Polarographic behaviour of metals in ethanolamines

Abstract

1. A systematic study of the polarographic behaviour of cadmium has been carried out employing mono-, di- and triethanolamines as the complexing agents at various pH values and in presence of (i) sodium hydroxide, (ii) sodium carbonate and (iii) ammonium chloride-ammonium hydroxide. 2. In base solutions containing triethanolamine, there is a marked tendency for the splitting up of the polarographic wave, while this phenomenon is almost absent when mono- and diethanolamines are used as complexing agents except when pH is below 11. 3. The polarographic reduction is reversible in solutions containing mono- and diethanolamines and mostly irreversible in triethanolamine solutions. An explanation has been suggested for the irreversibility of the process in triethanolamine solutions. 4. The formation of the following complexes is indicated from polarographic data:— $$ \begin{array}{*{20}c} {[Cd(Moen)_2 (OH)_2 ] [Cd(Moen)_3 (OH)_2 ] [Cd(Moen)_2 (CO)_1 ]} \\ {[Cd(Moen)_1 (NH_3 )_x ]^{ + + } [Cd(Dien)_2 (OH)_2 ] [Cd(Dien)_2 (CO_3 )_1 ]} \\ {[Cd(Trien)_1 (OH)_4 ]^{ - - } [Cd(Trien)_1 (NH_3 )_y ]^{ + + } [Cd(Trien)_1 (CO_3 )_x ]^{2 - x} } \\ \end{array} $$ 5. Dissociation constant and the Δ F° value for the dissociation of the complex are calculated from polarographic measurements in the case of reversible reduction processes. 6. The use of mono- and diethanolamine in the base solutions is suitable for the polarographic estimation of cadmium.