I don't have any specific experience in this area, but I went to PubMed and searched on "testosterone dihydrotestosterone derivatization." 54 citations came up. Undoubtedly some will not be helpful to you, but perhaps some will be. This paper, which I found with a slightly modified search and which mentions hypogonadism, claims baseline separation with pyridine 2,3-dicarboxylic acid: DOI: 10.1016/j.steroids.2008.01.018