Analysis of Azithromycin on the Alliance™ iS HPLC System: System Performance Under Challenging Method Conditions

Many regulated legacy monographs require buffers in the mobile phase to ensure reliable performance of the method. For these traditional gradient reversed-phase applications the mobile phase transitions from a buffered, aqueous mobile phase to an organic mobile phase. The proportions of each mobile phase during elution may cause the salt to become insoluble in the water/organic composition, resulting in potential precipitation of the salt. Furthermore, under these conditions there may be variability across different HPLC systems due to design differences.
For this application note, the USP monograph for Azithromycin Organic Impurities was chosen as a representative method for these conditions. This specific monograph mobile phases include a weak aqueous mobile phase buffer at a concentration of 12 mM, and a strong mobile phase with acetonitrile/methanol blend. The separation requires a gradient which has a strong elution of 25/75 coupled with a 75% organic mobile phase composition. This monograph was executed on multiple HPLC systems, using replicate injections of standards to investigate system suitability and performance differences across systems.