# Timed-Release Silica Microcapsules for Consistent Fragrance Release in Topical Formulations
## 3 Results and Discussion
### Quantitative Analysis of Fragrance Release from Silica Microcapsules Within Formulation  
We quantitatively analyzed the fragrance release from the pore-controlled silica microcapsules filled with patchouli compound fragrance oil using GC-MS. The patchouli compound fragrance oil contained six distinct fragrance components, of which three (DL-limonene, \(\alpha\)-guaiene, and patchouli alcohol) were selected for further investigation due to their high concentration, ease of analysis, and varying vapor pressures (Table 3). \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Ingredient** & **Retention Time** & **Ratio (\%)** &
\begin{tabular}{c} **Vapor Pressure** \\ **(mm Hg at 20 \({}^{\circ}\)C)** \\ \end{tabular} & **Odor Type** \\ \hline DL-Limonene & 8.066 & 38.64 & 1.03 [45] & Pine and citrus [46] \\ \hline
1,8-Cineole & 8.159 & 3.86 & 1.90 \({}^{\ast}\)[47] & Eucalyptus-like [48] \\ \hline Linalool & 9.045 & 6.06 & \(\sim\)0.05 [49] & Floral, citric, and fresh [50] \\ \hline Linalyl acetate & 11.62 & 6.38 & \(\sim\)0.10 [51] & Floral, sweet and citric [50] \\ \hline \(\beta\)-Patchouliene & 14.192 & 1.12 & 0.0141 [52] & - \\ \hline \(\alpha\)-Guaiene & 14.942 & 8.63 & 0.006 \({}^{\ast}\)[53] & Woody [54] \\ \hline Seychellene & 15.277 & 4.90 & 0.034 \({}^{\ast}\)[55] & - \\ \hline \(\alpha\)-Bulnesene & 16.034 & 9.68 & 0.009 \({}^{\ast}\)[56] & - \\ \hline Patchouli alcohol & 18.609 & 20.73 & \(<\)0.001 [57] & Woody [58] \\ \hline Total & \multicolumn{3}{c}{100.00} \\ \hline \hline \multicolumn{4}{c}{\({}^{\ast}\) Vapor pressure at 25 \({}^{\circ}\)C.} \\ \end{tabular}
\end{table} 
Table 3: Patchouli compound fragrance oil compositions analyzed by gas chromatography–mass spectrometry. Figure 4: (**A**) Fragrance retention of silica microcapsules in 2% SDS solution at 60 \({}^{\circ}\)C for accelerated storage test. (**B**) Fragrance qualitative evaluation of T4 silica microcapsules in the model formulation and (**C**) after incubation at 60 \({}^{\circ}\)C for four weeks. As described in Figure 4B,C, two cream formulations (A and B) were prepared for evaluation. A thin layer of each cream (14.8 mg) was applied to a glass slide (7.62 cm \(\times\) 2.54 cm), and the amount of fragrance released was measured over 16 h in an incubator at 50% humidity and 36 \({}^{\circ}\)C. The cream was applied based on the average amount used on an intermediate skin surface area (legs, arms, trunk, back, and abdomen) of 4000-14,000 cm\({}^{2}\), as reported by [PERSON] et al. [59]. Compared to Formulation A (Figure 5A), Formulation B (Figure 5B), which contained T4 silica fragrance microcapsules, exhibited a sustained release of fragrance for 16 h.  
For the two fragrance components prone to vaporization (DL-limonene and \(\alpha\)-guaiene), they were continuously released from Formulation B even after 4 h, whereas more than 90% of those in Formulation A had evaporated within the first 2 h. Patchouli alcohol, which has  
Figure 5: Evaluation of fragrance component remaining as function of drying time after application of model formulation analyzed by gas chromatography–mass spectrometry (GC–MS) of (**A**) Formulation A (control) and (**B**) Formulation B (applied silica microcapsules). a low vapor pressure, was observed to gradually evaporate over time in both formulations. Immediately after application, all three fragrance components evaporated simultaneously, leading to both formulations being perceived as having similar scent intensity (Figure 4B,C). However, over time, the scent from Formulation B, which contained fragrance microcapsules, was rated higher due to the sustained release of the three fragrance components. Taken together, the silica microcapsules enable the continuous and simultaneous release of all fragrance components, resulting in a prolonged fresh-scent perception for the user. This study demonstrated a novel approach to the application of silica microcapsules in practical formulations, allowing users to experience a continuous fresh scent.