A low-cost, colorimeter-based portable device, for rapid, on-spot determination of fluoride in water

ABSTRACT

Accurate fluoride measurement in water is required for selecting safe water sources or for treatment options to lessen its impact on public health. A low-cost, portable device has been developed as a rapid fluoride measurement system. It works with an optimal concentration of alizarin red S-zirconium complex (ARS-Zr, the sensor reagent). The device is an LED-phototransistor-based assembly to detect changes in light absorbance at 527 nm, due to monotonically decreasing ARS-Zr concentration with increasing fluoride concentration in water. We have optimised reagent composition in the device, enabling us with a wider fluoride detection range (0.2–9 ppm), rapidly within 4 min; simultaneously ensuring better reagent stability for up to 34 days. Limit of detection (LOD) and limit of quantification (LOQ) of the device are 0.2 and 0.6 ppm, respectively. The device replicates an analytical spectrophotometer’s performance, with a maximum error up to 5% in only a couple of cases. The hand-held device does not give any interference in the presence of even a very high 200 ppm concentration of other common heavy metals ($\mathrm{C}{\mathrm{a}}^{2+}$, $\mathrm{Z}{\mathrm{n}}^{2+}$,$\mathrm{F}{\mathrm{e}}^{2+}$, $\mathrm{M}{\mathrm{g}}^{2+}$,$\mathrm{C}{\mathrm{u}}^{2+}$) and anions ($\mathrm{C}{\mathrm{l}}^{-}$, ${\mathrm{N}\mathrm{O}}_3^{-}$, ${\mathrm{S}\mathrm{O}}_4^{2-}$, ${\mathrm{I}}^{-}$, CH₃COO⁻, ${\mathrm{C}\mathrm{O}}_3^{2-}$), which can be present in water. Fluoride concentration measurement above 1 ppm is unaffected, by even high phosphate concentration up to 10 ppm (typical phosphate level being only ≤ 2.3 ppm). Similarly, for silica concentration up to 10 ppm (typical silica level being 1-30 ppm), fluoride measurement remains unaffected. However, the presence of $\mathrm{F}{\mathrm{e}}^{3+}$ gives significant interference with fluoride. Overall, we demonstrate the device as an on-spot method, for rapid fluoride measurement, independent of TDS (57.6–151 ppm), pH (6.6–12.5) or conductivity (111.2–283 µS/cm) of the samples, at a low device cost of US$ 25 and reagent cost of 0.44 cents per sample.

KEYWORDS:

• Fluoride
• LED-phototransistor
• on-spot sensor
• sensor device
• selectivity

Acknowledgments

The authors thank Mr. Keerthi Vasan M, research intern in the laboratory of RB, for his significant help in conducting the initial fluoride measurement experiments. RB acknowledges partial funding support from Tata Centre for Technology and Design, IIT Bombay (Project number DO/2016-TATA001-034) for fabrication of the device. RB thanks Prof. Jayanta Chatterjee, Department of Electrical Engineering, IIT Bombay for providing very helpful guidance and discussion in designing the device in the early stages of the project.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Authors contribution

All authors contributed to the study’s conception and design. Material preparation, data collection and analysis were performed by both Shankar Ramachandran and Vishwesh Dutt Awasthi. The first draft of the manuscript was written by Shankar Ramachandran and later updated by Vishwesh Dutt Awasthi and finally corrected by Rajdip Bandyopadhyaya. All the authors have read and approved the final manuscript.

Data availability statement

The datasets used or analysed during the current study are available from the corresponding author upon reasonable request.

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/03067319.2023.2219973

Additional information

Funding

The work was supported by the Tata Centre for Technology and Design, Indian Institute of Technology Bombay [DO/2016-TATA001-034].