Ion-pair reversed-phase liquid chromatographic identification and quantitation of papaverine congeners

A reversed-phase ion-pair high-performance liquid chromatographic separation was developed for identification and quantitation of papaverine drug congeners, namely papaverine (1), moxaverine (2), drotaverine (3), and ethaverine (4) hydrochlorides. A synthetic reference mixture of the four congeners in the range 1-4 micrograms showed good separation. With a reference standard (codeine phosphate), the relative retention times to codeine were 1.356, 1.984, 2.46, and 2.91 (mean of six) for 1, 2, 3, and 4, respectively. Good linearity was obtained in the quantitation of 1 and 2 in the range 1-2 micrograms [correlation coefficient (r), 0.9978 and 0.9997, respectively] and 3 and 4 in the range 2-4 micrograms, (r, 0.9998 and 0.9991, respectively). Analysis of some commercial dosage forms containing one of these congeners showed good recovery with sufficient accuracy and precision. The method was sensitive and permitted the use of small sample sizes or unit doses.