Ion activity scales for use with selective ion-sensitive electrodes

Abstract

The development of a variety of selective ion-sensitive electrodes focuses attention on numerical scales for the activity of individual ionic species, for these electrodes measure the activity of the selected ion only relative to that of the same species in a reference solution of known or assigned ion activity. Nevertheless, scales of ion activity must be based on a convention from outside the realm of thermodynamics. Scales based on different conventions are discussed and compared. In dilute solutions of ionic strength less than 0.1, several reasonable conventions give equivalent results, but the situation is more complex in concentrated solutions where the specific properties of the individual ionic species must be taken into consideration. It is shown that a convention based on the hydration number of each ionic species makes allowance for these individual differences. The scales of ionic activity so derived are found to be consistent with the responses of ion-selective electrodes.

Decoupling of heart muscle cells: Correlation with increased cytoplasmic calcium activity and with changes of nexus ultrastructure

“…The calcium-sensitive microelectrode system was calibrated in an activity scale using a Ca-ion activity coefficient of 0.31 for Tyrode solution (calculated from the Debye-Huckel theory with the Guggenheim convention; compare Bates, 1973 ;Blaustein, 1974;Meier et al, 1977). Thus, Tyrode solution containing 3.6 mM CaC12 has an activity of 1.1 mM.…”

On the Relationship between the Rate of Salivary Flow and Salivary Fluoride Clearance

“…Bagg and Rechnitz [1973] measured fluoride ion activity in mixed alkali halide solutions and compared their data and those of other researchers with theoretical estimates. We have used their procedure, adapted from Robinson et al [1971], to calculate the requisite activity coefficients: log γ i = log γ NaF -log α -0.0078α (h Na -h F ) mφ (2) where γ NaF is the mean molal activity coefficient of NaF, h Na and h F are ion hydration numbers (taken to be 3.5 and 1.8, respectively), m is molality (of NaCl in the present case), φ is the osmotic coefficient [Bates, 1973] and α is the degree of dissociation of NaF ion pairs, for which α = 1 -m (γ NaF ) 2 /K, where K is the ion pair dissociation constant (taken to be 1.88). The corresponding estimates for the dilution factor, d' rel , now based on activity rather than concentration, are given in table 3 .…”

Evaporative evolution of a Na–Cl–NO[sub 3]–K–Ca–SO[sub 4]–Mg–Si brine at 95 °C: Experiments and modeling relevant to Yucca Mountain, Nevada

“…11 The sample cooled to room temperature and pH was measured within a half hour of sampling. The pH measurements for legs 3 and 4, where the ionic strength of the solution was greater than 0.1 molal, represent uncorrected values and have not been corrected for ionic strength.…”