Control system for an underwater coded aperture miniature mass spectrometer

Abstract

In situ measurements of the spatiotemporal distribution of dissolved gases in the ocean are useful for a wide variety of applications including monitoring biogeochemical cycles (e.g., methane, oxygen, and carbon dioxide fluxes), detecting pollutants, studying submarine groundwater discharge, and tracking chemical gradients in water columns or sediment interfaces. Over the past two decades, underwater membrane inlet mass spectrometry has emerged as a leading technology for in situ dissolved gas analysis, leveraging various mass analyzers such as quadrupole, ion trap, and cycloidal systems. While quadrupoles and ion traps face challenges such as water vapor interference and resolution limitations, cycloidal analyzers offer higher resolution at low mass-to-charge ratios with reduced power requirements. However, they have historically suffered from sensitivity and sequential analysis limitations. Recent advances, including ion array detectors and computational sensing, now enable simultaneous mass detection and improved sensitivity in cycloidal mass analyzers. This study introduces the development of an underwater coded aperture miniature mass spectrometer (UW-CAMMS), incorporating a cycloidal mass analyzer, ion array detector, and spatially coded apertures. A low-power electronic control system for the UW-CAMMS is designed and characterized, with performance comparable to laboratory-based systems, showcasing progress toward efficient, compact underwater dissolved gas monitoring. This technology can be used to study dynamic processes in marine, freshwater, and brackish systems with high spatial and temporal resolution.