Solid-phase extraction of aquatic organic matter: loading-dependent chemical fractionation and self-assembly

Abstract

<p>Dissolved organic matter (DOM) is an important component in marine and freshwater environments and plays a fundamental role in global biogeochemical cycles. In the past, optical and molecular-level analytical techniques evolved and improved our mechanistic understanding about DOM fluxes. For most molecular chemical techniques, sample desalting and enrichment is a prerequisite. Solid-phase extraction (SPE) has been widely applied for concentrating and desalting DOM. The major aim of this study was to constrain the influence of sorbent loading on the composition of DOM extracts. Here we show that increased loading resulted in reduced extraction efficiencies of dissolved organic carbon (DOC), fluorescence and absorbance, and polar organic substances. Loading-dependent optical and chemical fractionation induced by altered adsorption characteristics of the sorbent surface (PPL) and increased multilayer adsorption (DOM self-assembly) can fundamentally affect biogeochemical interpretations, such as the source of organic matter. Online fluorescence monitoring of the permeate flow allowed to empirically model the extraction process, and to assess the degree of variability introduced by changing the sorbent loading in the extraction procedure. Our study emphasizes that it is crucial for sample comparison to keep the relative DOC loading (DOC<sub>load</sub> [wt%]) on the sorbent always similar to avoid chemical fractionation.</p>

Solid phase extraction of ocean dissolved organic matter with PPL cartridges: efficiency and selectivity

“…A likely reason for this difference is that we passed about 2 mg C per gram of PPL sorbent (4-4.5 L of water), while these authors passed not more than 1 mg C per gram of sorbent, which seems to improve the recovery of DOM compounds. This assumption aligns with Kong et al (2021), who shown that increasing DOC loads led to lower DOC, absorbance and fluorescence extraction efficiencies. Furthermore, differences between studies could be due to location and/or DOM quality and quantity.…”

Molecular Composition of Dissolved Organic Matter in the Changjiang (Yangtze River) – Imprints of Anthropogenic Impact

“…As observed in other studies (Wang et al, 2019b;He et al, 2020;Pang et al, 2021) molecular formulas consisted primarily of the CHO elemental series (59-76%), followed by sulfur (12-24%) and nitrogen containing formulas (10-19%) in most samples (Table 1). For the 2010 samples, we adjusted extraction volumes to DOC concentrations to avoid loading-dependent fractionation as Kong et al (2021) suggested (Figure S1). The variation of (O/C) wa and (H/C) wa varied with the DOC loadings but did not differ between the two sampling periods.…”

“…a 254 , FI, SUVA 254 and florescence excitations emission matrix parallel factor components (McKnight et al, 2001;He et al, 2020). Recently it has been reported that one should be careful with such comparison analyses that were performed on original water and extracted samples (e.g., Wünsch et al, 2018;Kong et al, 2021). One detailed investigation elucidated that FT-ICR-MS formulas assigned to PARAFAC components represented ~40% of the total number of formulas identified and ~60% of total FT-ICR-MS peak intensities (Stubbins et al, 2014).…”