Spectrophotometric determination of cadmium (II) with 5-(2′-carbomethoxyphenyl)azo-8-quinolinol in presence of sodium dodecylsulphate as surfactant

The reaction between cadmium (II) and 5-(2 ' -carbomethoxyphenyl) azo-8-quinolinol in aqueous medium at pH 4.0-4.8 results in an insoluble complex. Addition of sodium dodecylsulphate gives a vermillion red coloured solution which is stable for at least 8 h. Beer's law is obeyed in the range 0.04-0.88 ppm of cadmium (II) at 503 nm. The molar absorptivity and Sandell's sensitivity at 503 nm are 1.05 x 10(5) 1 mol(-1) cm(-1) and 1.0 ng cm(-2), respectively. Alkali metals, alkaline earths, manganese (II) and chromium (VI) do not interfere. The interference of Cu(II), Pb(II), Ni(II), Fe(III), Co(II) and Mo(VI) is removed by extracting their complexes formed with the reagent at pH 5.5-6.5 in to methyl isobutyl ketone. However, Zn(II) and Hg(II) interfere. The method has been applied for the determination of cadmium (II) in borewell, tap and river and nallah (with suspected discharge of industrial waste) water samples. The results agree closely with the values obtained by atomic absorption spectrophotometry.