Time weighted average concentrations measured with Diffusive Gradients in Thin films (DGT).

Area of Science:

• Environmental Chemistry
• Analytical Chemistry
• Water Quality Monitoring

Background:

• Time-weighted average (TWA) concentrations are crucial for accurate water quality assessment.
• Diffusive Gradients in Thin films (DGT) devices offer a method for measuring TWA metal concentrations.
• The relationship between DGT-measured labile concentration (c_DGT) and TWA requires rigorous examination.

Purpose of the Study:

• To rigorously discuss and define the connection between DGT measurements (c_DGT) and Time-Weighted Average (TWA) metal concentrations.
• To evaluate the suitability of c_DGT as a proxy for TWA metal concentrations under various conditions.
• To identify factors influencing the accuracy of c_DGT in representing TWA metal concentrations, particularly in the presence of metal complexes.

Main Methods:

• Theoretical analysis of DGT measurements and TWA concentrations.
• Comparison of c_DGT with TWA concentrations in simple metal solutions and solutions containing ligands (e.g., Ni + NTA).
• Investigation of DGT performance under varying conditions, including short metal pulses and the presence of complexes.

Main Results:

• c_DGT represents the average DGT-labile metal concentration, correlating well with toxicity.
• In simple solutions without ligands and under perfect sink conditions, c_DGT accurately estimates TWA metal concentration.
• In the presence of complexes, c_DGT can underestimate TWA total metal concentration due to reduced lability and diffusivity of metal complexes.

Conclusions:

• c_DGT is a valuable indicator of average DGT-labile metal concentration and toxicity.
• The accuracy of c_DGT as a TWA metal estimator depends on solution chemistry, particularly the presence and nature of ligands.
• A correction factor can be applied to c_DGT to estimate TWA metal concentration in systems with a single dominant complex, like Ni-NTA.