All spectra were recorded from 400 to 600 nm with 2.0 nm
bandwidth and 2000 nm min−1 scan speed. The absorption
spectra (pH 5.0) of dithizonate complexes of bismuth, zinc
and a mixture of both ions are shown in Fig. 2. According to
Fig. 2, complexes of bismuth and zinc have absorption maxima
at 493 and 510 nm, respectively. Spectral bands of the
metal ions overlap strongly, rendering simultaneous determination
of these metal ions impossible by UV–vis absorbance
measurements