Arsenic (As) is a toxic metalloid that can be naturally occurring or enter drinking water through industrial processes. Long-term exposure to arsenic can lead to serious health problems such as skin lesions, cancer, and neurological disorders. First of all, only instrumental methods are suitable: HG-AAS, ICP-MS, etc.
Limit values for arsenic in drinking water
- Current limit in Germany (since 2013): 10 µg/L (0.01 mg/L) [Source]
- Planned limit value (from June 24, 2023): 4 µg/L (0.004 mg/L) [Source]
Qualitative detection reactions for arsenic
Various methods exist for the qualitative detection of arsenic in aqueous solutions. However, many of these traditional methods lack the sensitivity required to detect the low concentrations permitted in drinking water according to the above-mentioned limits.
1. Bettendorf test
Principle: Reduction of arsenic(III) ions by tin(II) chloride in hydrochloric acid solution, forming a brown precipitate of elemental arsenic.
Detection limit: The exact detection limit is not clearly documented, but is typically in the range of mg/L.
Assessment: Due to the relatively high detection limit, this method is not suitable for the detection of arsenic in drinking water below the legal limit values .
2. Gutzeit test
Principle: Formation of arsine (AsH₃) by reaction of arsenic with zinc and acid; AsH₃ reacts with silver nitrate paper to form a yellowish-brown stain.
Detection limit: This method is more sensitive than the Bettendorf assay, but may still have difficulty reliably detecting concentrations in the range of a few µg/L.
Assessment: Although more sensitive, this method is only partially suitable for the detection of arsenic in drinking water close to the current limit values .
More sensitive methods for trace analysis
Instrumental methods are used for the accurate determination of arsenic in drinking water:
- Atomic absorption spectroscopy with hydrogenating technique (HG-AAS): Very precise method for arsenic determination in trace levels.
- ICP-MS (Inductively Coupled Plasma Mass Spectrometry): Extremely sensitive, can detect arsenic in the ng/L range.
Conclusion
Most conventional qualitative detection methods, such as the Bettendorf or Gutzeit assay, are unsuitable for detecting arsenic in drinking water below legal limits due to their higher detection limits. Therefore, instrumental methods such as HG-AAS or ICP-MS are recommended for precise qualitative and quantitative determination of arsenic in drinking water.
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