Construction and evaluation of ion selective electrodes for perchlorate with a summing operational amplifier: application to pyrotechnics mixtures analysis
The construction and evaluation of an electrode selective to perchlorate with improved sensitivity, constructed like a conventional electrode (ISE), but using an operational amplifier to sum the potentials supplied by four membranes (ESOA) is described. The two types of electrodes, without an inner reference solution, were constructed using octylammonium chloride as sensor, a mixture of dibutylphthalate and o-nitrophenyloctyl ether as solvent mediator and PVC as plastic matrix, the membranes being obtained by direct application onto a conductive epoxy resin support. After the comparative evaluation of their working characteristics they were used in the determination of perchlorate in propellants, fulminating powders and fireworks. On all occasions, the results obtained by the ESOA were found to be similar to those obtained by the conventional ISE, but with higher precision. The limit of detection of the direct potentiometric method developed was found to be 0.1 g kg–1, and the precision and accuracy of the method, when applied to eight different samples of pyrotechnic mixtures, expressed in terms of mean relative standard deviation and average percentage of spike recovery were 0.4% and 100.5%, respectively. Adequate agreement was found between the results obtained by the potentiometric method and the reference methods, since the calculated relative errors ranged from +0.4% to –0.5%.