Kinetic mixture effects in diffusion gradients in thin films (DGT).

Area of Science:

• Environmental Chemistry
• Analytical Chemistry
• Geochemistry

Background:

• Diffusive Gradients in Thin-films (DGT) devices are crucial for measuring labile metal concentrations.
• The penetration of metal complexes into the resin domain of DGT devices influences their lability and accumulation.
• Understanding complex dissociation dynamics within the resin is key to accurate metal speciation analysis.

Purpose of the Study:

• To investigate the influence of complex penetration into the resin domain on the lability degree of metal complexes in DGT devices.
• To analyze the effect of ligand concentration and mixtures on metal accumulation and lability.
• To develop a predictive model for metal accumulation based on individual complex lability.

Main Methods:

• Numerical simulation of metal complex diffusion and dissociation within DGT devices.
• Analysis of the reaction layer extension into the resin domain.
• Modeling the impact of ligand excess and mixed ligand systems on metal accumulation.

Main Results:

• Complex dissociation within the resin domain is the dominant factor in metal accumulation.
• The influence of ligand concentration on lability is significantly reduced in DGT compared to voltammetric sensors.
• Interactions between complexes in mixed ligand systems can lead to cancellations, making total metal accumulation less sensitive.
• Predictions of metal accumulation based on individual complex lability show discrepancies of up to 10%.

Conclusions:

• The lability degree of metal complexes is strongly influenced by their penetration and dissociation within the DGT resin domain.
• Metal accumulation prediction in DGT systems can be achieved by considering individual complex lability, with potential for refinement using thicker resin gels.
• The findings offer a pathway to predict metal accumulation, even in complex environmental matrices with mixed ligands.