Abstract
Analytical procedures for polarographic determination of hydrosulphite in the presence of sodium hydroxide have been basically studied.
Sodium hydrosulphite used as the reduction process liquid in the dye chemical industry is commonly dissolved in sodium hydroxide. This sodium hydroxide is of availed as the supporting electrolyte in the polarographic method for the sodium hydrosulphite.
The polarographic current-voltage curve of the solution containing 0.01M sodium hydrosulphite and 0.1M sodium hydrosulphite shows two oxidation waves and a reduction wave. A principal oxidation wave shows a half-wave potential of -0.45 V vs. S. C. E., the same value being observed for sodium hydrosulphite and potassium hydrosulphite in the solution.
The wave is well-defined and its limiting current is governed by the maximum rate of diffusion of hydrosulphite ions to the surface of the dropping mercury electrode. The relative error of the method is within 10% for the solutions in the concentration range from 5×10-4M to 5×10-2M hydrosulphites. While the concentration of sodium hydrosulphite in the reduction process liquid is usually 0.1M or more, that is too concentrated to directly apply the polarographic method, a simple procedure of dilutionwith water is served enough because 1M or more of sodium hydroxide is also contained in the reduction process liquid.
The influences of the dyestuffs, thiosulphate and other chemicals, which may by contained in the process liquid, on the principal oxidation wave of the hydrosulphite are also described.
