Rethinking Fluoride Detection: A Zr–HQS Fluorescence Platform from Batch to Real-Time Flow Analysis

Author

• Tanmoy Chakraborty, University of Texas at ArlingtonFollow

Graduation Semester and Year

Spring 2026

Language

English

Document Type

Thesis

Degree Name

Master of Science in Chemistry

Department

Chemistry and Biochemistry

First Advisor

Dr. Purnendu K. Dasgupta

Second Advisor

Dr. Charles P. Shelor

Third Advisor

Dr. Gyeongjin Park

Abstract

Monitoring fluoride is important because fluoride is beneficial at low concentrations but can cause adverse health effects at elevated levels. In addition, released fluoride ions can serve as an indirect indicator of PFAS degradation or defluorination, making their accurate detection highly relevant. In this study, a fluorescence-based metal–ligand system was investigated for detecting fluoride at low concentrations.

Preliminary studies using the Fe-HQS system showed that Fe³⁺ forms higher-order of metal-ligand complexes with HQS. These complexes were not efficiently disrupted by low fluoride concentrations, resulting in weak fluorescence recovery and poor sensitivity. To overcome this limitation, a Zr–HQS system was investigated. Fluoride addition likely perturbed the Zr–HQS complex through the formation of stable Zr–F species, producing a reproducible fluorescence quenching response.

Systematic optimization of pH, buffer composition, buffer concentration, and Zr-HQS ratio showed that 50:50 µM Zr-HQS in 10 mM KHP at pH 4.0 provided the best batch response. The batch method showed good linearity, with an R² value of 0.9885 and a calculated LOD of 0.22 µM.

The method was further explored for real-time detection and was successfully adopted to Flow Injection Analysis (FIA) system. FIA parameters such as injection volume, flow rate, metal-ligand complex ratio, and mixing behavior were also investigated and optimized. The modified FIA system provided stable operation and µM-level fluoride detection, with an R² value of 0.9479 and an LOD of 12.0 µM. Overall, the Zr–HQS platform provides a promising fluorescence-based approach for low-level fluoride detection and has potential for future on-site, real-time fluoride monitoring.

License

This work is licensed under a Creative Commons Attribution-NonCommercial-No Derivative Works 4.0 International License.

Recommended Citation

Chakraborty, Tanmoy, "Rethinking Fluoride Detection: A Zr–HQS Fluorescence Platform from Batch to Real-Time Flow Analysis" (2026). Chemistry & Biochemistry Theses. 2.
https://mavmatrix.uta.edu/chemistry_theses2/2