A comparative study of the effect of o-nitrophenyl octyl ether and o-nitrophenyl pentyl ether as plasticizers on the response and selectivity of carrier-based liquid membrane ion-selective electrodes.
Lithium, potassium and caesium-selective microelectrodes were prepared by coating the tips of preconditioned silver wires, incorporated in a flow-cell, with PVC membranes containing four different ionophores. A dicarboxamide, a 14-crown-4 carboxylic acid, benzo-18-crown-6 and di-(tert-butylbenzo)-21-crown-7 ionophores were used in the electrode matrix. The first two ionophores were used in lithium ion-selective electrodes, the third in a potassium ion electrode and the fourth in a caesium ion electrode. Two different plasticizers, o-nitrophenyl octyl ether (NPOE) and o-nitrophenyl pentyl ether (NPP'E) were used. Enhancement of the signal and the slope of the calibration curve and improvement of the curve linearity were observed in all cases when NPP'E was used as plasticizer. A general trend of enhanced selectivity of the electrodes incorporating crown ether ionophores was also observed when NPP'E was the plasticizer.
Evaluation of some new 14- and 15-crown-formazans as carriers in cesium ion selective electrodes.
A number of new crown-formazans with 14 and 15 membered rings have been investigated as selective neutral carriers in cesium ion selective electrodes. Two plasticizers (NPOE and NPBnE) were studied. The new 14-crown-formazan 4a containing the 4-pyridyl N-oxide at the formazyl carbon exhibited the highest selectivity in cesium ion selective electrodes, especially towards the two low selectivity monovalent ions K(+) and NH4(+). Also, membranes containing the plasticizer NPBnE showed better cesium selectivity relative to most ions than those containing NPOE. Membranes containing 4a and variable compositions of plasticizers, potassium tetrakis-(p-chlorophenyl)borate (KTpClPB), and trioctylphosphine oxide (TOPO) were studied in order to prepare an electrode with the optimum cesium selectivity. The highest selectivity for cesium was achieved with the two electrodes designated d and e with membranes containing the ionophore 4a, NPBnE and KTpClPB with and without TOPO. Selectivities are reported relative to sodium, potassium, barium, calcium, ammonium, lithium, cobalt, and magnesium.
Silver–Gelatin Method for the Determination of Trace Amounts of Carbon Monoxide in Air
The use of silver–gelatin complex was found suitable for the determination of trace amounts of carbon monoxide in air. Silver–gelatin complex is reduced by carbon monoxide to give intensely colored sol. Measurement of the color intensity of the stable silver sol enables the determination of carbon monoxide successful under various environmental conditions. The detection limit is 2–100 ppm. The relative standard deviation for the determination of 10 ppm carbon monoxide is 2.6%.