SPECIATED AOX ANALYSIS BY COMBUSTION IC Adsorbable Organic Fluoride, Chloride, and Bromide in Water Samples
Most of the halogenated organic compounds found in nature are toxic, carcinogenic, and persistent. These compounds are harmful to the environment and need to be actively monitored to control environmental pollution. The sum parameter Adsorbable Organic Halogens (AOX) is the primary indicator for contamination of water, sediment, and soil by halogenated compounds. The AOX sum parameter combines organically bound compounds that contain chlorine, bromine, iodine, or fl uorine atoms, which can be adsorbed onto activated carbon.
One of the most critical sources of AOX in the environment is the use of halogenated chemicals in industrial industries such as; pulp and paper and textile. Smaller quantities of AOX are also formed during the routine chlorination or disinfection of swimming pools and cooling water. Some of the used halogens react with organic matter to form organic halogen compounds, which may be discharged into the environment as effl uent water or wastewater.
For many years AOX analysis by Microcoulometry was the accepted method for quantifying the halogen content in wastewater streams. The method consists of four main parts: collecting the organic halogens on activated carbon, washing with nitrate solution to remove interferences, combusting the carbon to form hydronated halogens, and quantifying the halogen content by microcoulometric titration. During the microcoulometric titration, the Cl− Ag+
, Br− to precipitate, where F- , and I− Results – 10 µg/L Standard Analyte
Fluoride in Demi water Chloride in Demi water Bromide in Demi water
Spiked Concentration (µg/L)
10.0 10.0 10.0
Table 1 - Results for AOF, AOCl, and AOBr Analysis in DI water Results – Spiked Samples Analyte
Fluoride in Tap Water Chloride in Tap Water Bromide in Tap Water
ions react with the remains in the titration cell solution.
This is why organic fl uorides are not included as part of the AOX analysis.
By substituting the detection technique with Ion chromatography it makes it possible to include Fluorine as well as speciate between the different halogens. The Combustion IC enables the determination of individual halogenated compounds (fl uoride, chloride, bromide, iodine) in aqueous matrices by a single analysis. Recently, several studies have focused on Perfl uoroalkyl and polyfl uoroalkyl substances (PFAS) found in aquatic systems and the environment. PFAS is a collective name for more than 6,000 potentially toxic substances that include a combination of fl uorine compounds and alkyl groups. PFASs are water, grease, and dirt repellent. They are used in various products including lubricants, food packaging materials, extinguishing foam, and non-stick coatings on cookware, clothing, textiles, and cosmetics. PFAS are highly mobile once introduced into the aquatic environment and are not removed by conventional wastewater treatment. The presence of Adsorbable Organic Fluoride (AOF) in aqueous matrices is an important indicator of potential PFAS contamination. The analyzed amount of AOF in these samples provides insight into numerous PFAS precursors, which can transform into persistent PFAS that pollute the aquatic environment.
Sample Information Sample Type Component
Concentration Methods Applicable
Fluoride in Surface Water Chloride in Surface Water Bromide in Surface Water
Concentration (µg/L) 2.8
10.5 9.5 6.9
28.3 30.0
Table 2 - Results for AOF, AOCl, and AOBr Analysis in Tap, and Surface Water System Description
Sample Preparation – The organically bound halogenated compounds can be fi ltered and adsorbed onto activated carbon by the batch or column method. TE Instruments offers sample preparation systems for both adsorption methods. In this study, the column method was executed. The column method describes taking a 100 mL sample (water), and using 2 columns (in series) fi lled with activated carbon to adsorb organic halogens by fi ltration. After fi ltration, the inorganic content is rinsed off and the activated carbon is eventually combusted at a high temperature. The second column is to assure that the breakthrough of the sample does not exceed 10% of the total value. Results of the samples are obtained by summing the analyzed concentrations from the fi rst and second column.
Introduction – The NEWTON solids autosampler automatically introduces the quartz cups carrying the activated carbon into the Boat introduction module. Once analyzed and cooled down, clean sample cups are retrievable from the clean cup container.
Combustion - The Combustion Unit is fi tted with a dual-zone furnace. Every sample is completely oxidized by pyrohydrolitic combustion in an oxygen-rich environment at a high temperature.
Water
Fluoride, Chloride, Bromide 0 – 100 µg/L -
A unique feature of the Xprep C-IC setup is the option to use a furnace combustion tube including a ceramic insert. While standard AOX by MCD analysis focuses on Chlorine, Bromine, and Iodine, the analysis of AOX by C-IC has a wider focus including Fluorine. This is where the power of the ceramic insert is helpful. In a standard situation, Fluoride attacks quartz glass and may damage the combustion tube over time. The ceramic
IET SEPTEMBER 2022
insert protects the furnace tube quartz material, resulting in a far longer lifetime compared to a standard quartz glass set up.
Collection – After combustion, an absorber solution is added automatically to the output gas stream to guarantee complete absorption of analytes in the Fraction Collection Unit. In this process, the H-X and X2
are converted to F-, Cl-, and Br-. These
negatively charged ions will be separated in the IC column. To Up to 65 combusted samples can be absorbed and stored in the individual absorption vials. The combusted and collected samples can be transferred to the IC immediately or stored for later analysis. A re-run of combusted samples is possible at any time if desired.
IC-Injection – Once sample preparation has been fi nalized, the absorbent containing the analytes is automatically transferred from the Fraction Collection unit towards any renowned IC. A six- way-valve and 100 µL sample loop are by default integrated at the front of the Fraction Collection Unit. The internal syringe pump
RSD (%) n=3
14.7 3.3 1.1 9.6 1.3 6.2
Spiked Concentration (µg/L)
10 10 10 25 25 25
Recovery %
106 102 105 100 103 103
Average (µg/L) 9.9
10.1 9.2
RSD (%) n=3
4.6 4.3 1.1
Recovery % 99
101 92
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