SPADNS Colorimetric Method to Quantify Fluorides in Water

Importance of the Topic

The accurate measurement of fluoride in water is critical for public health and regulatory compliance. Maintaining fluoride levels within recommended limits helps prevent dental caries while avoiding adverse effects such as fluorosis. Reliable, rapid analytical methods are essential for routine monitoring of drinking and environmental water.

Objectives and Study Overview

This application note presents a protocol for quantifying fluoride in water using the SPADNS colorimetric method adapted to the Agilent Cary 60 UV-Vis spectrophotometer. The aim was to establish a straightforward, automated workflow that produces a linear calibration curve from 0 to 1.4 mg/L and can be extended to 3.5 mg/L using nonlinear fitting.

Methodology and Instrumentation

The SPADNS method relies on the bleaching of a zirconium-dye complex by fluoride ions, monitored at 570 nm. Sample and reagent preparation steps include:

• Preparation of zirconyl and SPADNS reagents and mixing to generate the red indicator solution.
• Preparation of stock fluoride solutions and calibration standards (0.2–1.4 mg/L).
• Acidification and addition of the mixed reagent to each standard or sample.

Instrumentation used:

• Agilent Cary 60 UV-Vis spectrophotometer with quartz 10 mm cell.
• Agilent Cary WinUV software (Concentration module, v5.1.3.1042).

Analytical parameters:

• Wavelength: 570 nm; signal averaging time: 0.1 s; three replicates per measurement.
• Calibration fit: linear, minimum R² of 0.95000; extended range via quadratic fit if required.

Main Results and Discussion

A linear calibration curve between 0 and 1.4 mg/L fluoride exhibited a slope of –0.1872 and a correlation coefficient (R²) of 0.9993. The automated concentration report generated by the software includes:

• Calibration equation and statistics (mean absorbance, SD, %RSD).
• Sample concentrations calculated directly from the curve, reducing manual data processing.

Analysis of spiked water samples (0.5 and 0.7 mg/L) demonstrated accurate recoveries and low RSD values, confirming method precision and robustness.

Benefits and Practical Applications

The described workflow streamlines fluoride analysis by automating data acquisition, calibration, and reporting. Key advantages include:

• Rapid single-wavelength measurements and method setup.
• Automated calibration curve generation and concentration calculations.
• Flexibility to adjust fitting models for extended concentration ranges.
• Suitable for routine water quality monitoring in environmental, municipal, and industrial laboratories.

Future Trends and Opportunities

Emerging developments may enhance this approach by:

• Integrating online flow-injection analysis for real-time monitoring.
• Applying chemometric or machine-learning algorithms to improve calibration across complex matrices.
• Expanding colorimetric methods to simultaneous multi-analyte detection.

Conclusion

The Agilent Cary 60 UV-Vis spectrophotometer and Cary WinUV software provide a convenient, precise platform for SPADNS-based fluoride determination in water. The method delivers high linearity, low variability, and automated data handling, making it well suited for routine analysis and regulatory compliance.

Reference

1. Guidelines for Drinking-Water Quality, 4th Edition, WHO, 2011.
2. Shahroom NB, Mani G, Ramakrishnan M. Interventions in Management of Dental Fluorosis, an Endemic Disease: A Systematic Review. J Family Med Prim Care. 2019;8(10):3108.
3. Standard Methods 4500-F-A, B and D. Determination of Fluoride F- Spectrophotometric Method; Standard Methods for the Examination of Water and Wastewater, 22nd Edition, American Public Health Association.