Fluorimetric determination of vitamin K3 (menadione sodium bisulfite) in synthetic animal feed by high-performance liquid chromatography using a post-column zinc reducer.

A high-performance liquid chromatographic (HPLC) method for analysis of vitamin K3 (menadione), as the water-soluble sodium bisulfite salt, in synthetic animal feed is described. The menadione sodium bisulfite (MSB) is extracted with aqueous methanol, converted to oil-soluble menadione with sodium carbonate, and partitioned into n-pentane. After evaporation, the menadione is dissolved in methanol and analyzed by reversed-phase HPLC. The menadione is reduced on-line to its fluorescent 1,4-dihydroxy analogue by zinc reduction prior to fluorescence determination at 325 nm excitation wavelength and 425 nm emission wavelength. The fluorescence response was linear in the range 1 to 100 ng of menadione injected. Recovery experiments were performed on synthetic animal feed spiked at 20 and 200 mg/kg levels of MSB. Average recoveries from feed were greater than 90% with an average relative standard deviation of 5.5%. Additional confirmation of menadione in actual feed extracts was performed using capillary gas chromatography-Fourier transform infrared spectroscopy (GC-FT-IR). The HPLC-fluorescence and GC-FT-IR methods had lower limits of detection of 20 micrograms/kg and 2 mg/kg, respectively.