Underwater Mass Spectrometers for In Situ Monitoring of Dissolved Gases and Volatile Organic Compounds in Deep Ocean and Coastal Environments

Abstract

Pacific Environmental Technologies LLC (Pace Tech Hawaii), located in Honolulu, Hawaii, USA has developed a compact mass spectrometer-based instrument for multi-species determination of dissolved gases and volatile organic compounds which can function autonomously or semi-autonomously in water depths ranging to >4000 m. Mass spectrometers were chosen because of their potential for extremely high detection sensitivity (single ion counting is possible), isotopic resolution, and the wide dynamic range of their analytical response (allowing simultaneous detection from ppb to percent level). As such, they are extremely versatile instruments that can operate in true discovery mode for whatever the environment presents to the analyst. Besides the development of appropriate sample introduction procedures, the technical challenge is to successfully operate such instruments in situ and in very harsh environments, such as the bottom of the ocean. The present work builds upon our company’s previous experience in developing the deep-ocean mass spectrometer (DOMS) prototype. The DOMS employed a commercial quadrupole mass spectrometer and can operate for long periods at water depths of >4000 m, but was relatively slow, large and heavy, with fairly high power consumption at up to 100 watts. It featured a company-patented but more primitive “built- in” membrane introduction mass spectrometry (MIMS) desich can function autonomously or semi-autonomously in water depths ranging to >4000 m. Mass spectrometers were chosen because of their potential for extremely high detection sensitivity (single ion counting is possible), isotopic resolution, and the wide dynamic range of their analytical response (allowing simultaneous detection from ppb to percent level). As such, they are extremely versatile instruments that can operate in true discovery mode for whatever the environment presents to the analyst. Besides the development of appropriate sample introduction procedures, the technic