mass balance in stability study
I am doing a stability study of vitamin D3 injection. The Assay method for D3 quantitation is BP based UV method whereas impurities are identified using a validated HPLC method.
The stability profile of the product at different time points looks like this
Assay: 106.2%, 106.5%, 101.5%, 98.2%, 97.2%
% impurities: 0.12% , 0.14% , 0.19% , 0.25%, 1.17%
My query is that active is broken down about 9.0% from initial time point to last time point but I don't see 9.0% increase in impurities (but only 1.17%). Are these results acceptable even if we cannot find the mass balance? Is this significant increase in %impurity enough for presenting stability results?
Note: None of the impurities have RRF of more than 1.5.