Quantitative analysis of Pentalgin N tablets by gradient and isocratic high-performance liquid chromatography

Two procedures were proposed for the quantitative analysis of the drug Pentalgin N with the use of HPLC in gradient and isocratic modes. Analgin (dipyrone), caffeine, naproxen, phenobarbital, codeine, an analgin degradation product, and sodium sulfite (added to the test solution to stabilize analgin) were separated on a column (150 × 3.9 mm) packed with Nova-Pak C18 (4.0 μm) with elution with a 0.00625 M KH₂ PO₄ solution with an acetonitrile concentration gradient from 10 to 60 vol % in 10 min or on a column (150 × 3.9 mm) packed with Nova-Pak CN HP (4.0 μm) with elution with a 0.0110 M KH₂ PO₄ solution (pH 5.8) containing 5 vol % acetonitrile. The wavelength of the diode-array detector was 212 nm. Model solutions containing all of the active principles and additives of the tablets were analyzed, and the performance characteristics of both procedures were calculated. Both procedures afford reliable analytical results; however, the isocratic version is technically simpler and more preferable for product control in commercial production.