Determination of disopyramide phosphate in serum by high-performance liquid chromatography

A method is described for the quantitation of disopyramide phosphate (Norpace) in serum by high-performance liquid chromatography. The analysis utilizes ultraviolet detection at 254 nm with a 5-micrometers reversed-phase column and a mobile phase consisting of acetonitrile, ammonium dihydrogen phosphate buffer, acetic acid, and water. The determination requires 100 microliters of serum sample and the analysis time (9 min) is rapid. Serum extraction is a two-step process using chloroform, sodium carbonate, and hydrochloric acid. Although acid is used, columns produced sharp peaks with consistent retention times for 6-8 months. This method provides selectivity and sensitivity with a precision of 3.8%, average recovery of 92.9% and no interference from 18 commonly administered drugs.