Temperature Dependence of Dissolved Organic Matter Fluorescence

Area of Science:

• Environmental Chemistry
• Photochemistry
• Spectroscopy

Background:

• Organic matter fluorescence is a key indicator in environmental monitoring.
• Temperature significantly influences fluorescence measurements, necessitating corrections.
• Understanding the photophysics of organic matter is crucial for accurate analysis.

Purpose of the Study:

• To measure the temperature dependence of organic matter fluorescence apparent quantum yields (Φf).
• To determine apparent activation energies (Ea) for radiationless decay processes.
• To provide a physical basis for correcting fluorescence sensors for temperature effects.

Main Methods:

• Measured temperature-dependent Φf for diverse organic matter isolates and whole water samples.
• Calculated Ea using steady-state fluorescence data and the Arrhenius equation.
• Analyzed Ea variation with excitation wavelength.

Main Results:

• Aquatic-derived isolates and whole water samples showed temperature-dependent Φf with Ea values from 5.4 to 8.4 kJ mol⁻¹ at 350 nm.
• Soil humic acid isolates exhibited minimal temperature dependence.
• Observed a narrow range of Ea values across diverse samples, suggesting a common photophysical mechanism.

Conclusions:

• A consistent photophysical mechanism governs non-radiative decay in excited singlet states of organic matter.
• Temperature-dependent fluorescence analysis offers a fundamental, physical basis for sensor correction.
• This approach improves the accuracy of fluorescence-based environmental monitoring.