Measurement of TOC in Chloroisocyanuric Acid Used as Disinfectant

Importance of the Topic

Effective monitoring of total organic carbon (TOC) is essential for safeguarding water quality in facilities such as swimming pools, hot springs, and bathhouses. Accurate detection of recalcitrant disinfectants like sodium dichloroisocyanurate helps ensure public health and compliance with safety standards.

Objectives and Study Overview

The primary aim was to evaluate and compare two TOC measurement techniques for aqueous sodium dichloroisocyanurate solutions at 10 mgC/L and 5 mgC/L concentrations:

• Combustion oxidation using the TOC-LCPH analyzer
• Wet oxidation using the TOC-VWP analyzer

Methodology and Instrumentation

Sample preparation and analysis employed the non-purgeable organic carbon (NPOC) method: samples were acidified, sparged to remove inorganic carbon, and then measured for TOC.

Instrumentation details:

• Combustion oxidation (TOC-LCPH): high-temperature combustion at 680 °C with standard catalyst; 50 µL injection; 2-point calibration at 0 and 20 mgC/L (potassium hydrogen phthalate).
• Wet oxidation (TOC-VWP): chemical oxidation with sodium peroxodisulfate under UV irradiation and heating; 2500 µL injection; 2-point calibration at 0 and 10 mgC/L (potassium hydrogen phthalate).

Main Results and Discussion

• Combustion oxidation achieved high recoveries: 9.893 mgC/L (98.9%) at 10 mgC/L and 4.914 mgC/L (98.3%) at 5 mgC/L.
• Wet oxidation showed negligible detection: 0.0147 mgC/L (0.15%) at 10 mgC/L and 0.0077 mgC/L (0.15%) at 5 mgC/L.

The superior oxidizing power of the combustion method enabled complete decomposition of the chlorinated isocyanuric acids, whereas the wet oxidation approach lacked sufficient strength to quantify these recalcitrant compounds.

Benefits and Practical Applications

• Enables reliable TOC monitoring of disinfectants in water treatment and recreational facilities.
• Offers rapid analysis—single-sample results within 10–20 minutes using combustion oxidation.
• Delivers high sensitivity for organic compounds resistant to conventional wet oxidation methods.

Future Trends and Opportunities

Emerging directions include:

• Integration of continuous, real-time TOC monitoring systems for proactive water quality control.
• Miniaturization of combustion oxidation modules for portable field analysis.
• Coupling TOC analysis with advanced oxidative processes or hyphenated detection techniques for broader contaminant coverage.

Conclusion

The combustion oxidation TOC-LCPH analyzer outperformed the wet oxidation TOC-VWP in measuring sodium dichloroisocyanurate solutions, achieving nearly complete recovery and demonstrating its suitability for analyzing recalcitrant organic disinfectants. This capability supports enhanced water quality management in public and industrial applications.

Reference

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