Determination of Kinetic Parameters of Redox Reactions using CE-ICP-MS: A Case Study for the Reduction of Np(V) by Hydroxylamine Hydrochloride.

The rate constants k of the reduction of 5  ×  10-5  M Np(V) to Np(IV) by hydroxylamine hydrochloride (HAHCl) in 1 M HCl have been determined by CE-ICP-MS in the temperature range of ϑ  = 30-70°C and with varying concentrations of HAHCl from 1 M to 7.2 M. The reaction was found to have (pseudo)first order kinetics with respect to HAHCl. The experimental results for k ranged from 0.0029(1) min-1 (ϑ  =  40°C, c(HAHCl)  =  3 M) to 0.039(7) min-1 (ϑ  =  60°C, c(HAHCl)  =  7.2 M). The activation energy of the reaction was determined as EA   =  (72 ± 10) kJ/mol. These results and a comparison with literature data show that the coupling of CE to ICP-MS provides a powerful analytical tool for the investigation of the kinetic aspects of redox reactions of actinides at low concentrations. On the basis of this proof-of-principle study, the method presented here can be extended to the investigation of the kinetic parameters of other redox systems containing different actinides (or transition metals) and oxidants/reductants. This article is protected by copyright. All rights reserved.