Lead is not present in any nutrient solutions. Due to possible environmental contamination,  Pb²⁺ ions must  be tested for. Ideally, lead should not be present in any trace. This makes it all the more important to test both the air and the water used (contaminated, for example, by old lead pipes, deposits on leaves due to dust and air pollution).

There are various methods for determining lead:

• Atomic absorption spectroscopy (AAS): Very precise method for the quantitative determination of lead.
• Complexometric titration with EDTA: A reliable method for the determination of lead with indicator color change.
• Dithizone spectrophotometry: A colorimetric method for determining lead concentrations.

Detailed complexometric titration of lead with EDTA

1. Principle of the method

Lead ions (Pb²⁺) react with ethylenediaminetetraacetic acid (EDTA, C₁₀H₁₆N₂O₈) to form a stable complex:

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

2. Chemicals

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

1. Pour 10 mL of the nutrient solution into a 250 mL Erlenmeyer flask.
2. Add 10 mL of acetate buffer solution (pH 5-6).
3. Add 2-3 drops of xylenol orange indicator.
4. Titrate with 0.01 mol/L EDTA until the color changes from red to yellow.

5. Calculation of lead concentration

The concentration of Pb is calculated using the formula:

6. Example calculation:

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

Conclusion

Complexometric titration with EDTA using xylenol orange as indicator is a precise method for the quantitative determination of lead.