Development and use of screening methods to determine chromium (VI) and brominated flame retardants in electrical and electronic equipment
The International Electrotechnical Commission published an international standard in January 2009, including procedures for the determination of RoHS substances in electrotechnical products, IEC 62321³.
The standard will be available from IEC or Danish Standards.
Neither the RoHS Directive nor the Danish Executive Order prescribes that analyses should be performed in accordance with a particular standard, but in future, IEC 62321 will obviously be used internationally to test electrical and electronic products for RoHS compliance.
A detailed description of how to perform the analyses can be found in IEC 62321, and the description below only covers the analysis principles.
IEC 62321 describes one method for determination of PBDEs and PBBs in polymers: gas chromatography combined with mass spectrometry (abbreviated GC/MS).
The first step is to extract the substances from the plastic - in many cases a time-consuming process requiring harsh solvents. The solvent used depends on the type of plastic, which, if unknown, it is necessary to determine by means of infrared spectroscopy or similar methods. Possible solvents include acetone, tetrahydrofuran, toluene, hexane, methylene chloride, chloroform and methanol. According to the standard, an exact determination of PBDEs or PBBs cannot be expected for polymer types that are not easily soluble.
After extraction, inject the sample into a gas chromatograph in order to separate the substance congeners and determining the congener concentration using a mass spectroscope connected with the gas chromatograph.
The results will typically be reported as the sum of the different groups of congeners as follows:
The total concentration of PBDEs is calculated by adding the concentration of all PBDE congeners (a similar procedure is used for PBBs). As mentioned in Chapter 2, the technical products will typically contain a mixture of several congeners.
IEC 62321 describes two methods for testing the presence of chromium(VI) in chromated surfaces of metallic pieces and one method for quantitative determination of chromium(VI) in materials.
All the methods are based on colorimetric determination of the chromium(VI) content. The methods are based on the reduction of chromium(+VI) to chromium(+III) in a reaction with 1.5 diphenylcarbazide oxidised to 1.5 diphenylcarbazone, which yields a characteristic reddish purple colour with an absorption maximum of approx. 540 nm.
The result is typically given in mg/L in the test liquid, which can be converted to mg of chromium(VI)/cm² surface, if the surface area of the sample is known. As the chromium layer constitutes only a very small part of the sample, a conversion to the concentration in the total sample will presumably show a chromium(VI) concentration far below 0.1%. Consequently, the result cannot be used directly to determine whether the sample includes a homogeneous material containing more than 0.1% chromium(VI), and the standard does not provide any instructions as to the interpretation of results in relation to the limit value of 0.1%.
If the thickness of the chromium layer is known, a rough estimate of the concentration of chromium(VI) in this layer can be made. There is no easy method to measure the thickness of the layer, and it is therefore necessary to use literature values for the type of chromium passivation in question. For example, the passivation layer for a yellow passivation on zinc (yellow chromated) is typically 0.3 - 0.6 µm. In connection with the screening method development, calculations of the concentration in the passivation layer have been made for different yellow chromated screws, assuming a layer of 0.45 µm and extraction of all the chromium(VI) in the layer. According to the calculations, a concentration of 0.1% in the surface layer would correspond to measuring approx. 0.1 mg/L in the test liquid (see Annex 1 for more details). It could thus be calculated that the yellow chromated screws tested contained 0.1 - 6.6% chromium(VI) in the 0.45 µm thick surface layer. For blue chromated and bright surface layers that are thinner than the yellow ones, 0.1% in the surface layer would correspond to a lower concentration in the test liquid. It is therefore fair to assume that a concentration of >0.1 mg/L in the test liquid means that there is more than 0.1% in a homogeneous material. This is an interpretation, however, and there is no official statement to the effect that the test results can be converted in this way.
IEC 62321 describes one method for determination of chromium(VI) in materials: The method can be used to determine chromium(VI) in plastic and other homogeneous materials. The method cannot be used to determine chromium(VI) in thin coatings for which the test methods described above should be applied.
As mentioned, the method is based on colorimetric determination of the chromium(VI) content. The method is based on the reduction of chromium(+VI) to chromium(+III) in a reaction with 1.5 diphenylcarbazide oxidised to 1.5 diphenylcarbazone, which yields a characteristic reddish purple colour with an absorption maximum of approx. 540 nm.
The first step is an extraction where about 5 g of the material is placed in an extraction container and chromium(VI) is extracted at 90-95°C with an alkaline solution of sodium hydroxide (NaOH) and sodium carbonate (Na2CO3). The chromium(VI) content in the filtered sample is determined by adding 1.5 diphenylcarbazide and measuring the absorbance at 540 nm using a spectrophotometer. The result is typically given in mg/kg of chromium(VI) and can be used directly to determine whether the material contains < 0.1% chromium(VI).
Presumably, the estimated price of a determination of chromium(VI) in a plastic is approx. DKK 3,200 for the first analysis and DKK 2,500 for the subsequent analyses (excluding VAT, February 2009).
 Electrotechnical products - Determination of levels of six regulated substances (lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls, polybrominated diphenyl ethers)