How is EPR Used to Track Free Radicals in Water Pollution?

A current and global pollution issue is hazardous organic waste which is spread widely in water by military, industrial, and domestic sources. Advanced Oxidation Processes (AOPs) are good techniques to remove the contaminants which are not biologically degradable.

AOPs are based on the chemistry of hydroxyl radicals (^•OH), which are non-selective ROS, they can oxidize water pollutants into inactivated end-products, yielding carbon dioxide and salt.

The optimization and design of AOPs rely on a number of parameters, including additional reactants, reaction time, and reagent dosage. The optimal conditions must be established to reduce operating costs and attain the most effective treatment.

The most reactive species in AOPs is the hydroxyl radical, and its interaction with the pollutants establishes the efficiency of the oxidation process. So, it is vital to grow the yield of hydroxyl radicals produced during AOPs. An EPR study on pharmaceutical residues is shown in Figure 1 (1).

Figure 1. AOP – pulsed corona plasma - EPR study on pharmaceutical residues.

Seven resistant pharmaceutical agents (Diclofenac, Ibuprofen, Diazepam, etc.) decomposed by pulsed corona plasma produced in water were included in the research. The degradation of Diclofenac measured by HPLC correlates directly to the increased hydroxyl radical concentration over time and discovered that hydroxyl radicals identified by EPR cause the decomposition of pharmaceutical compounds.

By employing the EPR spin-trapping method, the user can identify, quantify and monitor intrinsic production of short-lived radicals like hydroxyl radicals generated through AOPs. Unstable radicals are transformed into stable radicals in spin trapping experiments by reactions with spin-trapping agents, and so are detected by EPR.

EPR in Environmental Use – Working with Customers

The application of EPR, like those detailed above, has also been propelled by developments in instrumentation. The fundamentals of resolution, sensitivity, and stability are all linked to the magnet or microwave technology inside the spectrometer. Users and instrument manufacturers, such as Bruker, have worked closely to push the boundaries of application and produce increasingly powerful, flexible and stable EPR spectrometers.

At the forefront of EPR research, decades of experience have made Bruker’s benchtop instruments which are suitable for a large scope of laboratory types. The quality control e-scan,  the desktop research quality EMXnano, and the compact microESR all need minimal infrastructure and low cost of ownership for customers.

Customers worldwide are using the latest in EPR technology for their environmental applications. An example is the Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences that is carrying out two projects funded by the Ministry of Science and Technology and National Nature Science Foundation of China (NSFC).

In the State Key Laboratory of Environmental Chemistry and Eco-toxicity (SKLECE) at Research Center for Eco-Environmental Sciences (RCEES), Guorui Liu, associate professor position discusses the goals for these projects:

One of the important aims of these two projects is clarifying the free radical mechanisms during formations of dioxins and other unintentional persistent organic pollutants (POPs). The samples we tested using EPR include airborne particles, fly ash from industrial plants and contaminated soils. We also performing the in-situ monitoring of free radicals formed during designed thermochemical reactions of organic chemicals.

For over a decade the SKLECE has worked with Bruker with three years of communication in the area of free radicals monitored by EPR. Guorui Liu and her team bought the EMX-plus X-band EPR and FT-MS from Bruker, helping the team to progress in the clarification of EPFR formation, contamination, and control.

Guorui Liu details the techniques utilized for environmental research and the scope for further development with Bruker for methods in complex environmental samples:

We previously used GC/MS or GC/HRMS for monitoring POPs contaminations and we use EPR for detection of free radicals or EPFRs in environmental samples. However, the accurate attribution of the free radicals in complex environmental samples can still prove a challenge by EPR alone. We see scope to collaborate with Bruker to develop methods for the structure identification of EPFRs in complex environmental samples.

References

1. Banaschik R. et al., Degradation and intermediates of Diclofenac as instructive example for decomposition of recalcitrant pharmaceuticals by hydroxyl radicals generated with pulsed corona plasma, J. Hazard Mater. (2018) 342 651

This information has been sourced, reviewed and adapted from materials provided by Bruker BioSpin - NMR, EPR and Imaging.

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