Spectrophotometric determination of Co(II) using 1-(1-methyl-1h-pyrazol-3-yl-azo)-naphthalen-2-ol

For the first time, the interaction of cobalt(II) with a new photometric reagent 1-(1-methyl-1H-pyrazol-3-yl-azo)-naphthalen-2-ol was studied by spectrophotometric method. It was established that on adding of 1-(1-methyl-1H-pyrazol-3-yl-azo)-naphthalen-2-ol into the solution containing Co(II) ions, the occurrence of red-purple colour is observed, while 1-(1-methyl-1H-pyrazol-3-yl-azo)-naphthalen-2-ol itself is yellow-orange coloured at the conditions of interaction. The optimal conditions for the maximum yield of the coloured compound were established: 0.2 M ammonia buffer solution with a pH of 9.0 in a water-ethanol solution (ethanol concentration was 38 % v/v). It was established by mole ratio method, that the ratio of cobalt(II) with the analytical reagent in the coloured complex is 1 : 2. It is most likely that the coordination of cobalt with azo reagent takes place with the participation of naphthol’s OH-group, as well as of azo group of 1-(1-methyl-1H-pyrazol-3-yl-azo)-naphthalen-2-ol. In addition, two axial positions are most likely occupied by ammonia molecules. Sensitive and rapid method of cobalt(II) spectrophotometric determination using the absorption shoulder of the complex at λ max = 490 nm was developed (LOD = 4.6·10 -7 M). When using ammonium tartrate and potassium pyrophosphate as masking reagents, spectrophotometric determination of cobalt is possible in the presence of significant concentration excesses of concomitant metal ions. The accuracy of the method of cobalt(II) spectrophotometric determination using 1-(1-methyl-1H-pyrazol-3-yl-azo)-naphthalen-2-ol was confirmed during the estimation of Co(II) content in complex model solutions by the “added-found” approach, as well as in the samples of white wine. Keywords : cobalt(II), spectrophotometric determination, pyrazole, azo dye.