Forced degradation studies are typically performed using HPLC and UV detectors to understand the degradation pathway of pharmaceuticals and to insure all impurities are accounted. In these studies, performing mass balance or the conservation of mass is crucial. However, given the range of impurities and their chemical and physical properties, mass balance studies can be challenging. These challenges may be due to co-elution of impurities and the active pharmaceutical ingredient (API), the presence of undetected components, or differences in response of the impurities to theAPI: all of which can lead to poor recoveries or a lack of understanding of the degradation pathway. To address these difficulties, multiple orthogonal detectors based on different principles can be used to measure or identify compounds with different chemical or physical properties.
In this presentation we will evaluate mass balance using a triple detection system consisting of a photodiode array (PDA), evaporative light scattering detector (ELSD) and a mass detector. These studies will be performed in two parts. First, the relative response of impurities and an active pharmaceutical will be evaluated. Since UV relative response is based on the ratio of UV peak area to concentration or mass, both the UV and ELSD detector will be used to determine relative response for related compounds in reference to the API. The difference in linearity between the two detection techniques will be addressed by converting the non-linear ELSD response to linear using standard mathematical principles. These results will be compared against more established techniques, including the use of standards and the slope ratios. In the second part, the relative response ratios will then be used to perform mass balance. Specifically, mass balance recoveries of the degraded samples will be determined using chromatographic software tools.