Tomohiro Uchimura

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

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.

Evaluating the Aging of Multiple Emulsions Using Resonance-Enhanced Multiphoton Ionization Time-of-Flight Mass Spectrometry.

Resonance-enhanced multiphoton ionization time-of-flight mass spectrometry was applied to measurements of multiple emulsions with no pretreatment; a method for the quantitative evaluation of aging was proposed. We prepared water-in-oil-in-water (W/O/W) multiple emulsions containing toluene and m-phenylenediamine. The samples were measured immediately following both preparation and after having been stirred for 24 h. Time profiles of the peak areas for each analyte species were obtained, and several intense spikes for toluene could be detected from each sample after stirring, which suggests that the concentration of toluene in the middle phase had increased during stirring. On the other hand, in the case of a W/O/W multiple emulsion containing phenol and m-phenylenediamine, spikes for m-phenylenediamine, rather than phenol, were detected after stirring. In the present study, the time-profile data were converted into a scatter plot in order to quantitatively evaluate the aging. As a result, the ratio of the plots where strong signal intensities of toluene were detected increased from 8.4% before stirring to 33.2% after stirring for 24 h. The present method could be a powerful tool for evaluating multiple emulsions, such as studies on the kinetics of the encapsulation and release of active ingredients.

Laser ionization time-of-flight mass spectrometry for the evaluation of a local microenvironment in an emulsion

This study verified that laser ionization time-of-flight mass spectrometry (LI-TOFMS) is applicable to the evaluation of a local microenvironment in an emulsion. Sodium dodecyl sulfate (SDS) and toluene were used as a disperser and as an extraction solvent, respectively, and were added to a model sample of an aqueous styrene solution. The emulsion sample was introduced into LI-TOFMS and a series of mass spectra were obtained. Then, the time courses of styrene and toluene were constructed by extracting peak areas of the corresponding species. As a result, the signal intensities of both styrene and toluene were sometimes increased suddenly, which could be recognized as spikes. Moreover, many spikes arising from both species simultaneously appeared. The maximum signal intensity of the styrene spike was 27-fold higher than the signal intensity of styrene obtained from an aqueous solution, while the signal intensity other than that from spikes was decreased by about one-third of that of an aqueous solution. These results suggest that the styrene in the aqueous solution was extracted into small toluene droplets. This method was also applied to an aqueous solution containing styrene as well as m-phenylenediamine as a hydrophilic compound. Consequently, the selective extraction of styrene to the solvent droplets was observable due to the difference in the partition coefficient. LI-TOFMS has several characteristic superiorities such as selectivity and robustness, and all the ions induced can be detected. That is, a number of constituents can be measured in an individual small droplet, which is irreplaceable in the direct evaluation of the local microenvironment in an emulsion sample. Therefore, LI-TOFMS can be useful in the measurement of time-dependent concentrations and/or condition changes such as with emulsion polymerization.

Application of laser ionization mass spectrometry for the analysis of pyrolysis products from TiO2 nanoparticles treated with a silane coupling agent

Laser ionization time-of-flight mass spectrometry (LI/TOFMS) was applied to the analysis of pyrolysis products from TiO2 nanoparticles treated with phenyltriethoxysilane (PTES). The first step was to measure the decomposition products from silanized TiO2 nanoparticles by gradual heating in a gas chromatograph (GC) oven. As a result, a molecular ion peak was not observed for PTES, whereas a peak for the benzene ion was prominent. However, a molecular ion peak and some fragment ion peaks did appear in the mass spectrum of PTES, whereas a peak for the benzene ion did not. These results indicated the existence of compounds that were different from PTES on the surface of the silanized TiO2 nanoparticles that were used in the present study. In addition, a toluene ion peak was observed when heating in a GC oven, but that of phenol, rather than toluene, was confirmed when a pyrolyzer was used for rapid heating. A plausible explanation for these results could be the existence of water in the vicinity of silanized TiO2 nanoparticles when the pyrolysis products were generated. In the present study, the products generated by heating a glass filter paper or TiO2 nanoparticles on to which PTES had been dropped were also measured using a pyrolyzer in order to confirm whether the adsorption conditions could be identified. As a result, a peak for benzene, but not for PTES, was observed by heating TiO2 nanoparticles, whereas a molecular ion of PTES was prominent when a glass filter paper was heated. These results suggest that the present method can reveal the differences in silane coupling agents and can be used to evaluate whether these agents remain on the target sample or have been chemisorbed.

