Analysis

Analysis

Quantitative Analyse von Aluminium

Aluminum occurs in nutrient solutions primarily as the aluminum ion (Al³⁺) or as hydroxo complexes. Essential for some plants (e.g., peas, corn, sunflowers, and cereals). Can be toxic to some plants at concentrations above 10 ppm. Sometimes used to produce flower pigments (e.g., hydrangeas). Variable micronutrient.

There are different methods for determining aluminum:

Complexometric titration with EDTA: Formation of a stable Al-EDTA complex.
Spectrophotometry with eriochrome cyanine R: color development by complex formation.
Atomic absorption spectroscopy (AAS): High-precision determination of aluminum.

Detailed titration of aluminum with EDTA

1. Principle of the method

Aluminum ions (Al³⁺) react with ethylenediaminetetraacetic acid (EDTA, C₁₀H₁₆N₂O₈) to form a stable chelate complex:

Al ³⁺ + EDTA ⁴⁻ \to [Al(EDTA)] ⁻

The endpoint of the titration is detected using the xylenol orange indicator. The color changes from yellow to red .

2. Chemicals

0.01 mol/L EDTA solution (C₁₀H₁₆N₂O₈)
Buffer solution (pH 5, acetate buffer)
Xylenol orange (indicator)

3. Experimental setup

Required equipment:

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

4. Implementation

Pour 10 mL of the nutrient solution into a 250 mL Erlenmeyer flask.
Add 10 mL of acetate buffer solution (pH 5).
Add 2-3 drops of xylenol orange indicator.
Titrate with 0.01 mol/L EDTA until the color changes from yellow to red.

5. Calculation of the aluminum concentration

The concentration of Al³⁺ is calculated using the formula:

c (Al ³⁺) = \frac{V EDTA \cdot c EDTA \cdot \frac{1}{1}}{V Probe}

6. Example calculation:

EDTA concentration: 0.01 mol/L
Consumed volume: 7.8 mL (0.0078 L)
Sample volume: 50 mL (0.050 L)

c (Al ³⁺) = \frac{0.0078 \cdot 0.01 \cdot 1}{1 \cdot 0.050} = 0.00156 mol/L = 1.56 mmol/L

Conclusion

Complexometric titration with EDTA is a reliable method for the quantitative determination of aluminum in nutrient solutions.

Other names for xylenol orange:

- C₃₁H₃₂N₂O₁₃S
- C₃₁H₂₈N₂Na₄O₁₃S (Tetranatriumsalz)
- 3,3-Bis(N,N-bis(carboxymethyl)aminomethyl)kresolsulfonphthalein

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legend

PA: Stands for "pro analysi" or "analytically pure" and means that the substance can be used for analytical procedures, as the content of foreign substances is specified.
ACS: Stands for American Chemical Society and refers to chemicals that meet the standards of the American Chemical Society.

Chemicals and laboratory equipment required for nutrient analysis in hydroponic solutions

We recommend titration for home analysis. This is by far the most cost-effective method and, for occasional tests, probably the most sensible one in terms of cost and effort.

Here you will find a summary of the chemicals and laboratory equipment you will need to analyze the respective components in your nutrient solutions. The articles on the respective tests, with a detailed procedure for each "substance" and a sample calculation, can be found in the Analysis section .

Chemicals reference :

https://www.carlroth.com/de/de/massloesungen/massloesungen-utility-ready/c/web_folder_716991

https://www.laboratoriumdiscounter.nl/de/chemikalien/

Burette straight NS stopcock 50 ml graduation 01 ml

Necessary material

Burette:

25ml in increments from 0.1ml to 0.05ml, available from Amazon to Aliexpress for prices ranging from approximately €25 to €660. The price difference also lies in the quality.

Magnetic stirrer + magnetic stir bar. No heating is necessary for our analyses :

Magnetic stirrers cost €30 to €300. You can also purchase them from lab supply retailers. These prices should be viewed with skepticism. They can exceed €1,000. Personally, I don't understand where the additional costs come from.

Erlenmeyer flask:

Approximately €5 to €50. The flask used for the analysis does not need to be heat-resistant (borosilicate glass/Pyrex), so you can also perform the titration in a drinking glass.

Necessary chemicals

Analysis of aluminum (Al)

Chemicals required:

0.01 mol/L EDTA solution (C₁₀H₁₆N₂O₈)
Buffer solution (pH 5, acetate buffer)
Xylenol orange (indicator)

Required laboratory equipment:

burette
Erlenmeyer flask
pipette
Magnetic stirrer

Analysis of arsenic (As)

Chemicals required:

0.01 mol/L iodine solution (I₂)
1 mol/L hydrochloric acid (HCl)
0.1 mol/L sodium thiosulfate solution (Na₂S₂O₃)
Starch solution (indicator)

Required laboratory equipment:

burette
Erlenmeyer flask
pipette
Magnetic stirrer

Analysis of Lead (Pb)

Chemicals required:

0.01 mol/L EDTA solution (C₁₀H₁₆N₂O₈)
Acetic acid/acetate buffer solution (pH 5-6)
Xylenol orange (indicator)

Required laboratory equipment:

burette
Erlenmeyer flask
pipette
Magnetic stirrer

Analysis of boron (B)

Chemicals required:

Sodium hydroxide (NaOH, 0.01 mol/L) – for the titration of boron.
Mannitol – to form the boron-mannitol complex.
Phenolphthalein – as an indicator for color detection.

