Sample Residual ratio (%) reference (surfactant free) 92.6 Polyoxyethylene (20) stearyl ether 1% 91.2 Polyoxyethylene (20) stearyl ether 2% 95.3 Polyoxyethylene (20) stearyl ether 5% 94.3 Polyoxyethylene (20) stearyl ether 8% 96.4

Table 3: Effect of nano-capsulation and the concentration of polyoxyethylene (20) stearyl ether on the stability of α-lipoic acid in the aqueous solution.