A 250 lg/mL stock solution of vitamin
K1 (vit K1) (Sigma–Aldrich, Steinheim, Germany) was prepared in
ethanol:methanol (50:50 v/v). This solution is stable at least 1½
year at 20 C. The exact concentration was determined from
E1%
1 cm ¼ 419 at 248 nm in petroleumether