Ion-selective electrodes for anionic surfactants using a cyclam derivative as ionophore.
The cyclam derivative 1,4,8,11-tetra(n-octyl)-1,4,8,11-tetraazacyclotetradecane (L) has been used as carrier for the preparation of PVC-based membrane ion-selective electrodes for anionic surfactants. Different membranes were prepared using L as ionophore, tetra-n-octylammonium bromide (TOAB) as cationic additive and dibutyl phthalate (DBP) or o-nitrophenyl octyl ether (NPOE) as plasticizers. The final used electrode contained a membrane of the following composition: 56% DBP, 3.4% ionophore, 3.8% TOAB and 36.8% PVC. This electrode displays a Nernstian slope of -60.0+/-0.9 mV/decade in a 2.0 x 10(-3) to 7.9 x 10(-6) mol dm(-3) concentration range and a limit of detection of 4.0 x 10(-6) mol dm(-3). The electrode can be used for 144 days without showing significant changes in the value of slope or working range. The electrode shows a selective response to dodecyl sulfate (DS-) and a poor response to common inorganic cations and anions. The selective sequence found was DS->ClO4->HCO3->SCN->NO3- approximately CH3COO- approximately I->Cl->Br->IO3- approximately NO2- approximately SO3(2-)>HPO4(2-)>C2O4(2-)>SO4(2-), i.e. basically following the Hoffmeister series except for the hydrophilic anion bicarbonate. Most of the potentiometric coefficients determined are relatively low indicating that common anions would not interfere in the DS- determination. A complete study of the response of the electrode to a family of surfactant was also carried out. The electrode showed a clear anionic response to DS- and to Na-LAS and a much poorer response to other anionic surfactants and to non-ionic surfactants. Also the electrode shows certain non-linear cationic response in the presence of cationic and zwitterionic surfactants. The electrode was used for the determination of anionic surfactants in several mixtures, and the results obtained were compared to those found using a commercially available sensor.
Lizondo-Sabater
Josefa
J
Instituto de Química Molecular Aplicada, Departamento de Química, Universidad Politécnica de Valencia, Camino de Vera s/n, 46022 Valencia, Spain.
Martínez-Máñez
Ramón
R
Sancenón
Felix
F
Seguí
M A Jesús
MA
Soto
Juan
J