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# Advanced Analysis of Water Disinfection By-Products: HPSEC-ICP-MS organic matter characterization method

Mohamad Shalak, David Dumoulin, Pierre-Jean Superville, Justine Criquet

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Mohamad Shalak, David Dumoulin, Pierre-Jean Superville, Justine Criquet. Advanced Analysis of Water Disinfection By-Products: HPSEC-ICP-MS organic matter characterization method. 4th IWA Specialized International Conference on Disinfection and DBPs, Oct 2024, Almeria, Spain. hal-05288596

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Submitted on 29 Sep 2025

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# Advanced Analysis of Water Disinfection By-Products: HPSEC-ICP-MS organic matter characterization method

M. Shalak, D. Dumoulin, P. J. Superville, J. Criquet †

* Univ. Lille, CNRS, UMR 8516 - LASIRE, Laboratory of Advanced Spectroscopy for Interactions, Reactivity and Environment, Lille F-59000, France

Mohamad.shalak.etu@univ-lille.fr

Justine.criquet@univ-lille.fr

**Abstract:** Representing generally more than 60% of the total halogenated compounds formed, identifying unknown disinfection by-products is a major challenge. The conventional determination of halogenated compounds through AOX (Adsorbable Organic halogens) in water is a laborious procedure, highlighting the pressing need for more efficient, specific and sensitive techniques. We developed an innovative method for the speciation of organic and inorganic halogens through the coupling of a chromatographic separation and an elemental detector: HPSEC-ICP-MS. This technique could provide more information than conventional total halogenation (AOX) measurements without any sample preparation. The method was optimized using Suwannee River organic matter extract to detect and quantify low quantities of organic bromine (2.5 and 7.5 ppb for LOD and LOQ respectively) and iodine (0.2 ppb and 0.6 ppb). The methodology finally allows the speciation of organic and inorganic halogens within 15 min without pretreatment of the aqueous sample.

**Keywords:** Chlorination; disinfection by-products; HPLC-ICP-MS; organic matter; SRNOM.

## INTRODUCTION

Chlorination of waters containing bromide and iodide can result in the formation of reactive brominated and iodinated compounds, particularly reactive towards phenolic structures (Hu and al., 2006). This can lead to the formation of more toxic disinfection by-products than their chlorinated analogues.

The field of disinfection by-products still includes a significant fraction (up to more than 60% represented by DBP-X) that remains unexplored and is believed to originate from highly polar and heavy organic entities (Richardson, 2011). One research goal in recent decades has been to develop methods capable of characterizing unknown disinfection by-products. This is important for better understanding the health risks of DBPs and identifying those that may be responsible for human health effects.

This paper deals with the development of an innovative method for the quantification of brominated and iodinated fractions using a liquid chromatography system (HPSEC) coupled to an elemental detector (ICP-MS: Inductively Coupled Plasma – Mass Spectrometer). Here we discuss the analytical approach to monitor the halogenation of organic matter by bromine (Br) and iodine (I) using the HPSEC-ICP-MS method. This study presents the experimental conditions, development stages, and solutions used in the development of this method.

## MATERIAL AND METHODS

The method was developed using a standard extract of humic substance from the Suwannee River (Suwannee River SRNOM from the International Humic Substances Society - IHSS). The organic matter extract was subjected to halogenation using different doses of oxidants HOBr and HOI. Each experiment used 1 mL of previously dissolved SRNOM organic material introduced into 10 mL of pH 8 phosphate buffer,
resulting in a concentration of 5.3 mgC/L. Samples were treated with varying doses of oxidants to achieve HOBr and HOI concentrations of 1, 2, 5, 10, and 20 µM. After 24 hours, the samples were analyzed using HPSEC-ICP-MS. The organic matter is in large excess compared to the dose of oxidant applied therefore, no oxidant residuals persist.

