Linear polyamines as carriers in thiocyanate-selective membrane electrodes.
The polyamines, octyl-[2-(2-octylamino-ethylamino)-ethyl]-amine (L(1)) and octyl-{2-[2-(2-octylamino-ethylamino)-ethylamino]-ethyl}-amine (L(2)), have been used as anion ionophores in PVC-based membrane ion-selective electrodes. Different electrodes were prepared containing L(1), or L(2), and o-nitrophenyl octyl ether (NPOE) or bis(2-ethylhexyl)sebacate (DOS) as plasticizers. The response of the electrodes was tested in two different buffers, HEPES-KOH (pH 7) and MES-KOH (pH 5.6). Electrodes containing L(1) and L(2) with NPOE (E1 and E2, respectively) showed a Nernstian response for thiocyanate with a good response time. The detection limit, linear range and slope for electrode E1 were 3.8x10(-6)moldm(-3), 1x10(-5) to 1x10(-1)moldm(-3) and -57.2mVdecade(-1) at pH 5.6 and 4.47x10(-6)moldm(-3), 1.95x10(-5) to 1x10(-1)moldm(-3) and -58.1mVdecade(-1) at pH 7.0. For electrode E2 the detection limit, linear range and slope found were 2.63x10(-6)moldm(-3), 7.94x10(-6) to 1x10(-1)moldm(-3) and -58.5mVdecade(-1) at pH 5.6 and 1.23x10(-5)moldm(-3), 7.95x10(-5) to 1x10(-1)moldm(-3) and -46.0mVdecade(-1) at pH 7. In contrast, electrodes containing DOS as plasticizers gave only response at pH 5.6 (detection limit, linear range and slope at pH 5.6 were 3.16x10(-5)moldm(-3), 1x10(-4) to 1x10(-1)moldm(-3) and -52.6mVdecade(-1)). Selectivity coefficients for different anions with respect to thiocyanate were calculated. The electrode E2 at pH 5.6 was also used for the determination of SCN(-) by potentiometric titrations with Ag(+) ions with good results. The electrode E2 was also used to determine concentrations of thiocyanate in biological samples.
Seguí
M A Jesús
MA
Centro de Investigación en Química Molecular Aplicada, Departamento de Química, Universidad Politécnica de Valencia, Camino de Vera s/n, 46071-Valencia, Spain.
Lizondo-Sabater
Josefa
J
Martínez-Máñez
Ramón
R
Sancenón
Felix
F
Soto
Juan
J