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The ionophore 1,4,7,10,13-penta(n-octyl)-1,4,7,10,13-pentaazacyclopentadecane(L1) was used for the development of miniaturised perchlorate-selective electrodes in thick-film technology. Different PVC membranes containing L1 and the plasticizers o-nitrophenyloctyl ether (NPOE), dibutyl phthalate (DBP), bis(2-ethylhexyl)sebacate (DOS) and dibutylsebacate (DBS) were prepared and placed on a graphite working electrode manufactured byusing thick film serigraphic technology. The perchlorate selective electrode containing DBSas plasticizer showed a potentiometric Nernstian response of -57 mV per decade in a rangeof perchlorate concentration from 1 x 10-4 to 1 x 10-1 M with a detection limit of 5 x 10-5 M.The ion selective electrodes containing DBP and NPOE as plasticizers exhibit a workingrange from 6.3 x 10-5 to 1 x 10-1 M and 7.4 x 10-5 to 1 x 10-1 M for perchlorate, respectively,with a detection limit of ca. 2.2 x 10-5 M. For all three electrodes a response time of ca. 5 s was found. The prepared electrodes do not show appreciable decay of the slope for at least 25 days. Potentiometric selectivity coefficients (log KpotClO4-,X-) with respect to the primaryanion perchlorate were evaluated using the fixed interference method. These coefficients areof the order of 10-1.7 or smaller, indicating the relatively poor interference of the differentanions studied.