Passive Sampler Exchange Kinetics in Large and Small Water Volumes Under Mixed Rate Control by Sorbent and Water...

Area of Science:

• Environmental Chemistry
• Analytical Chemistry
• Chemical Engineering

Background:

• Exchange kinetics of organic compounds between passive samplers and water are often influenced by diffusion within the sorbent material.
• Accurate modeling is essential for reliable environmental monitoring and chemical analysis.

Purpose of the Study:

• To present and discuss a diffusion model for predicting organic compound exchange kinetics in passive samplers.
• To evaluate the model's applicability to various sampling conditions and compound types (polar and nonpolar).

Main Methods:

• A mathematical model based on cosines (space) and exponentials (time) was developed.
• The model was applied to scenarios with fixed aqueous concentrations (open systems) and fixed amounts (closed systems).
• Numerical implementation in software and spreadsheets was detailed, considering accuracy and key parameters like Biot number and phase ratio.

Main Results:

• Diffusion models are infrequently required for nonpolar compounds using standard single-phase polymer samplers.
• Sorbent/water phase ratio significantly impacts the time to reach equilibrium in batch sorption studies.
• Sorbent-controlled kinetics are probable for polar organic compounds sampled with extraction disks, necessitating a reevaluation of sampling rate models.

Conclusions:

• The developed diffusion model provides a framework for understanding complex exchange kinetics in passive sampling.
• Model application highlights the importance of considering sorbent properties and system conditions for accurate environmental monitoring.
• Current sampling rate models may need revision for certain passive samplers, particularly those used for polar organic compounds.