kindly refer attachment. Any advice on equivalency between two different analytical methods (in-house and compendial method)? For related substances test using spike sample preparation?
If I understood your question, the problem is how to compare internal and official methods. I can add some literature on this issue, I hope it is interesting for you
Pay attention that you should compare the results received by your and standard methods using statistical parameters for Validition: precision (repeatibility or reproducibility) and trueness (random and systematic errors) using Fischer and Student coefficients and Recovery.