I am currently working on a drug-loading process that should be examined by UV detection. One of the processes I have to apply to detect the therapeutic agent concentration is utilizing Cerium Ammonium Nitrate. I have completed the standard curve for my drug with its sodium salt, which is the general form of my drug in the market. Hence, for some reason, I needed to modify my drug with polyamines like PEI. I have noticed recently that the presence of PEI in my solution would affect the final results of the UV detection. It completely suppresses the Ceric Nitrate in the solution and results in no UV peak.

My question is, has the presence of PEI possibly had such an effect on my final result? How should I manage to overcome this issue?