Selectivity coefficient table

Selectivity As described earlier, most ion-selective electrodes respond to more than one analyte. For many ion-selective electrodes, however, the selectivity for the analyte is significantly greater than for most interfering ions. Published selectivity coefficients for ion-selective electrodes (representative values are found in Tables 11.1 through 11.3) provide a useful guide in helping the analyst determine whether a potentiometric analysis is feasible for a given sample. 

According to the nine assumptions and approach a) for the diffusion potential inside the membrane the selectivity coefficient Kg , can be expressed by other parameters. Table 3 shows the results for the different kinds of membranes 66). In some cases the expressions for K J i contain ion-mobilities inside the membrane... 

Table 3. The selectivity coefficient KJfij expressed by other parameters 66)...

Table 4.17 Selectivity coefficients for some common cations and anions...

Fig. 7 shows the progressive transformation of montmorillonite to iliite/smectite interlayers by the gradual development of both the characteristic Cs and Rb high selectivity profiles observed for pure illite and the high Cs-Rb selectivity at+ race fadings. The data can be simulated (see table VI for the Ca - Cs case) using a consistent set of intrinsic selectivity coefficients and identical site group capacities for the Ca-Cs and... 

Approximate selectivity coefficients for the exchange of various cations for lithium ions on a sulphonated polystyrene, a typically strong acid resin, are given in Table 18.1. The values are relative to Li = 1.0. The selectivity coefficient between two ions is the ratio of their selectivities relative to lithium. Hence, for a sodium-hydrogen exchange ... 

Alternatively, the use of ionophores may enhance the selectivity of the matrix. Several ionophores have been used for the detection of metals. Simon reported a neutral ionophore with a Nile Blue derivative and an azo compound for the detection ofpotassium.(86)Table 7.4 shows the selectivity coefficients of several ionophores. 

Results of analogous permeation studies for the hydrophobic toluene molecule are shown in Fig. 20. Now the opposite selectivity pattern is observed i.e., toluene is preferentially transported in the R = -CieHjj membranes. This can be illustrated by defining the alternative selectivity coefficient aci6/0H (Table 3). As was the case for aoH/cia. the acie/on values increase with decreasing tubule diameter. In addition to toluene, acie/on values were determined for p-xylene and naphthalene in the i.d. = 1.9 nm membranes. The following acu/on values were obtained 2.8 for toluene, 6.2 for j9-xylene, and 16 for naphthalene. 

We should be aware that many analytical samples are unlikely to be completely clean , that is, contain a single analyte. Table 3.3 lists a series of precautions by which we can hope to overcome the problem of interference when the selectivity is known to be poor, i.e. the selectivity coefficient is numerically small. 

THE COLUMNS OF CONTRAST COEFFICIENTS FOR THE THREE-FACTOR INTERACTIONS OF THE HALF-FRACTION FACTORIAL DESIGN FOR FOUR FACTORS SELECTED FROM TABLE 3.8... 

Table 3. Potentiometric Selectivity Coefficients for PVC Matrix Liquid Membranes Based on Calixl6)arene Hexaester or Dibenzo-18-crown-6 ...

Pavlov et al. (1979) directly gives the values of the affinity coefficient (I based on the molar volumes for selected compounds (Table 1.22). 

Because of the numerous choices for molecular descriptors, weighting factors, and similarity coefficients, there are many ways in which the similarities between pairs of molecules can be calculated. The most used molecular descriptors for defining similarity are probably the 2D fingerprints (22). The bit strings of the molecular fingerprints are used to calculate similarity coefficients. Table 2.3 lists several selected similarity coefficients that can be used with various 2D fingerprints (23). The Tanimoto coefficient is the most popular one (22). 

The equilibrium constant is called the selectivity coefficient, because it describes the relative selectivity of the resin for Li+ and Na+. Selectivities of polystyrene resins in Table 26-3 tend to increase with the extent of cross-linking, because the pore size of the resin shrinks as cross-linking increases. Ions such as Li+, with a large hydrated radius (Chapter 8 opener), do not have as much access to the resin as smaller ions, such as Cs+, do. 

Table 26-3 Relative selectivity coefficients of ion-exchange resins... 

Table 6.2 Estimates of Apparent Standard Exchange Current Densities /q Exchange Current Ratios i o, i/o,K and Selectivity Coefficients Obtained by Different Methods ...

Table 5. Selectivity Coefficients for the DNNS-Based Electrodes [9]...

Table 4.1, reproduced from Meylan and Howard (1991), lists the 59 bond contributions, and Table 4.2 lists correction factors. These groups and factors when combined, yield the log (base 10) water to air partition coefficient. Table 4.3 compares the two methods and can be used to guide the method selection process. The original paper gives specimen calculations... 

When operating conditions cannot be changed, one can select a valve with a treacherous flow path, either of the multiple-port or multiple-flow-path variety. Valves that are most likely to cavitate are the high-recovery valves (ball, butterfly, gate) having low FL and Fc coefficients (Table 2.67). Therefore, if cavitation is anticipated, low recovery valves with high Fc and FL coeffi-... 

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