Use of variable pH interface to a mass spectrometer for the measurement of dissolved volatile compounds

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Abstract
A wide variety of dissolved chemicals can be measured continuously with some specificity by directly interfacing a relatively inexpensive mass spectrometer to a solution. Specifically, we describe the construction and initial use of a membrane interace to a mass spectrometer which allows the continuous measurement of the concentration of dissolved volatile compounds in buffered aqueous solution. In addition to volatile compounds that do not dissociate appreciably at pH 7 (e.g., ethanol, ethylene glycol), volatile acids and bases, such as acetic acid or ammonia, can be measured with the interface is operated within the range 1⩽pH⩽12. We also discuss the sensitivity of the system to variations in flow rate and describe a satisfactory method for providing sufficiently constant flow rates.
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