Amphoterics with weakly basic nitrogen

There are four possible approaches to the determination of WW type amphoterics. They are  

Titration with sodium dodecyl sulphate in acid solution. The solution must be at least 0.1 M in hydrogen ion, but otherwise the procedure is straightforward. Potentiometric titration is preferred. 

In two-phase titration using either A or B, it may be more effective to add a measured excess of titrant, shake very thoroughly, allow the layers to separate, run off the chloroform, add fresh chloroform and back-titrate the excess. 

Titration with NaTPB. The solution must be at least 0.1 M in hydrogen ion. Potentiometric titration is preferred, but two-phase titration should be satisfactory. It may be more effective to add a measured excess of NaTPB, filter or centrifuge (or run off the chloroform layer) and determine the excess by precipitation with potassium, filtration and weighing. 

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Nonionics and WW or amphoterics present. The previous procedure would include all amphoterics with weakly basic nitrogen (WW and SW) in the anionic fraction. If a WW amphoteric is present the simplest procedure is to combine the two columns described, with the cation exchanger first. The WW amphoteric is retained on the cation exchanger and the anionics on the anion exchanger, from which they are eluted as described. 

Nonionics and WW or WS amphoterics present. The previous procedure would include betaines and amphoterics with weakly basic nitrogen in the cationic fraction. 

All cations, including weak bases, amine oxides, betaines, amphoterics all bases not sulphobetaines with weakly basic nitrogen... 

Imidazoles are amphoteric compounds with a basic, pyridine-type nitrogen (they are about 106 times more basic than oxazoles and 104 times more basic than thiazoles173), and (where the NH is unsubstituted) a weakly acidic, pyrrole-type amino nitrogen in the ring. In consequence, imidazoles readily form salts with acids and often form salts (or complexes) with metals. The sparingly soluble silver salts formed by imidazoles have been used by Giesemann et al.174 as intermediates in the synthesis of 1-triphenylmethylimidazoles. Normally, however, the salts formed with acids are more important in isolation and purification procedures. 

Evaporate both solutions to a low volume, dilute to about 10 ml with water and carry out the indicator test on small portions of each of them in both acid and alkaline solution. The solution from the cation exchange column contains only anionics, soaps, SW and SS sul-phobetaines and nonionics, and the solution from the anion exchange column contains only cationics with both weakly and strongly basic nitrogen, betaines, SS sulphobetaines and nonionics. WW amphoterics are retained by both columns. 

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