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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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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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 (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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Düngerstoff-Rechner
für Hydroponik (PPM ⇄ mol ⇄ g/L)

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Molybdenum occurs in nutrient solutions mainly as molybdate ion (MoO₄²⁻) .

There are various methods for determining molybdenum:

• Atomic absorption spectroscopy (AAS): High-precision determination of Mo.
• Thiocyanate spectrophotometry: formation of a red Mo-thiocyanate complex.
• Redox titration with iron(II) sulfate: reduction of molybdenum(VI) to molybdenum(III).

Detailed titration of molybdenum with iron(II) sulfate

1. Principle of the method

Molybdate ions (MoO₄²⁻) are reduced in acidic solution with iron(II) sulfate (Fe²⁺):

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Nickel occurs in nutrient solutions mainly as nickel ion (Ni²⁺) .

There are various methods for determining nickel:

• Atomic absorption spectroscopy (AAS): High-precision determination of nickel.
• Complexometric titration with EDTA: Formation of a stable Ni-EDTA complex.
• Spectrophotometry with dimethylglyoxime (DMG): color development by complex formation.

Detailed titration of nickel with EDTA

1. Principle of the method

Nickel ions (Ni²⁺) react with ethylenediaminetetraacetic acid (EDTA, C₁₀H₁₆N₂O₈) to form a stable complex:

The endpoint of the titration is detected using the murexide indicator . The color change occurs from violet to yellow-orange .

2. Chemicals

• 0.01 mol/L EDTA solution (C₁₀H₁₆N₂O₈)
• Buffer solution (pH 9-10, NH₃/NH₄⁺ buffer)
• Murexide (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 10 mL of buffer solution (pH 9-10).
3. Add 2-3 drops of murexide indicator.
4. Titrate with 0.01 mol/L EDTA until the color changes from violet to yellow-orange.

5. Calculation of nickel concentration

The concentration of Ni is calculated using the formula:

6. Example calculation:

• EDTA concentration: 0.01 mol/L
• Consumed volume: 12.4 mL (0.0124 L)
• Sample volume: 50 mL (0.050 L)
  $c\left(\mathrm{Ni}\right)=\frac{0.0124\cdot 0.01\cdot 1}{1\cdot 0.050}=0.00248\text{mol/L}=2.48\text{mmol/L}$

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Nitrogen is present in nutrient solutions in various forms, including:

• Ammonium (NH₄⁺) – Plant-available, often as NH₄Cl or (NH₄)₂SO₄.
• Nitrate (NO₃⁻) – The most important nitrogen source for plants.
• Organically bound nitrogen – In proteins, amino acids or urea.

The determination is carried out using various methods:

• Kjeldahl method: Digestion of organic nitrogen compounds and titration of ammonium.
• Ion chromatography: separation of NH₄⁺ and NO₃⁻.
• Spectrophotometry: Determination of NO₃⁻ via the Griess reaction.
• Titration: Direct determination of NH₄⁺ with formaldehyde or back titration.

Detailed titration of ammonium with formaldehyde

1. Principle of the method

The titration is based on the reaction of ammonium ions (NH₄⁺) with formaldehyde (HCHO) , which produces methyleneimine (CH₂=NH) and water:

The resulting CH₂=NH increases the pH value as H⁺ ions are consumed. The solution is then back-titrated with hydrochloric acid (HCl) .

2. Chemicals

• Formaldehyde solution (37%)
• Hydrochloric acid (HCl), c = 0.05 mol/L
• Indicator: Methyl red or bromocresol green

3. Experimental setup

Required equipment:

• Burette (25 mL, division 0.1 mL)
• Erlenmeyer flask (100 mL)
• Pipette (10 mL)
• pH meter or indicator paper

4. Implementation

1. Use a pipette to transfer 10 mL of the nutrient solution into a 100 mL Erlenmeyer flask.
2. Add 5 mL of formaldehyde solution and mix well.
3. Add indicator (e.g. methyl red).
4. Titrate with 0.05 mol/L HCl until the color changes from yellow to red.

5. Calculation of the ammonium concentration

The concentration of NH₄⁺ is calculated from the consumption of the HCl solution: 

6. Example calculation:

• HCl concentration: 0.05 mol/L
• Consumed volume: 7.2 mL (0.0072 L)
• Sample volume: 50 mL (0.050 L)
• $c({\mathrm{NH}}_4⁺)=\frac{0.0072\cdot 0.05}{0.050}=0.0072\text{mol/L}=7.2\text{mmol/L}$

Advantages of titration:

• Simple and cost-effective experimental setup.
• Relatively quick implementation.
• Enables precise determination at medium concentrations.

Disadvantages of titration:

• Influence by other nitrogen compounds.
• Requires careful pH control.

Comparison to other methods

Conclusion

The choice of method for nitrogen analysis depends on the specific analytical requirements, the required sensitivity, and the available equipment. Titration is a suitable method for the rapid and cost-effective determination of ammonium, while other methods such as the Kjeldahl method or ion chromatography may be superior in certain contexts.

