Simple and Fast Voltammetric Method for Assaying Monacolin K in Red Yeast Rice Formulated Products

The red yeast rice formulated products, used worldwide as cholesterol-lowering dietary supplements, have the main active ingredient monacolin K which is actually lovastatin registered as the first statin drug. In this work, a rapid and simple square-wave voltammetric method was developed for determination of monacolin K based on the electrochemical reduction of the carbonyl group in lactone ring. Considering the pH dependence of current response and the interconversion of monacolin K to its acid form, the Britton-Robinson buffer of pH 5.0 was selected as a supporting electrolyte for analytical measurements. The net square-wave voltammetric response of monacolin K was shifted towards more negative potential values by increasing the concentration of analytes. The peak current was linearly proportional to monacolin K concentration in the range of 0.25–20 μg/mL. The fully validated method was successfully applied for fast screening and direct voltammetric determination of monacolin K in red yeast rice products formulated in various dosage forms. To evaluate the proposed voltammetric method, the results obtained were compared with those obtained by HPLC methods.