Spectrofluorimetric study of the β-cyclodextrin:vitamin K3 complex and determination of vitamin K3

Vitamin K3 (menadione) is an oil-soluble vitamin and not naturally fluorescent but yields fluorescence when it is reduced. However, it is possible to yield a fluorescent derivative in the region of 407 nm in aqueous medium when complexed to β-cyclodextrin (CD). A 1:1 stoichiometric ratio and a formation constant of 373±34 l mol−1 were obtained for the binary inclusion complex between menadione and β-CD. The measurements were performed at pH 6.2 adjusted by adding 0.1 mol l−1 citrate buffer solution and 6.4×10−3 mol l−1 of β-CD concentration. The calibration graph was linear over the range 0.1–2.0 mg l−1 with a repeatability of 2.2%; the detection limit was 0.022 mg l−1 and the limit of quantification limit was 0.073 mg l−1. The procedure was applied to pharmaceutical formulations.