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Context: The fertilizer calculation program and its results regarding the calculated pH value.

What the program does not do:

• No dynamic chemical equilibrium (no pKa model)
• No exact activity calculation
• No EC/buffering influences

The program currently calculates the pH purely from the net charge of the ion balance , especially from OH⁻ excesses , but:

A real nutrient solution such as Steiner's solution has a complex buffering effect and cannot be calculated solely by the cation/anion balance .

The model calculates:

• Charge balance = cation charge – anion charge
• → if > 0 → interpreted as OH⁻ concentration → basic
• pOH = –log₁₀([OH⁻]), pH = 14 – pOH

BUT:
Just because the net charge is positive does not mean that OH⁻ is present.

Example:

• Ca²⁺, Mg²⁺, K⁺ → no basic ions
• NO₃⁻, PO₄³⁻ → no “strong” acids
• KH₂PO₄ has a buffering acidic effect
• Chelates such as Fe-EDTA have a slightly acidic effect

"We"  suspect OH⁻ , although there is none.

No acid-base reaction in this model

It does not model any of these real effects:

• Proton release / uptake (H⁺, OH⁻)
• Dissociation constants (pKa) of:
  • H₂PO₄⁻ ↔ HPO₄²⁻ + H⁺
  • BOH₃ (boric acid)
  • EDTA complexes
• Buffer systems (e.g. phosphate buffer)

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In chemical analysis, very small masses are measured. The following units are commonly used:

• Milligram (mg): 1 mg = 1 × 10⁻³ g
• Microgram (µg): 1 µg = 1 × 10⁻⁶ g
• Nanogram (ng): 1 ng = 1 × 10⁻⁹ g

Übersichtstabelle

Illustrative examples

To better understand the scale, the following comparisons may be helpful:

• Milligram (mg): One milligram is approximately 1/50 of a drop of water . A single drop of water weighs approximately 50 mg.
• Microgram (µg): A microgram is equal to 1/1,000 of a milligram. You can imagine it as a fraction of a tiny speck of dust or the mass of a small bacterial cell, which is typically in the range of a few micrograms.
• Nanogram (ng): A nanogram is 1/1,000,000 of a milligram or 1/1,000 of a microgram. This corresponds to the mass of a few molecules or tiny particles and is extremely small.

For example, a value of 5 µg/L corresponds to:

• 5 µg/L = 5 × 10 ⁻⁶ g/L

These units and their scientific notation are essential for precisely quantifying very small amounts of substances, as is often the case in environmental analysis and drinking water testing. In chemistry, the mole is also used depending on the situation (usually when specifying concentrations) .

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Simple analytical methods for pesticides, fungicides and herbicides in soil and water

Various methods can be used to analyze pesticides, fungicides, and herbicides in soil and water samples. Especially for laboratories working with commercially available chemicals, the following relatively simple methods are suitable:

1. Thin layer chromatography (TLC)

Thin-layer chromatography is a cost-effective and relatively simple method for separating and qualitatively identifying different classes of pesticides.
Advantages:

• Simple equipment (TLC plates, solvent, UV lamp, spray reagents)
• Fast pre-screening method
• Low costs

After developing the plate, the spots can be visualized under UV light or by special spray reagents to assess the presence of pesticide residues.

2. Enzyme inhibition tests

Enzyme inhibition tests, such as the acetylcholinesterase inhibition test, are particularly suitable for organophosphate pesticides.
Advantages:

• Easy to perform in microtiter plates
• Semi-quantitative assessment of pesticide contamination
• High sensitivity for certain pesticide classes

3. Colorimetric tests

Some pesticides, fungicides, and herbicides react with specific chemical reagents and cause a color change.
Benefits:

• Visual recognition by color change
• No expensive instruments required
• Relatively quick results

4. Immunoassays (e.g. ELISA)

ELISA kits are available for specific pesticides and offer high specificity.
Advantages:

• High specificity and sensitivity
• Fast analysis, often automatable

Note: While these kits are relatively easy to use, they are often expensive and may be less "chemical" in the traditional sense, as they are based on pre-prepared reagents.

Conclusion

Titration methods are generally suitable for determining nutrients present in relatively high concentrations (macronutrients). However, for pesticides, fungicides, and herbicides, which often occur in very low concentrations (trace elements), classic titration reaches its limits.
Recommendations:

• Use thin-layer chromatography (TLC) as a screening method to obtain a qualitative statement about the presence of various active ingredients.
• Complement the detection with enzyme inhibition tests or colorimetric tests for specific pesticide classes.
• If necessary, immunoassays (ELISA) can also be used to refine the results.

Overall, laboratories working with commercially available chemicals, especially TLC, can use simple enzymatic and colorimetric methods to obtain initial indications of the presence of pesticides, fungicides and herbicides in soil and water.

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