Measurement of AOX with combustion IC

Importance of the Topic

AOX (adsorbable organically bound halogens) determination is a key parameter in environmental monitoring for quantifying nonpolar chlorinated hydrocarbons and related halogenated compounds in water and solid matrices. The rise of persistent perfluorinated pollutants has extended the analytical scope to organofluorine (AOF), underscoring the need for advanced workflows capable of simultaneous multi-halogen analysis.

Goals and Study Overview

This study evaluates a combustion ion chromatography (CIC) approach for concurrent determination of AOX components (Cl, Br, I) and AOF (F). Key objectives include preventing charcoal loss during automation, optimizing detection limits, and comparing classical coulometric AOX measurement with speciation by IC to enhance information yield.

Methodology and Instrumentation

Analytical workflow:

• Sample enrichment by passing water samples through activated charcoal columns or shaking with charcoal.
• Charcoal fixation using two drops of glycerol to prevent particle loss during autosampling and combustion.
• Combustion via hydropyrolysis in oxygen with automatic water addition, converting bound halogens to halide and oxyanion species.
• Absorption into ultrapure water for aqueous samples and 100 mg/L H2O2 for solids; matrix peak removal using Metrosep A PCC 2HC/4.0.
• IC separation on Metrohm A Supp 5 columns with 3.2 mmol/L Na2CO3 and 1.0 mmol/L NaHCO3 eluent at 0.7 mL/min and 200 μL injection, coupled to conductivity and UV detection.
• Instrumentation: Metrohm CIC system comprising an autosampler, combustion and absorber modules, chemical and CO2 suppressors, conductivity and dual-wavelength UV detectors.

Main Results and Discussion

• Detection limits of ~2 μg/L for AOF, ~5 μg/L for AOCl, and ~1 μg/L for AOBr and AOI with 100 mL sample volumes.
• Glycerol fixation effectively prevented charcoal loss for up to 24 hours without increasing halogen blanks.
• Retention times for halide and related oxyanions were highly reproducible, with no practical interferences observed.
• Calculated AOX from halogen equivalents closely matched directly measured AOX in both effluent and sewage sludge samples, validating method accuracy.

Benefits and Practical Applications

• Simultaneous multi-halogen speciation (Cl, Br, I, F) and extension to organofluorine offers richer analytical insights than classical AOX.
• High sensitivity and robustness support regulatory compliance, industrial quality control, and environmental risk assessments.
• Automation minimizes sample handling errors and increases throughput in routine laboratory workflows.

Future Trends and Opportunities

• Extension to organosulfur and other heteroatom-bound sum parameters.
• Further reduction of blank values through optimized charcoal materials and ultraclean reagents.
• Integration with real-time data analytics and remote monitoring for smart environmental surveillance.
• Application to emerging contaminants in complex matrices such as biosolids, sludge, and industrial byproducts.

Conclusion

The combination of combustion IC with glycerol-fixed activated charcoal delivers a sensitive, automated, and comprehensive approach for AOX and AOF analysis. This method enhances speciation detail, ensures reliable performance, and fulfills contemporary regulatory and industrial requirements.

References

1. EN ISO 9562:2004 Water quality – Determination of adsorbable organically bound halogens (AOX).
2. Oleksy-Frenzel et al. Combined charcoal preconcentration and IC for organically bound halogens, Journal of Chromatography A.
3. Analytical application of CIC for perfluorinated compounds, Journal of Chromatography A.
4. Metrohm Combustion IC system application note WP-041EN, 2018.
5. Hessenwasser GmbH & Co. KG internal recommendations for AOX/AOF analysis.