The Response Behavior of a Polyacrylamide–Benzo-15-C-5 Electrode to Sodium and Calcium Ions in Acetonitrile and Its Application to the Study of Their Complexing with Other Basic Aprotic Solvent Molecules

Abstract

The response behaviors of an ionophore-conjugated polymer-based ion sensor, which consists of a polyacrylamide (PAA) coupled to benzo-15-crown-5 (B15C5), for Na+ and Ca2+ in acetonitrile (AN) and N-methylpyrrolidinone (NMP) were studied. The PAA–B15C5 electrode showed a Nerstian response to Na+ in AN and Ca2+ in AN and NMP. The electrode was then applied to investigate the complexation of Na+ in AN with such other solvent molecules (D) as N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO); the successive complex formation constants and Gibbs energies of transfer of Na+ in AN to DMF or DMSO and AN to AN–D mixtures were obtained. Reasonable responses of the electrode to an activity change of Na+ due to the solvation of the basic solvent molecules could be certified. The complex formation constant of Ca2+ in AN with such D as DMF, NMP, N,N-dimethylacetamide (DMA), DMSO and hexamethylphosphoric triamide could be obtained by the electrode. The association constants of Ca2+ with CF3SO3− in AN, propylene carbonate, DMF, and DMSO were determined conductometrically and the constant in AN (K1AN = 1.02 × 104 dm3 mol−1) was used for correcting the variation of calcium ion-activity due to a concentration change of Ca(CF3SO3)2 in AN.

Development and Application of Ion-Selective Electrodes in Nonaqueous Solutions

“…Examples of the responses to Ca 2+ in AN, PC, and NMP obtained at the PAA-[B15C5] electrode are given in both Table 2 32,34 and Fig. 2 (line 1).…”

“…34 3·2·2 Correction of ion-activity of non-completely dissociated compounds The variation of the calcium ion activity, aCa 2+ , due to ion association with CF3SO3 -, was estimated by using equations described in a previous report. 34 As a result, the slope of the calibration curve (22.6 mV/paCa 2+ in concentration) was corrected to 29.7 mV/paCa 2+ (line 1 in Fig. 2).…”

“…2). 34 The method described here could be used both to estimate the ion activities and to confirm the response of the electrodes in a solvent of low dielectric constant, in which the ion activities of the electrolytes are affected by the ion association.…”

“…6,34 The emf change, DE, which is the potential difference between the initial and steady potentials obtained at each addition of quite a small volume of other solvents, were analyzed by a method proposed by Cox et al 45 Some examples of the Gibbs energy of transfer,…”