# Ultrasound-Assisted Extraction of \(\beta\)-Asarone from Sweet Flag (_Acorus calamus_) [PERSON]
## 3 Results and Discussions
### The Kinetics of Ultrasonic-Assisted Extraction of \(A\). calamus  
The ultrasound-assisted extraction was carried out to improve the extraction of \(\beta\)-asarone from \(A\). _calamus_. The increasing \(\beta\)-asarone yield of extraction upon sonication duration of 30 min for 1:100 and 1:50 solid-to-solvent ratios are shown in Figures 5 and 6, respectively for sonication power of 30 (\(\Delta\)), 50 (\(\times\)), 70% (\(\square\)); and in the absence of sonication, with the presence of temperature (\(\Circle\)) and without (\(\Diamond\)). The extract yield was calculated from the calibration curve of the purified \(\beta\)-asarone constructed using HPLC technique as  
Figure 3: **(a)** The chemical structure, **(b)** UV, **(c)** IR and **(d)** HRMS spectra of \(\beta\)-asarone. shown in Figure S1 in SI. The lines in the figures were plotted with the calculated values modelled according to Equation (1). The extraction progress plots revealed the typical trend of the extraction curve commonly observed. The curves are described by the two important mechanistic stages during extraction--the washing and diffusion mechanism [36]. Washing refers to the initial stage of extraction where the volatile oil is relatively easier to be washed out and is usually characterized by the rapid increase in the extraction plot. The high rate of extraction is due to the location of the active compounds at various sites of the plant matrices. As the samples are soaked in the medium, the solvent pervades into the plant matrices and solubilized the easily accessible solutes, washing them out. The affected solutes in this stage are those located near the surface or originally adsorbed on the surface of the matrices. Therefore, the more compounds available on the surface, the higher the rate of the washing mechanism. On the other hand, the solutes located in the interior or enclosed within the structure of the plant matrices will only be diffused out by the solvent diffusion process. The diffusion process represents the later stage of the extraction plot where the increment of extract yield happens at a slower rate, even though the two stages in the mechanism work in different manners, simultaneously. Thus, the two processes cannot be completely distinguished in the discussion. However, the domination of one process over the other is clearly evident in the plots shown in Figures 5 and 6. The rapid increase in yield extract within \(\sim\) the first 10 min of the extraction indicates the dominanover the diffusion stage, whilst the slow increment of the extract yield that follows indicates the dominance of the diffusion stage over the washing stage. To kinetically explain the \(\beta\)-asarone extraction yield during the washing and diffusion stages, the progress of extraction is fitted to the [PERSON] and [PERSON]'s model as shown in Equation (1). The washing rate coefficient is kinetically depicted by \(\mathrm{k_{w}}\) values, and the diffusion rate coefficient is depicted by \(\mathrm{k_{d}}\) values. The extract yield, \(\mathrm{Y_{t}}\) of the extraction in the presence and absence of ultrasound aid is also shown in Table 1 below. Before we delve into the effect of ultrasound assistance, a quick look at the extract yield in Table 1 showed a higher amount of extract yield at 1:50 as compared to the 1:100 solid-to-solvent ratio. This indicates that extracting 1.0 g of Acorus calamus in 50 mL of ethanol is practical even though it was initially doubted during the experiment. This is because it is known that a larger solid-to-solvent ratio results in a higher concentration gradient, thus allowing more solvent penetration into the material [37]. Therefore, the lower amount of ground _A. calamus_, the higher surface contact between plant material, and hence the greater the improvement of the extraction yields. The larger amount of \(\beta\)-asarone extracted at a higher solid-to-solvent ratio (1:50) proved that having 1.0 g of ground _A. calamus_ in 50 mL of ethanol is efficient and suitable for further investigation in this study.