Lead
Precise rapid tests for water and waste water samples
In nature, Lead is only rarely found as a genuine metal (pure element). In bound form, exclusively lead(II) compounds are found, especially sulfides, such as galena (PbS), and salts. Certain types of drinking water can dissolve lead compounds depending on the percentages of oxygen and free carbon dioxide. Due to use of lead pipes in water pipelines, special care should be exercised here, as lead compounds are highly toxic. This is a particular problem with soft waters. In hard water, lead carbonate and lead sulfate are formed on the inner wall of lead pipes. Thereby, the lead is protected from further attack of the water.
Lead is primarily used due to its very good corrosion resistance to mineral acids. In addition, it is a malleable metal with a low melting point and low hardness but high density. Therefore, lead is widely used in batteries and also for absorption of X-rays or gamma rays.
Lead compounds are toxic, since they inhibit hemoglobin synthesis.
Our Lead Products
Reaction basis 🧪
Depending on the test (NANOCOLOR® tube or standard test), one of two different reactions is underlying:
(a) PAR method: Lead(II) ions form a red dye with 4-(pyridyl-2-azo)resorcinol (PAR) in the presence of cyanide. In the presence of interfering heavy metals, the red dye is selectively destroyed. In this case the corresponding color weakening is evaluated photometrically. The photometric determination is carried out at 520 nm.
(b) Dithizone method (solvent extraction method): Lead(II) ions react with dithizone (diphenyl thiocarbazone) in the presence of cyanide to form primary lead dithizonate. This is converted to a pink complex by liquid extraction in an organic phase (e.g. tetrachlorethylene or carbon tetrachloride). Dithizone (C13H12N4S) is a powder whose needles have a purplish-black metallic sheen.
Sample preservation 🧪
After adjusting the pH to a value of 1–2 with nitric acid, the sample can be preserved for storage for up to 1 month (storage vessel: PE or glass bottle).
Tips & tricks 🧪
- Decomposition
- The decomposition cannot be performed with NANOCOLOR® NanOx Metal. The reagents therein contain carbonates that form insoluble lead carbonate with the lead ions. Detection is then no longer possible.
- Background information
- Only dissolved lead(II) ions are detected. For the determination of total lead, decomposition with the decomposition kit (REF 918 08) must be performed prior to analysis.
- Sea water suitability
- Sea water analysis is not possible.
- pH
- The pH of the sample must be complied with in both methods.In the PAR method this is around 3–6, in the dithizone detection method at 1–3. If necessary, adjust the pH with nitric acid or sodium hydroxide.
- Interferences
- Many ions influence the detection reaction with PAR, which can result in deviating results. The instruction leaflet of the tube test specifies these ions.
- Dithizone forms stable complexes with other thiophilic (“sulfur-loving”) ions as well. Therefore some ions interfere. Exact specifications as to which ions interfere in what concentrations are indicated in the instruction leaflet.
- Further interfering ions are listed in the instruction leaflet.
- Turbidity
- Turbid solutions must be filtered prior to the determination of dissolved lead; turbidity leads to incorrect results: For coarsely dispersed turbidities, use qualitative filter paper (e.g. MN 615), for moderately dispersed turbidities, use glass-fiber paper (e.g. MN 85/70 BF) or or membrane filtration set GF/PET 0.45 μm, for finely dispersed turbidities, use membrane filtration kit 0.45 μm or GF/PET 0.45 μm.
