Extractive Spectrophotometric Determination of Cobalt as a Mixed Thiocyanate-Promethazine Complex

Department of Post-graduate Studies and Research in Chemistry, University of Mysore, Manasagangotri, Mysore-570 006, India Manuscript received 12 July 1979, revised 15 November 1979, accepted 20 December 1979 A new spectrophotometric method for the determination of traces of cobalt based on the extraction of blue cobalt-thiocyanate-promethazine ion-association complex into chloroform from 1.5-4.5M sulphuric acid medium is described. Beer's law is valid over the concentration range 0.5-45 ppm of cobalt(Il). The complex which is stable for over a week has an absorption maximum at 618-616 nm and its molar absorptivity is 1.39 x 103 1 mole-1 cm-1. Many common ions do not interfere. The proposed method offers higher sensitivity than that of the classical reaction with thiocyanate and can be used in media of wider range of acidity and no problems arise from instability