Assay of the related substances in alprostadil for injection with the correction factor

To establish a method using the correction factor for the determination of the related substance in alprostadil for injection.The assay was carried out on a C₁₈ column (250 mm×4.6 mm，5 μm) with the mobile phase of 0.007 mol/L phosphate buffer solution(pH 6.50)-acetonitrile-methanol (70∶25∶5) at a flow rate of 1.5 mL/min.The column temperature，the detection wavelength and the injection volume were set at 30 °C,196 nm,and 20 μL,respectively.The relative retention time and the correction factor between prostaglandin A₁ and alprostadil，prostaglandin B₁ and alprostadil were determined.The relative retention time was used to determine the position of prostaglandin A₁ and prostaglandin B₁，the correction factor was used to determine the content of prostaglandin A₁ and prostaglandin B₁ impurities in alprostadil.Good linear relationships of alprostadil，prostaglandin A₁and prostaglandin B₁ were obtained over the concentration range of 0.125 - 50.0 μg/mL (r=0.999).The relative retention time between prostaglandin A₁ and alprostadil was 2.70，the relative retention time between prostaglandin A₁ and alprostadil was 2.87；the correction factor between prostaglandin A₁ and alprostadil was 2.296；the correction factor between prostaglandin B₁ and alprostadil was 1.681.This method was proved to be simple，accurate and reliable to determine the related substance of alprostadil for injection without standard substances of prostaglandin A₁ and prostaglandin B₁.