# Permeation Effect Analysis of Drug Using Raman Spectroscopy for Iontophoresis
## 3 Results  
To visualize the presence of penicillin sodium in mouse skins after drug penetration experiments (Figure 3), we measured and compared the Raman spectra of the three experimental groups: three different concentrations of the penicillin sodium solution (0.16 g\(\cdot\)mL\({}^{-1}\), 0.24 g\(\cdot\)mL\({}^{-1}\), and 0.48 g\(\cdot\)mL\({}^{-1}\)), untreated mouse skins, and mouse skins of small mice after conducting iontophoresis drug penetration experiments (Group A). Figure 3: The Raman spectra of three different concentrations of penicillin sodium solution (0.16 g\(\cdot\)mL\({}^{-1}\), 0.24 g\(\cdot\)mL\({}^{-1}\), and 0.48 g\(\cdot\)mL\({}^{-1}\)), and the Raman spectrum of the mouse skin after the drug permeation experiment without iontophoresis. Figure 2: The experimental instrument for Raman measurement. In Figure 3, the shaded bands are the characteristic peak bands selected in the spectral analysis, and their tentative attributions were marked in the figure according to the explanation in Table 1.  
For the Raman spectrum of the untreated skin of mice in Figure 3, the peak at 1003 cm\({}^{-1}\) was assigned to phenylalanine, and the keratin conformation structure was seen through the amide I (1658 cm\({}^{-1}\)) and amide III (1194 cm\({}^{-1}\) and 1236 cm\({}^{-1}\)) peaks. The peak at 1446 cm\({}^{-1}\) was related to proteins and/or lipids. For the Raman spectra of the three different concentrations of the penicillin sodium solution (0.16 g\(\cdot\)mL\({}^{-1}\), 0.24 g\(\cdot\)mL\({}^{-1}\), and 0.48 g\(\cdot\)mL\({}^{-1}\)) in Figure 3, the Raman characteristic peaks of the penicillin sodium solution were located at 847 cm\({}^{-1}\), 1002 cm\({}^{-1}\), 1032 cm\({}^{-1}\), 1373 cm\({}^{-1}\), and 1597 cm\({}^{-1}\). The peaks at 1002, 1032, 1373, and 1597 cm\({}^{-1}\) were attributed to the stretching vibration of the benzene ring, O-CH\({}_{3}\) stretching of methoxy groups, in-plane deformation of COH and CH\({}_{2}\), and the oscillation of the carboxyl group, respectively. For the Raman spectrum of the mouse skin after the drug permeation experiment without iontophoresis (Group A) in Figure 3, it can be viewed as a superposition of the Raman spectrum of untreated mouse skin with the Raman spectra of the penicillin sodium solution. For the experimental groups with different concentrations of the penicillin sodium solution and the same action time (Group B, Group C, and Group D), compared with the Raman spectrum of the mouse skin after the drug permeation experiment without iontophoresis (Group A), the Raman spectral distribution was similar, but there were differences in the height (intensity) of some characteristic peaks. As shown in Figure 4, the peak at 1597 cm\({}^{-1}\) significantly changed with the increase in drug concentration in Group B, Group C, and Group D compared with other peaks marked in Figure 4. The peaks (570, 1194, 1236, and 1446 cm\({}^{-1}\)) had virtually no significant change, and the differences in our intuitive observations were due to the relative changes caused by the change in the peak intensity at 1597 cm\({}^{-1}\). For the experimental groups with different action times and the same concentrations of the penicillin sodium solution (Group B, Group E, and Group F), compared with the Raman spectrum of the mouse skin after the drug permeation experiment without iontophoresis (Group A), the Raman spectral distributions were similar, but there were also differences in the height (intensity) of some characteristic peaks. As shown in Figure 5, the peak at 1597 cm\({}^{-1}\) slightly changed with the increase in action time in Group B, Group E, and Group F compared with other peaks marked in Figure 5.