I have a working FT-IR method that can quantify dimethicone in a product using the absorbance of the Si-Me bond at 1260 cm-1. This works for the majority of our samples. However, there is one problematic product that contains about 5 other silicones in addition to the claimed active ingredient. These other silicones make up about 20% of the product while the active ingredient is at 1%. The placebo has approximately the same absorbance as the sample. As far as I know, the FT-IR has no way of distinguishing between silicones (although chemometrics or ELSD has been mentioned but not yet pursued).

My question is, can I just quantitate the total dimethicone/silicone content of the sample? For example, if I get an absorbance of 0.5 A for a 1.0% sample, then test an unknown sample which reads 0.5 A, can I just say that that unknown sample is 1.0%? Maybe if I have enough points on my calibration curve?