Characterization of Black Carbon in Natural Waters by FT-ICR Mass Spectrometry.

Highly condensed aromatic molecules are ubiquitous in natural waters. These molecules form during the incomplete combustion (i.e. pyrolysis) of organic matter, and during the decomposition of black carbon in soils. We review the current state of knowledge on black carbon in dissolved organic matter (DOM) and discuss several mass spectrometric techniques for identifying “black DOM” based upon its molecular properties. Much of the discussion focuses on results obtained with electrospray ionization (ESI) Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. We also discuss a newer tool for mass spectrometry studies of black carbon – atmospheric pressure photoionization (APPI). APPI is a very sensitive means of ionizing aromatic molecules of low polarity and low volatility. We discuss some early results from the application of APPI FT-ICR mass spectrometry to DOM from the North Atlantic Ocean, and findings of some novel black DOM molecular structures. Finally, we present a preliminary assessment of quantitative reliability of the ESI and APPI FT-ICR mass spectrometry that is based upon a methods comparison to ¹³C nuclear magnetic resonance and combustion elemental analyses.