Steric exclusion chromatography is a form of liquid chromatography that separates molecules based on their size. This technique can be used to separate various fractions present in organic matter, such as biopolymers (BP), humic substances (HS), and low molecular weight (LMW) (Zhao and al., 2009). The Agilent SEC-3 column (3 µm, 100 Å, 7.8 x 300 mm) was used for steric exclusion. The sample components interact with the stationary phase of the column, which contains particles with pores of varying sizes that the sample molecules penetrate. This separates the different fractions of organic matter, each with a specific retention time. See Table 1 for chromatographic conditions.

The different halogenated organic matter fractions are then identified using ICP-MS. This technique creates a high-temperature plasma from an ionized gas, which desolvates, atomizes and ionizes the sample constituents. A collision/reaction chamber eliminates interference, and the resulting ions are filtered by a quadrupole and directed to a mass spectrometer for analysis. Adjustments to the ICP-MS parameters have improved the sensitivity of the method for detecting bromine and iodine. Table 1 illustrates the ICP-MS conditions applied. Ions are detected by an electron multiplier when they reach a dynode (Paucot, 2010), allowing for quantification of the concentration of these two halogens incorporated into organic matter. A direct calibration is all that is needed to convert the area of the recorded signals into concentrations (Burgot and al., 2011). The standards chosen for the quantification of brominated and iodinated signals are 4-bromophenylacetic acid and sodium diatrizoate.

<table><caption>**Table. 1** Conditions of HPSEC-ICP-MS method.</caption><thead><tr><th>Method</th><th>HPSEC-ICP-MS</th></tr></thead><tbody><tr><td><strong>HPSEC conditions</strong></td><td></td></tr><tr><td>Mobile phase</td><td>Phosphate buffer 1g/L</td></tr><tr><td>Flow rate</td><td>0.8 mL/min</td></tr><tr><td>Injection volume</td><td>100 µL</td></tr><tr><td>Elution time</td><td>20 min</td></tr><tr><td>Column temperature</td><td>25 °C</td></tr><tr><td><strong>ICP-MS conditions</strong></td><td></td></tr><tr><td>Nebulizer</td><td>Micromist</td></tr><tr><td>Argon flow rates (Make-up)</td><td>0.1 mL/min</td></tr><tr><td>Nebulizer chamber</td><td>Scott type at 2°C</td></tr><tr><td>RF power (Plasma)</td><td>1600 W</td></tr><tr><td>Sampling depth</td><td>9 mm</td></tr><tr><td>Cones / lenses</td><td>Ni / x-lens</td></tr><tr><td>Collision gas</td><td>Helium (4.5 mL/min) for Br</td></tr><tr><td>Discrimination voltage</td><td>5 V</td></tr><tr><td>Acquisition frequency per isotope</td><td>0.3 sec</td></tr></tbody></table>

## RESULTS AND DISCUSSION

Halogenations were performed using an extract of humic substances to ensure controlled experimental conditions. A contact time of 24 hours was applied to ensure complete consumption of the oxidant (when applied as the limiting reagent). Different doses of oxidants were used (from 1 to 20 µM).
For samples halogenated with HOBr, analysis by HPSEC-ICP-MS revealed two peaks, as shown in **Figure 1a**. The first peak corresponds to the incorporation of bromine into the organic matter extract. The second pic was identified as bromide, with retention time of 10.2 minutes.

Additionally, three peaks were obtained by HPSEC-ICP-MS for HOI halogenation corresponding to iodine incorporated on the humic substance, iodate and iodide, respective to the increasing retention time (Figure 1b).

The area of these peaks was converted to concentration using 4-bromophenylacetic acid and sodium diatrizoate as calibration standards for bromine and iodine respectively.

<figure><img src="image_3.png" /><figcaption>**Figure 1** HPSEC-ICP-MS chromatograms obtained for the analysis of humic substance (HS) halogenated by (a): HOI and (b): HOBr at 10 µM.</figcaption></figure>

The percentage of halogen incorporation into the humic substance was determined for each dose of oxidant solution. The percentage of bromine and iodine incorporation decreases with increasing doses of oxidants. This decrease is due to the reduction in the number of active sites available on the organic matter. Additionally, both halogens have a similar tendency to react with organic matter.