Required laboratory equipment:

burette
Erlenmeyer flask
pipette
Magnetic stirrer

Analysis of Calcium (Ca)

Chemicals required:

EDTA (0.01 mol/L) – for titration of calcium.
Eriochrome Black T – as an indicator for color recognition.
Ammonia buffer solution (pH 10) – to stabilize the pH value.

Required laboratory equipment:

burette
Erlenmeyer flask
pipette
Magnetic stirrer

Analysis of chlorine (Cl)

Chemicals required:

Silver nitrate (AgNO₃, 0.01 mol/L) – for the precipitation of chloride as AgCl.
Potassium chromate (K₂CrO₄) – as an indicator for Mohr titration.
Nitric acid (HNO₃, 1 mol/L) – to control the pH value.

Required laboratory equipment:

burette
Erlenmeyer flask
pipette
Magnetic stirrer

Analysis of iron (Fe)

Chemicals required:

EDTA (0.01 mol/L) – for titration of iron.
Xylenol orange – as an indicator for color recognition.
Acetic acid/sodium acetate buffer solution (pH 5-6) – to control the pH value.

Required laboratory equipment:

burette
Erlenmeyer flask
pipette
Magnetic stirrer

Analysis of Potassium (K)

Chemicals required:

Sodium tetraphenylborate (Na[B(C₆H₅)₄]) – for the precipitation of potassium.
Indicator (e.g. toluene extract) – for color detection.

Required laboratory equipment:

burette
Erlenmeyer flask
pipette
Magnetic stirrer

Analysis of cobalt (Co)

Chemicals required:

0.01 mol/L EDTA solution (C₁₀H₁₆N₂O₈)
Buffer solution (pH 10, NH₃/NH₄⁺ buffer)
Eriochrome Black-T (indicator)

Required laboratory equipment:

burette
Erlenmeyer flask
pipette
Magnetic stirrer

Analysis of Copper (Cu)

Chemicals required:

EDTA (0.01 mol/L) – for titration of copper.
Indicator (e.g. Eriochrome Black T) – for color recognition.
Ammonia buffer solution (pH 10) – to stabilize the pH value.

Required laboratory equipment:

burette
Erlenmeyer flask
pipette
Magnetic stirrer

Analysis of lithium (Li)

Chemicals required:

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

Required laboratory equipment:

burette
Erlenmeyer flask
pipette
Magnetic stirrer

Analysis of magnesium (Mg)

Chemicals required:

EDTA (0.01 mol/L) – for titration of magnesium.
Indicator (e.g. Eriochrome Black T) – for color recognition.
Ammonia buffer solution (pH 10) – to stabilize the pH value.

Required laboratory equipment:

burette
Erlenmeyer flask
pipette
Magnetic stirrer

Analysis of manganese (Mn)

Chemicals required:

Potassium permanganate (KMnO₄, 0.01 mol/L) – for the titration of manganese.
Sulfuric acid (H₂SO₄, 1 mol/L) – for dissolving manganese compounds.
Indicator (e.g. Murexide) – for color detection.

Required laboratory equipment:

burette
Erlenmeyer flask
pipette
Magnetic stirrer

Analysis of molybdenum (Mo)

Chemicals required:

Iron(II) sulfate (FeSO₄, 0.01 mol/L) – for the titration of molybdenum.
Sulfuric acid (H₂SO₄, 1 mol/L) – to control the pH value.
Distilled water – for dilution.

Required laboratory equipment:

burette
Erlenmeyer flask
pipette
Magnetic stirrer

Analysis of nickel (Ni)

Chemicals required:

0.01 mol/L EDTA solution (C₁₀H₁₆N₂O₈)
Buffer solution (pH 9-10, NH₃/NH₄⁺ buffer)
Murexide (indicator)

Required laboratory equipment:

burette
Erlenmeyer flask
pipette
Magnetic stirrer

Analysis of phosphorus (P)

Chemicals required:

Lanthanum(III) chloride (LaCl₃, 0.01 mol/L) – for the titration of phosphate.
Nitric acid (HNO₃, 1 mol/L) – to control the pH value.
Sodium rhodizonate – as an indicator for color detection.

Required laboratory equipment:

burette
Erlenmeyer flask
pipette
Magnetic stirrer

Analysis of sulfur (S)

Chemicals required:

Barium sulfate solution (BaSO₄) – for precipitating the sulfur.
Diluted HCl – for acid adjustment.
Indicator (e.g. methyl orange) – for color detection during titrations.

Required laboratory equipment:

burette
Erlenmeyer flask
pipette
Magnetic stirrer

Analysis of nitrogen (N)

Chemicals required:

Formaldehyde (37% solution) – for complex formation with ammonium.
HCl (0.01 mol/L) – for back titration.
Indicator (e.g. Thoron) – for color detection of the endpoint.

