## 2 Materials and Methods
### Apparatus  
The experimental apparatus used in the present study is shown in Figure 1. A system comprised of a pair of concentric deactivated fused-silica capillaries (GL Sciences, Tokyo, Japan) was used for the sample introduction [13]. An emulsion was introduced through an inner capillary (55 cm in length, i.d. 15 \(\upmu\)m, o.d. 150 \(\upmu\)m), and ambient air was introduced through an outer capillary (35 cm in length, i.d. 320 \(\upmu\)m, o.d. 450 \(\upmu\)m). The tip of the inner capillary on the side of a TOFMS was set 1.5 mm inward from the tip of the outer capillary in order to insure the introduction of a liquid sample via the evacuation force of TOFMS vacuum, although the corresponding length was set at 2-3 mm in previous reports [13; 28; 29; 30; 31; 32]. The tips were indirectly heated at 40 \({}^{\circ}\)C by a heater mounted in the flange of a TOFMS. The height of the prepared sample was 4 cm in a sample container, and the inner capillary was inserted into a container 1.5 cm from the bottom through a small hole in the lid. A flow meter (RK-1250, Kofloc, Kyoto, Japan) allowed adjustment of the rate of ambient air from an outer capillary to 2 mL/min. The pressure of the vacuum chamber of the TOFMS was 1 \(\times\) 10\({}^{-2}\) Pa during measurement.  
In the present study, a compact microscopic system was constructed of an objective (G plan Apo 20\(\times\), NA 0.28, Mitutoyo, Kanagawa, Japan), an imaging lens (MT-1, Mitutoyo), a light source (MegaLight100, AS ONE, Osaka, Japan), and a digital camera (DIGITAL SIGHT DS-U1, Nikon, Tokyo, Japan) in order to monitor the emulsion flowing through the inner capillary. The objective was set so that the length between the sampling point of the sample container and the microscopic observation point was 30 cm.  
The MPI-TOFMS used in the present study has been reported elsewhere [13; 28; 30; 31; 32], and is only briefly described here. The fourth harmonic of a nanosecond Nd:YAG laser (GAIA II, 266 nm, 4 ns, 10 Hz, Rayture Systems, Tokyo, Japan) was employed for MPI. The pulse energy was adjusted to 20 \(\upmu\)J, and a plano-convex lens (\(f=200\) mm) was used to focus the pulses 2 mm from the tip of the outer capillary. A linear-type TOFMS with a drift length of 60 cm was used in the present study. A digitizer (AP240, 1 GHz, 1 GS/s, Acqiris/Agilent Technologies, Tokyo, Japan) was used to acquire the ion signals. Following the introduction of a creamed emulsion, measurement of the transparent portion was recorded after the signal for toluene was confirmed. After the dispersion of toluene, measurement of the white-turbid emulsion was simultaneously begun when the inner capillary was inserted into the sample container. In both experiments, laser pulses were not irradiated for the first 30 s in order to determine the ground (zero) level. In the present study, the series of mass spectra were recorded without averaging. It is worth noting that a huge amount of data will be obtained during long-time  
Figure 1: Schematic diagram of the apparatus. An enlarged view of a pair of concentric capillary columns for sample introduction is also shown.  
measurements, which complicates processing. Therefore, the series of mass spectra were consecutively (and separately) recorded, and, as a result, a slight time interval of ca. 2 s existed between the end of one recording and the beginning of the next. In the present study, the time profile for toluene was constructed by extracting the areas of both the molecular ion (M\({}^{+}\)) peak and the [M \(-\) H]\({}^{+}\) peak (\(m/z\) 92 and 91, respectively) from the series of mass spectra. In detail, the \(m/z\) window applied to the extractions was set between 90.1 and 92.8 in order to extract almost all the signals for the above two peaks.