Reproducibility tests were conducted using varying doses of HOI and HOBr, specifically 1, 2, and 5 µM. The results demonstrated good reproducibility in terms of percentage incorporation, with an average of 31%, 27%, and 22% for iodine and an average of 29%, 25%, and 22% for bromine for doses of 1 µM, 2 µM, and 5 µM, respectively. The standard deviation was less than 5%, which reinforces the reliability of the data obtained.

To evaluate the detection and quantification limits of the HPSEC-ICP-MS method for bromine and iodine signals in organic matter, two humic substance samples were halogenated with HOBr and HOI. The concentrations of incorporated bromine and iodine were determined using HPSEC-ICP-MS. The samples were analyzed in quadruplicate, and the percentage differences from theoretical values were calculated. Acceptable error percentages are 15% for detection limits and 5% for quantification limits. We established a limit of detection (LOD) of 2.5 ppb and a limit of quantification (LOQ) of 7.5 ppb for bromine, and an LOD of 0.2 ppb and an LOQ of 0.6 ppb for iodine.

To investigate the impact of reducing agents on iodine- and bromine-halogenated organic matter, three series of halogenation experiments were conducted. HOI and HOBr were used as oxidizing solutions, and each solution was tested in triplicate. No additions were made after 24 hours in the first triplicate, while ascorbic acid and sulfite were added in the second and third triplicates. The samples were then analyzed.
<table><caption>**Table. 2** Influence of reductants on HS halogenated</caption><thead><tr><th>Samples</th><th>I-HS<br>(%)</th><th>Br-HS<br>(%)</th></tr></thead><tbody><tr><td>without reductants</td><td>32,1</td><td>29,8</td></tr><tr><td>with ascorbic acid</td><td>28,8</td><td>27,4</td></tr><tr><td>with sulfite</td><td>25,2</td><td>28,4</td></tr></tbody></table>

**Table. 2** shows a decrease in the percentage of iodine incorporation into organic matter in the presence of reducing agents. It is evident that reducing agents have an impact on the degradation of the bond between iodine and organic matter. Similarly, the incorporation of bromine into organic matter also exhibited a slight decrease in the presence of reducing agents. However, the decrease in bromine incorporation into organic matter falls within the error margin of the incorporation percentages. Therefore, reducing agents do not appear to affect bromine incorporation into organic matter.

The HPSEC-ICP-MS method presented is an advanced analytical technique for characterizing halogenated organic compounds in water. Conventional methods for assessing total halogenated compounds often have limitations, but this innovative approach overcomes these challenges, providing a more detailed and comprehensive understanding of water quality. The presented results contribute to the ongoing improvement on water quality monitoring proposing a single method without pretreatment to quantify organic and inorganic iodine and bromine species.

## REFERENCES

Burgot, G., & Burgot, J. L. 2011. *Méthodes instrumentales d'analyse chimique et applications: Méthodes chromatographiques, électrophorèses, méthodes spectrales et méthodes thermiques*. Lavoisier.

Hu, J., Jin, X., Kunikane, S., Terao, Y., & Aizawa, T. 2006. Transformation of pyrene in aqueous chlorination in the presence and absence of bromide ion: kinetics, products, and their aryl hydrocarbon receptor-mediated activities. *Environmental science & technology*, 40(2), 487-493

Paucot, H. ICP-MS: 2010. Couplage plasma induit par haute fréquence-spectrométrie de masse. *Ed. Techniques Ingénieur*.

Richardson, S. D. 2011. Disinfection By-Products: Formation and Occurrence in Drinking Water. *Encyclopedia of environmental health*, 2, 110-136.

Zhao Z.Y., Gu J.D., Li H.B., Li X.Y., & Leung M.Y. 2009. Disinfection characteristics of the dissolved organic fractions at several stages of a conventional drinking water treatment plant in Southern China. *J Hazard Mater.* 172(2-3):1093-9.