AOF – Adsorbable organically bound fluorine

So that it is possible to obtain a comprehensive picture of the contamination of a sample with fluorine despite often low concentrations, the analysis of the sum parameter AOF (adsorbable organically bound fluorine) is an essential tool. This parameter is often used to monitor and analyse surface water, drinking water and waste water.

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AOF enrichment for sample preparation

What is AOF?

AOF represents an important sum parameter in environmental analytics and reflects the overall levels of organic fluorine compounds in samples. Along with AOF, there are other parameters such as TF (total fluorine), TOF (total organic fluorine) and EOF (extractable organic fluorine) that acquire the related specific aspects of fluorine contamination. AOF and EOF take into account both PFAS (per- and polyfluoroalkyl substances) as well as non-PFAS compounds with similar characteristics.

The characteristics of adsorbable organic fluorine compounds

AOF describes a group of fluorine compounds defined by their capacity for adsorption, their organic nature and the specific form of the chemical bonding of fluorine. Adsorption refers to a physical characteristic of these materials: they adhere or accumulate on the surface of another material without penetrating its volume. This process takes place at the boundary between two phases, for example between a solid surface and a liquid or a gas.

AOF: stability, persistence and resilience

The classification as "organic" refers to the chemical composition of compounds that contain carbon – often in combination with other elements such as hydrogen, oxygen and nitrogen. Organic fluorine compounds comprise numerous substances, including those manufactured synthetically such as the widely used per- and polyfluoroalkyl substances (PFAS). They are water and oil-repellent and are very stable. Carbon-fluorine compounds are known for their extraordinary strength and contribute to the durability and persistence of many organic fluorine compounds in the environment. In summary, AOF describes a group of fluorine compounds that, due to their chemical structure and their physical-chemical characteristics, can be analysed as sum parameters.

What is a sum parameter?

Sum parameters or summary impact and material parameters are used to describe comprehensively certain substance groups and substance classes. In analytical conditions specified for the sum parameters, most individual substances in a substance class are acquired by means of a common feature; as a consequence they can be measured with significantly less effort than a large number of individual substances. As a rule, the analysis of the sum parameter provides sufficient information about the hazard potential.

The analysis of the sum parameter AOF
at Quality Analysis

 

The analysis of the sum parameter AOF provides crucial insights into the presence and concentration of organic fluorine compounds in environmental samples, in particular in water. As an essential screening parameter, AOF permits the efficient preliminary estimation of the fluorine contamination including PFAS (per- and polyfluoroalkyl substances) as well as other organic compounds containing fluorine.

  • Determination of the sum parameter AOF in accordance with DIN 38409-59
  • Quick, reliable screening of AOF in various water samples to obtain a complete picture of the fluorine contamination in your sample
  • Highly precise analytics by means of the use of combustion ion chromatography (CIC)
  • Precision and highest accuracy during the acquisition of organic fluorine compounds
  • Quick, reliable results
  • Our analysis meets the applicable standards such as ASTM D7359-08 and ASTM D5987-96(2007) as well as DIN 38409-59

AOF analytics for monitoring and evaluation

AOF analytics are of major importance for monitoring the quality of water and the evaluation of environmental pollution because, compared to more complex methods such as TOP assay or specific analysis using LC-MS/MS or GC-MS/MS, they permit easier and more direct quantification. The use of AOF in parallel with a sum parameter such as AOX can provide a comprehensive picture of the organic fluorine and halogen contamination in a sample, which is imperative for effective environment management. The inclusion of the method in DIN 38409-59 underlines the scientific and regulatory significance of AOF analytics for the identification and evaluation of PFAS contamination in the environment.

How is the sum parameter AOF analysed?

AOF analysis, a key method in the non-specific screening of per- and polyfluoroalkyl substances (PFAS), utilises combustion ion chromatography (CIC) for a precise, sensitive measurement. This method is crucial for the evaluation because it permits a quick, efficient estimation of potential contamination by PFAS and other organic fluorine compounds.

