# Role of membrane porosity in passive sampling of aquatic contaminants for stable isotope analysis: enhancement of analyte accumulation rates and selectivity

## TL;DR

Increasing membrane pore size in water samplers speeds up contaminant collection without affecting isotope analysis accuracy, making it easier to study low-concentration pollutants.

## Contribution

Increasing membrane porosity enhances analyte accumulation rates and selectivity in passive samplers while preserving isotopic integrity.

## Key findings

- Increasing membrane pore size from 0.1 to 8 μm increased mass accumulation rates of atrazine, S-metolachlor, and boscalid by 3.0-3.5 times.
- Larger pores did not compromise isotopic integrity, with Δδ13C ≤ +0.4±0.1‰ and Δδ15N ≤ -0.6±0.4‰.
- Larger pores showed enhanced selectivity for target analytes over humic acids without increased biofouling.

## Abstract

Compound-specific isotope analysis (CSIA) is a potent method for illustrating the in situ degradation of aquatic contaminants. However, its application to surface and groundwater is hindered by low contaminant concentrations, typically in the nanogram-per-litre range, requiring the processing of large water volumes. Polar organic chemical integrative samplers (POCIS) have shown promising results when combined with CSIA, yet their extended deployment time to accumulate sufficient analyte mass remains a major limitation. In our study, we addressed this issue by increasing the pore size of the polyethersulfone membrane (PES) from 0.1 to 8 \documentclass[12pt]{minimal}
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\begin{document}$$\upmu $$\end{document}μm. This resulted in significant increases in the mass accumulation rates of atrazine (3.5-fold), S-metolachlor (3.4-fold), and boscalid (3.0-fold). Importantly, the larger pore sizes did not compromise isotopic integrity, with \documentclass[12pt]{minimal}
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\begin{document}$$\Delta \delta ^{13}$$\end{document}Δδ13C\documentclass[12pt]{minimal}
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\begin{document}$$\le +0.4\pm 0.1$$\end{document}≤+0.4±0.1‰ and \documentclass[12pt]{minimal}
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\begin{document}$$\Delta \delta ^{15}$$\end{document}Δδ15N\documentclass[12pt]{minimal}
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\begin{document}$$\le -0.6\pm 0.4$$\end{document}≤-0.6±0.4‰, both within accepted uncertainties. Additionally, we observed an enhanced selectivity of the larger pores towards the target analytes over humic acids, whereas no significant increase in (bio)fouling potential was detected for the 8 \documentclass[12pt]{minimal}
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\begin{document}$$\upmu $$\end{document}μm membrane, as demonstrated by gravimetric analysis, SEM measurements, mass accumulation rates, and isotope ratios of fouled and unfouled POCIS. Our findings show that increasing the membrane pore size from 0.1 to 8 \documentclass[12pt]{minimal}
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\begin{document}$$\upmu $$\end{document}μm reduces deployment time and expedites the accumulation of analyte mass required for gas chromatography isotope ratio mass spectrometry, offering a promising method to expand CSIA for low-concentration pesticide analysis in the field.

The online version contains supplementary material available at 10.1007/s00216-025-05756-9.