RESUMEN
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.
RESUMEN
The new ligand 7-methyl-7,13-di-octyl-1,4,10-trioxa-13-aza-7-azonia-cyclopentadecane (L(1)) has been designed, synthesised and used as ionophore in the development ion-selective electrodes for anionic surfactants. Different PVC-membrane anionic-surfactants-selective electrodes were prepared by using L(1) as ionophore and bis(2-ethylhexyl)sebacate (BEHS), dibutyl phthalate (DBP) and nitrophenyl octyl ether (NPOE) as plasticizers. The PVC-membrane electrode containing L(1) and NPOE (electrode E1) showed a Nernstian response to lauryl sulfate with a slope of -59.5mV per decade in a range of concentrations from 1.3x10(-6) to 6.8x10(-3)M and a detection limit of 6.0x10(-7)M. The electrode E1 also showed a reasonable response to other alkyl sulfates and alkylbenzene sulfonates, whereas it does not respond to carboxylates and to cationic and non-ionic surfactants. A similar electrode to E1 but additionally containing the cationic additive n-octylammonium bromide was also prepared (electrode E2) and compared with the response of E1. Selectivity coefficients for different anions with respect to lauryl sulfate were determined by means of the fixed interference method considering lauryl sulfate as the principal anion and using a concentration of 1.0x10(-2)moldm(-3) for the corresponding interfering anion. The selectivity sequence found for the electrode E1 was: LS(-)>SCN(-)>ClO(4)(-)>CH(3)COO(-)>I(-)>HCO(3)(-)>Br(-)>NO(3)(-)>NO(2)(-)>Cl(-)>IO(3)(-)>phosphate>SO(3)(2-)>C(2)O(4)(2-)>SO(4)(2-). Electrode E1 showed remarkably better selectivity coefficients than electrode E2.
RESUMEN
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.
RESUMEN
The new cyclic polyazacycloalkane 1.4,8,11-tetra(n-octyl)-1,4,8,11-tetraazacyclotetradecane (L1) was synthesised and the copper(II) complex [Cu(L1)]2+ characterised. Different electrodes were prepared using the [Cu(L1)]2+ complex as ionophore, PVC as plastic matrix and o-nitrophenyl octyl ether (NPOE), bis(2-ethylhexyl) sebacate (BEHS) or dibutyl phthalate (DBP) as plasticizers. The electrode containing DBP showed a Nernstian response over a wide pH range and a fast response time (ca. 3 s) whereas NPOE and BEHS gave near-Nernstian slopes. Selectivity coefficients for the different anions with respect to perchlorate were calculated. The response of the electrodes basically followed the Hofmeister sequence, suggesting that interaction of the ionophore with the anions is via electrostatic forces rather than due to anion coordination to the axial sites of the square-planar [Cu(L1)]2+ complex.
