USE OF VARIABLE PH INTERFACE TO A MASS-SPECTROMETER FOR THE MEASUREMENT OF DISSOLVED VOLATILE COMPOUNDS

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.