Determination of vitamin D 2 in emulsified nutritional supplements by solid-phase extraction and column-switching high-performance liquid chromatography with UV detection

Abstract

This paper deals with a method for solid-phase extraction of trace amounts of vitamin D 2 (VD 2, 19 ng/g) from emulsified nutritional supplements, which contain 50 kinds of compounds, followed by column-switching high-performance liquid chromatography (HPLC) with UV detection at 265 nm. VD 2 is present at 1000–20 000 000 times lower concentration than other components. Bond Elut C 18 cartridge was chosen as for the emulsified nutritional supplements after comparison with eight other types. A sample solution was applied to the solid-phase extraction cartridge and VD 2 was eluted by methanol followed by HPLC. The effects of sample pH, eluent composition and eluate volume on the retention and elution of VD 2 on Bond Elut C 18 cartridge were examined. The resulting method was simple, rapid (analysis time: ∼20 min), sensitive (detection limit: ∼0.1 ng per injection (200 μl) at a signal-to-noise ratio 3:1), and reproducible (relative standard deviation: ∼6.2%, n=5). The calibration graph for VD 2 was linear in the range of 0.1–3 ng per injection (200 μl). Recovery of VD 2 was ∼80% by the standard addition method.