X-ray fluorescence (XRF) is a well-established technology for screening and quantification of toxic metals and compounds. The toxic metal content in electronic goods is regulated by global directives, like RoHS-3, WEEE, ELV, the Administration on the Control of Pollution Caused by Electronic Information Products (Chinese equivalent of RoHS) and other similar directives. All these directives have a slightly different scope but the commonalities are the restriction of cadmium, lead, mercury, hexavalent chromium and several brominated phenylic flame retardants. ASTM F2617- 15 is a well-accepted test method to quantify the concentration of the restricted elements and compounds. This application note demonstrates the capabilities of the Epsilon 1 for small spot analysis to comply with ASTM F2617-15, even with an analyzing spot size of 0.8 x 1.2 mm.
Measurements were performed using an Epsilon 1 EDXRF spectrometer, equipped with a 15 W, 50 kV silver X-ray anode tube, 6 filters, high-resolution silicon drift detector, a collimator to produce a small analyzing spot on the sample and a color camera for sample positioning. The data were 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 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 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) are calculated based on the measurement time.
Table 2. Calibration details
(* RMS: root mean square. The more accurate calibrations have the smaller RMS values). Elements in bold are restricted by RoHS-3 or similar regulations
Figure 2. Calibration graph for Cd. The gray point is the measured intensity for ERM® -EC681k and is not part of the calibration.
Accuracy and precision
The accuracy of the calibration is validated using a globally accepted Certified Reference Material (CRM) from the European Reference Materials institute IRMM: ERM® -EC681k. Two discs were measured 20 times and the average concentrations together with the standard deviations (1 sigma) are shown in the first three columns in Table 3. The average concentrations are in good agreement with the certified concentrations of the CRM.
Table 3. Comparison of the certified and measured concentration of ERM® -EC681k
Elements in bold are restricted by RoHS-2 or similar regulations.
* indicative values only
Complying with ASTM F2617-15
The precision of two successive measurements is an important requirement of ASTM F2617. The test method describes that the maximum difference between two successive measurements can only exceed the maximum permitted difference in 1 out of 20 measurements. The maximum differences between successive measurements and the maximum permitted differences by ASTM F2617-15 are shown in the last two columns of Table 3.
For all the RoHS restricted elements the maximum measured difference was below the limit set by the ASTM test method. The results of the measured differences for lead (Pb) are graphically illustrated in Figure 3. Clearly Epsilon 1 satisfies the requirements set in ASTM F2617-15.
Figure 3. Graphical representation of the repeatability test of Pb in ERM® -EC681k standard, combined with the legal limits of ASTM F2617-15
The results clearly demonstrate the excellent capability of Epsilon 1 for small spot 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-3 or equivalent. Furthermore, the repeatability of the measurements demonstrate that the Epsilon 1 for small spot analysis is a very stable instrument for trace analysis of Cr, Br, Cd, Hg and Pb in compliance with ASTM F2617-15.