A HIGH-PERFORMANCE LIQUID RADIOCHROMATOGRAPHIC ASSAY FOR THE SIMULTANEOUS ANALYSIS OF ILOPROST AND MISOPROSTOL

A high-performance liquid chromatographic (HPLC) method utilizing ultr aviolet absorbance coupled with radioisotope detection was developed f or the precise and simultaneous determination of iloprost and misopros tol. This assay allows complete resolution of iloprost diastereoisomer s and has a total run time of approximately twenty minutes. Samples we re prepared for chromatographic analysis by extracting a mixture of tr itiated drugs from rat plasma with acetonitrile. The resulting solutio ns were chromatographed on a reversed phase Zorbax Rx-C8 column using 0.02M potassium phosphate (pH 3.0), acetonitrile, and methanol (46:30: 24, v/v) at a flow rate of 1.7 mL/min. 2-Naphthoic acid was employed a s an internal standard. The correlation coefficient for varying concen trations of tritiated iloprost (12.7 Ci/mmol specific activity) from 2 .18 ng/mL to 21.8 ng/mL was 0.995, and the correlation coefficient for concentrations of tritiated misoprostol (50 Ci/mmol specific activity ) from 0.617 ng/mL to 6.17 ng/mL was 0.993. The high selectivity and s ensitivity of this assay make it useful for the simultaneous quantitat ion of iloprost and misoprostol.