A highly sensitive spectrophotometric method for the determination of cobalt(ii) using the chromogenic reagent 4,4A-diazobenzenediazoaaminoazobenzene (BBDAB) was developed. The optimum conditions for the chromogenic reaction of cobalt(ii) with BBDAB were studied in the presence of Triton X-100 and sodium tetraborate. The calibration graphs were rectilinear in the range 0-7 mg per 25 cm 3 cobalt(ii). The apparent molar absorptivity is 1.72 3 10 5 dm 3 mol 21 cm 21 with a Sandell's sensitivity of 0.00035 mg cm 22 . The method was applied to the determination of cobalt in soil and vitamin B 12 with satisfactory results.
A highly sensitive spectrophotometric method for determination of cadmium by the chromogenic reagent 2-pyridinediazoaminoazobenzene (Cadion Py) has been developed. In the presence of Triton X-100 and NH3-NH4Cl buffer solution, the optimum conditions for colour reaction of cadmium with Cadion Py, the molar absorptivity of which is 1.92 X lo5 1 mol-1 cm-l at 530 nm, are studied. Elimination of interfering ions at ten-fold concentration is achieved by adding a mixed masking agent. Trace amounts of cadmium in water or waste water samples has been satisfactorily determined by the method.
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