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Testing AOX levels in water and wastewater samples

What is AOX testing for and where is it used?

Adsorbable organic halogen (AOX) testing is a way to estimate contamination of solid and liquid samples with specific halogenated compounds, such as pesticides. AOX is an important, internationally-measured contamination parameter and the standardised method according to ISO 9562 is often used to determine it. A major application of AOX analysis is in water testing; raw, waste, drinking, ground- and surface water can all be investigated in this way.

The Multi X2500 AOX -TOX Analyser

AOX Autosampler

What is the traditional method of blend uniformity testing in the pharmaceutical industry?

The traditional method of blend uniformity testing in the pharmaceutical industry involves stopping the blender after a given time and withdrawing 10 samples at predefined locations specified by the current International Conference on Harmonization (ICH) guidelines.

How do I analyse AOX in wastewater?

Both batch and column methods can be employed for AOX analysis, although the column method is less time- and labour-intensive. AOX sample preparation involves acidifying to pH ≤ 2 using concentrated HNO3 before refrigerating. Shortly before the test, mix the samples with nitrate stock solution according to ISO 9562 and add to the adsorption chamber.

The APU Sim from Analytik Jena is ideal for this sample preparation phase and uses syringes to pump the sample solution onto activated charcoal columns. This step prompts the halide ions to adsorb onto the carbon’s surface. Next, the APU sim automatically rinses any non-adsorbed, inorganic chloride from the activated carbon.

Prior to the determination of AOX in water samples, blank value determinations as well as measurements with control standards should be conducted. The sample preparation for 18 samples and three blank values can be completed in approximately 3.5 hours with the APU sim, which can process six samples within 45 minutes.

To determine AOX quantity, the activated carbon, now enriched with halides from the water sample, is combusted. During this process the organic halogen compounds are converted to gaseous hydrogen halides, HX. The Multi X2500 Analyzer from Analytik Jena performs this combustion at 950°C. After drying, the combustion gases are transferred to a microcoulometric measurement cell where the halide species can be quantified within a working range of 1 to 100 µg chloride.

How can I comply with ISO 9562?

The APU Sim and Multi X2500 Analyzer from Analytik Jena comply automatically with ISO 9562 guidelines by design. The standardised method required to comply is described above and more information can be found here.

What is better, batch or column method for AOX analysis?

Both the batch and column methods have useful applications within AOX analysis. The batch, or shaking, method is mandatory for sewage sludge and other solid samples, but can be applied to fluid water samples. This method is the default for older equipment, which cannot perform the column method.

This traditional batch approach is slower because operators cannot incorporate an autosampler into the process, meaning fresh samples must be introduced every five minutes. Therefore, the batch method is more time- and labour-intensive. Furthermore, the open nature involves a higher risk of contamination from the lab environment and the process lacks an opportunity for a control to assess the completeness of the AOX adsorption step.

In contrast, the column method cannot analyse solid samples but offers advantages like more control over AOX adsorption to activated carbon and better capability to deal with high organic halogen concentrations, up to 1 mg/L Cl- versus ≤ 500 mg/L Cl- for the batch method. Prefilled AOX columns for adsorption reduce the risks of contamination and handling errors by minimising contact with the lab environment. Additionally, the column method allows for a high degree of automation, which enables a high sample throughput and minimal maintenance effort.

How can I deal with high levels of particulates in my sample when analysing for AOX?

The column method is superior for high particulate count samples because of the ability to include a filter column upstream of the cylinders filled with activated carbon. This triplex set-up is unique to the Analytik Jena products. Without filtration, this stage of AOX testing can be seriously affected when solid particles block the surface of the carbon and therefore reduce its adsorption capacity. This filter column ensures the particles are separated and thus also prevents the activated carbon columns from becoming clogged with the debris from the sample.

What to do next?

Below, you can find links to the Multi X2500 Analyzer page. However, if you require more information, such as detailed application notes or a conversation with a member of our team, please contact us using the methods provided below.

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