Methods for the quantitative determination of ergosterol, cholesterol, and 7-dehydrocholesterol are based upon the spectrophotometric measurement of the optical densities of the characteristic absorption maxima of the reaction products resulting from the treatment of the chloroform solutions of these sterols with an antimony trichlorideacetyl chloride reagent. The absorption spectra of the reaction products of the three sterols are distinctly different. By this method it is possible to differentiate between ergosterol and 7-dehydrocholesterol. This differentiation is not possible by the direct ultraviolet spectrophotometric method. A comparison has been made of results obtained by both the direct spectrophotometric and the antimony trichloride method in the determination of ergosterol in three different types of yeast and one mold extract.
the standard curve, gives the concentration of DDT. The use of an alternate solvent, ethylene chloride, having a peak absorption of 530 µ is described.
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