ALEX WENSLEYAlex Wensley is the Metals Lead at Polymer Solutions, an independent testing laboratory. He earned his MS in Materials Science at Virginia Tech and earned his PE licensure in North Carolina. In addition to his strong educational background he has years of experience with forensic and metallurgical engineering, to include failure analysis and quality control work.
The medical device and medical product industries will soon be impacted by pending changes to the Restriction of Hazardous Substances (RoHS) directive, number 2002/95/EC. RoHS is short for Directive on the Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment. It was originally adopted by the EU in February 2003.
It is critical for companies within this marketplace to understand the RoHS directive, analytical approaches to RoHS testing, and sample considerations.
Understanding the RoHS Directive
The RoHS directive in electrical and electronic equipment (2002/95/EC) placed the following limits on certain hazardous substances in manufactured products:
- lead (0.1 wt %);
- mercury (0.1 wt %);
- cadmium (0.01 wt %);
- hexavalent chromium (0.1 wt %);
- polybrominated biphenyls (PBB) (0.1 wt %); and
- polybrominated diphenyl ethers (PBDE) (0.1 wt %).
As it currently stands, the RoHS directive applies to product areas such as IT and telecommunications, consumer, lighting, and electric equipment. Additionally, the directive applies to household appliances, electronic tools, toys, sports equipment, automatic dispensers, and semiconductor devices.
However, additions to the directive (2011/65/EU) will impact medical device and medical product manufacturers in the near future.
As of July 22, 2014, all medical devices and monitoring and control instruments must meet the established RoHS limits. Additionally, as of July 22, 2016, all in vitro diagnostic medical devices will be subject to RoHS mandates.
The Analytical Approach for RoHS Testing
The initial step to ensure compliance with RoHS regulations is to use X-ray fluorescence spectroscopy (XRF) for a screening test. This inexpensive and quick technique scans a sample and determines if the elemental concentrations within a sample are less than the mandated limits. If the sample passes this initial assessment, then it is found to be RoHS compliant and no additional testing is required. Conversely, the sample will be considered to fail RoHS testing if it contains levels of cadmium, mercury, or lead in excess of the listed limits. Chromium and bromine present unique challenges as compared to the other restricted substances.
The XRF only measures the total amount of chromium and bromine present, but does not give any information as to whether the chromium or bromine detected are in acceptable forms. Therefore, the results are inconclusive for chromium if the sample contains in excess of 0.1 wt %. Further testing would be necessary to determine whether the chromium is in an acceptable form, such as trivalent chromium.
Of all the restricted substances, screening for PBB and PBDE by measuring the bromine present is the most difficult analytical challenge. Bromine is only a fraction of the total weight of the brominated compounds. Thus, the allowable bromine level has to be set low enough that the total weight of the compounds does not exceed the 0.1 wt % limit. To account for this, the allowable limit is set to 0.023 wt % when conducting the screening.
If the initial screening provides inconclusive results for any of the restricted substances, a more in-depth analysis should be performed. The following analytical techniques can be used for a more thorough analysis:
- Inductively coupled plasma (ICP) is used for a more in-depth analysis of the levels of lead, mercury, and cadmium.
- Gas chromatography coupled with mass spectrometry (GC-MS) can be used if bromine was measured higher than 0.023% during screening. This technique can determine if the levels of bromine measured are PBB or PBDE.
- Ultraviolet-visible spectroscopy (UV-Vis) is the analytical tool used if chromium is measured higher than 0.1% during screening, as Uv-Vis can determine if the form of chromium present is hexavalent.
Sample Considerations for RoHS Testing
There are three critical sample considerations to bear in mind when submitting a product or device for RoHS compliance testing: sample size, the sample matrix, and the homogeneity of the sample.
Many XRF’s commonly measure samples from 3 to 8 millimeters in diameter, and the minimum thickness depends on the density of the material. Lightweight polymer samples can have a minimum thickness of a few millimeters, while denser samples, like heavy metals, can have a minimum thickness of tens of micrometers. If polymer samples are too thin, then they can be stacked in layers to compensate or the operator could increase the XRF scan time.
Different sample matrices can yield different XRF quantitations. For instance in polymers, concentrations of restricted substances in polyethylene (PE) will read higher than equivalent levels of restricted substances in poly-vinyl chloride (PVC) because the PVC matrix will absorb certain x-rays. Knowing the sample matrix will help the testing lab calibrate their equipment accordingly to ensure accurate results.
If a sample matrix is homogenous, then testing only has to be performed once and the cost to the client is minimised. If the sample matrix is not uniform, then the sample can be tested multiple times in different locations or the sample can be prepared in such a way that it becomes homogenous.
Partner with an Educated and Experienced Lab
When seeking RoHS testing ensure you partner with a testing lab that understands the mandates, the analytical approach, and the vital sample considerations. The lab should have the equipment, expertise, and quality system necessary to provide accurate analysis and reliable results.
About the author: Alex Wensley is the Metals Lead at Polymer Solutions, an independent testing laboratory. He earned his MS in Materials Science at Virginia Tech and earned his PE licensure in North Carolina. In addition to his strong educational background he has years of experience with forensic and metallurgical engineering, to include failure analysis and quality control work.