# Permeation Effect Analysis of Drug Using Raman Spectroscopy for Iontophoresis
## 4 Discussion  
Based on the attribution analysis of the characteristic peaks of the Raman spectra for the drug-associated mouse skins and the other mouse skins in Figure 3 and Table 1, there were overlaps between the characteristic peaks in the Raman spectra of the penicillin sodium solution and the Raman spectra of the mouse skin. Five stable and highly differentiated characteristic peaks were selected for the experimental analysis: 570 cm\({}^{-1}\), 1194 cm\({}^{-1}\), 1236 cm\({}^{-1}\), and 1446 cm\({}^{-1}\) represent mouse skins, and 1597 cm\({}^{-1}\) represents the penicillin sodium solution. For the experimental groups in Figures 4 and 5, the integral intensities of the above-mentioned five spectral peaks were obtained after spectrum fitting, as shown in Table 2.  
The intensity ratios of the spectral peaks were used to further analyze the enhanced permeation effect for different concentrations of the penicillin sodium solution and different action times. The ratios of spectral peak intensities (heights or areas) were applied for the quantitative analysis [33; 34], which included the drug quantitative determination inside skin [35]. Combining the above analysis and data, four spectral peak intensity ratios (1597 cm\({}^{-1}\)/570 cm\({}^{-1}\), 1597 cm\({}^{-1}\)/1194 cm\({}^{-1}\), 1597 cm\({}^{-1}\)/1236 cm\({}^{-1}\), and 1597 cm\({}^{-1}\)/1446 cm\({}^{-1}\)) was selected as the reference factors to measure the enhanced permeation effect, as shown in Table 3.  
As shown in Figure 6, compared with Group A, the penetration enhancement effect of Groups B, C, and D had the same increasing trend, which was noted by observing the ratios of the corresponding spectral peaks (1597 cm\({}^{-1}\)/570 cm\({}^{-1}\), 1597 cm\({}^{-1}\)/1194 cm\({}^{-1}\), 1597 cm\({}^{-1}\)/1236 cm\({}^{-1}\), and 1597 cm\({}^{-1}\)/1446 cm\({}^{-1}\)). However, with the increasing concentration of the penicillin sodium solution, the enhancement trend slowed down. The ratio of the corresponding spectral peaks at 1597 cm\({}^{-1}\)/1446 cm\({}^{-1}\) was more obvious. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Peaks (cm\({}^{-1}\))** & **570** & **1194** & **1236** & **1446** & **1597** \\ \hline
**A** & 152 \(\pm\) 18 & 162 \(\pm\) 17 & 123 \(\pm\) 15 & 160 \(\pm\) 14 & 121 \(\pm\) 19 \\
**B** & 125 \(\pm\) 12 & 134 \(\pm\) 18 & 111 \(\pm\) 14 & 160 \(\pm\) 12 & 612 \(\pm\) 64 \\
**C** & 100 \(\pm\) 13 & 101 \(\pm\) 11 & 90 \(\pm\) 11 & 151 \(\pm\) 15 & 886 \(\pm\) 102 \\
**D** & 106 \(\pm\) 14 & 108 \(\pm\) 9 & 105 \(\pm\) 14 & 203 \(\pm\) 23 & 1223 \(\pm\) 169 \\
**E** & 86 \(\pm\) 10 & 128 \(\pm\) 14 & 92 \(\pm\) 13 & 147 \(\pm\) 18 & 684 \(\pm\) 98 \\
**F** & 130 \(\pm\) 12 & 194 \(\pm\) 18 & 134 \(\pm\) 17 & 224 \(\pm\) 28 & 1115 \(\pm\) 126 \\ \hline \hline \end{tabular}  
**A**: The intensity of corresponding spectral peaks in drug permeation experiment without iontophoresis; **B**: the intensity of corresponding spectral peaks in drug permeation experiment with 0.16 g\(\cdot\)mL\({}^{-1}\) and 20 min; **C**: the intensity of corresponding spectral peaks in drug permeation experiment with 0.24 g\(\cdot\)mL\({}^{-1}\) and 20 min; **D**: the intensity of corresponding spectral peaks in drug permeation experiment with 0.48 g\(\cdot\)mL\({}^{-1}\) and 20 min; **E**: the intensity of corresponding spectral peaks in drug permeation experiment with 0.16 g\(\cdot\)mL\({}^{-1}\) and 30 min; **F**: the intensity of corresponding spectral peaks in drug permeation experiment with 0.16 g\(\cdot\)mL\({}^{-1}\) and 40 min. All results are expressed as mean \(\pm\) S.E.  
\end{table} 
Table 2: Corresponding Raman spectral characteristic peak intensities after resolution of overlapped peaks.