STABILITY AND RELEASE KINETICS OF NATURAL OIL MICROEMULSIONS 31 Figure 3. HPLC chromatograms of (A) 1.25 μg/mL nicotinamide standard solution, (B) a blank ME (MEO2), and (C) a nicotinamide-loaded ME (MEO2-N).

JOURNAL OF COSMETIC SCIENCE 32 RELEASE PROFILES AND KINETICS OF NICOTINAMIDE-LOADED MES MEC1-N and MEO1-N were selected for evaluation of in vitro release behavior because these formulations had the same ratios of components but different oil type. In addition, these MEs provided no appearance change and their active remaining was more than 90% after being stored at 4°C and RT for 3 mo. The release profi les of MEC1-N and MEO1-N in Figure 4 showed that nicotinamide was slowly released from both MEs. The amount of nicotinamide released from MEO1-N was signifi cantly higher than that from MEC1-N (p 0.05, t-test) because of different degrees of oil unsaturation. Olive oil contained 71.530% unsaturated oleic acid, whereas virgin coconut oil contained 48.102% saturated Table IV Validation Results of HPLC Technique for Nicotinamide Analysis Parameter Value Linearity (r2) 1.0000 Accuracy (%recovery) 98.26 ± 0.06–100.95 ± 0.13 Intra-day precision (%RSD) 0.03–0.19 Inter-day precision (%RSD) 0.03–1.10 LOD (μg/mL) 0.02 ± 0.00 LOQ (μg/mL) 0.05 ± 0.00 Table V Viscosity of MEC1-N, MEC2-N, and MEO1-N after Storage at Three Different Temperatures for 3 mo Time (month) Temperature Viscosity (cps) at 100 rpm MEC1-N MEC2-N MEO1-N Initiala – 222.65 ± 0.17 259.94 ± 0.00 230.55 ± 0.17 1 4°C 178.23 ± 4.55 225.58 ± 2.94 189.06 ± 2.79 RT 169.31 ± 3.09 209.06 ± 3.09 207.31 ± 8.13 45°C 169.31 ± 2.94 209.06 ± 6.44 207.31 ± 7.73 2 4°C 203.39 ± 1.53 246.51 ± 17.66 221.05 ± 13.05 RT 211.65 ± 2.48 252.40 ± 2.05 225.75 ± 6.09 45°C 226.20 ± 2.98 242.70 ± 10.88 256.55 ± 0.25 3 4°C 211.75 ± 6.60 239.05 ± 1.70 224.62 ± 15.15 RT 218.09 ± 1.16 232.75 ± 8.61 238.08 ± 13.45 45°C 202.36 ± 3.46 241.65 ± 1.24 190.19 ± 2.08 a Viscosity values were initially measured when the samples were left at RT overnight after preparation. Table VI Percentage of Nicotinamide Remaining in MEC1-N, MEC2-N, and MEO1-N after Storage at Three Different Temperatures for 3 mo Formulation Nicotinamide remaining (%) 4°C RT 45°C MEC1-N 90.10 ± 1.31 93.44 ± 2.40 88.22 ± 0.41 MEC2-N 91.53 ± 2.50 90.76 ± 1.89 90.46 ± 0.60 MEO1-N 94.42 ± 1.71 91.59 ± 1.36 89.49 ± 2.11