If you compare this to testosterone, you will notice that the methyl group on C10 has been removed and the oxygen on C3 has been reduced to a hydroxyl (-OH) group. These two changes reduce the number of bonds on all the carbons, so aromatization occurs, and alternating double bonds form. In order for aromatase to function and aromatize a steroid, the steroid must have a methyl group attached to the C10. This is another example of the lock and key model. For this reason, Nandrolone does not aromatize and is not converted to an estrogen. It does not have the methyl group.
Steroid isolation , depending on context, is the isolation of chemical matter required for chemical structure elucidation, derivitzation or degradation chemistry, biological testing, and other research needs (generally milligrams to grams, but often more  or the isolation of "analytical quantities" of the substance of interest (where the focus is on identifying and quantifying the substance (for example, in biological tissue or fluid). The amount isolated depends on the analytical method, but is generally less than one microgram.  [ page needed ] The methods of isolation to achieve the two scales of product are distinct, but include extraction , precipitation, adsorption , chromatography , and crystallization . In both cases, the isolated substance is purified to chemical homogeneity; combined separation and analytical methods, such as LC-MS , are chosen to be "orthogonal"—achieving their separations based on distinct modes of interaction between substance and isolating matrix—to detect a single species in the pure sample. Structure determination refers to the methods to determine the chemical structure of an isolated pure steroid, using an evolving array of chemical and physical methods which have included NMR and small-molecule crystallography .  : 10–19 Methods of analysis overlap both of the above areas, emphasizing analytical methods to determining if a steroid is present in a mixture and determining its quantity.