Poly(vinyl chloride)-based membranes of macrocycles 4,11-dimethyl-2,4,9,11-
tetraethyl-1,5,8,12-tetraaza cyclotetradeca-1,8-diene (I) and 4,11-dioxa-2,
9-dimethyl- 1,5,8,12-tetraaza cyclotetradeca-1,8-diene (II) with sodium tet
raphenyl berate (STB) as an anion excluder and dibutyl phthalate (DBP), dio
ctyl phthalate (DOP), dibutylbutyl phosphonate (DBBP) and 1-chloronaphthale
ne (CN) as plasticizing solvent mediators were prepared and investigated as
magnesium selective electrodes. The best performance was observed having t
he composition (II)-PVC-STB-DBP in the ratio 2:10:1:7, which works well ove
r a wide concentration range (1.9 x 10(-6) to 1.0 x 10(-1) M) with a Nernst
ian slope of 29 mV per decade of activity between pH 2.5 and 6.5. These ele
ctrodes have been found to be chemically inert showing a fast response time
of 15 s and were used over a period of 3 months with good reproducibility
(S = +/- 0.2 mV). The selectivity coefficient values for mono-, di- and tri
valent cations indicate excellent selectivity for Mg2+ over a large number
of cations. The electrodes have also been used successfully in partially no
n-aqueous medium and as an indicator electrode in the potentiometric titrat
ion of Mg2+ with EDTA. Anions such as Cl- and SO42- do not interfere in the
working of the electrode. The practical utility of the membrane sensor has
also been observed in solutions contaminated with detergents (cetyltrimeth
yl ammonium bromide and sodium dodecyl sulphate). Above all, the membrane s
ensor has been very successfully used to analyse some babyfood products and
soft drinks for the determination of Mg2+. (C) 1999 Elsevier Science B.V.
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