The titration of amino- and carboxyl-groups in amino-acids, polypeptides, etc. parts IV-VI.— Estimations in presence of formol and alcohol

Abstract

In the well-known formol titration method of Sörensen (22), neutralised formaldehyde is added to the solution of the amino-acid (or other compound containing —NH2) and standard alkali run in until the production of a red colour with penolphthalein. An explanation of this method that has often been advanced in text-books and elsewhere is that the original amino-acid is neutral because the basic—NH2neutralises the acidic —CO2H, and that with the addition of formalde-hyde the basic character of the —NH2is destroyed, with the result that the acidic —CO2H is free to be titrated.