Quantitative Evaluation of the Creaming of Emulsions via Resonance-Enhanced Multiphoton Ionization Time-of-Flight Mass Spectrometry

Abstract

The creaming behavior of an oil-in-water (O/W) emulsion was quantitatively evaluated via resonance-enhanced multiphoton ionization time-of-flight mass spectrometry. Styrene O/W emulsions were prepared with initial styrene concentrations of 1 and 4 g/L, and the height at the center of the sample was monitored. A peak area of the molecular ion of styrene was set as the signal intensity, for which a time profile was constructed from a series of mass spectra. As a result, the averaged time profiles showed that the signal intensities increased once and then decreased with the onset of creaming. In addition, in order to fit an experimentally obtained time profile, a modified fit function was proposed. Based on the fit results, the ratios of the increases and decreases in signal intensities were different between the two emulsions-higher in the case of an O/W emulsion with a higher initial oil concentration. On the other hand, the duration of the enhancement of the signal intensity with the onset of creaming was independent of the initial oil concentration. The present method offers the possibility to quantitatively evaluate the creaming behavior of an emulsion without pretreatment, and, therefore, would be useful for confirming the stability and quality assurance of emulsions.

Using Resonance-Enhanced Multiphoton Ionization Time-of-Flight Mass Spectrometry to Evaluate the Movement of a Constituent in a Multiple Emulsion

“…Resonance-enhanced multiphoton ionization time-of-flight mass spectrometry (REMPI-TOFMS) using ultraviolet laser pulses is a highly selective analytical method for analyzing a sample with a complex mixture. − For example, real-time analysis of volatile compounds generated from roasting coffee and of aromatic compounds in the environment have been reported. Recently, we used REMPI-TOFMS for real-time monitoring of an emulsion without pretreatment. − In that case, the time profile of a peak area of a species of analyte was obtained from a series of mass spectra. Until now, when an O/W emulsion containing a hydrophobic compound (toluene) as a species of analyte was measured, a base signal and sudden positive signals based on the base signal appeared on the time profile.…”