Background

European Directives on Recycling and Hazardous Substances

The European Union (EU) has introduced legislation on electrical and electronic equipment in relation to its composition and the levels to which it should be recycled. This legislation has its origin in the EU Directives relating to Waste Electrical and Electronic Equipment (WEEE) and to the Restriction of Hazardous Substances (RoHS) in new products. Manufacturers will need to ensure that their products (and their components) comply in order to sell in the European market. If they do not comply, they will need to redesign their products.

Another EU directive, End-of Life Vehicles (ELV), aims to reduce, or prevent, the amount of waste produced from ELVs and increase the recovery and recycling of materials or components. The ELV Directive banned lead, cadmium, mercury and hexavalent chromium from products, with some exemptions, from 1 July 2002. The RoHS Directive will ban the placing on the EU market of new electrical and electronic equipment containing more than agreed levels of lead, cadmium, mercury, hexavalent chromium, polybrominated biphenyl (PBB) and polybrominated diphenyl ether (PBDE) flame retardants from 1 July 2006. The limits for these substances required by both directives are given in Table 1.

Table 1. Limits for RoHS and ELV directives.

Element	Limit
Pb, Hg, Cr6+, PBB*, PBDE*	0.1wt%
Cd	0.01wt%

Note: *only for RoHS directive

Directives on Materials Recycling in the Rest of the World

In other parts of the world similar directives are being introduced including electronic waste recycling legislation in the USA, often referred to as California RoHS, and the adoption of RoHS in China. Given the rigorous demands of such legislation, X-ray fluorescence spectroscopy (XRF) has emerged as the optimal solution for elemental analysis of heavy metals in a wide variety of materials, including brass.

Analysis of Cadmium and Lead in Brass

This note demonstrates the capability of the Epsilon 5 energy-dispersive XRF spectrometer for the analysis of Cd and Pb in bulk brass samples. In addition, results are presented for the analysis of Cd in brass samples of various shapes and sizes, since such samples are likely to be encountered when analyzing product sub-assemblies.

Measurement Criteria

Measurement criteria The application was set up and calibrated using five brass certified reference materials (MH1 to 5) from MBH Analytical Ltd (UK). The measurement conditions are given in Table 2.

Table 2. Analytical parameters used for the application set-up. *This is the maximum current; for each measurement the current is adjusted to obtain maximum 50% detector dead-time.

Element	Secondary Target	Measurement live time (s)	kV	mA*
Cd	CsI	300	100	6
Pb	Zr	300	100	6

Accuracy

Figures 1 and 2 show calibration curves for Cd and Pb in brass samples and a summary of the calibration data is given in Table 3. These data show a good correlation between the certified concentrations and the measured intensities. The calibration RMS indicates the accuracy of the method. It is a statistical comparison (1 sigma) of the certified chemical concentrations of the standards with the concentrations calculated by the regression in the calibration procedure. In addition, a certified reference material (BNF C48.06) was analyzed as an unknown sample. A comparison of the certified and measured values for Cd and Pb is shown in Table 4.

Figure 1. Calibration curve for Cd in brass.

Figure 2. Calibration curve for Pb in brass.

Table 3. Calibration details.

Element	Cd	Pb
Concentration Range (wt%)	0.0012-0.026	0.0065-0.33
RMS (wt%)	0.0006	0.0072
Correlation coefficient	0.9988	0.9989

Table 4. Results of the analysis of CRM BNF C48.06 as unknown sample.

Element	Cd	Pb
Certified (wt%)	0.008	0.025
Measured (wt%)	00.0078	0.024

Precision and Instrument Stability

CRM BNF C48.06 was measured 20 times consecutively in a single day to show the repeatability of the Epsilon 5. The reproducibility was determined by measuring the same sample once per day over a 10-day period. The repeatability and reproducibility data are shown in Table 5. No drift correction was applied during the precision studies.

Table 5. Repeatability (20 measurements consecutively) and reproducibility (10 measurements over 10 days)

Element	Cd	Pb
Repeatabaility
Mean wt%	0.0077	0.024
RMS	0.00001	0.0016
RMS rel%	1.73	6.43
Reproducibility
Mean wt%	0.0077	0.024
RMS	0.0002	0.0014
RMS rel%	1.95	5.86
CSE
CSE rel%	1.08	3.02

The repeatability and reproducibility are both excellent and are nearly identical. Comparison of the relative RMS values with the counting statistical error (theoretically, the minimum possible error) shows the excellent precision of both the instrument and the method.

Detection Limits

The detection limits for Cd and Pb in brass are given in Table 6 and are based on 100 seconds live time measurement. The higher detection limit for Pb is caused by the very strong absorption of the Pb fluorescent line by the two major elements in brass, Cu and Zn. The LLD’s are calculated from:

Where:

s = sensitivity (cps/ppm)
r_b = background count rate (cps)
t_b = live time (s)

Table 6. Detection limits.

Element	Cd	Pb
LLD (100s)	3.5ppm	30ppm

Analysis of Cd in Brass Samples of Various Shape and Size

It is possible to measure small irregular shaped samples (samples that do not cover the complete opening diameter of the sample cup) by setting up a calibration using the Raleigh line of the secondary target as ratio channel. The intensity of this line has proven to be proportional to the sample size (area) and can thus be used to correct for variations in intensity due to differences in size. For the analysis the small samples were put in a P2 liquid cup in which the sample was fixed between two thin foils (e.g. polypropylene). The samples illustrated in Figure 3 were measured as unknowns and the results are shown in Table 6. A comparison of these results with the results obtained from a subsequent ICP analysis of the samples, shows that there is a very close agreement between the XRF (Epsilon 5) and ICP techniques.

Table 6. Results for the analysis of Cd in brass samples of various size and shape.

Sample Weight (mg)	Cd (ppm) E5 results	Cd (ppm) ICP result
987	71	70
213	37	40
59	66	68
64	67	68