A comparison of immobilization sol-gel methods for an optical chemical hydrazine sensor

Optical-fibre chemical sensors are of great interest in nuclear fuel reprocessing, because of remote, real-time measurements and lack of waste. An intrinsic optical chemical sensor for hydrazine has been developed to optimize its concentration in the Purer process. p-Dimethyl-aminobenzaldehyde (p.DMAB) has been chosen as the reactive molecule. This paper reports on immobilization sol-gel methods to synthesize host matrices for p.DMAB. Two ways of immobilization are investigated: physical entrapment in a microporous structure and covalent bonding in a mesoporous one. The physical characteristics and the analytical performances of such sensors are reported. The sensing scheme of the sensor depends on several parameters. The mass transfer of the analyte between the solution and the matrix is governed by the diffusion process and influences the response time of the sensor. The method of immobilization of the reactive molecule and the nature of the host matrix govern the lifetime of the sensor. The third parameter, which is not often mentioned, relies on the interactions between the diffused species and the surface of the host matrix, which modify its response time and its reversibility.