High resolution electrospray ionization mass spectrometry and 2D solution NMR for the analysis of DOM extracted by C₁₈ solid phase disk

We propose and demonstrate an approach involving use of C₁₈ solid phase disk extraction coupled with high resolution mass spectrometry for obtaining non-invasive molecular level information on dissolved organic matter (DOM) from river water. With this approach, DOM extraction from acidified natural water can be achieved rapidly with a simple filtration setup at a remote field site. From total organic carbon and UV-Vis absorbance measurements, we show that a large portion (over 60%) of the original DOM in water is recovered without the interference of salts. NMR analysis indicates that the C₁₈-isolated material has a similar distribution of functional groups as the original DOM but 2-D NMR details are greatly enhanced. Electrospray ionization mass spectrometry and high resolution mass spectrometry were employed to study DOM at molecular level. Highly resolved mass spectra of DOM (resolving power (δm/m_50%) > 80,000 at m/z < 600) reveal that there are many pairs of peaks that differ by the exact masses of -H₂, -O, or -CH₂ indicative of possible homologous series of structures.