Selective Gas-Phase\nDepletion of Chemical Contaminants\nin Dissolved Organic Matter Increases Compositional Coverage by FT-ICR\nMass Spectrometry

Fourier transform\nion cyclotron resonance mass spectrometry\nof\ndissolved organic matter (DOM) extracted from environmental samples\nprovides molecular speciation that enables visualization of compositional\ntrends in the fate and cycling of biogenic and anthropogenic organics.\nOften, chemical contamination is introduced during field sampling\n(i.e., remote locations, cannot use glass). Further, preconcentration\nof DOM by solid-phase extraction often results in chemical contamination.\nWhen chemical noise is a dominant fraction of the ion signal, mass\nspectral performance is degraded by reduction of the ion trap analyte\naccumulation capacity and enhanced ion cloud dephasing during ICR\ndetection. We have developed gas-phase ion depletion of unwanted chemical\ncontaminants during ion injection into the linear RF ion trap of the\nhybrid linear ion trap 21 T FT-ICR mass spectrometer that improves\ndetection of analytes by removing unwanted chemical noise. We demonstrate\nimprovements in signal-to-noise ratio, dynamic range, and the number\nof observed analytes in dissolved organic matter samples that results\nin a 40–100% increase in the number of identified analytes.\nIn many cases, the number of peaks observed per nominal mass more\nthan doubles over select <i>m</i>/<i>z</i> regions.\nThis gas-phase “clean-up” can salvage precious samples\nchallenged by sampling location, sample volume, or collection protocols\nthat cannot be avoided and maximizes the compositional information\nobtained. Further, this approach is generalizable and extendable to\nany hybrid linear ion trap instrument platform (e.g., LTQ-Orbitrap\nor linear ion trap-TOF). We highlight the power of gas-phase depletion\nwith electrospray ionization, but this method is also applicable to\nother ionization modes.