Abstract: The reaction between tetraphenylborate and some alkaloids including aconitine, ber- berine, brucine, cinchonine, chelidonine, narcotine, quinine, etc., was studied ampero- metrically in the pH range of 2.2-10.2; the reactivity was found to depend on the basi- city of the alkaloid and on the pH of the reaction medium. An expression is given which relates the pK_b of the alkaloid and the pH of the reaction medium; when the pK_b of an alkaloid is known, the approximate pH values at which a precipitation titration is feasible can be calculated.