A sensitive derivative spectrophotometric method is described for the
determination of microamounts of cobalt based on the integration of li
quid-liquid separation and reaction, in dichloroethane, of the analyte
with 3-(4-phenyl-2-pyridinyl)-5-phenyl-1,2,4-triazine (PPT) and 2,4,6
-trinitro-phenol (picric acid). Cobalt was thus determined in the rang
e 7.2-500 ng/ml. The method has a high selectivity with a detection li
mit of 2.2 ng/ml. The relative standard deviations were 3.2 and 1.5% f
or 20 and 100 ng/ml cobalt, respectively. The proposed method was appl
ied to the determination of the analyte in vitamins.