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. 
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Most modern steroid enemas are foam based - as the likelihood of someone with colitis being able to retain a water based enema is quite low. These act topically applying the steroid directly to the colon - with only small amounts being absorbed into the bloodstream. This makes side effects less likely. The downside is that they can only reach the descending colon and rectum - so for those with extensive colitis oral steroids may be needed. A combination of Entocort and steroid enemas can provide topical treatment to the majority of the colon - again minimizing side effects. As the two main steroid enemas differ quite greatly I will cover them separately.