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.

Calibration curve for Cd in brass.

Figure 1. Calibration curve for Cd in brass.

Calibration curve for Pb 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)
rb = background count rate (cps)
tb = 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.

Various shaped small brass samples (scale in cm).

Figure 3. Various shaped small brass samples (scale in cm).

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
Conclusions

The Epsilon 5 is fully capable of analyzing Cd and Pb in brass at trace levels. The levels required by the ELV, RoHS and WEEE directives (0.01 and 0.1 wt% for Cd and Pb, respectively) are easily met with the Epsilon 5. Furthermore, in the event that future regulated limits become even stricter (especially for Cd), Epsilon 5 has the performance to quantify Cd five times lower than the current limits. Measurements are accurate and precise and the method benefits from simple, essentially hazard-free, sample preparation. The results show that even small samples, with various shapes, can be analyzed with a high accuracy. The stability of the Epsilon 5 is such that individual calibrations can be used for months or even years. Time consuming re-standardizations are unnecessary and the resulting data are highly consistent over time.