# Interfacial Separations by a Polydimethylsiloxane Layer. Molecular Modeling of Coated Stir Bar Extraction of Organics from Aqueous Solutions

## TL;DR

This paper uses molecular simulations to study how temperature affects the extraction of organic compounds using a PDMS-coated stir bar, showing that higher temperatures improve extraction efficiency.

## Contribution

The study introduces molecular dynamics simulations to predict temperature-dependent sorption behavior in PDMS without using octanol–water partitioning as a proxy.

## Key findings

- MD simulations revealed a nonmonotonic temperature dependence of log P [PDMS/water] values.
- Higher temperatures increase the number of organic molecules in the PDMS phase due to enhanced diffusion and sorption capacity.
- SBSE performance can be optimized by adjusting temperature, improving trace-level extraction sensitivity.

## Abstract

Separation processes
relying on interfacial interactions, such
as the stir bar sorptive extraction represent one of the most critical
methods of analyte trace organic detection and extraction in environmental,
food, and biomedical samples. While the use of polydimethylsiloxane
(PDMS) as a sorptive coating in SBSE has exhibited high sensitivity
and efficiency; the molecular mechanisms involved are less explored.
We report molecular simulation studies using molecular dynamics (MD)
to investigate the absorption of organic compounds including phenol,
chlorophenol, guaiacol, benzyl alcohol, and phenethyl alcohol at the
aqueous-PDMS interface, and focus on temperature-dependent behavior.
By employing an appropriate force field for PDMS, organic compounds,
and water, these simulations directly predict PDMS-water partition
coefficients, log P [PDMS/water], diffusion coefficients, and solubilities
in the PDMS phase without relying on octanol–water partitioning
as a surrogate. An important result of the MD simulations in this
work is our ability to predict the temperature dependence of the log
p(PDMS/water). Results reveal a nonmonotonic temperature-dependent
sorption trend for log P [PDMS/water] values. However, we find that
with increasing temperature, the absolute number of organic molecules
in the PDMS phase increases, driven by enhanced molecular diffusion
and PDMS’s significant sorption capacity. The findings demonstrate
that performing SBSE at elevated temperatures can enhance analyte
uptake, improving the analytical sensitivity of trace level extractions,
where achieving sufficient analyte concentration in the sorptive phase
is critical for reliable detection and quantification in a wide variety
of applications in environmental monitoring, food safety, and biomedical
analysis. These simulations predict that temperature is a good parameter
for the optimization of operating conditions of SBSE. Our results
also highlight the ability of MD simulations to reliably capture complex
molecular level interactions governing SBSE performance, aligning
well with experimental trends and observed behaviors.