Simultaneous analysis of tocopherols, tocotrienols, phospholipids, γ-oryzanols and β-carotene in rice by ultra-high performance liquid chromatography coupled to a linear ion trap-orbitrap mass spectrometer

Abstract

A rapid ultra-high performance liquid chromatography with a linear ion trap-orbitrap high resolution mass spectrometer (UHPLC-LTQ-Orbitrap HRMS) method for the determination of 21 nutrients in rice was developed. A simultaneous separation of tocopherols (α-, β-, γ-, δ-), tocotrienols (α-, β-, γ-, δ-), phospholipids, γ-oryzanols and β-carotene was achieved in less than 13 min. The detection was performed using a LTQ-Orbitrap MS detector using full scan in positive ion mode. This method was validated according to linearity, limits of detection and quantitation, reproducibility and recoveries. A regression coefficient (r² > 0.99) was obtained within a range of 0.05–10 μg mL⁻¹ for tocopherols, tocotrienols and β-carotene, 0.1–50 μg mL⁻¹ for phospholipids and 0.001–10 μg mL⁻¹ for γ-oryzanols. The method gave detection limits (S/N, 3) of 0.2 to 1.9 ng mL⁻¹ and quantitation limits (S/N, 10) of 0.7 to 6.3 ng mL⁻¹. Relative standard deviations, which were applied to estimate repeatability, ranged from 2.3 to 9.6%. Recoveries within a range of 80.6–109.6% for all the analytes were obtained. The mass accuracy for 21 validated compounds was ≤3 ppm. Furthermore, quantitative determination showed that rice processing could cause content changes of nutritional composition between brown and white rice. The total ion current fingerprint profile (TICFP) could reveal the significant differences between the two types of rice samples (brown and white rice) from different regions. This method allowed fast and convenient analysis for the determination of nutrients in rice, which indicated that the Orbitrap technology is beneficial for food testing.