Kosuke Izutsu

Voltammetry at a trioctylphosphine oxide-coated glassy carbon electrode and its use for the determination of trace uranyl ions after preconcentration

Abstract The voltammetric characteristics of a trioctylphosphine oxide (TOPO)-coated glassy carbon (GC) electrode and its use in the determination of trace uranyl ions are described. Among various substances examined, only uranyl ions were effectively concentrated into the TOPO layer on the GC electrode at 0 V vs. Ag/AgCl electrode and gave a reduction wave when the electrode potential was scanned in a negative direction. Some substances could reach the GC surface through the TOPO layer and reacted electrochemically, but others could not pass the TOPO layer. A method is given for the determination of uranyl ions in 0.5 M NaCl adjusted to pH 4 with acetate buffer after preconcentration; the detection limit is 2 × 10−9 M, and uranyl ions between 2 × 10−9 M and 2 × 10−7 M can be determined. The method is very selective for uranyl ions, suggesting possible application in the analysis of sea water. A preliminary investigation for artificial sea water showed tha a simple pretreatment involving boiling at pH 2.5 (to remove dissolved carbon dioxide) made the determination possible.

Experimental studies of the liquid junction potential between electrolyte solutions in different solvents: Part II. Role of the solvent-solvent interactions

Abstract To investigate the factors influencing the liquid junction potential between electrolyte solutions in different solvents, emfs of a cell with a salt bridge were measured by changing electrolytes and solvents in each compartment of the cell in a variety of ways. The results showed that the liquid junction potential contained a component which was influenced to a considerable extent by the solvents, but was almost independent of the kinds and concentrations of the electrolytes, provided that the electrolytes were not strongly solvated. The influence of the solvents on the component could, in many cases, be correlated with the Lewis acid-base properties and the mutual heats of solution of the solvents at the junctions, supporting explicitly the existence of a factor in the liquid junction potential which can be attributed to the solvent-solvent interactions.

Complex formation of univalent cations in acetonitrile with other solvents. Study of potassium ion complex formation with a cation-sensitive glass electrode

The formation constants of the complexes formed between potassium ion and other solvents in acetonitrile have been obtained potentiometrically by using a univalent cation-sensitive glass electrode. The formation constants of the mono-complexed potassium ions were 1.5 with dimethylformamide, 2.0 with dimethylacetamide, 2.4 with N-methylpyrrolidone, 2.8 with N-methylformamide, 2.9 with dimethyl sulfoxide, and 6.9 with hexamethylphosphoramide. Within the concentration ranges of the solvents studied (0.35–0.7 M for different solvents), only up to 1:2 K+: solvent species were detected, in contrast to the results for other univalent cations. Rubidium ion could not be studied effectively because of unsatisfactory response of the glass electrode. The complex formation constants of various univalent cations in acetonitrile with other solvents are summarized and discussed in detail.

Acid-base equilibria in γ-butyrolactone studied by use of pH-ISFETs

Abstract pH-ISFETs were used in the study of acid-base equilibria in γ-butyrolactone (GBL). After the spectrophotometric determination of the pKa value of 3,5-dichloropicric acid, the pKa values and homo-conjugation constants of various acids (including the conjugate acids of bases) were determined potentiometrically using a Ta2O5-type pH-ISFET. The values of pKa in GBL were in a linear relation with those in propylene carbonate (PC) and 1.0 units smaller on average. The difference in pKa between GBL and PC was mainly attributable to the difference in proton solvation. The autoprotolysis constant of GBL, roughly estimated by a rapid titration with a Si3N4-ISFET, was about 30 on the pKSH scale. A comparative study was made of the response speeds of the Ta2O5- and Si3N4-type pH-ISFETs and a conventional pH-glass electrode. The result was Si3N4-ISFET > Ta2O5-ISFET > glass electrode. Because GBL is not stable against acids and bases, the use of pH-ISFETs was much more convenient than the use of the conventional glass electrode.

Experimental studies of the liquid junction potential between electrolyte solutions in different solvents Part III. Some additional evidence for the existence of an electrolyte-independent component

Resultats fondes sur les mesures des forces electromotrices de 2 cellules identiques contenant ou non lelectrolyte MX=Me 4 NClO 4 , Et 4 NClO 4 , Pr 4 NClO 4 , etc

Experimental studies of the liquid junction potential between electrolyte solutions in different solvents: Part V. Use of a cell with a mixed solvent/mixed solvent junction

Resultats detudes realisees avec une cellule a electrodes dargent et utilisant les solvants S 1 -acetonitrile (AN); (S 2 +S 2 1 )=(DMSO+H 2 O), (DMF+H 2 O) ou (MeOH+H 2 O) et (S 3 +S 3 1 )=(AN+H 2 O), (DMSO+AN) (DMSO+H 2 O), (DMF+AN) ou (DMF+H 2 O), de part et dautre de la jonction

