Fat-Soluble Vitamin and Carotenoid Analysis in Cooking Oils by Ultra-Performance Convergence Chromatography

In the current study, a rapid ultra-performance convergence chromatography (UPC2) method for the determination of seven fat-soluble vitamins (vitamin A: retinol, retinyl acetate; vitamin D: ergocalciferol, cholecalciferol; vitamin E: α-tocopherol; vitamin K: phylloquinone, menaquinone) and three carotenoids (lutein, lycopene, β-carotene) in various cooking oils was developed. Fat-soluble vitamins could be separated within 8 min on a UPC2 system with a BEH column (3.0 × 100 mm, 1.7 μm) at 50 °C, using a gradient elution with a mobile phase of carbon dioxide and 2-propanol (99.9:0.1/99.2:0.8/99.9:0.1), at a flow rate of 2 mL/min and the automatic back pressure regulator (ABPR) set to 1800 psi. Carotenoids were separated within 3 min on a similar UPC2 system with an HSS C18 SB column (3.0 × 100 mm, 1.8 μm) at 40 °C, under isocratic conditions with a mobile phase of carbon dioxide and ethanol (75:25; v/v). The flow rate was set to 1.5 mL/min and the ABPR to 1800 psi. The limits of detection (LODs) and quantification (LOQs) were ranging between 0.01 and 1.17 μg/mL and from 0.05 and 3.59 μg/mL for fat-soluble vitamins while carotenoid detection limits fell in the range of 0.03–0.11 μg/mL and of 0.10–0.38 μg/mL, respectively. The results showed excellent linearity for both methods (R 2 0.9993–0.9999). A recovery study with standard addition technique into a selected coconut oil sample resulted in more than 90 % recovery for retinyl acetate, retinol, and vitamin K1 and K2, whereas the recovery for vitamin D2 and D3 ranged between 70 and 80 %. The lowest recovery of 68–70 % was found for α-tocopherol while almost comparable recovery rates above 80 % were observed for all three carotenoids.