Just to give my question some more context, I am not presently using HFBA or studying testosterone. Instead, I am teaching the method of isotope dilution on a very basic level, and I was planning to use testosterone as an example, inasmuch as it appears in a textbook I consulted and also in one paper I found. However, I am not sure how to approach the one curious fact of there being two HFB groups. There is one hydroxyl group on testosterone, which is distant from the unsaturated ketone.