AOF enrichment for sample preparation

Sample preparation for AOF Analysis

In accordance with DIN EN ISO 9562, the sample is initially prepared using adsorption on activated carbon, a method that effectively isolates the organic fluorine compounds. This pre-treatment makes it possible to free the sample of inorganic fluoride and therefore to ensure the high accuracy of the measurement results by subsequently washing the activated carbon using sodium nitrate (NaNO3). For the determination of the AOF, contrary to other adsorbable organically bound halogens (i.e. AOCl, AOBr and AOI), it is also crucial that the sample has a neutral pH value to prevent the adsorption of inorganic fluorine.

CIC for fluorine analysis

Breakdown of fluorine compounds into their ionic constituents

The actual measurement is made based on the pyrohydrolytic combustion of the enriched carbon at 1050 °C, a step that breaks down the organic fluorine compounds into their ionic constituents. An aliquot of this solution is then injected automatically into the ion chromatograph (IC) for the analysis. These ions are then analysed in the ion chromatograph; the use of a large volume sample further increases the sensitivity of the method.

CIC chromatogram of the AOF analysis

The result

The AOF-CIC method permits the measurement of fluoride ions (F-) in a concentration range from 1 to 100 µg/L with a limit of detection (LOD) of 0.5 µg/L F-, as per DIN 32645. This high sensitivity underlines the precision of the method during the identification and quantification of traces of organic fluorine compounds. Along with PFAS, the AOF analysis also acquires non-PFAS compounds with similar characteristics, including pesticides, pharmaceutical products and other compounds containing fluorine often ignored during specific analyses.

AOF and PFAS

AOF, the sum parameter for adsorbable organic fluorine, plays a crucial role in the context of the identification of PFAS (per- and polyfluoroalkyl substances) in environmental samples. AOF not only acquires PFAS as part of the halogens, but also numerous other organic fluorine compounds. For this reason, an elevated AOF value in a sample can be an indication of the presence of PFAS, although it does not indicate their presence exclusively. The breadth of the AOF spectrum means that a high value could also be caused by other organic compounds containing fluorine.

AOF analytics for the evaluation of environmental pollution

A significant AOF value is therefore an indicator for the need for more detailed analyses. It sets the starting point for specific analyses to identify and determine quantitatively specific PFAS compounds or other relevant organic fluorine compounds in the sample. In this context, AOF analysis acts as an effective screening instrument that smooths the way for detailed, specific environmental analyses and therefore represents a fundamental tool for the evaluation of environmental pollution due to compounds containing fluorine.

AOF analytics in practice

AOF analysis for wastewater analytics
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waste water

In waste water treatment plants or during the preparation of drinking water, AOF analysis can be used to evaluate the effectiveness of methods for removing organic fluorine compounds. A comparison of the AOF values before and after the treatment provides information about how well the method removes organic fluorine compounds.

AOF analysis for environmental monitoring
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Environmental monitoring

For environmental authorities and organisations, the determination of AOF provides a way of monitoring and evaluating the contamination of bodies of water, the ground and other environmental media with organically bound fluorine. This analysis can contribute to the identification of sources of contamination and to the evaluation of risks for ecosystems and human health.

AOF analysis for process control
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Industrial process control

In the chemical industry, in particular during the manufacture of fluorinated chemicals, AOF analytics can be used to monitor production processes and for quality control on the end-products. Precise knowledge of the fluorine content is vital for process efficiency and compliance with product standards.

Summary: AOF

The sum parameter AOF provides important information about contamination due to organic fluorine compounds in environmental and industrial samples, including PFAS and non-PFAS. AOF, together with other sum parameters such as EOF and AOX, permits a comprehensive understanding of fluorine and halogen contamination. The method is essential for effective environmental management and helps during the monitoring of water quality and the evaluation of environmental pollution.

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Julia Banzhaf

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+49 7022 2796-631
j.banzhaf@qa-group.com

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