A COMPARISON OF IMMOBILIZATION SOL-GEL METHODS FOR AN OPTICAL CHEMICAL HYDRAZINE SENSOR

Optical-fibre chemical sensors are of great interest in nuclear fuel r eprocessing, because of remote, real-time measurements and lack of was te. An intrinsic optical chemical sensor for hydrazine has been develo ped to optimize its concentration in the Purer process. p-Dimethyl-ami nobenzaldehyde (p.DMAB) has been chosen as the reactive molecule. This paper reports on immobilization sol-gel methods to synthesize host ma trices for p.DMAB. Two ways of immobilization are investigated: physic al entrapment in a microporous structure and covalent bonding in a mes oporous one. The physical characteristics and the analytical performan ces of such sensors are reported. The sensing scheme of the sensor dep ends on several parameters. The mass transfer of the analyte between t he solution and the matrix is governed by the diffusion process and in fluences 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 menti oned, relies on the interactions between the diffused species and the surface of the host matrix, which modify its response time and its rev ersibility.