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

Significance of the topic

Quality control in beverage production requires rapid, sensitive detection of fluorescent compounds such as quinine. Fluorescence spectrophotometry coupled with fiber optics offers nondestructive, in situ measurement with minimal sample preparation, reducing downtime, contamination risk, and overall cost of ownership.

Objectives and study overview

This application note demonstrates a streamlined method for quantifying quinine in beverages using an Agilent Cary Eclipse fluorescence spectrophotometer with a fiber optic dip probe. It compares fiber optic measurements to traditional cuvette‐based analysis to validate accuracy, reproducibility, and efficiency.

Methodology and instrumentation

• Instrumentation: Agilent Cary Eclipse fluorescence spectrophotometer equipped with a black quartz fiber optic liquid probe (10 mm path length) and standard 10×10 mm quartz cuvettes
• Calibration standards: Quinine sulphate in 0.05 M H2SO4 prepared at concentrations from 0.1 to 1.0 mg/L in PET vials
• Measurement procedures:
  
  • Cuvette method: fill cuvette, record spectrum, clean and dry between samples
  • Fiber optic method: dip probe into sample vial, record emission spectrum, wipe probe tip between runs
• Sample analysis: Four commercial tonic waters diluted 1:100 in 0.05 M H2SO4 and measured as unknowns

Main results and discussion

Calibration curves obtained by both cuvette and fiber optic methods exhibited excellent linearity with R2 values above 0.9998 at an excitation wavelength of 350 nm and emission at 450 nm. The fiber optic approach reduced total analysis time by about one third by eliminating cuvette handling. Quinine concentrations in the tonic water samples ranged from 53 to 65 ppm, all below the FDA limit of 83 ppm.

Benefits and practical applications of the method

• Increased throughput by removing cuvette cleaning and preparation steps
• Reduced risk of cross-contamination and sample waste
• High sensitivity and selectivity characteristic of fluorescence detection
• Suitable for in situ screening in quality control and production environments

Future trends and possibilities

Fiber optic fluorescence analysis is likely to see broader adoption in real-time process monitoring, with trends toward miniaturized, multiplexed probes, remote and inline measurements, integration with automated control systems, and expanded applications across food, pharmaceuticals, and environmental analysis.

Conclusion

The Agilent Cary Eclipse with fiber optic accessory provides fast, accurate, and reproducible quantification of fluorescent analytes such as quinine in beverages. It matches the performance of traditional cuvette methods while significantly improving workflow efficiency, reducing contamination risks, and lowering operational costs, making it ideal for routine QA/QC fluorescence analysis.

References

• Christensen J. Foodfluor – Food Fluorescence Library, University of Copenhagen, 2005
• Chen GQ et al. Spectrosc. Spectral Anal. 2009, 29, 2518–2522
• O’Reilly JE. J. Chem. Educ. 1975, 52, 610–613
• Anon. Code of Federal Regulations Title 21, Vol. 3, FDA, 2014