DGT measurement in low flow conditions: diffusive boundary layer and lability considerations

Area of Science:

• Environmental Science
• Analytical Chemistry
• Water Quality Monitoring

Background:

• A diffusive boundary layer (DBL) can form around diffusive gradients in thin film (DGT) devices.
• This DBL may significantly affect metal measurement results in aquatic environments.
• Previous studies suggested methods to assess DBL impact.

Purpose of the Study:

• To evaluate the impact of DBL on metal measurements using DGT in water.
• To investigate metal complex dissociation kinetics in wastewater using DBL calculations.
• To assess the influence of water velocity on DGT measurements with restricted gels.

Main Methods:

• Laboratory experiments with DGT devices at various stirring speeds (0-400 rpm).
• Field deployments in a canal with controlled water velocity (0.07-3 cm s(-1)).
• Analysis of metal-ligand interactions and dissociation kinetics in wastewater.

Main Results:

• The error from ignoring the DBL was consistently lower than analytical error, even in low flow conditions.
• The DBL facilitates metal complex dissociation, expanding the lability window beyond the hydrogel's steric limits.
• Restricted gels' ability to exclusively sample inorganic species under these conditions is questionable.
• Lead (Pb) exhibited strong interactions with ligands in wastewater, showing limited mobility.

Conclusions:

• The DBL's impact on metal measurement accuracy by DGT is less significant than previously thought, especially concerning analytical error.
• The DBL plays a crucial role in metal complex dissociation and lability in natural waters.
• Wastewater characterization through metal-ligand kinetic signatures is feasible, with Pb showing strong complexation.