Required laboratory equipment:

burette
Erlenmeyer flask
pipette
Magnetic stirrer

Analysis of mercury (Hg)

Chemicals required:

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

Required laboratory equipment:

burette
Erlenmeyer flask
pipette
Magnetic stirrer

Analysis of silicon (Si)

Chemicals required:

0.01 mol/L sodium fluoride (NaF) solution
0.01 mol/L lanthanum (III) chloride (LaCl₃) solution
Buffer solution (pH 3, acetic acid/sodium acetate buffer)
Alizarin complexone (indicator)

Required laboratory equipment:

burette
Erlenmeyer flask
pipette
Magnetic stirrer

Analysis of zinc (Zn)

Chemicals required:

EDTA (0.01 mol/L) – for titration of zinc.
Indicator (e.g. Eriochrome Black T) – for color recognition.
Ammonia buffer solution (pH 10) – to stabilize the pH value.

Required laboratory equipment:

burette
Erlenmeyer flask
pipette
Magnetic stirrer

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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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Quantitative Analyse von Arsen

Arsenic (As) is not found in any nutrient solutions. It occurs in the following forms: arsenite (As³⁺) and arsenate (As⁵⁺) . It is highly toxic.

The following methods are available for determination:

Atomic absorption spectrometry (AAS) with hydride generator (HG-AAS): High sensitivity.
Inductively coupled plasma mass spectrometry (ICP-MS): Very precise.
Spectrophotometry with silver diethylthiocarbamate: color development by complex formation.
Electrochemical methods (e.g. ASV): High sensitivity.
Iodometric titration: Suitable for As³⁺.

Titration of arsenic with iodine solution (I₂)

1. Principle of the method

Arsenic(III) ions (As³⁺) are oxidized to arsenic(V) by iodine (I₂) in acidic solution:

As ³⁺ + 2 I ₂ + 2 H ₂ O \to As ⁵⁺ + 4 I ⁻ + 4 H ⁺

The endpoint is detected using starch solution as an indicator ( blue → colorless ).

2. Chemicals

0.01 mol/L iodine solution (I₂)
1 mol/L hydrochloric acid (HCl)
0.1 mol/L sodium thiosulfate solution (Na₂S₂O₃)
Starch solution (indicator)

3. Experimental setup

Required equipment:

Burette (25 mL, division 0.1 mL)
Erlenmeyer flask (250 mL)
Magnetic stirrer
Graduated pipettes (10 mL, 50 mL)

4. Implementation

Add 10 mL of 1 mol/L HCl to 10 mL of nutrient solution.
Carefully heat the solution to 40°C.
Slowly add 0.01 mol/L iodine solution while stirring.
After the yellow color disappears, add starch solution.
Continue titrating until the blue color disappears.

5. Calculation of the arsenic concentration

The concentration of As³⁺ is calculated as follows

:

c (As) = \frac{V I₂ \cdot c I₂ \cdot \frac{1}{2}}{V Probe}

6. Example calculation

Used iodine solution: 7.5 mL (0.0075 L)
Concentration of iodine solution: 0.01 mol/L
Sample volume: 50 mL (0.050 L)

c (As) = \frac{0.0075 \cdot 0.01 \cdot \frac{1}{2}}{0.050} = 0.00075 mol/L = 0.75 mmol/L

Conclusion

Iodometric titration is a simple, cost-effective method for the quantitative determination of arsenic in nutrient solutions. Alternatively, AAS or ICP-MS offer greater accuracy.

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The term borate species refers to the various chemical forms (species) in which boron can exist in a solution. The form depends strongly on the pH value .

Important borate species

1. Boric acid (H₃BO₃) – undissociated, neutral

Predominant at pH < 7
Acts as a weak Lewis acid
Exists mainly as uncharged molecules

Reaction in water:

H_{3} BO 3 + H 2 O \leftrightarrow [_{B (OH 4)]} ⁻ + H ⁺

2. Tetrahydroxoborate ion ([B(OH)₄]⁻) – anionic

Predominant at pH > 9
Formed by the reaction of boric acid with hydroxide ions (OH⁻)
Important for the titration of boron with NaOH

3. Polycondensed borates

At higher concentrations and certain pH ranges, boron can form borate oligomers or polyborates
An example is the tetraborate ion [B₄O₇]²⁻

4. Boron-mannitol complex

By adding mannitol, boron forms a stable complex
This complex acts like a strong acid
Can be titrated by NaOH

Summary

pH range	Predominant borate species
pH < 7	Boric acid (H₃BO₃)
pH 7 – 9	Equilibrium between H₃BO₃ and [B(OH)₄]⁻
pH > 9	Tetrahydroxoborate ion ([B(OH)₄]⁻)
With mannitol	Boron-mannitol complex (titratable with NaOH)

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Analysis

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Important borate species

1. Boric acid (H₃BO₃) – undissociated, neutral

2. Tetrahydroxoborate ion ([B(OH)₄]⁻) – anionic

3. Polycondensed borates

4. Boron-mannitol complex

Summary

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