Molecular Mapping of Sorbent Selectivities with Respect to Isolation of Arctic Dissolved Organic Matter as Measured by Fourier Transform Mass Spectrometry

Abstract

The objectives of this study were to identify molecular features characteristic to arctic DOM from the Kolyma River basin and to elucidate structural imprints induced by a choice of the sorption technique. To achieve this goal, DOM was isolated from the Kolyma River basin with a use of three nonionic sorbents: Amberlite XAD-8 resin, PPL- and C18 - SPE cartridges, and one anion exchanging resin-diethylaminoethyl (DEAE) -cellulose. The structural studies were conducted with a use of electrospray ionization Fourier Transform Ion Cyclotron Resonance (ESI FT-ICR) mass spectrometry and liquid state (1)H NMR spectroscopy. The DOM isolates obtained with a use of PPL and C18 cartridges were characterized with higher content of aliphatic compounds as compared to XAD-8 and DEAE-isolates. In total, for all arctic DOM isolates we observed predominance of hydrogen saturated compounds with high H/C values of identified formulas from FT-ICR MS data. (1)H NMR spectroscopy studies have confirmed this trend and revealed high contribution of alkyl-chain protons into the spectral density of the arctic DOM reaching 43% for PPL isolates.

Solid-phase extraction-stepwise elution (SPE-SE) procedure for isolation of dissolved organic matter prior to ESI-FT-ICR-MS analysis

“…Ionization of the low-efficiency compounds will be suppressed with the increase of the high-efficiency compounds [33,34], limiting the detection of compounds with low ionization efficiency at low concentration [24,34]. Conventionally, one-step elution uses an organic solvent such as methanol to elute all the DOM components into one sample [18,19]. The present study provided a simple method using stepwise elution by MeOH/H 2 O with various ratios to divide the compounds in DOM into three fractions with different NOSC, a parameter representing the polarity of compounds in DOM since it is directly related to the H/C and O/C ratios of a compound [28].…”

“…), silica-based sorbents (C 8 , C 18 , etc. ), and polymer-based sorbents (styreneedivinylbenzene copolymer, PPL) have been tested for their ability to isolate DOM from natural waters [18,19]. Among these, PPL sorbent has become a widely accepted medium for the isolation of DOM from natural waters due to its ease of application, high extraction efficiency and the highly representative character of the DOM in isolates [18,21].…”

“…However, recent studies have observed that a great number of compounds in DOM such as highly oxygenated tannin-like molecules [22,23], nitrogenous compounds with high hydrophilic character [23], and fatty-acid-like molecules [24] are preferentially lost during the single-step SPE procedure for a variety of SPE sorbents, such as XAD, C 18 and PPL [19,22e26]. To solve this problem, combinations of different isolation methods such as dialysis and SPE [24], ultrafiltration and SPE [25] or SPE with a combination of different sorbents [19,23,26] have been attempted recently in order to obtain a more accurate molecular representation of DOM. Nevertheless, the combination of different isolation methods is highly laborious, time-consuming, and hard to optimize and standardize.…”

Proposed Guidelines for Solid Phase Extraction of Suwannee River Dissolved Organic Matter

“…This putative selectivity of the PPL sorbent toward hydrophobic and low-molecular-weight molecules in DOM has been previously reported. 30,42 Comparing Suw-water with Suw-RO, aliphatics and olefins were depleted in Suw-RO, whereas CRAM and, in particular, carbohydrates and some methoxy groups (OCH 3 ) were more abundant in Suw-RO. Interestingly, common aromatic molecules (δ H = 6.7−7.8 ppm) were also more abundant in Suw-RO than in Suw-water, with no obvious discrimination of electron-donating (δ H < 7 ppm), electronneutral (δ H = 7.0−7.3 ppm), and electron-withdrawing (δ H > 7.3 ppm) substituents.…”

“…Unlike the silica-based sorbent C18 and classical XAD-8 resin, PPL resin isolated representative DOM components with an abundance of aliphatic groups, and it was recommended for DOM extraction from natural waters. 30 Furthermore, in contrast to DOM isolated by means of a reverse osmosis/electrodialysis (RO/ED) process and SPE with XAD sorbents, PPL-based SPE allowed the isolation of marine DOM with beneficial properties for both high-field Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) and nuclear magnetic resonance (NMR) spectroscopy detection, while showing appreciable DOC recovery. 13,31 Despite approval of its use for DOM isolation and the critical dependence of all science developed from isolated polydisperse SPE-DOM, the DOM isolation parameters of SPE with PPL sorbent have not yet been systematically investigated.…”