Dissolved Organic Nitrogen (DON) of wet deposition in Erhai basin (EWD) was characterized at the molecular level by using electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). The structure and composition of DON were investigated by the combined ESI FT-ICR MS, UV-Vis absorbance and fluorescence techniques. The FT-ICR MS measurements indicate that a large (∼790) number of organic species present in the wet deposition, in which DON account for 18.3%, with most of DON containing a single nitrogen atom. The typical relative molecular mass of the DON species was found to be in the range of 200-400 Da. Approximately 57.2% of DON species are highly unsaturated (DBE (Double Bond Equivalent) > 5) with the nitrogen- and sulfur-containing species, which are probably represented mainly by active nitrooxy organosulfates, accounting for ∼ 19.3% of the total DON. The low average SUVA254 and A253/A203 values (0.02 and 0.06, respectively), indicates that the aromaticity of the EWD samples is particularly weak. The average values of E2/E3 and E4/E6 in the EWD samples were 6.84 and 1.84, respectively. This is a clear indication of the low degree of humification of EWD samples, in agreement with ESI FT-ICR MS measurements. Our study demonstrates that multiple experimental techniques combined with FT-ICR MS, UV-Vis absorbance and fluorescence can be efficiently used for in-depth studying the DON at the molecular level. Thus it allows us to achieve a deep and insightful understanding of the DON structure and composition.
Keywords: Characterization; DON; ESI FT-ICR MS; Erhai; Wet deposition.
Copyright © 2016 Elsevier Ltd. All rights reserved.