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.
Improved lithium ion-selective electrode based on a lipophilic diamide as neutral carrier
Abstract A lithium ion-selective solvent polymeric membrane based on the lipophilic diamide N , N , N' , N' ,-tetraisobutylcyclohexane- cis -l,2-dicarboxylic diamide is described. Selectivity coefficients for lithium ions over other alkali metal ions are greater than 100 and over alkaline earth metal cations are about 1000.
An Ultrasensitive Analytical Method Based on Chemiluminescence Sensing Electrochemical Parallel Catalytic Reaction Event
An ultrasensitive electrochemiluminescence (ECL) method on the combination of electrochemical parallel catalytic reaction and chemiluminesence signal sensing was proposed for improving ECL analytical characteristics using vanadate(V) as a representative. Vanadate(V) could be electrochemically reduced to generate vanadate(II) which could be chemically oxidized by potassium periodate to regenerate vanadate(V) and give parallel catalytic wave effect. Then, the reduced product of potassium periodate could react with butyl-rhodamine B to emit a sensitive chemiluminescence signal. The chemiluminescence intensity was correlative with vanadate(V) concentration. The investigation on the electrochemical reaction rate constant (k0) confirmed that the speed of electrochemical reaction was faster than that of the subsequent chemiluminescence reaction. The possibility of the combination of electrochemical parallel catalytic reaction with chemiluminescence signal sensing was proved. The similar ECL behaviors could be observed at zirconia nanowires-Nafion modified electrode. Because of the separation and enrichment effect of the modified electrode on vanadate(V), the selectivity and sensitivity was further improved greatly. Based on these findings, a new concept on the combination of electrochemical parallel catalytic reaction and chemiluminesence signal sensing was proposed and an ultrasensitive ECL method for the determination of vanadate(V) was developed at zirconia nanowires-Nafion modified electrode. Under the optimum experimental conditions, the ECL intensity was linear with the concentration of vanadate(V) in the range of 2.0×10−12 mol/L–2.0×10−10 mol/L. The detection limit was 8.0×10−13 mol/L, which was more than 6 orders of magnitude lower than that observed by electrochemical current transduction for electrochemical parallel catalytic reaction at zirconia nanowires-Nafion modified electrode.