A chemical ionization mass spectrometer for continuous underway shipboard analysis of dimethylsulfide in near-surface seawater

[摘要] A compact, low-cost atmospheric pressure, chemical ionization massspectrometer ("mini-CIMS") has been developed for continuous underwayshipboard measurements of dimethylsulfide (DMS) in seawater. The instrumentwas used to analyze DMS in air equilibrated with flowing seawater across aporous Teflon membrane equilibrator. The equilibrated gas stream was dilutedwith air containing an isotopically-labeled internal standard. DMS isionized at atmospheric pressure via proton transfer from water vapor, thendeclustered, mass filtered via quadrupole mass spectrometry, and detectedwith an electron multiplier. The instrument described here is based on alow-cost residual gas analyzer (Stanford Research Systems), which has beenmodified for use as a chemical ionization mass spectrometer. The mini-CIMShas a gas phase detection limit of 220 ppt DMS for a 1 min averagingtime, which is roughly equivalent to a seawater DMS concentration of 0.1 nMDMS at 20°C. The mini-CIMS has the sensitivity, selectivity, and timeresponse required for underway measurements of surface ocean DMS over thefull range of oceanographic conditions. The simple, robust design andrelatively low cost of the instrument are intended to facilitate use inprocess studies and surveys, with potential for long-term deployment onresearch vessels, ships of opportunity, and large buoys.

[学科分类] 海洋学与技术