SECTION III-(B)-DRUG ASSAY PROCESSES 



The Pharmacopoeia gives in detail the various processes suited to the 

 assay of the various drugs specified. By careful manipulation, using these 

 methods, the pharmacist may reach definite results as to the quality and 

 strength of the article under examination. The student .in pharmacy 

 should, however, be familiar with the general principles which underlie 

 the process of drug assay. A brief outline of these principles may be 

 here in place. 



Principles of Alkaloidal Assay. The immiscible solvents, such as 

 chloroform, ether, benzol, amylic alcohol, etc., are employed. Any of 

 these liquids, when shaken with water or acidulated water, will mix with 

 the aqueous liquid only for a time. On standing for a few minutes they 

 will separate into two distinct layers, one of these being the aqueous layer, 

 the other the immiscible solvent (mostly ethereal in character). 



If equal volumes of ether and water be shaken together and a solution 

 of the extract of belladonna added to the mixture and a few drops of sul- 

 phuric acid, it will be found that the belladonna alkaloids will be dissolved 

 out and will be contained in the aqueous (acidulated) layer, not in the 

 ethereal layer, because it is the general property of alkaloidal salts to be 

 soluble in water, and to be insoluble in ether. The acid having converted 

 the atropine and the hyoscyamine of the extract into a salt (sulphate), 

 it therefore will be taken up and retained by the aqueous layer. If to 

 these two liquids (the ether and the acidulated solution of the alkaloidal 

 salt) there is now added a sufficient quantity of ammonia water to neu- 

 tralize the acid and make the aqueous liquid slightly alkaline, and the 

 fluids be again mixed and allowed to stand as before, it will be found that 

 the alkaloids (of belladonna) are no longer in the aqueous layer but in 

 the upper (ethereal) layer. It is the general property of free alkaloids, 

 themselves, with few exceptions, to be soluble in ether (chloroform, etc.) 

 and to be insoluble in water. It might be stated therefore, as a general 

 principle, that alkaloids, as a rule, are soluble in the immiscible fluids 

 (ether, chloroform, amylic alcohol), etc., while their salts are insoluble in 

 these fluids. Alkaloidal salts, on the other hand, are insoluble in the im- 

 miscible fluids, but are soluble in water. Advantage is taken of this 

 property in the assay of alkaloidal drugs. 



For general directions for alkaloidal assay, see Part II, No. 15 (Proxi- 

 mate Assays) U.S.P. IX, p. 593. 



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