INDYK&WOOLLARD: JOURNAL OF AOAC INTERNATIONAL VOL. 83, NO. 1, 2000 123

Determination of Vitamin K in Milk and Infant Formulas by Liquid Chromatography: Collaborative Study

(a) Preparation of test sample.

(1) Digestion.—-Weigh 1.0 g powder or 10.0 g liquid into test tube. Include both reagent blank and quality control sample in each analytical schedule. Dissolve powder in ca 15 mL warm water (>>>> Add 1.0 g potassium carbonate and mix.

(2) Extraction.—-(Note: Take precautions to prevent concentration of extracts through uncontrolled solvent evaporation.) Add 30.0 mL hexane, stopper, and shake vigorously for ≥10 min using mechanical shaker. Let stand in the dark, preferably refrigerated, until layers separate. If this is slow (>10 min) or incomplete, then centrifuge at ca 1000 rpm (ca 200 g) for 10 min (decant portion of supernatant into smaller centrifuge tube if necessary). Transfer 1.00 mL (fortified samples) or 5.00 mL (nonfortified samples) of upper hexane phase into a vial. Evaporate under nitrogen flow to dryness. (Note: Larger extract volumes may be required, with the option of rotary evaporation, dependent on sensitivity of fluorescence detector.) These dried extracts may be held for 3–-5 days in the dark at