SPANDS Colorimetric Method to Quantify Fluorides in Water

Significance of the Topic

Monitoring fluoride concentrations in water supplies is critical for public health. Controlled fluoridation reduces dental decay, but excessive levels can cause fluorosis and other adverse effects. International guidelines recommend maintaining fluoride between 0.5 and 1.5 mg/L. Accurate, rapid, and cost-effective analytical methods are essential for regulatory compliance and consumer safety.

Objectives and Overview of the Study

This application note demonstrates the use of the SPANDS colorimetric method, implemented on the Agilent Cary 60 UV-Vis spectrophotometer and Agilent Cary WinUV software, to quantify fluoride in water. The goals were to streamline sample analysis using the Concentration module, establish a calibration curve over the linear range (0–1.4 mg/L), and validate precision and accuracy for routine water monitoring.

Methodology and Instrumentation

The study employed:

• Agilent Cary 60 UV-Vis spectrophotometer with a 10 mm quartz cell
• Agilent Cary WinUV Concentration module (v5.1.3)

Sample preparation followed standard SPANDS protocols:

• Acid-zirconyl reagent prepared from ZrCl₂·8H₂O and HCl
• SPANDS dye solution stored in amber to protect from light
• Mixed acid-zirconyl-SPANDS reagent generated by combining equal volumes
• Stock fluoride solution: 100 mg/L from NaF
• Calibration standards: 0.2–1.4 mg/L via serial dilution

Analytical settings:

• Wavelength: 570 nm
• Signal averaging: 0.1 s
• Replicates: 3 per sample
• Calibration fit: Linear, R² ≥ 0.950

Main Results and Discussion

A linear calibration curve (0–1.4 mg/L) exhibited a slope of –0.1872 and R² = 0.9993. Automated data acquisition and analysis produced a comprehensive report with:

• Mean absorbance and standard deviation
• Calibration equation and correlation coefficient
• Calculated sample concentrations with %RSD

Known fluoride samples (0.5 and 0.7 mg/L) were analyzed successfully, with results matching expected values within acceptable variability. The method can be extended to 3.5 mg/L using a quadratic fit.

Benefits and Practical Applications

The integrated UV-Vis platform offers:

• Rapid single-wavelength measurements
• Automated calibration curve generation
• Streamlined software workflows reducing manual data handling
• Flexibility to customize reports and fit types

This approach supports water quality monitoring in municipal and laboratory settings, ensuring compliance with health standards.

Future Trends and Applications

Emerging directions include:

• Field-deployable UV-Vis instruments for on-site fluoride testing
• Automated multi-analyte methods combining SPANDS with other colorimetric assays
• Advanced software integration for cloud-based data management and remote monitoring
• Expanded linear ranges through novel calibration models and chemometric techniques

Conclusion

The Agilent Cary 60 UV-Vis spectrophotometer, coupled with the Cary WinUV Concentration module, provides a convenient, precise, and user-friendly platform for SPANDS-based fluoride quantification. The established method delivers reliable results within the linear 0–1.4 mg/L range, and software automation significantly reduces time and potential errors.

References

1. World Health Organization. Guidelines for Drinking-Water Quality, 4th Edition, 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, APHA.