Standardization of thiosulfate titrant for copper determinations

Significance of the topic

The accuracy of thiosulfate titrant standardization is critical for reliable copper determinations in chemical analysis. Precise titrant concentration ensures consistent results in quality control, environmental monitoring, and industrial processes where copper quantification affects safety, compliance, and product performance.

Objectives and overview of the study

This application note describes the standardization of a mixed sodium thiosulfate/potassium iodide titrant for thermometric titration of copper. A high-purity copper standard solution is prepared and titrated to determine the exact molarity of the titrant. Emphasis is placed on minimizing iodine volatilization and side reactions by generating iodine just prior to its reduction.

Methodology and instrumentation used

The procedure comprises:

• Preparation of a 0.2 mol/L Cu(II) stock by dissolving weighed copper foil in nitric acid, expelling nitrogen oxides by boiling, and treating with sulfamic acid.
• Dilution to volume in a volumetric flask for consistent concentration.
• Thermometric titration under controlled conditions: titrant addition rate 2 mL/min, single exothermic endpoint detection, data smoothing factor 50, stirrer speed setting 6, and a 15 s delay before measurement.

Key instruments:

• Thermometric titrator with a Thermoprobe sensor for temperature endpoint detection.
• Automatic burette (Dosino) for precise titrant delivery.
• PTFE-coated magnetic stir bar and hot-plate stirrer.
• Standard laboratory glassware: volumetric flasks, wide-mouth Erlenmeyer flask, fume hood.

Main results and discussion

Four aliquots of the 0.2 mol/L Cu(II) solution (15–30 mL) were titrated in duplicate. The plot of mL titrant vs. mmole Cu2+ yielded a linear equation y = 0.99894 x + 0.04713, R2 = 1.00000. From the slope, titrant molarity was calculated as 1.00106 mol/L. The method blank (intercept) was 0.0471 mL. This high linearity and minimal blank indicate excellent precision and negligible side reactions when iodine is generated immediately before titration.

Benefits and practical applications of the method

The standardized titrant supports:

• Rapid and reproducible copper assays in routine laboratories.
• Elimination of systematic errors from titrant concentration drift.
• Adaptability for other redox titrations requiring precise endpoint detection.

Future trends and opportunities

Advances may include integration of microfluidic titration platforms, real-time data analytics for endpoint prediction, and extending thermometric titration to trace-level determinations and complex matrices. Coupling with spectroscopic or electrochemical sensors could enhance multi-analyte workflows.

Conclusion

The thermometric standardization of a sodium thiosulfate/potassium iodide titrant demonstrated outstanding accuracy (1.00106 mol/L) and precision, with minimal blank interference. This reliable protocol is well suited for quality control of copper in diverse applications.