Characterisation of riverine dissolved organic matter using a complementary suite of chromatographic and mass spectrometric methods

Abstract

Dissolved organic matter (DOM) plays a fundamental role in nutrient cycling dynamics in riverine systems. Recent research has confirmed that the concentration of riverine DOM is not the only factor regulating its functional significance; the need to define the chemical composition of DOM is a priority. Past studies of riverine DOM rested on bulk quantification, however technological advancements have meant there has been a shift towards analytical methods which allow the characterisation of DOM either at compound class or more recently molecular level. However, it is important to consider that all analytical methods only consider a defined analytical window. Thus, herein, we explore the use of a hierarchy of methods which can be used in combination for the investigation of a wide range of DOM chemistries. By using these methods to investigate the DOM composition of a range of streams draining catchments of contrasting environmental character, a wide range of compounds were identified across a range of polarities and molecular weight, thereby extending the analytical window. Through the elucidation of the DOM character in stream samples, information can be collected about likely the sources of DOM. The identification of individual key compounds within the DOM pool is a key step in the design of robust and informative bioassay experiments, used to understand in-stream ecosystem responses. This is critical if we are to assess the role of DOM as a bioavailable nutrient resource and/or ecotoxicological factor in freshwater.

Probing Molecular-Level Dynamic Interactions of Dissolved Organic Matter with Iron Oxyhydroxide via a Coupled Microfluidic Reactor and an Online High-Resolution Mass Spectrometry System

“…Raeke et al also reported that very polar compounds were poorly extracted by SPE during DOM analysis but these compounds also showed low MS signal responses . Overall, no analytical method is capable of achieving comprehensive characterization of DOM . The analytical window of HRMS for DOM is jointly influenced by the selectivity of SPE, LC retention, ionization source, and MS detectors, among others. − …”

“…55 Overall, no analytical method is capable of achieving comprehensive characterization of DOM. 56 The analytical window of HRMS for DOM is jointly influenced by the selectivity of SPE, LC retention, ionization source, and MS detectors, among others. 57−59 We further evaluated the reproducibility of the developed method in terms of elution profile, mass peak detection, and mass peak intensity 41,60,61 since good reproducibility is the basis for reliable and semiquantitative analysis of MS data.…”

Determining patterns in the composition of dissolved organic matter in fresh waters according to land use and management

“…Such elevated nutrient concentrations are commonly observed in UK agricultural catchments (Yates et al 2019a). Contradictory observations from Graeber et al (2012) and others (Sachse et al 2005) suggest catchments with a high proportion of agricultural activity export structurally complex DOM, characterised by elevated DOC concentrations and a dominance of humic-like fluorescent DOM, though other studies (Lloyd et al 2021;Mena-Rivera et al 2021) indicate DOM in agricultural catchments has a high proportion of lower molecular weight compounds resulting from microbial processing of terrestrially derived DOM. Similarly, both Yates et al (2019a) and Williamson et al (2021) in a pan-UK study concluded that higher DOC, higher Specific UV Absorbance (SUVA) and higher DOC:DOC ratios were consistently observed in peaty catchments than in lowland intensively farmed agricultural catchments.…”