O. M. Petrukhin

Potentiometric selectivity of ion-selective electrodes for alkaline-earth elements based on podands with phosphoryl terminal groups

Abstract Dependence of the analytical characteristics (detection limits, DLs) and potentiometric selectivity K ij pot ) of the ion-selective electrodes (ISEs) based on phosphoryl-containing podands on the structures was investigated. It was demonstrated that the DL was determined by complex facilitated transfer energy. It was shown that the DLs of the majority of the ionophores weakly depend on the lipophilicity of the ionophores. Ionophore selectivity is determined by the difference of the facilitated transfer energies of both test and interfering ions and by the properties of the electrochemical system. Stability of complexes makes a major contribution to the energy accompanied with the transfer of the complex and is determined by the disposition of metaldonor atoms of ionophore bonds and by other properties of the electrochemical system, specifically, the dielectric permeability of the medium. Increasing the denticity by increasing the ethyleneglycol chain number leads to the transformation of Ca Ba to Ba Ca - selectivity . The introduction of the two-fold excess of the sodium tetraphenylborate (mol% to ionophore) in membrane composition results in increasing barium selectivity for alkali and alkaline-earth elements. An ISE for the determination of barium was prepared.

Influence of lipophilic anionic compounds on the selectivity of ion-selective electrodes based on podands with phosphoryl complexing groups

Abstract The dependence of the potentiometric selectivity of ion-selective electrodes (ISEs) based on phosphoryl-containing podands on concentration of the lipophilic compounds (sodium tetraphenylborate or potassium tetrakis-p-Cl-phenylborate) was investigated. It was demonstrated that the selectivity of the Ca- or/and Ba-selective electrodes over the alkali metals (AMs) and alkaline-earth metals (AEMs) increases with the lipophilic compound content. In case of AMs the changes of the selectivity is larger than for AEMs. It was shown that employment of the more lipophilic compound, namely, the potassium tetrakis-p-Cl-phenylborate, leads to the greater selectivity growth than for the sodium tetraphenylborate. A qualitative model which describes the potential-formation mechanism at the introduction of the lipophilic compounds in membrane composition was proposed.

Bubble-through flow cell for rapid continuous-flow analysis with ion-selective electrodes

Abstract A fast-response flow cell with ion-selective electrodes was constructed for continuous-flow measurements in air-segmented streams without debubbling. The flow system was optimized for fluoride and chloride determinations. With a flow-rate of 4 ml min−1 a sampling rate of 480 h−1 was achieved for chloride determinations; the average relative standard deviation in all instances was better than 2%.

Segmental flow injection with ion-selective electrodes for the determination of fluoride in water

Abstract A flow analyser with enhanced sampling frequency combining the features of flow-injection and continuous-flow analysis is described. Parameters of the analyser were optimized to ensure the highest rate of analysis allowed by the bubble-through flow cell with fluoride-selective electrodes. Fluoride was determined in 0.1-ml water samples with a sampling rate as high as 720 h−1 and a relative standard deviation better than 1%.

Improvement of Analytical Parameters of ISEs Based on Phosphoryl-Containing Podands

Dependence of analytical characteristics of ion-selective electrodes (ISEs) based on ionophores with phosphoryl-containing podands on concentration of the lipophilic anionic compounds (sodium tetraphenylborate or potassium tetrakis-p-Cl-phenylborate) and on lipophilic properties of these additives are investigated. It was demonstrated that incorporation of a substoichiometric amount of the lipophilic anionic compounds leads to an abrupt increase in selectivity of the Ca- or/and Ba-selective electrodes over the alkali metals (AMs) and alkaline-earth metals (AEMs) and to a significant improvement in the detection limits (DLs) of the ISEs. In case of AMs the changes in the selectivity is larger than for AEMs. The influence of more lipophilic compounds on the potentiometric selectivity and on the DL of the ISE was investigated. The qualitative proposed model describing the effect of the nature and content of the lipophilic anionic compound in the membrane composition on change of the analytical parameters of the ISE based on phosphoryl-containing ionophores is proposed.