The titration of amino- and carboxyl-groups in amino-acids, polypeptides, etc. Parts I—III.—Investigations with aqueous solutions

Abstract

The development of the modern theory of titration and its application to analytical operations have greatly increased the scope of the volumetric method, and added considerably to its precision and refinement. In the following pages it will be shown on theoretical grounds that both the basic and acidic groups in amphoteric electrolytes are capable of estimation by a variety of acidimetric and alkalimetric methods, and experimental data will be presented to demonstrate that considerable accuracy is possible when the titrations are controlled by the conditions demanded by theoretical considerations. These methods find a practical application in the determination and identification of amino-acids as well as of the more complex ampholytes which result from the hydrolytic breakdown of proteins ; and results obtained by such methods are much more nearly quantitative than those resulting from actual separation and weighing of the constituents or their derivatives—a general method of attack in the past. Only two processes have hitherto been available for the estimation of amino-acids by titration, both depending on the acidity of the carboxyl group, that of Sörensen being carried out in presence of formol, and that of Foreman in presence of alcohol: these methods have remained to a large extent empirical and of somewhat limited application.