Conductometric method for the quantitative analysis of Pb(II) and Cd(II) with 2-mercapto-5-R-amino-1, 3, 4-thiadiazole derivatives.

摘要

The reactions of the cations with 2-mercapto-5-R-amino-1,3,4-thiadiazole derivatives were studied conductometrically with the purpose of establishing a new conductometric method for the quantitative analysis of Pb(II) and Cd(II). Aqueous solutions of Pb(NO3)2 and Cd(CH3COO)2 were titrated with hidroalcoholic solutions of 2-mercapto-5-amino-1,3,4-thiadiazole (MATD), 2-mercapto-5-allylamino-1,3,4-thiadiazole (MA1ATD) and 2-mercapto-5-acetylamino-1,3,4-thiadiazole (MAcATD) and 2-mercapto-5-phenilamino-1,3,4-thiadiazole (MFATD) in different concentrations. The reactions takes place at pH 6.5 (realised with acetate buffer). A linear classical titration curves was obtained. In solutions more concentrated than 10(-2) M just one equivalence point can be noticed, corresponding to 1:2 Me:R stoechiometries. For concentration less than 10(-2) M two equivalence point were observed at 1:1 and 2:1 ratio of Me:R, indicating the step formation of the complex. Accurate conductometric determinations can be made using the second break points of the titration curves as equivalence points. The amounts of Cd(II) and Pb(II) taken and recovered are good, with an error less than 1%.