Determination of Low Levels of Sulfate by Barium Chromate Displacement

Význam tématu

Sulfate determination at low concentrations is critical for monitoring environmental waters, industrial process streams and quality control in manufacturing. Accurate quantification at the milligram-per-liter level helps ensure compliance with regulatory limits, assess contamination sources and optimize treatment processes.

Cíle a přehled studie / článku

This application note describes a thermometric titration method for quantifying sulfate in aqueous samples at concentrations from approximately 2 to 20 mg/L as SO₄²⁻. The study outlines the principle of barium chromate displacement, the titration procedure, method performance and blank correction.

Použitá metodika a instrumentace

The procedure is based on precipitation of sulfate by acidified barium chromate, followed by basification to remove excess barium as chromate precipitate. The residual soluble chromate, proportional to original sulfate, is titrated with standard ferrous ion to a thermometrically determined endpoint.

• Sample acidification with HCl and methyl orange indicator
• Addition of barium chromate reagent in 0.25 M HCl, followed by 10 min stirring
• Basification with concentrated ammonia to precipitate residual BaCrO₄
• Quantitative transfer, dilution and filtration to obtain clear filtrate for titration
• Titration of 50 mL aliquots with 0.1 M Fe(II) solution after a 60 s equilibration and acid pre-dose
• Data smoothing and endpoint detection via temperature rise

Key operating parameters:

• Titrant flow rate: 2 mL/min
• Stirring speed: setting 6 on 802 stirrer
• Data smoothing factor: 40
• Equilibration delay: 60 s

Hlavní výsledky a diskuse

Validation using sodium sulfate standards (nominal 26.9 to 107.7 mg/L SO₄²⁻) showed close agreement between nominal and measured values, with mean recoveries within 1–2 mg/L. Regression of titrant volume versus sulfate concentration yielded a slope of 0.0087 mL per mg/L and R² of 0.9989. The method blank averaged –0.0726 mL, emphasizing the need for blank determination for each reagent batch due to slight solubility and stoichiometry variability of commercial barium chromate.

Přínosy a praktické využití metody

• High sensitivity for trace sulfate analysis in drinking, natural and process waters
• Rapid titration with minimal sample preparation beyond filtration
• Thermometric endpoint avoids color interference and subjective endpoint detection
• Suitable for routine quality control in environmental and industrial laboratories

Budoucí trendy a možnosti využití

Advances may include integration of automated flow-through thermometric titration for online monitoring, miniaturized calorimetric sensors for field deployment and coupling with multivariate data analysis for simultaneous measurement of multiple anions.

Závěr

The barium chromate displacement thermometric titration provides a reliable, precise and sensitive approach for low-level sulfate determination. With appropriate blank correction and optimized operating parameters, the method is well suited for diverse water quality applications.

Použitá instrumentace

• Thermometric titrator with temperature sensor and automated titrant burette
• Magnetic stirrer (802 model)
• Glassware: volumetric flasks, beakers, pipettes
• Whatman filter papers (grades 5, 6, 40 or 42)

Reference

• Foster MD. Volumetric determination of sulfate in water: the barium chromate method. Ind Eng Chem Anal Ed. 1936;8(3):195–196.