Cadmium (Cd) is a toxic heavy metal that can get into drinking water through industrial processes, agricultural activities or corrosion of pipes. It can cause kidney, liver and bone damage.
Limit values for cadmium in drinking water
- EU limit (according to Directive 98/83 / EC): 5 µg / L (0.005 mg / L) [Source]
- WHO guideline: 3 µg / L (0.003 mg / L) [Source]
- EPA (USA) limit: 5 µg / L (0.005 mg / L) [Source]
Qualitative detection reactions for cadmium
There are various methods for the qualitative detection of cadmium in aqueous solutions. However, it should be noted that many of these methods do not have the sensitivity required to detect the low concentrations that are permitted in drinking water according to the limit values mentioned above.
1. Detection with dithizone
Principle: With cadmium ions, dithizone forms a colored complex that shows an intense color.
Detection limit: The detection limit for cadmium with dithizone is approximately 3 µg / L (0.003 mg / L), which corresponds to the WHO guideline. [Source]
Rating: Suitable. Due to the sufficient sensitivity, the dithizone test can be used for the qualitative detection of cadmium in drinking water.
2. Detection with potassium iodide (KI test)
Principle: Cadmium ions react with potassium iodide to cadmium iodide under certain conditions.
Detection limit: The exact detection limit is not clearly documented, but is typically in the range of mg / L.
Rating: Due to the higher detection limit, this test for the detection of cadmium in drinking water is below the legal limit values not suitable.
3. Detection with sulfuric acid (H ₂ SO ₄ test)
Principle: Cadmium ions can react with sulfuric acid under certain conditions.
Detection limit: Similar to the AI test, the detection limit is in the range of mg / L.
Rating: Not sensitive enough for the detection of cadmium in drinking water below the legal limit values.
More sensitive methods for trace analysis
Instrumental methods are used for a more precise determination of cadmium in drinking water:
- Atomic absorption spectroscopy (AAS): Very precise method for traces of cadmium with a detection limit of up to 0.1 µg / L. (Source)
- ICP-MS (Inductively Coupled Plasma Mass Spectrometry): Extremely sensitive, cadmium can detect in the ng / L range.
- Anodic Stripping Voltammetrie (ASV): Electrochemical method for trace analysis.
Conclusion
The qualitative analysis of cadmium can be carried out with dithizone, since this test has sufficient sensitivity to detect the low concentrations that are permitted in drinking water according to the legal limit values. Other classic detection methods such as the potassium iodide or sulfuric acid test are not suitable for this purpose due to their higher detection limits. Instrumental methods such as AAS or ICP-MS are recommended for precise quantitative determination.
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