Determination of vitamin K-1 in medical foods by liquid chromatography with postcolumn reduction and fluorometric detection

A liquid chromatographic (LC) method is described for the determination of vitamin K-1 in medical foods, The sample is enzymatically digested with lip ase and alpha-amylase and extracted with 1% sodium bicarbonate solution-iso propanol (1 + 1), After C-18 solid-phase extraction, vitamin K1 is separate d by nonaqueous reversed-phase LC, converted to the hydroquinone by postcol umn zinc reduction, and quantitated by fluorescence detection. The limit of detection is 8 pg (3 sigma), and the limit of quantitation is 27 pg (10 si gma) on column. Linear response ranged from 0.1 to 1.0 ng vitamin K1 (r = 0 .9999), The mean recovery (n = 38) for all spiking levels was 101.6 +/- 2.8 5%. Analysis of Standard Reference Material 1846, Infant Formula, gave a me an value of 0.95 +/- 0.088 mg vitamin K/kg (K or K1?)(n = 31) with a coeffi cient of variation of 9.26.