A rapid quantitative method for humic substances determination in natural waters.

Area of Science:

• Environmental Chemistry
• Analytical Chemistry
• Water Quality Analysis

Background:

• Humic substances (HS) are crucial organic components in natural waters, influencing water quality and biogeochemical cycles.
• Accurate quantification of HS is essential for environmental monitoring and understanding aquatic ecosystems.
• Existing methods for HS determination can be time-consuming or require specialized equipment.

Purpose of the Study:

• To develop a simple, rapid, and sensitive method for determining humic substances (HS) at microgram levels in natural waters.
• To validate the proposed assay against established reference methods for water sample analysis.
• To characterize the binding interaction between Toluidine Blue and humic substances.

Main Methods:

• A spectrophotometric assay utilizing the dye Toluidine Blue (TB) to bind with HS molecules.
• Measurement of the decrease in absorbance at 630 nm due to the formation of a dye-HS complex.
• Calibration of the method using HS standards up to 40 mg L(-1) and validation with natural water samples.

Main Results:

• The method demonstrated a detection limit of 0.8 mg L(-1) for HS.
• A relative standard deviation of 3.5% was achieved for replicate measurements.
• Binding equilibrium constants and site densities were calculated using Langmuir adsorption isotherm theory, indicating strong binding affinity.

Conclusions:

• The proposed Toluidine Blue assay is a rapid, sensitive, and feasible method for HS determination in natural waters.
• The results obtained were consistent with reference methods, confirming the accuracy and reliability of the new assay.
• This method offers a valuable tool for routine environmental water quality monitoring and research.