Determination of vitamin K1 in emulsified nutritional supplements by solid-phase extraction and high-performance liquid chromatography with postcolumn reduction on a platinum catalyst and fluorescece detection

Determination of small amounts of vitamin K1 (0.8 μg/g) in nutritional supplements with high fat content (20 mg/g) was performed by solid-phase extraction and high-performance liquid chromatography (HPLC) with fluorescence detection after reduction on a platinum oxide catalyst. The concentration ratio of plant oils to vitamin K1 (0.8 μg/g) was about 25 000:1. A sample solution was applied to a solid-phase extraction cartridge and vitamin K1 was eluted with ethanol, followed by HPLC. The proposed method was simple, rapid (analysis time: ca. 12 min), sensitive [detection limit: ca. 0.1 pg per injection (100 μl) at a signal-to-noise ratio of 3:1], highly selective and reproducible [relative standard deviation: ca. 1.3% (n=5)]. The calibration graph of vitamin K1 was linear in the range of 0–2 pg per injection (100 μl). Recovery of vitamin K1 was over 90% by the standard addition method.