Addressing Challenges of Membrane Clogging in AF4-UV-ICPMS Analysis for Size Determination of Trace Elements in Acidic, Organic-Rich Peat Bog Waters

The analysis of colloid-associated trace elements (TEs) in acidic, organic-rich waters (pH 3.8-5.8) using AF4-UV-ICPMS often necessitates the use of neutral or weakly alkaline carriers (pH 7-8.6). Employing acidic mobile phases has been deemed impractical due to the substantial sorption of colloids onto a 0.3 kDa polyethersulfone (PES) membrane and greatly reduced separation performance. This has greatly restricted the determination of potentially bioavailable forms of TEs (i.e., < 1 kDa) in acidic, organic-rich waters. To address this issue, porewaters from <i>Sphagnum</i> moss and peat were investigated. Membrane clogging was more pronounced in peat porewaters, where a higher deposition rate of dissolved organic matter onto the membrane was observed compared to that in moss waters. This adsorption is driven by membrane-colloid interactions, with colloids in peat porewaters exhibiting weaker electrostatic repulsion due to their higher positive ζ-potentials. Considering the actual pore size and clogging tolerance of the membrane, it is advisable to employ a 5 kDa PES membrane for peat porewaters, while a 1 kDa PES membrane suits moss waters better. Employing the optimal method enables the separation of TEs within the 0.5-20 kDa size range. Operating within a metal-free, ultraclean laboratory, TEs are detectable at the ng·L^-1 level. By enabling precise and accurate separation of dissolved TEs into their size species in these peat bog waters at an appropriate pH, this method addresses diverse size profiles. This information is crucial for comprehending the chemical forms, transformations, mobility, and potential bioavailability of TEs in peat bogs.