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Organic halogen compounds are a major class of persistent pollutants that can be toxic to aquatic organisms even at low concentrations. Commonly produced as byproducts of industrial processes such as paper and pulp bleaching, their release into surface, ground and seawater can have long-lasting environmental consequences. The use of accurate, sensitive and convenient methods for determining levels of organic halogens in wastewater is therefore essential.

Organic halogen wastewater analysis using automated combustion ion chromatography

Levels of organic halogens in water are often measured in terms of adsorbable organic halogen (AOX), representing the total amount of organically bound fluorine, chlorine and bromine that can be adsorbed from water onto activated carbon and expressed as its chloride equivalent.

One of the most widely used methods for AOX analysis is automated combustion ion chromatography (CIC). Samples analyzed by automated CIC are first combusted at temperatures of at least 900 °C. This combustion step converts halogen-containing compounds to hydrogen halides or elemental halogens, while sulfur-containing compounds are oxidized to sulfur dioxide. These gaseous combustion products are then passed into an oxidizing absorption solution, which is subsequently analyzed by ion chromatography.

Unlike other methods for AOX analysis, such as amperometric titration, automated CIC provides data on halogen speciation and additional information about adsorbable organic fluorine, making it an extremely valuable technique for this application. You can learn more about the benefits of using CIC for the analysis of extractable organic fluorine in water in our recent webinar.

Sensitive, reagent-free ion chromatography systems are delivering more reliable analyses

To achieve reliable results by CIC, high-resolution chromatographic separation and sensitive detection are critical. Fortunately, recent advances in automated CIC technologies are helping more analysts achieve confident AOX measurements through improved instrument sensitivity, accuracy and ease of use.

The Thermo Scientific Dionex Integrion HPIC system is a highly versatile platform for CIC that offers several design features to ensure sensitive and reproducible analyses, such as a thermally regulated detector compartment and forced-air column oven. A key feature of the Dionex Integrion HPIC system is its automated eluent generation capability, which frees analysts from the need to prepare eluents manually, driving greater reproducibility in gradient concentrations by removing a potential source of error. What’s more, because the platform can operate at high-pressures of up to 5,000 psi, it also supports the use of small (4 μm) particle size columns, which offer faster analyses, improved sensitivity and more accurate peak integration compared with larger particle size columns.

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Achieving precision with automated combustion ion chromatography

The accuracy and precision of the Dionex Integrion HPIC system for the analysis of AOX in wastewater was put to the test in a recent app note, available here.

Our scientists used a method developed in accordance with the US Environmental Protection Agency’s Clean Water Act and Resource Conservation and Recovery Act, as well as Chinese Environmental Protection Law. In this analysis, AOX was absorbed using granular activated carbon (GAC), and the sample and GAC were washed to remove inorganic halides. Following combustion, analytes were separated using a Thermo Scientific Dionex IonPac AS18-4μm column.

In calibration tests, excellent retention time stability and peak area precision were recorded, consistent with the enhanced performance typically achieved when using electrolytically generated high-purity potassium hydroxide eluents.

The regulatory compliant method was then used to analyze three wastewater samples obtained from local water plants. Wastewater samples were spiked with AOX working standard stock solutions and analyzed in triplicate (Figure 1). The Dionex IonPac AS18-4μm column resulted in impressive separation resolution and sensitive AOX detection, achieving excellent recoveries of 95–105% for AOF, AOCl and AOBr.

Driving improvements in organic halogen wastewater analysis

Automated CIC enables precise, reliable and compliant analysis of organic halogens in wastewater, with the latest platforms offering enhanced reproducibility, sensitivity and ease of use.

You can read more about automated CIC for the analysis of organic halogens in wastewater in this app note, or watch our webinar to learn more about the benefits of using CIC for organic fluorine water analysis applications.

Figure 1. Determination of AOX in (A) wastewater and (B) spiked wastewater samples using the Thermo Scientific Dionex Integrion HPIC system.

Figure 1. Determination of AOX in (A) wastewater and (B) spiked wastewater samples using the Thermo Scientific Dionex Integrion HPIC system.