Experimental studies of the liquid junction potential between electrolyte solutions in different solvents part IV. A study using mixed-solvent salt bridges

Abstract The problem of the liquid junction potential (ljp) between different solvents was studied by measuring the emfs of a cell with a mixed-solvent salt bridge: Ag‖5 m M AgClO 4 , 5 m M Et 4 NClO 4 (S 1 );1 m M Et 4 NClO 4 (S 1 ); 0.1 M MX (S 3 + S′ 3 ); 1 m M Et 4 NClO 4 (S 2 );5 m M Et 4 NClO 4 , 5 m M AgClO 4 (S 2 )‖Ag. For 130 different combinations of solvents S 1 , S 2 , and (S 3 +S′ 3 ), the emfs were measured by changing the composition of (S 3 + S′ 3 ) from pure S 3 to S′ 3 . Though there were exceptions, the emfs in many cases changed linearly or nearly linearly with the volume fraction of the mixed solvents. It was considered that the results were obtained because the component of the Ijp which was due to the solvent-solvent interactions at the mixed solvent/pure solvent junctions often changed in linear or near-linear relations with the volume fraction of the mixed solvent. A preliminary experiment showed some possibility of similar relations also to hold for mixed solvent/mixed solvent junctions.

Liquid junction potential between different solvents: Component due to the differences in electrolyte concentrations and ionic mobilities

Abstract Among the three components of the liquid junction potential at a junction between different solvents, the component due to the differences in electrolyte concentrations (or activities) on the two sides of the junction and the differences between the cationic and anionic mobilities was investigated. An equation was derived for the component at a junction with the same electrolyte (MX) on the two sides, where t represents the ionic transport numbers and a the electrolyte activity. Linear variations of t and a were assumed at the interphase region of the junction. The equation was confirmed experimentally to be approximately valid in many cases and may be used in estimating the component. In some cases, apparent deviations from the equation were observed. The deviations were attributed to the influence of electrolyte concentration, which caused partial decreases in the component due to the solvent-solvent interactions at the junction. Some theoretical and experimental studies were also carried out for a junction with different electrolytes (MX and NY) on the two sides,

Potentiometric study of complexation and solvation of lithium ions in some solvents related to lithium batteries

Abstract The complexing of lithium ion in propylene carbonate (PC) with glymes (H 3 CO(CH 2 CH 2 O) n CH 3 ) of n = 1 to 4 was studied potentiometrically using a univalent cation-sensitive glass electrode. The lithium ion in PC was assumed to be solvated by four PC molecules. For monoglyme (DME), each of the two-step complexing was considered to be the replacement of two solvating PC molecules by one DME molecule. Complexing of up to two molecules was assumed for diglyme but of one molecule for tri- and tetraglymes. Equations were derived to relate the glyme concentration and the potential of the glass electrode, taking the effect of solvent dielectric constant into account, and complex formation constants were obtained. The values of β 1 were 1.5, 15, 46 and 68 mol −1 L for mono-, di-, tri- and tetraglymes, respectively. The lithium ion activity in mixtures of PC-DME, PC-dimethyl carbonate (DMC), PC-diethyl carbonate (DEC) and PC-ethylmethyl carbonate (EMC) was also studied with the same electrode. In PC-DME, the lithium ion activity was lowest at around 60 (v/v)% DME. The variation in the lithium ion activity was explained considering the complexing of the lithium ion with DME and the effects of dielectric constant to the lithium ion solvation and ion association. In the mixtures of PC with DMC, DEC and EMC, the variation in the lithium ion activity was explained only by the effects of dielectric constant to the lithium ion solvation and ion association.

Experimental studies of the liquid junction potential between electrolyte solutions in different solvents: Part VII. Role of ionic solvations

The liquid junction potential (ljp) at c1MX(S1) ¦c2 MX(S2) was studied experimentally, paying special attention to component (b) which was caused by the differences in ionic solvation on the two sides of the Junction. A simplified equation containing the Gibbs energies of transfer of M+ and X− from S1 to S2 was used to obtain the calculated values of component (b) (Ej(b)calc for various combinations of MX and S1/S2. A cell with the junction shown above was constructed and the variation of the emf with MX was measured for various S1/S2. The variation of the emf, when corrected appropriately for the effect of other ljps in the cell, was in linear correlation with Ej(b)calc, though the slopes of the linear relations were smaller than unity and somewhat dependent on S1/S2. The corrected emf variation was found to be almost independent of the concentration ratio c1/c2. Thus, the corrected emf variation was considered to correspond to the variation of the actual values of component (b) (Ej(b)act). A tentative method is proposed of estimating Ej(b)act by multiplying Ej(b)calc by the slopes. In some cases,Ej(b)act was larger than 150 mV; but it was usually within ± 10 mV when MX = Et4NPic.