Liquid chromatographic determination of manidipine in serum with electrochemical detection

A highly sensitive and selective method for determining a dihydropyridine calcium antagonist, manidipine, by liquid chromatography using column switching with electrochemical detection was developed. Manidipine in serum was extracted by a rapid and simple procedure based on C₈ bonded-phase extraction and then silica extraction. Manidipine and nilvadipine as an internal standard were separated on a C₈ bonded-phase HPLC column and detected by high conversion efficiency amperometric detection at +0.7 V. Manidipine and nilvadipine (I.S.) were separated from an endogenous interference peak in serum and concentrated on a pre-column (C₁₈) by column switching using an isocratic mobile phase, and then the corresponding fractions were introduced to an analytical column with a C₈ stationary phase. Determination of manidipine was possible over the concentration range 0.5–10 ng/ml: the limit of detection was 0.3 ng/ml. The recovery of manidipine added to serum was 93.1–98.4% with coefficients of variation of less than 7.1%. The method is applicable to drug level monitoring in the serum of healthy volunteers treated with manidipine and to the analysis of pharmacokinetics.