AbstractA novel kinetic method for the determination of trace amounts of Co(II) has been developed. The proposed method based on the catalytic effect of Co(II) on the oxidation of xylenol orange tetra sodium salt by H2O2in the presence of cationic surfactant (N‐dodecylpyridinium chloride). Co(II) at μg.mL−1was determined spectrophotometrically by measuring the decrease in the absorbance of xylenol orange at 577 nm by the differential method. The method is precise, selective, and sensitive. The detection limit of the procedure was 0.058 μg.mL−1. The relative standard deviation for the replicate determination (n = 6) of 0.7 μg.mL−1was 1.285%. The results compared satisfactorily with those of atomic absorption spectrometry. The method was successful for the analysis of Co(II) in veterinary and synthet