The Impact Of Instrument Characteristics On The Method Migration Of A Challenging USP Assay

By Anthony Dovell and Paula Hong

USP monographs are designed to equip users with the essential information necessary for conducting specific tests. Scientists utilize these monographs for a wide array of purposes, including identification tests, limit tests, and the analysis of potency and purity. When it comes to LC chromatographic assays, the monograph specifies the fundamental system suitability criteria required to ensure that the system is operating at the level necessitated for analysis. Although a single monograph can be analyzed across different LC systems, this may result in slight variations in outcomes while still adhering to the system suitability standards. This variation often stems from system design differences. For instance, binary and quaternary pumps differ in design, and although these configurations may be compliant, they might not be ideal for every monograph, potentially affecting system suitability outcomes. This is particularly true for methods with challenging conditions or those outside of the system's typical operating parameters.

One example is the USP monograph for azithromycin organic impurities, which involves a lengthy, shallow mobile phase gradient (0.5% B/column volume), relatively high salt content (12 mM), and a low wavelength (210 nm). Together, these factors can lead to system suitability challenges if the performance is suboptimal. To evaluate the influence of different systems on this method, the organic impurities monograph was tested across multiple chromatographic systems, each with unique design features and instrument characteristics.