Fluorescence detection for phosphate monitoring using reverse injection analysis

Area of Science:

• Analytical Chemistry
• Environmental Science
• Optical Sensing

Background:

• Accurate measurement of dissolved reactive phosphate is crucial for environmental monitoring.
• Existing methods may lack portability or in situ capabilities.
• Flow analysis offers advantages in sample throughput and reagent consumption.

Purpose of the Study:

• To present a novel compact flow-through fluorescence detector for flow analyses.
• To demonstrate the detector's functionality for dissolved reactive phosphate determination.
• To enable in situ measurements by decoupling the analytical setup from environmental pressure.

Main Methods:

• Utilized a glass capillary for detecting diffusely emitted fluorescence.
• Employed axially coupled LED light for fluorescence excitation and a photodiode for collection.
• Implemented a reversed flow injection analysis system.
• Used Rhodamine 6G fluorescence quenching by phosphomolybdate for phosphate quantification.

Main Results:

• Achieved a measuring range of 0-40 µg L⁻¹ PO₄-P.
• Obtained detection limits of 0.22 µg L⁻¹ PO₄-P in water and 0.45 µg L⁻¹ PO₄-P in seawater.
• Reached a sampling frequency of up to 300 samples per hour.
• Demonstrated repeatability between 0.6% and 4.6% RSD.

Conclusions:

• The developed compact fluorescence detector is effective for dissolved reactive phosphate analysis.
• The system is suitable for in situ applications in both freshwater and seawater.
• The detector offers high sensitivity, rapid sampling, and good repeatability.