulations.
The accuracy of the calibration is checked using a globally accepted Certified Reference Material from the Institute for Reference Materials and Measurements (IRMM): ERM® -EC681k. The measured concentrations are in good agreement with the certified concentrations for the most important RoHS elements, Table 3.
Table 3. Comparison of the certified and measured concentration of ERM® -EC681k
Accurate calibration results (cont.)
Figure 2 shows the calibration graph for Cd. The graph illustrates the very good correlation between the cadmium concentrations and the measured intensities.
Figure 2. Calibration graph for Cd. The green point is the measured intensity for ERM® -EC681k
To test the instrument precision, RoHS Calibration Standard was measured more than 600 times consecutively, over five days, Figure 3. The average concentration, certified concentration, maximum difference between successive measurements and maximum allowed difference by ASTM F2617 are listed in Table 4. Clearly Epsilon 1 satisfies the requirements set in ASTM F2617, which allows excedence of the difference only in one case in twenty.
Table 4. Repeatability results of RoHS Calibration Standard
Figure 3. Graphical representation of the repeatability test of Cd in RoHS Calibration Standard, measured over five days, combined with the legal limits.
The results clearly demonstrate the excellent capability of Epsilon 1 for the analysis of Cr, Br, Cd, Hg, Pb, Zn, As, Sn and Sb in polyolefins. The high resolution and sensitivity of the silicon drift detector combined with powerful software algorithms make it possible to quantify traces of metals within the limits required by environmental regulations like RoHS or equivalent. Furthermore, the repeatability of the measurements demonstrate that the Epsilon 1 is a very stable instrument for trace analysis of Cr, Br, Cd, Hg and Pb in accordance with ASTM F2617.