Cadmium, quantitativ analysis

Cadmium (Cd) is primarily present as Cd²⁺ ions.

Alternative Methods for Cadmium Analysis

• Atomic Absorption Spectroscopy (AAS): High sensitivity and accuracy.
• Inductively Coupled Plasma Mass Spectrometry (ICP-MS): Very precise for trace analysis.
• Spectrophotometry with Dithizone: Color development through complex formation.
• Complexometric Titration with EDTA: Suitable for the quantitative determination of Cd²⁺.

Titration of Cadmium with EDTA

1. Principle of the Method

Cadmium ions (Cd²⁺) form a stable complex with Ethylenediaminetetraacetic Acid (EDTA, C₁₀H₁₆N₂O₈):

The endpoint is detected using Eriochrome Black T as an indicator (color change from wine red to blue).

2. Chemicals

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

3. Experimental Setup

Required Equipment:

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

4. Procedure

1. Add 10 mL of the nutrient solution to a 250-mL Erlenmeyer flask.
2. Add 10 mL of buffer solution (pH 10).
3. Add 2-3 drops of Eriochrome Black T indicator.
4. Titrate with 0.01 mol/L EDTA until the color changes from wine red to blue.

5. Calculation of Cadmium Concentration

The Cd concentration is calculated using the formula:

6. Example Calculation

• EDTA concentration: 0.01 mol/L
• Volume used: 9.2 mL (0.0092 L)
• Sample volume: 50 mL (0.050 L)

Conclusion

The complexometric titration with EDTA is a precise method for the quantitative determination of cadmium in nutrient solutions. For more accurate trace analysis, AAS or ICP-MS is recommended.

Quantitative cadmium analysis in hydroponic systems is essential for quality assurance due to the high toxicity of this heavy metal. Cadmium is considered highly toxic even at trace concentrations and is actively absorbed by plants, where it causes growth disorders, chlorosis and ultimately necrosis. The EU Drinking Water Directive sets the limit value for cadmium at 0.005 mg/L (5 μg/L), which can serve as a guide for the maximum tolerable concentration in nutrient solutions. For most crops, the first toxic effects occur at cadmium concentrations of 0.01–0.1 mg/L in the nutrient solution. The exposure limits for cadmium compounds in air are 0.002 –0.01 mg/m³, which underlines the exceptional toxicity.Graphite tube AAS or ICP-MS is required for analytical determination because flame AAS is unsuitable for the required detection limits in the lower μg/L range. Sample preparation requires the utmost care and cleanroom conditions to exclude contamination. Regular cadmium checks are mandatory, particularly when using recycled water or industrial wastewater.

sourcesEU Drinking Water Directive 98/83/EC. German Research Foundation (2021). MAK and BAT values list. WHO (2011). Guidelines for Drinking-water Quality.