Automated photometric determination of lead using the Optrode

Importance of the Topic

Lead analysis in environmental and industrial samples is critical for health protection, regulatory compliance and process control. Automated photometric titration at trace to higher levels offers rapid, precise and reproducible quantification, reducing manual intervention and improving laboratory throughput.

Objectives and Study Overview

This application note presents an automated back-titration method for lead determination using a photometric endpoint detector (Optrode). Key goals include minimizing sample preparation, ensuring clear equivalence point detection with xylenol orange indicator, and demonstrating method precision and reliability.

Instrumentation

• Titrando 907 photometric titrator
• Robotic USB Sample Processor 815
• Swing head 786 with swing arm
• Titration head and sample rack for 28×200 mL beakers
• Dosinos (5 mL, 10 mL×2, 20 mL, 50 mL) and stirrer
• Optrode detector set at 574 nm for endpoint monitoring

Methodology

No sample pretreatment is required. A 5–7 mL aliquot of lead standard solution is placed in a 200 mL beaker, diluted with water, then 10 mL acetate buffer (pH 4.9), 5 mL 0.1 mol/L Na2EDTA and 0.5 mL xylenol orange are added. Back-titration is performed with 0.1 mol/L ZnSO4 under constant stirring. Photometric monitoring at 574 nm identifies the color change at the equivalence point. Typical parameters: MET U mode, stirring rate 8, 60 s pause, signal drift limit 20 mV/min, volume increment 0.05 mL, endpoint criterion 15 mV.

Main Results and Discussion

Six replicates yielded a mean lead concentration of 10.557 g/L with a relative standard deviation of 1.33%. The clear photometric signal and low variability confirm the robustness of the automated titration. Factors affecting precision include reagent purity, buffer pH control and optical path stability.

Benefits and Practical Applications

• Fully automated procedure reduces operator workload and risk of human error
• High precision and reproducibility support quality assurance in environmental and industrial laboratories
• Minimal sample preparation streamlines analysis of aqueous lead samples
• Photometric endpoint detection ensures reliable equivalence point determination even with colored indicators

Future Trends and Potential Applications

Integration of multi-element titration systems, miniaturized flow-through photometric detectors and advanced data analytics could expand applicability to continuous monitoring in water treatment, soil extracts and biological matrices. Coupling with ion-selective electrodes or spectroscopic detectors may enable simultaneous multi-analyte determination.

Conclusion

The automated photometric back-titration using the Optrode provides a rapid, accurate and user-friendly method for lead quantification. Its proven precision and ease of use make it suitable for routine environmental and industrial analysis, with future developments likely to broaden its scope and efficiency.