Determination of the Electrostatic Potential of Oil-in-Water Emulsion Droplets by Combined Use of Two Membrane Potential-Sensitive Dyes

Electrochemically controlled cocrystallisation of caffeine:1-hydroxy-2-naphthoic acid

The formation of caffeine and 1-hydroxy-2-naphtoic acid cocrystals at a water–oil interface was controlled by potential difference, Δwoϕ, favouring one polymorphic form of the cocrystal.

Electrochemically Modulated Liquid-Liquid Extraction for Sample Enrichment

A new sample preparation method is proposed for the extraction of pharmaceutical compounds (Metformin, Phenyl biguanide, and Phenformin) of varied hydrophilicity, dissolved in an aqueous sample. When in contact with an organic phase, an interfacial potential is imposed by the presence of an ion, tetramethylammonium (TMA⁺), common to each phase. The interfacial potential difference drives the transfer of ionic analytes across the interface and allows it to reach up to nearly 100% extraction efficiency and a 60-fold enrichment factor in optimized extraction conditions as determined by HPLC analysis.

Is the Oil | Water Interface the Simplest and Best Suited Model for Understanding Biomembranes?

Many studies have been conducted by using the oil (O) | water (W) interface as a simple model for understanding ion transfer (IT) or electron transfer (ET) across biomembranes. In this review, we revisit the usability of the O | W interface as a biomembrane model. For understanding biomembrane IT, the O | W interface is the simplest and best suited model. For example, the standard Gibbs transfer energy of drug ions at the O | W interface is a useful measure for evaluating their membrane permeability in a conventional in vitro assay, called PAMPA. However, the O | W interface is not necessarily a good model for understanding biomembrane ET. This is because no net current can be observed with the O | W interface, owing to the ET-coupled proton transfer. In such a case, the self-assembled monolayer (SAM) formed on a metal electrode serves as a better model for understanding biomembrane ET.

Evaluating the Creaming of an Emulsion via Mass Spectrometry and UV-Vis Spectrophotometry

The creaming behavior of a turbid oil-in-water emulsion was observed via the processes of multiphoton ionization time-of-flight mass spectrometry (MPI-TOFMS) and ultraviolet-visible spectrophotometry (UV-vis), and the results were compared. The transmittance measurement by UV-vis showed that the turbidity of the toluene emulsion was decreased with time. However, non-negligible errors are common in the measurement of a sample with high turbidity. The online measurement by MPI-TOFMS detected many spikes in the time profile, which revealed the existence of toluene droplets in the emulsion. A smooth time profile suggested that the signal intensity had initially increased, and then decreased with time; the initial concentration of toluene was 3 g/L, which had decreased by half after 60 min. The signal behavior obtained using MPI-TOFMS differed only slightly from that obtained using UV-vis. Since a change in turbidity is not the same as a change in the local concentration of an oil component, MPI-TOFMS is useful for the analysis of a turbid emulsion and offers additional information concerning the creaming phenomenon of an emulsion.

Development of Multiphoton Ionization Time-of-Flight Mass Spectrometry for the Detection of Small Emulsion Droplets

A system for measuring small oil droplets in an oil-in-water (O/W) emulsion was developed using multiphoton ionization time-of-flight mass spectrometry. In the present study, a capillary column with an inner diameter of 15 µm was used for sample introduction. Moreover, a compact microscopic system was constructed for observing an emulsion flowing through a capillary column. As a result, the length for sample introduction was shortened, which is preferable for the direct evaluation of an emulsion. Using this system, the minimum diameter of a detectable toluene droplet in an O/W emulsion was decreased to 1.7 µm. The present system could be used to evaluate the local microenvironment and stability of an emulsion.