Direct mass-spectrometric measurement of methane and its volatile homologues in water

The direct quantitative measurement of the concentration of water-dissolved saturated hydrocarbons using a portable membrane-inlet precalibrated magnetic mass-spectrometer is suggested. The particularity of the instrument’s response to the presence of desired compounds in a test sample is taken into consideration. The feasibility of using this portable instrument in real-time oil and gas search on the continental shelf is discussed. Laboratory test data for the methane, ethane, propane, and butane concentrations in air and water samples are presented, from which the sensitivity of the instruments to the components, are determined. The gas concentrations in the water samples lie in the range from several parts per billion (ppb) to several hundred ppb. These values are close to the lower limits of prospecting criteria as applied to oil fields.