Spectrophotometric study of n,n'-bis (2-sulphoethyl)dithio-oxamide as a reagent for palladium

N,N'-bis(2-Sulphoethyl)dithio-oxamide forms two water-soluble yellow chelates with palladium(II), in strong hydrochloric acid solution or in buffered weak acid solution; with excess of reagent, a 1Pd:2R complex is always obtained. The absorption maximum occurs at 425 mμ in 6 M hydrochloric acid and at 382 mμ in buffered weak acid solution (pH 6.6). The colour is formed more slowly in strong acid solution, but there are fewer interferences. Relatively high concentrations of Co²⁺, Ni²⁺ and Hg²⁺can be tolerated, as well as smaller concentrations of Ir³⁺, Rh³⁺ and Cr³⁺. The molar absorption coefficients are 12,860 and 10,840 respectively in 6 M hydrochloric acid and buffered weak acid solution. The standard deviation in both cases is 0.004 absorbance units, i.e. respectively 0.033 and 0.039 μg of Pd.