Lithium occurs in nutrient solutions primarily as the lithium ion (Li+) . Li+ can increase the chlorophyll content of some plants (e.g., potato and pepper plants). A non-essential micronutrient.

There are different methods for determining lithium:

• Atomic absorption spectroscopy (AAS): High-precision method for determining lithium.
• Flame photometry: A simple and sensitive method for measuring lithium.
• Complexometric titration with EDTA: A less common method, but possible with selected indicators.

Detailed precipitation titration of lithium with ammonium tetraphenylborate

1. Principle of the method

Lithium ions (Li⁺) react with ammonium tetraphenylborate (NH₄BPh₄) and form a poorly soluble precipitate:

The end point of the titration is determined by turbidity or gravimetrically.

2. Chemicals

• 0.01 mol/L ammonium tetraphenylborate solution (NH₄BPh₄)
• Ethanol-water mixture as solvent
• Phenolphthalein as a turbidity indicator

3. Experimental setup

Required equipment:

• Burette (25 mL, division 0.1 mL)
• Erlenmeyer flask (250 mL)
• Pipette (10 mL)
• Magnetic stirrer

4. Implementation

1. Pour 10 mL of the nutrient solution into a 250 mL Erlenmeyer flask.
2. Add 20 mL of ethanol-water mixture.
3. Titrate with 0.01 mol/L ammonium tetraphenylborate solution until a permanent turbidity is visible .

5. Calculation of the lithium concentration

The concentration of lithium is calculated using the formula

:

6. Beispielrechnung:

• Ammoniumtetraphenylborat-Konzentration: 0,01 mol/L
• Verbrauchtes Volumen: 7,5 mL (0,0075 L)
• Probenvolumen: 50 mL (0,050 L)

Fazit

Die Fällungstitration mit Ammoniumtetraphenylborat ist eine zuverlässige Methode zur quantitativen Bestimmung von Lithium in Nährstofflösungen.

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Category: Analysis

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• Lithium (en)

There are different methods for determining manganese:

• Atomic absorption spectroscopy (AAS): High-precision determination of Mn²⁺.
• Oxidimetric titration with KMnO₄: direct determination by redox reaction.
• Complexometric titration with EDTA: Precise determination by chelation.
• Spectrophotometry: Color complex formation with suitable reagents.

Detailed titration of manganese with potassium Permanganate (KMnO₄)

1. Principle of the method

Manganese ions (Mn²⁺) are oxidized by potassium Permanganate (KMnO₄). In acidic solution, Mn²⁺ reacts with KMnO₄ according to the equation:

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• Manganese

Mercury (Hg) is a highly toxic heavy metal that is normally not found in drinking water. However, it can get into the environment through industrial emissions, mining activities or fossil fuels. Due to its toxicity and enrichment in organisms, the detection of mercury in drinking water is of great importance.

Limit values for mercury in drinking water

• EU limit: approx. 1 µg / L (0.001 mg / L) for inorganic mercury
• WHO guideline: approx. 6 µg / L (0.006 mg / L) (depending on the shape of the mercury)

Alternative analytical methods for mercury

• Cold vapor atomic absorption spectrometry (CVAAS): Very sensitive, suitable for trace analysis.
• Inductively coupled plasma mass spectrometry (ICP-MS): Extremely sensitive, detection in the ng / L range.
• Anodic Stripping Voltammetrie (ASV): Electrochemical method with high sensitivity.
• Spectrophotometry with dithizone: Color reaction that enables qualitative proof.

Qualitative detection reaction using dithizone

The method can be used with Dithizone for a qualitative analysis of mercury in drinking water. Dithizon reacts with Hg ²⁺ to form an intense red colored chelate complex.

1. Principle of method

In the reaction, Dithizone is converted to a stable Hg-Dithizone complex with Hg ²⁺:

Hg²⁺+Dithizon→[Hg (Dithizon)]

The resulting complex shows an intense red-violet color that is visible even at very low concentrations.