Multiphoton Ionization Time-of-Flight Mass Spectrometry for the Detection of Bioactive Lignan

Multiphoton ionization time-of-flight mass spectrometry (MPI-TOFMS) combined with a pulsed laser for sample vaporization was developed for the detection of a low-volatile compound in a solution. A solution containing Taiwanin A ((3E,4E)-3,4-bis(1,3-benzodioxol-5-ylmethylene)dihydro-2(3H)-furanone), which is a lignan that has an anticancer effect, was employed in the present study. Consequently, Taiwanin A could be detected by irradiating a laser pulse for vaporization to an inlet nozzle, rather than by heating. Therefore, the present method could be effective for detecting compounds with lower volatilities in a liquid sample.

A Quantitative Analysis of an Oil Component in an Emulsion by Multiphoton Ionization Mass Spectrometry

The first quantitative analysis of an oil component in an emulsion was achieved by multiphoton ionization time-of-flight mass spectrometry (MPI-TOFMS). An oil-in-water (O/W) emulsion was prepared. Styrene (0 - 5000 ng μL-1) and Triton X-100 were used as the oil phase and the disperser, respectively. Toluene was employed as an internal standard. We obtained a series of mass spectra, and then constructed the time profiles for styrene and toluene. As a result, we found several spikes from both time profiles when measuring emulsions with higher concentrations of styrene. Moreover, the timing of spikes for toluene coincided with that of styrene. These results suggested the movement of toluene into styrene droplets in the prepared emulsion. Furthermore, we constructed calibration curves of styrene using both the absolute calibration curve method and an internal standard method. Linear calibration curves were obtained in the concentration range investigated in the present study; the coefficients of determination obtained by both methods were 0.9956 and 0.9986, respectively.

Online Monitoring of a Styrene Monomer and a Dimer in an Emulsion via Laser Ionization Time-of-Flight Mass Spectrometry

Laser ionization time-of-flight mass spectrometry was applied to the online monitoring of a styrene monomer and dimer in an emulsion. During the measurement of a styrene monomer oil-in-water emulsion for this study, a styrene dimer, 1,3-diphenylpropane, was dropped into the emulsion. As a result, signal spikes from both analytes occurred simultaneously, which suggested that either the dimer had moved to the monomer droplets or that the monomer and dimer droplets had aggregated. We concluded that this method could be useful for the direct monitoring of monomers and oligomers in the early stages of emulsion polymerization.

Rapid Evaluation of the Bioremediation of Fuel Oil in Soil by Gas Chromatography–Laser Ionization Time-of-Flight Mass Spectrometry

ABSTRACT Gas chromatography–laser ionization time-of-flight mass spectrometry (GC-LI-TOFMS) was applied to the analysis of fuel oil in soil and soil treated by bioremediation. To demonstrate rapid and selective measurement, only filtered samples after extraction of fuel oil from soil were prepared. The required time for preparing three sample solutions from an oil-contaminated soil sample was only ca. 30 min. The degree of the decrease in the fuel oil in a soil sample by vaporization was confirmed by GC-LI-TOFMS, and after 7 days, the five peak areas arising from the constituents in fuel oil were decreased to between 39 and 79% of their original values. Next, the effect of bioremediation was confirmed by the addition of microbes (Rhodococcus sp. and Acinetobacter sp.). As a result, after 7 days, the five peak areas were decreased to between 61 and 81% of the values of the first decreases, after allowing for the effect of vaporization. This method showed sufficient selectivity, robustness, and rapidity for the measurement of oil-contaminated soil treated by bioremediation, which is essential for the evaluation of real environmental remediation.

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.

Application of Laser Ionization Time-of-Flight Mass Spectrometry for the Direct Measurement of a Silane Coupling Agent in Slurries

Laser ionization time-of-flight mass spectrometry (LI-TOFMS) was applied to the direct measurement of a silane coupling agent in slurries. In the present study, a slurry with dispersed TiO2 nanoparticles treated with phenyltriethoxysilane (PTES) was prepared. As a result, the peaks for PTES could be observed from the slurry sample containing unreacted PTES, and no peaks were observed from the slurry sample where unreacted PTES was removed by washing. This method can be used to directly analyze surface coating agents, such as PTES in slurries, and would be useful for obtaining a direct understanding of the characteristics of slurries.