Direct determination of verapamil in urine and serum samples by micellar liquid chromatography and fluorescence detection

Verapamil, a calcium channel antagonist, is one of the most commonly prescribed drugs in the treatment of hypertension. In this work, it was determined in serum and urine samples by a sensitive and precise chromatographic procedure without any pre-treatment step in a C18 column using a micellar mobile phase of 0.15 M sodium dodecyl sulfate and 5% pentanol at pH 7. Fluorescence detection set at 230 nm (excitation) and 312 nm (emission) was used. Verapamil is eluted at 12.5 min with no interference by the protein band or endogenous compounds. Linearities (r > 0.998), as well as intra- and inter-day precision, were studied in the validation of the method. LODs were also calculated to be 11.0, 18.5 and 20.2 ng/mL in micellar solution, serum and urine, respectively. Recoveries in the biological matrices were in the 97–99% range. Drug excretion in urine was studied in a volunteer receiving treatment for hypertension, and verapamil, as an unchanged drug, was separated from other metabolites. The procedure developed can be useful in the field of toxicology and clinical analysis.