Mass balance – the practical application of the Law of Conservation
of Mass to chemical synthesis and degradation – is a concept
that is used throughout the pharmaceutical industry. During synthetic
route development, mass-balance calculations are used to
assess yields and efficiency of chemical transformations. In pharmaceutical
development, mass-balance assessments indicate
material losses that are typical of any multi-step manufacturing
process [1]. A mass-balance approach is commonly used to establish
the potency of an active pharmaceutical ingredient (API) reference
standard by subtracting non-API components from 100% [2].
Finally, with respect to drug stability and associated analytical
methods, mass balance is defined by the International Conference
on Harmonization (ICH) as ‘‘the process of adding together the assay
value and levels of degradation products to see how closely