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.
Lithium-selective polymeric membrane electrodes based on dodecylmethyl-14-crown-4.
Lithium-selective electrodes were prepared with polymeric membranes containing dodecyl-methyl-14-crown-4 as a neutral carrier. The effects of the crown ether content in the membrane and the type of membrane solvent on the electrode properties were investigated. Typical Li+-selective electrodes showed a linear Nernstian response in the activity range 1 × 10–5–1 M LiCl, preferring lithium to sodium and hydronium ions by factors of 150 and 6800, respectively. Addition of trioctylphosphine oxide to the membrane enhanced the lithium selectivity over sodium in the electrode, although it had adverse effects on the lithium selectivity over hydronium ion and the detection limit. The determination of lithium in artificial serum samples was also attempted with these lithium-selective electrodes.
Mathematical Modeling of Scour and Deposition
Electronic computers are opening up the field of sedimentation engineering by permitting the analysis of problems which heretofore have required too much time and effort. Movable stream bed profiles are being calculated in addition to water surface profiles. The initial gradation of sediment material in the stream bed may be prescribed to facilitate the calculation of an armor layer. This gradation is continually changed by the computer program in response to sediment particles being deposited on the stream bed and material on the stream bed being removed to satisfy transport capacity. Hydraulic sorting of sediment by grain size is accomodated. The stream bed does not have to be represented by a single grain size. Retardance of motion because of armor layer is calculated.