Determination of stearic acid and 12-hydroxyoctadecanoic acid in PEG-60 hydrogenated castor oil by HPLC-ELSD after alkaline hydrolysis

Abstract

A rapid and simple method for the determination of stearic acid and 12-hydroxystearic acid in PEG-60 hydrogenated castor oil by high performance liquid chromatography with evaporative light scattering detection was established. The oil sample was first pretreated by alkaline hydrolysis. The analysis was performed on a Zhongpu Develop XD-C18 column (250 mm × 4.6 mm, 5 µm) with gradient elution of methanol and 1% acetic acid aqueous solution at a flow rate of 1.2 mL·min−1 and a column temperature of 40 °C. The drift tube temperature of the evaporative light scattering detection system was set at 40 °C, and the pressure of carrier gas (N2) was 337 kPa. The regression equation revealed a good linear relation (r = 0.9993–0.9995) during the test ranges (119.1–1190.7 μg·mL−1 for 12-hydroxystearic acid, 10.7–107.4 μg·mL−1 for stearic acid). The detection limits of 12-hydroxystearic acid and stearic acid were 1.1 and 2.5 μg·mL−1, the limits of quantitation were 3.2 and 7.4 μg·mL−1, respectively. And the mean recoveries were 101.5 and 101.0%, the corresponding relative standard deviations (RSDs) were 2.1 and 2.8%, respectively. The RSDs corresponding to repeatability (n = 6) were both less than 1.7% in terms of precision. As to the stability, the test results remained stable after 8 h at room temperature (RSDs were both less than 2.6%). The developed method showed high sensitivity, recovery, repeatability and stability, which indicated that the method could be applied as a quality evaluation method for the determination of stearic acid and 12-hydroxyoctadecanoic acid in PEG-60 hydrogenated castor oil.