Method for Determination of Anions in sodium hydroxide
Applications | 2003 | Thermo Fisher ScientificInstrumentation
Monitoring anionic impurities such as chlorate in concentrated sodium hydroxide is critical for chlor-alkali production quality control. Accurate quantification ensures process efficiency, product purity and compliance with safety and environmental regulations.
This study presents a validated ion chromatographic method to quantify six anions—chloride, nitrite, sulfate, phosphate, chlorate and nitrate—in 50% (w/v) sodium hydroxide. The procedure covers sample pretreatment, chromatographic separation and detection, ensuring reliable measurements in highly caustic matrices.
The analytical workflow comprises:
Chromatograms demonstrate clear separation of all target anions within a 25-minute runtime. Key observations:
This method offers:
Advances may include:
The described ion chromatographic approach reliably quantifies key anions in concentrated NaOH, enabling enhanced process control and product quality assurance in chlor-alkali operations. Its straightforward sample preparation and robust separation make it suitable for industrial laboratories.
• Dionex Corporation. Application Note 151: Method for Determination of Anions in Sodium Hydroxide. LPN 1552, 2003.
Ion chromatography
IndustriesEnergy & Chemicals
ManufacturerThermo Fisher Scientific
Summary
Importance of the Topic
Monitoring anionic impurities such as chlorate in concentrated sodium hydroxide is critical for chlor-alkali production quality control. Accurate quantification ensures process efficiency, product purity and compliance with safety and environmental regulations.
Objectives and Study Overview
This study presents a validated ion chromatographic method to quantify six anions—chloride, nitrite, sulfate, phosphate, chlorate and nitrate—in 50% (w/v) sodium hydroxide. The procedure covers sample pretreatment, chromatographic separation and detection, ensuring reliable measurements in highly caustic matrices.
Methodology and Instrumentation
The analytical workflow comprises:
- Sample Dilution and Pretreatment
• Dilute 50% NaOH samples 1:50 to 0.38 N.
• Condition OnGuard-H cartridges with deionized water.
• Pass diluted sample at 4 mL/min, discard first 3 mL, collect next 1 mL for injection. - Chromatographic System
• Instrument: Single-channel ion chromatograph with conductivity detector.
• Guard Column: IonPac AG9.
• Analytical Column: IonPac AS9.
• Suppressor: Anion MicroMembrane Suppressor (AMMS).
• Eluent: 1.8 mM Na2CO3 / 1.7 mM NaHCO3 at 1.0 mL/min.
• Regenerant: 20 mN H2SO4 at 3–5 mL/min. - Standard Preparation
• Stock standards (1000 ppm) prepared individually in DI water.
• Mixed calibrant: combine volumes of stocks to yield 1.0–25.0 ppm for each analyte.
Main Results and Discussion
Chromatograms demonstrate clear separation of all target anions within a 25-minute runtime. Key observations:
- OnGuard-H pretreatment removes caustic interferences, restoring peak shape and resolution.
- Retention times remain stable under specified eluent conditions.
- Background conductivity (12–16 µS) and system pressure (300–600 psi) are consistent across runs.
Benefits and Practical Applications
This method offers:
- High sensitivity and reproducibility for routine QC in chlor-alkali plants.
- Minimal sample handling and robust cartridge-based cleanup.
- Compatibility with existing ion chromatography platforms for rapid deployment.
Future Trends and Potential Applications
Advances may include:
- Integration of automated online sample pretreatment to reduce manual intervention.
- Coupling with mass spectrometry for expanded anion profiling.
- Development of greener eluents and suppressors to minimize waste.
- Miniaturized and portable ion chromatography systems for field monitoring.
Conclusion
The described ion chromatographic approach reliably quantifies key anions in concentrated NaOH, enabling enhanced process control and product quality assurance in chlor-alkali operations. Its straightforward sample preparation and robust separation make it suitable for industrial laboratories.
Reference
• Dionex Corporation. Application Note 151: Method for Determination of Anions in Sodium Hydroxide. LPN 1552, 2003.
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