A simple spectrophotometric method for the determination of cobalt in industrial, environmental, biological and soil samples using bis(salicylaldehyde)orthophenylenediamine

Bis(salicylaldehyde)orthophenylenediamine (BSOPD) has been proposed as new analytical reagent for the direct non-extractive spectrophotometric determination of cobalt. It reacts with cobalt in slightly acidic (0.0002–0.001 M H2SO4) 50% 1,4-dioxanic medium to form a red–orange chelate with a molar ratio 1:1. The reaction is instantaneous and the maximum absorbance was obtained at 458 nm and remains constant for over 24 h. The average molar absorption coefficient and Sandell’s sensitivity were found to be 1.109 × 104 l mol−1 cm−1 and 20 ng cm−2 of Co(II), respectively. Linear calibration graph was obtained for 0.1–15 mg l−1 of Co(II) with a correlation coefficient value of 0.995 for Co-BSOPD complex. Large excess of 44 cations, anions and complexing agents do not interfere in the determination. The method was successfully used in the determination of cobalt(II) from synthetic mixture and certified reference materials for the purpose of validating the method and the results of analyses were found to be excellent agreement with those of actual values. This developed method was also used for determination of cobalt in some environmental waters (potable and polluted), biological (blood and urine) and soil samples and solution containing both cobalt(II) and cobalt(III). The results of the proposed method for biological samples were comparable with AAS and were found to be in good agreement. The method has high precision and accuracy (s = ± 0.01 for 0.5 mg l−1).