Liquid-Phase Cyclic Chemiluminescence for the Identification of Cobalt Speciation.

Accurate discrimination of metal species is a significant analytical challenge. Herein, we propose a novel methodology based on liquid-phase cyclic chemiluminescence (CCL) for the identification of cobalt speciation. The CCL multistage signals () of the luminol-HO reaction catalyzed by different cobalt species have different decay coefficients . Thereby, we can facilely identify various cobalt species according to the distinguishable values, including the complicated and structurally similar cobalt complexes, such as analogues of [Co(NH)X] (X = Cl, HO, and NH), Co(II) porphyrins, and bis(2,4-pentanedione) cobalt(II) derivatives. Especially, the number of substituent atoms also influences the value greatly, which allows excellent discrimination between complexes that only have a subtle difference in the substituent group. In addition, linear discriminant analysis based on provides a complementary solution to improve the differentiating ability. We performed density functional theory calculations to investigate the interaction mode of HO over cobalt species. A close negative correlation between the adsorption energy and the value is observed. Moreover, the calculation of energy evolutions of HO decomposition into a double hydroxide radical shows that a high level of consistency exists between the activation energy barrier and the value. The results further demonstrate that the decay coefficient of the CCL multistage signal is associated with the catalytic reactivity of the cobalt species. Our work not only broadens the application of chemiluminescence but also provides a complementary technology for speciation analysis.