Comparison of Low Molecular Weight Dissolved Organic Matter Compositions in Lake Inba and Kashima River by Orbitrap Mass Spectrometry

Abstract

Lake Inba, which serves as a drinking water source in Chiba Prefecture, Japan, has not complied with the environmental standard for COD (3 mg/L) since the 1970s. The high level of dissolved organic matter (DOM) caused by eutrophication in the lake has risen the concern of water treatment. To understand the compositions and sources of DOM in Lake Inba, this study compared molecular compositions of low molecular weight DOM (LMW-DOM, <1 kDa) in the lake and a major river flowing to the lake. Water samples were collected from Lake Inba and Kashima River in June 2015. After solidphase extraction, LMW-DOM was analyzed by Orbitrap mass spectrometry coupled with electrospray ionization. Based on the accurate mass data, 1,263 and 1,393 molecular formulae were assigned for the lake and river samples, respectively. Among them, 1,193 formulae were shared between the lake and the river, indicating that Kashima River was the representative source of LMW-DOM in the lake at the sampling occasion. Elemental composition of molecular formula demonstrated that 61% of the shared formulae were composed of carbon, hydrogen and oxygen. Hydrogen to carbon ratio and oxygen to carbon ratio of these common molecules were similar to the fingerprints of lignin and tannin.

Molecular-Level Changes in Dissolved Organic Matter Compositions in Lake Inba Water during KMnO₄ Oxidation: Assessment by Orbitrap Mass Spectrometry

“…Lake Inba in the Chiba Prefecture is the most polluted lake in Japan. Details of the lake are described elsewhere [23]. Water sampling was conducted on 16 September 2016 to evaluate the methodology to screen DCOD Mn components by Orbitrap MS.…”

“…DOM was concentrated and desalted via solid phase extraction (SPE; Bond Elut PPL cartridge, Agilent Technologies, Santa Clara, USA) [26]. The extraction procedure is described elsewhere [23]. The recovery of DOM was evaluated based on DOC.…”

“…Mass data was obtained in the range m/z 100-1,000. The operational conditions of ESI Orbitrap MS are described elsewhere [23].…”

“…The recent advent of high-resolution mass spectrometry (HRMS) techniques, such as Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) and Orbitrap mass spectrometry (Orbitrap MS), have allowed the molecularlevel characterization of DOM [16][17][18][19][20][21][22][23][24]. The combination of soft ionization and HRMS enables the analysis of individual DOM components, which comprise low molecular weight compounds.…”

A Demonstration of Mass-spectrometric Exploration of Organic Ecotoxicants from Simulated Sewage-treatment-plant Effluents

“…Hogenboom et al [21] evaluated the toxicity of the leachates from polluted landfill soils with a zebrafish embryo toxicity test, and identified two causative ecotoxicants by a non-targeted mass spectrometric analysis with a LC-ESI-Orbitrap MS. In other reports [22][23][24][25][26][27][28][29][30][31], these inventions help us explore, elucidate or identify unknowns in water samples. Unfortunately, a large number of components are generally detected in STP effluents when analyses are conducted by a non-targeted mass spectrometric analysis by the nature of a precursor ion analysis (so-called a full scan).…”