SPANDS Colorimetric Method to Quantify Fluorides in Water

Importance of the Topic

Accurate fluoride measurement in water is critical for public health monitoring and regulatory compliance. Fluoride occurs naturally in groundwater and is often added to drinking water to prevent dental decay. However, excess fluoride exposure can lead to adverse health effects such as fluorosis and neurological impacts. The SPANDS colorimetric method offers a reliable approach to quantify fluoride concentrations in the range relevant to safe drinking water standards.

Objectives and Study Overview

This application describes the development of a rapid, automated method to quantify fluoride in water using the SPANDS colorimetric reaction on the Agilent Cary 60 UV-Vis spectrophotometer. By leveraging the Concentration module in Agilent Cary WinUV software, the study aims to streamline calibration, data acquisition, and concentration calculations, minimizing manual data processing.

Instrumentation

• Agilent Cary 60 UV-Vis spectrophotometer
• Quartz cuvette, 10 mm pathlength
• Agilent Cary WinUV software, Concentration module (version 5.1.3.1042)

Methodology and Protocol

The SPANDS method relies on a color-displacement reaction: fluoride ions displace SPANDS dye from a zirconyl-SPANDS complex, causing a reduction in absorbance at 570 nm proportional to fluoride concentration. Key steps include:

• Preparation of reagents:
  • Zirconyl-acid reagent (ZrCl2·8H2O in HCl)
  • SPANDS dye solution
  • Mixed acid-zirconyl-SPANDS reagent
• Standard solutions:
  • Stock fluoride (100 mg/L)
  • Working standards (0.2–1.4 mg/L) in 50 mL volumes
• Instrument setup:
  • Wavelength: 570 nm
  • Replicates: 3
  • Fit type: Linear (extended range via quadratic fit to 3.5 mg/L)
• Procedure:
  • Zero the instrument with reference solution
  • Add 10 mL zirconyl-SPANDS reagent to each standard or sample
  • Measure absorbance at 570 nm in triplicate
  • Automated generation of calibration curve and concentration report

Main Results and Discussion

A linear calibration curve (0–1.4 mg/L) exhibited a slope of –0.1872 and R² = 0.9993, demonstrating excellent method linearity. Analysis of test samples (0.5 and 0.7 mg/L fluoride) confirmed accurate quantification, with minimal relative standard deviations. The Cary WinUV software automatically applied the calibration model to unknown samples, significantly reducing analysis time and manual calculation errors.

Benefits and Practical Applications

The integrated spectrophotometer–software solution delivers:

• Fast method setup and data acquisition
• Automated calibration and concentration reporting
• Reduced hands-on data processing
• Robust performance for routine water quality monitoring and QA/QC laboratories

Future Trends and Applications

Advancements may include deployment of portable UV-Vis instruments for field testing, integration with automated sample handling systems, and expansion of the software’s calibration capabilities for higher concentration ranges. Coupling with online data management and cloud-based analytics will further streamline water quality surveillance.

Conclusion

The Agilent Cary 60 UV-Vis spectrophotometer, combined with the Cary WinUV Concentration module, provides a convenient, precise, and automated platform for fluoride determination by the SPANDS colorimetric method. Its ease of use and reliable performance support efficient water quality analysis in research, regulatory, and industrial settings.

References

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