Ultra-high-resolution Mass Spectra of Dissolved Organic Matter in the Absorption Mode

Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) is a state-of-the-art technique for the non-targeted analysis of complex organic mixtures such as dissolved organic matter (DOM) at the molecular level, and has been extensively used in the high-throughput analysis of disinfection byproducts (DBPs). Compared to the traditional magnitude mode, the absorption mode of Fourier transform can considerably improve the signal-to-noise ratio and resolving powder of peaks identified in the FT-ICR MS spectra. However, information regarding the advantages of absorption mode in the analysis of DBPs is still limited. In this study, the FT-ICR MS analysis in the chlorination of surface and groundwater was performed to demonstrate the advantages of the absorption mode for DOM and DBPs analysis. The results showed that, compared with the magnitude mode, the absorption mode can significantly (P<0.05) improve the resolution (1.89-1.97 folds) and signal-to-noise ratio value (1.61-1.73 folds) of DOM, including DBPs, and remarkably reduce the mass error for formula assignment and peak intensity deviation of the peaks with large deviations. The absorption mode identifies fewer peaks but has more assigned formulas (1.21-1.39 folds). Moreover, the absorption mode is mainly favorable to the number of identified peaks for DBPs but has limited effects on decreasing the peak intensity deviation of DBPs peaks due to their low intensity at the environmental levels of chlorination reagents. The results highlight the great potential of the absorption mode technology based on FT-ICR MS for the non-targeted analysis of DOM and emerging pollutants, including DBPs.