Laser ionization/time-of-flight mass spectrometry for the direct analysis of emulsions

Abstract

A direct method for the monitoring of emulsions was developed using laser ionization/time-of-flight mass spectrometry. A pair of concentric capillaries stably introduced an oil-in-water microemulsion into a mass spectrometer. The system was applied to the monitoring of a milky white emulsion. With this system, the average of the peak areas was calculated to monitor the local concentration of dispersed toluene, which was related to a collapse of the emulsion. Strong spikes appeared, particularly when the emulsion was measured during high turbidity, which suggested the existence of highly concentrated toluene in the emulsion. The mass of the constituents was measurable in both micro- and macroemulsions. Therefore, this method could be widely applied to emulsion studies that are needed for stability evaluation and quality control.