Development of an underwater mass-spectrometry system forin situchemical analysis

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Abstract
Progress in the design, construction and packaging of small portable mass spectrometers for operation on autonomous underwater vehicles (AUVs) is described. Our first deployable version consists of a membrane introduction interface coupled with a linear quadrupole mass filter for in situ detection and quantification of dissolved gases and volatile organic compounds. We present laboratory results which demonstrate that sub-parts-per-billion detection limits have been achieved for toluene. The mass-spectrometer system is compatible with AUV constraints and operates on 24 V dc, consuming of the order of 100 W of power. Technical challenges of performing underwater mass spectrometry are addressed, in particular sample introduction from the water column and the maintenance of a vacuum system. Initial operation will be in shallow water of 30 m depth or less. Alternative versions of interfaces and mass spectrometers are also discussed. We anticipate that providing the capability of performing in situ underwater mass-spectrometric analysis will have a significant impact in the areas of marine science and environmental monitoring.