Using Resonance-Enhanced Multiphoton Ionization Time-of-Flight Mass Spectrometry to Quantitatively Analyze the Creaming of an Emulsion

Abstract

In this study, we used a quantitative analytical method to indicate creaming behavior in an emulsion. An oil-in-water emulsion was directly measured by resonance-enhanced multiphoton ionization time-of-flight mass spectrometry, and the time profiles of the peak areas of an oil component, styrene, were obtained at heights of 1, 2, and 3 cm from the bottom of a sample that had a height of 4 cm. All time profiles roughly indicated that the signal intensity increased once, then decreased, and finally settled. Moreover, we proposed a fitting equation for the time profiles by subtracting two sigmoid functions, whereby the degree of the signal increases at the initial stage, the degree of the signal decreases after the increase, and the times for continuing the higher signal intensities were all longer as the monitoring positions were raised. This method would surely provide useful information about emulsions that undergo creaming behavior.

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

“…The preparation procedure was similar to that in a previous report. 29 First, 0.12 g of SDS was dissolved in 40 mL of water in a 50-mL vial container. Next, either 44 or 176 μL of styrene, for emulsions with concentrations of either 1 or 4 g/L, respectively, was added, and processed in a homogenizer at 5000 rpm for 10 min.…”

“…Figure 1 shows the experimental apparatus. The REMPI-TOFMS used in the present study was similar to that used the previous study, 23,29 and is briefly described here. The fourth harmonic emission of a Nd:YAG laser (GAIA II, 266 nm, 4 ns, 10 Hz, Rayture Systems, Tokyo) was used as an ionization light source for REMPI.…”

“…In the previous report, we proposed a fit function for fitting the signal behavior obtained from an emulsion during creaming. 29,30 In that study, we used this fit function to evaluate the creaming of O/W emulsions measured at different monitoring heights. In the present study, as follows, a modified fit function was proposed for fitting the obtained time profiles shown in Figs.…”

“…Very recently, using an O/W emulsion that is prone to creaming behavior, we demonstrated the differences in the time profiles of an oil component at different monitoring heights, and proposed a fit equation for the time profiles that would allow a quantitative evaluation of the creaming behavior. 29,30 In the present study, the fit function that was previously proposed was modified to allow a general-use evaluation of the creaming behavior of an emulsion. O/W emulsions with different initial oil concentrations were measured without pretreatment, and the changes in the oil concentration arising from creaming were discussed.…”

Laser Mass Spectrometry

“…12 Moreover, they developed a new analytical tool, GC/MPI-TOFMS combined with a post-column on-line chemical reaction system for the trace analysis of nitro-PAHs in PM2.5. 13 Uchimura's group applied MPI-TOFMS to the direct analysis of emulsions; they have evaluated the creaming behaviors of emulsions 14,15 as well as a phase inversion by temperature changes. 16 Schade et al achieved the simultaneous detection of PAHs as well as positive and negative inorganic ions in singleparticle mass spectrometry.…”