Hydrocarbon seep monitoring using in situ deep sea mass spectrometry

Abstract

Absfmct -Hydrocarbon seep monitoring is a area applicable for new advances in mass spectrometry. Recent developments are allowing unprecedented levels of trace contaminant measurement in the deep-ocean. With funding from the U.S. National Science Foundation (NSF), our engineering design team constructed a new mass spectrometer-based in situ analysis system for work in the deep ocean environment over prolonged deployment periods.Our design goals were a depth capability of up to 4,000 m water depth (400 bars hydrostatic pressure) and autonomous operation for periods of up to sir months to a year, depending upon type of exteFa1 battery system used or other deployment circumstances, e.g., availability of a power cable or fuel cell power source. We chose a membrane introduction mass spectrometry (MIMS) sampling approach, which allows for dissolved gases and volatile organics introduction into the MS vacuum system. The MIMS approach and the hydrophobic, silicon-coated membrane chosen both draw upon our previous experience with this technology in the deep ocean. The membrane has been tested to 400 bars in a series of long-term hydrostatic pressure tests, which extends the 200-bar working depth rating of this membrane by a factor of 2.

A Review of the Emerging Field of Underwater Mass Spectrometry

“…Most UMS systems employ linear quadrupole mass filters (e.g., Short et al, 1999;McMurtry et al, 2005; Schlüter and FIGURE 3 | Ion current dependency on hydrostatic pressure for a range of dissolved gases and VOCs at 35 • C: (a) methane, (b) nitrogen, (c) oxygen, (d) hydrogen sulfide, (e) argon, (f) carbon dioxide, (g) dimethyl sulfide, (h) chloroform, (i) toluene. Blue (*) data were obtained as hydrostatic pressure was increased and red (+) data as pressure was decreased.…”

“…Copyright 2007 American Chemical Society. Gentz, 2008;Wankel et al, 2010) which are robust, compact, and relatively inexpensive (McMurtry et al, 2005). The power requirements for quadrupole mass filters contribute significantly to the overall system's power consumption, as they must operate using rather high direct current (DC) and radio frequency (RF) voltages applied to the four rods of the analyzer.…”

“…Ion traps have also been used in UMS systems, and have a wider mass range than linear quadrupoles or small cycloidal analyzers (650 amu vs. a few hundred amu; McMurtry et al, 2005). However, the membrane inlet typically limits the range of m/z of compounds introduced into the mass spectrometer to <300 amu, so the full range of the ion trap cannot be utilized.…”

“…Ion traps can operate at even higher pressures than linear quadrupoles, and they can perform multiple stages of mass spectrometry with no modifications (Badman and Cooks, 2000). Conventional size ion traps require high RF fields, however, and have much higher power requirements than linear quadrupoles, adversely affecting deployment length (McMurtry et al, 2005).…”

“…Establishing and maintaining a high vacuum is possible with mechanical, throughput vacuum pumps. This process involves two stages: a roughing pump (usually a diaphragm pump) first brings the pressure down to about 10 −1 Torr, and then a turbomolecular (turbo) pump further drives the pressure down to 10 −5 -10 −7 Torr (McMurtry et al, 2005). Turbo pumps can create a much higher vacuum range but cannot exhaust directly to atmospheric pressure.…”