Dear Kelly, I wholeheartedly agree with all of Steven's recommendations and would also add that access to a sample or version of the product that you know for certain to be free from any tampering (known as an ' authentic reference standard') will always help address such a question. If you don't have access to a reference sample, a chemistry-based approach could be very difficult to answer for any chemist other than an expert in the particular product sub-category (or sub-sub category! - the categories you mention are so broad it could be an impossible challenge to find anyone with detailed chemical knowledge about all components in the category). Even then, and even given an authentic standard, this could be quite an 'expensive' project to tackle purely with analytical chemistry. Your best bet (AFTER notifying the FDA about your concern and after consulting with an expert on the particular products in question) might be to work with a specialist in forensic analysis (one with a solid background in chemistry, of course!). Also keep in mind, for any given problem like this, it could be incredibly expensive to obtain 'certainty' but relatively easy to obtain a 'likelihood' of tampering - so be prepared to answer a question like 'exactly how certain do you need to be?'. by the way I'm an analytical chemist with no formal training in forensics, but have much experience being asked about approaching problems like this using analytical chemistry techniques. In many cases, the answers can be much more rapidly (and inexpensively) obtained through good old-fashioned logic (and including a chemist while employing problem-solving exercises based on paradigms such as Six Sigma or Total Quality Management!).
