A Derivative Spectrophotometric Method for the Simultaneous Determination of Cadmium and Cobalt in Environmental and Standard Samples

A highly sensitive and green method using a non-selective reagent, 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP), in the presence of a cationic surfactant, cetylpyridinium chloride, has been elaborated for simple and rapid trace level determination of Cd(II) ions by derivative spectrophotometry. Photometric parameters, i.e., lambda(max), molar absorption coefficient, and Sandell's sensitivity, of Cd(II)-5-Br-PADAP complex formed in cationic micellar medium at 9.5 pH are 558 nm, 1.26 x 10(5) L/mol cm, and 0.89 ng/cm(2), respectively. The developed method is highly sensitive with a lower detection limit of 0.04 mu g/L and a wide Beer's law determination range of Cd(II) ions from 0.04 to 1.1 mu g/mL. Effects of a few foreign ions and masking agents have been examined to enhance the method selectivity. The sensitivity and selectivity of the proposed method have also been improved by recording the absorption spectra in higher derivative modes and measuring derivative amplitudes of the analyte at the isodifferential point of strongly interfering Co(III) ions. Cd(II) ions have been successfully determined at the isodifferential point or zero cross-over point of Co(III)-5-Br-PADAP complex and vice versa for Co(III) ions. Subsequently, Cd(II) and Co(III) ions have been determined simultaneously in synthetic binary mixtures in the derivative modes without any prior separation with a relative error of 2.23 and 2.37% in the presence of 19- and 6-fold excess of Co(III) and Cd(II), respectively. This rapid, green, and non-extractive procedure has been applied for the simultaneous determination of Cd(II) and Co(III) in standard reference materials and environmental samples to verify the accuracy, precision, and applicability of the proposed method without the use of any toxic organic solvents.