2. Chemicals

• 0,01 mol/L Dithizon-Lösung (C₁₃H₁₂N₄S)
• Diluted sulfuric acid (H ₂ SO ₄) – to adjust a suitable acidic environment
• Chloroform (CHCl ₃) – optional, for extracting the colored complex to improve visibility
• Pufferlösung (from. B. Essigsäure / Natriumacetate, pH 4 – 5)

3. Experimental setup

Required devices:

• Bürette (25 mL, division 0.1 mL)
• Erlenmeyer flask (250 mL)
• Pipettes (10 mL and 50 mL)
• Magnetic stirrer
• Separating funnel (for chloroform extraction, if used)

4. Implementation

1. Transfer 10 mL of the drinking water sample into a 250 mL Erlenmeyer flask.
2. Add 5 mL of the buffer solution (pH 4 – 5) to adjust the pH.
3. Add 5 mL to the 0.01 mol / L Dithizone solution and mix the sample thoroughly.
4. Optional: perform a chloroform extraction in a separating funnel to isolate the colored complex.
5. Watch the color change. An intense red-violet hue indicates the presence of Hg ²⁺ ions.

Conclusion

The Dithizone test is a qualitative method that, due to its high sensitivity, is suitable for the detection of mercury in drinking water. It can already make Hg ²⁺ concentrations in the µg / L range visible, which is sufficient compared to the legal limit values (approx. 1 – 6 µg / L). However, instrumental methods such as CVAAS, ICP-MS or ASV should be used for a precise quantitative determination.

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• Mercury qualitative analysis

Mercury (Hg) does not occur naturally in plant nutrient solutions. It is a heavy metal that is highly toxic to plants, animals, and humans.

Nevertheless, mercury can enter plants from contaminated soil, water sources, or the air. It is usually absorbed in the form of Hg²⁺ ions or organic mercury compounds such as methylmercury (CH₃Hg⁺).

There are various methods for determining mercury:

• Atomic absorption spectroscopy (AAS): Highly sensitive method for determining traces of mercury.
• Cold vapor atomic absorption spectroscopy (CVAAS): A special form of AAS that is particularly suitable for mercury.
• Inductively coupled plasma mass spectrometry (ICP-MS): High-precision method for determining extremely low mercury concentrations.
• Voltammetry: Electrochemical method for the determination of Hg²⁺ in solutions.
• Spectrophotometry with dithizone: Color reaction of Hg²⁺ with dithizone results in a quantifiable color change.
• Potentiometric titration with dithizone: A rare method for Hg²⁺ detection.

Detailed titration of mercury with dithizone

1. Principle of the method

Mercury ions (Hg²⁺) react with dithizone (C₁₃H₁₂N₄S) in a complexometric titration, forming a stable, colored Hg dithizonate:

The end point of the titration is identified by a clear color change from red to violet .

2. Chemicals

• 0.01 mol/L dithizone solution (C₁₃H₁₂N₄S)
• Sulfuric acid (H₂SO₄, diluted)
• Chloroform (CHCl₃, for extraction)
• Buffer solution (pH 4-5)

3. Experimental setup

Required equipment:

• Burette (25 mL, division 0.1 mL)
• Erlenmeyer flask (250 mL)
• Pipette (10 mL)
• Magnetic stirrer
• Separatory funnel for chloroform extraction

4. Implementation

1. Pour 10 mL of the nutrient solution into a 250 mL Erlenmeyer flask.
2. Add 5 mL of buffer solution (pH 4-5).
3. Add 5 mL of dithizone solution and shake vigorously.
4. Titrate with 0.01 mol/L Hg²⁺ standard until the color changes from red to violet .
5. For better sensitivity, chloroform extraction can be performed.

5. Calculation of the mercury concentration

The concentration of Hg is calculated using the formula:

6. Example calculation:

• Dithizone concentration: 0.01 mol/L
• Consumed volume: 7.2 mL (0.0072 L)
• Sample volume: 50 mL (0.050 L)

Conclusion

Titration with dithizone is a possible method for determining mercury in solutions, but is rarely used because more sensitive techniques such as CVAAS or ICP-MS are more accurate.

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Category: Analysis

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