DIRECT AMPEROMETRIC TITRATION OF AMINES WITH SODIUM TETRAPHENYLBORATE SOLUTION

The direct amperometric titration of amines with sodium tetraphenylborate solution based upon anodic depolarization at a dropping mercury electrode by the use of excess TPB titrant, was systematically investigated. The influence of various factors such as pH, volume of titration mixture, quantity of sample in a definite volume to be titrated were studied. Based upon the above observations, a method is proposed as follows: Pipette 0.5-2.0 ml (at a concentration of about 2×10^-2M) of samples of various amines into a 50 ml beaker and add 1% HAc to make a volume of about 10-20 ml. The dropping mercury electrode serves as the polarographic anode. Titrate the amines with 0.05 M standard Na-TPB solution (pH 8) at 0.18 V using the saturated NaCl bridge and S.C.E. as reference. After each addition, stir for one minute and allow the solution to obtain a steady current value, then record the galvanometric reading. The end point is graphically plotted with current versus milliliters of titrant; sharp breaks are obtained. The Na-TPB solution was standardized volumetrically by the standard mer- curic solution. Organic bases so determined include aniline, methyl aniline, diethylamine, ephedrine hydrochloride, dimethylaniline, trimethylamine hydrochloride, triethylamine hydrochloride, urotropine, and tetraethylammonium iodide. The relative error of this method is 2%. The more soluble salts of aliphatic primary amines such as methylamine, ethyl- amine, n-butylamine, and even in the case of ephedrine hydrochloride could not be ac- curately titrated. The application of this method to titrate the amines depend largely upon the structure of the amines and the solubility of amine-TPB salts. This method was also successfully applied to titrate the nitrogen containing drugs such as chlopromarzine, cinchophene, quinine sulphate, atropine sulphate, antipyrine, aminopyrine, rivanol, and strychnine.