Abstract
Estriol occurs in urine as water-soluble conjugates, but water-insoluble estriol is usually used as a primary standard to calibrate analytical methods. Estriol solutions in ethanol cannot be carried through commonly used methods and are therefore unsatisfactory. With caution, estriol in aqueous NaOH can be used in most methods except those involving separation of conjugates on columns. Estriol sulfonates are only satisfactory in direct methods which do not involve preliminary purification steps. Concentrates of partially purified conjugates are easily prepared, and these could be used as reliable secondary standards in all methods provided that they are accurately calibrated.
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