Quantify Quinine in Beverages Using the Agilent Cary Eclipse Spectrofluorometer and a Fiber Optic Dip Probe

Significance of the Topic

Fluorescence spectrophotometry is a cornerstone of modern QA/QC in food and beverage production due to its exceptional sensitivity and selectivity. Integrating fiber optic sampling with the Agilent Cary Eclipse spectrofluorometer addresses challenges of speed, contamination risk, and room-light interference, enabling rapid, accurate in situ analysis of intrinsically fluorescent compounds such as quinine.

Objectives and Study Overview

This application note evaluates a streamlined workflow for quantifying quinine in tonic water samples. The goals are to compare traditional cuvette-based measurements with fiber optic dip probe sampling, demonstrate reproducibility, minimize sample handling, and confirm compliance with regulatory quinine limits.

Methodology and Used Instrumentation

• Instrumentation: Agilent Cary Eclipse fluorescence spectrophotometer featuring engineered room-light immunity.
• Accessory: Fiber optic liquid dip probe with a black quartz base and 10 mm path length.
• Sample preparation: Quinine sulfate standards (0.10–1.00 mg/L) prepared in 0.05 M H₂SO₄; four commercial tonic waters diluted 1:100 prior to analysis.
• Data processing: Emission measured at 450 nm following excitation at 350 nm; calibration and sample data handled in Agilent Scan software (WinFLR).

Main Results and Discussion

Calibration curves from both cuvette and fiber optic methods exhibited coefficients of determination (R²) ≥ 0.9998, indicating equivalent linearity and sensitivity. Emission spectra recorded with the probe matched those obtained with the sample compartment closed, confirming immunity to ambient light. Quantified quinine concentrations in four tonic water brands ranged from 53 to 65 ppm, all below the FDA maximum of 83 ppm.

Benefits and Practical Applications

• Analysis time reduced by approximately one third through elimination of cuvette filling, cleaning, and drying steps.
• Lower contamination risk and sample carryover due to direct dip probe measurements.
• Minimal solvent and waste generation enhances laboratory sustainability and cost-effectiveness.
• Applicability to in situ monitoring on production lines supports real-time quality control.

Future Trends and Possibilities

Advancements may include integration of fiber optic fluorescence probes into automated process analytical technology (PAT) frameworks, expansion to other intrinsic fluorophores (vitamins, amino acids, toxins), and incorporation of chemometric models for multi-component analysis. Miniaturized and portable spectrofluorometers could further extend on-site monitoring and field applications.

Conclusion

The Agilent Cary Eclipse with fiber optic dip probe offers a robust, rapid, and contamination-resistant solution for fluorescence-based quantification in food and beverage analysis. It matches or exceeds traditional cuvette performance while simplifying workflow and reducing operational costs.

References

• Christensen J. Foodfluor – Food Fluorescence Library. University of Copenhagen; 2005.
• Chen GQ, Wu YM, Wang J, Zhu T, Gao SM. Spectroscopy and Spectral Analysis. 2009;29:2518–2522.
• O’Reilly JE. J Chem Educ. 1975;52:610–612.
• Anon. Code of Federal Regulations Title 21, Vol 3. U.S. FDA; 2014.