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 for direct analysis of liposome-encapsulated compounds

The direct measurement of compounds encapsulated into liposomes without pretreatment allows verification of both the encapsulation efficiency and the release rate of liposomes in their original state. In the present study, the direct analysis of liposomes was conducted via resonance-enhanced multiphoton ionization time-of-flight mass spectrometry (REMPI-TOFMS). When analyte species (2-phenoxyethanol) encapsulated in liposomes were measured online, spike signals appeared in a time profile of the peak area for 2-phenoxyethanol, which suggested a dispersion of the compound in this sample. In addition, the spikes disappeared when the liposomes collapsed following the addition of a Triton X-100 aqueous solution. These results strongly suggest that the appearance of spikes arises from the compound encapsulated into the dispersed liposomes. REMPI-TOFMS has an inherent characteristic of superior selectivity, which suggests that this process would be useful for achieving a precise evaluation of the release properties of target compounds even in a liposome sample containing a large variety of components.

Sample preparation conditions for the real-time measurement of W/O emulsions by resonance-enhanced multiphoton ionization time-of-flight mass spectrometry

Analysis of an emulsion in its original dispersed condition is quite important for quality assessment and quality control. In the present study, the practical experimental conditions of the real-time measurement of a water-in-oil (W/O) emulsion were examined via resonance-enhanced multiphoton ionization time-of-flight mass spectrometry (REMPI-TOFMS). A W/O emulsion was prepared using cyclohexane as the oil phase with toluene as an analyte species. A time profile of the peak area for toluene was constructed based on the mass spectra. Normally, the negative spikes of a base signal are detected in a time profile when analyte molecules are dispersed in an oil phase. In this case, however, the positive spikes were unexpectedly detected rather than the negative ones. Though several factors could be relevant for the occurrence of the positive spikes, these spikes could have been suppressed by the addition of a small amount of n-alkane when the oil phase was prepared in the present study. The practical experimental conditions for the analysis of a W/O emulsion in real-time revealed that this method would be applicable to the analysis of an oil-in-water-in-oil (O/W/O) emulsion where the outer phase is also an oil phase.