This is a study involving pre purification of steroid samples before mass spec or chromatography. The info, of course , has a wider range of interest than that for those who can use it to there own end. Or for the good of others.
Steroids are hydrophobic compounds and do not dissolve
significantly in aqueous media and are thus added to the matrix dissolved in
ethanol, methanol, or other polar solvent which is miscible with water. The volume
of such a solvent should be as small as possible in comparison with the volume of
fluid used for analysis to prevent denaturation of any protein. Sometimes, the
steroid is added to a glass container, the solvent evaporated off and the fluid for
analysis added. This practice is not to be recommended since steroids, when added
in this way, can be adsorbed to the surface of the glass and may not subsequently
be dissolved in the matrix, even when the glass has been inactivated by prior
treatment with dimethyldichlorosilane. In addition, some steroids can be destroyed
when evaporated to dryness on glass surfaces, particularly when the glass has
previously been cleaned by treatment with chromic acid, a practice which used to
be common but is now no longer so.
Methods for purification vary and its good to know more than one type. Therefore...
The main drawback of
liquid–liquid extraction is emulsion formation, though centrifugation will often
overcome this situation but is time-consuming. Standing extraction tubes in dry ice
to freeze the aqueous phase is a useful way of decanting an upper organic layer.
While the modern trend has been to move away from such extractions because of
the need to restrict use of toxic and/or flammable solvents and the problems of disposal, such extractions should not be completely discarded and there may well
be situations where such procedures can still be useful.
Indeed, a recent publication
(Hill et al., 2007), describing the measurement of pregnanolones in third trimester
pregnancy plasma, used ether for extraction, freezing the aqueous phase in solid
CO2
/ethanol, and pouring off the ether layer. After evaporation to dryness, the residue
was further purified by partitioning between n-pentane: 80% methanol in water
(1:1)
Tbc later..