The RoHS (Restriction of Use of Restricted Substances) regulation limits the concentrations of certain hazardous substances used in the manufacture of electrical and electronic equipment (EEE). The hexavalent form of chromium (Cr(VI) or Cr+6) is among these dangerous substances and should not be above a certain limit according to RoHS regulation.
Limit set for hexavalent chromium (Cr(VI)) under the RoHS regulation:
- 0.1% by weight per homogeneous material, ie 1000 ppm.
Hexavalent chromium is carefully monitored in industry for its toxicity. It can also be found in some coatings used as corrosion inhibitors.
The main methods used for the determination of hexavalent chromium (Cr(VI)):
1. **XRF (X-Ray Fluorescence) Spectroscopy**: XRF can be used for general detection of chromium, but cannot directly distinguish between Cr(III) and Cr(VI). For this reason, XRF is usually used for the initial scan and results are usually verified by another method.
2. **Color methods**: Analysis can be done by spectrophotometric methods using specific color reactions for the detection of Cr(VI). In particular, the diphenylcarbazide reagent reacts with Cr(VI) to form a purple complex.
3. **ICP-MS (Inductively Coupled Plasma-Mass Spectrometer) and ICP-OES (Inductively Coupled Plasma-Optical Emission Spectroscopy)**: These methods can be used for general detection of chromium, but cannot directly distinguish the valence state. Specific determination of Cr(VI) can be made using special procedures during sample preparation.
4. **Ion chromatography**: It is another method used for Cr(VI) detection. This technique can directly detect the Cr(VI) concentration in the sample.
The choice of these methods depends on the sample matrix to be analyzed, the sensitivity required, the detection limits, and other application-specific requirements.
To ensure RoHS compliance, manufacturers and importers must verify that materials and components used throughout the supply chain are Cr(VI) free or below allowable limits. This must be taken into account both during the product design and development phase and during the manufacturing process.