Determination of menadione in an animal feed using supercritical fluid extraction and HPLC with electrochemical detector.

Menadione (vitamin K3) is extracted from spiked rat chow using supercritical fluid carbon dioxide at 8000 psi and 60 degrees C. Quantitative extraction requires only 20 min. The extraction does not suffer from the problems associated with conventional solvent extraction of lipophilic materials from animal feeds. Menadione is determined in the extract, which does not require further cleanup, using reversed-phase high-performance liquid chromatography (HPLC) with reductive mode electrochemical detection at a silver electrode at -0.75 V vs. calomel. The minimum detectable quantity by the detector is 125 pg of menadione, and the response is linear over at least 4 orders of magnitude; however, the minimum quantity extractable is about 20 micrograms/g of feed. Repetitive extracts of a spiked feed sample over a five-day period show an average recovery of 90.5% with a relative standard deviation of 2.2% at the 1 mg/g level.