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.
Electrode membrane and solvent extraction parameters relating to the potentiometry of polyalkoxylates
Poly(vinyl chloride)(PVC) matrix membrane electrodes containing various amounts and compositions of liquid ion-exchanger were studied in order to investigate their response to aqueous solutions of Antarox CO-880 as a model polyalkoxylate. The liquid ion-exchanger used in the membrane was based on solutions in 2-nitrophenyl phenyl ether of the tetraphenylborates of complexes with barium of either Antarox CO-880 or Antarox CO-430 polyethoxylates. Barium ion-responses were also noted.The electrodes recommended for use with polyalkoxylates in aqueous solutions are formed from an Antarox CO-430 based liquid ion-exchanger. The master membrane used for making the electrodes should consist of 0.40 g of the liquid ion-exchanger in 0.17 g of PVC, that is 70% of sensor in 30% of the immobilising polymer.Neither Antarox CO-430 (Series A) nor Antarox CO-880 (Series B) type electrodes respond to the methyl glucoside polypropoxylates Glucam P10 and P20, but, conversely, Glucam P10 and P20 (Series C) type electrodes respond more effectively to Antarox CO-880 polyethoxylate in aqueous solution than they do to either of the propoxylates. This and the better response to Glucam P20 compared with Glucam P10 is consistent with the relative stability of metal-polyalkoxylate complexes according to data obtained on the solvent extraction of metal ions into dichloromethane by the polyalkoxylates, based on studies of the large polarisable picrate and dipicrylamine anions.Solvent extraction data show that the complexing tendencies of the various polyalkoxylates studied with barium, magnesium and zinc ions are generally in the order of Antarox CO-730 > PEG 1500 > Antarox CO-880 > Glucam P20 > Glucam P10 > Antarox CO-430. There is a correlation between these and electrode qualities for cations and also with regard to the response of these electrodes towards alkoxylates. However, other factors can also be involved such as those impressed by the substituent tail attached to the end of the alkoxylate chain.
Electrochemical detection of copper(II) at a gold electrode modified with a self-assembled monolayer of penicillamine
A penicillamine (PCA) self-assembled monolayer (SAM) was prepared on a gold electrode. It has been found that the modified electrode exhibited a selective response to copper ions. As demonstrated by cyclic voltammetric experiments, the SAM-based electrode showed an attractive ability to preconcentrate efficiently traces of copper(II) from solutions. Under optimum conditions, the anodic peak current was proportional to the concentration of Cu(II) in the range from 8.0 × 10−7 to 1.0 × 10−4 M with a detection limit of 4.0 × 10−7 M. Moreover, this modified gold electrode is also characterized by excellent repeatability, showing a relative standard deviation of 3.2% for nine successive measurements of 1.0 × 10−5 M Cu(II). The PCA/Au SAM gold electrode was used for the determination of Cu(II) in a tap water sample and the results showed a good agreement with the data obtained by atomic emission spectrometry.