Coefficient selectivity

The stoichiometric ion exchange reaction between two counter-ions A and B may be written [Pg.105]

Numerous investigators have shown that for an ion exchange reaction at equilibrium, the distribution of counter-ions between the two phases is not equal. Thus for a particular exchanger one ion is generally preferred over the other and the exchanger is said to exhibit selectivity. [Pg.106]

The experimentally observed selectivity shown by an exchanger is often represented by the value of the separation factor, cr , which is defined by the equation [Pg.106]

For theoretical treatments of ion exchange it is preferred to define equilibrium in terms of the selectivity coefficient K, which is the mass action relationship written for the reaction according to a defined choice of concentration units [Pg.106]

The above coefficients on different concentration scales are termed the [Pg.106]

Recovery factor Reduced column length Reduced plate height Reduced velocity Relative retention ratio Retardation factor d Retention time Retention volume Selectivity coefficient Separation factor... [Pg.83]

The more a deviates from unity for a given pair of ions, the easier it will be to separate them. If the selectivity coefficient is unfavorable for the separation of two ions of the same charge, no variation in the concentration of H+ (the eluant) will improve the separation. [Pg.1116]

A measure of a method s freedom from interferences as defined by the method s selectivity coefficient. [Pg.40]

The selectivity of the method for the interferent relative to the analyte is defined by a selectivity coefficient, Ka,i... [Pg.40]

The selectivity coefficient is easy to calculate if kj and kj can be independently determined. It is also possible to calculate Ka,i by measuring Sjamp in the presence and absence of known amounts of analyte and interferent. [Pg.40]

A method for the analysis of Ca + in water suffers from an interference in the presence of Zn +. When the concentration of Ca + is 100 times greater than that of Zn +, an analysis for Ca + gives a relative error of -1-0.5%. What is the selectivity coefficient for this method ... [Pg.40]

Solving for kzn gives a value of 0.5. The selectivity coefficient, therefore, is... [Pg.41]

Knowing the selectivity coefficient provides a useful way to evaluate an inter-ferent s potential effect on an analysis. An interferent will not pose a problem as long as the term K/ i X i in equation 3.7 is significantly smaller than or A,i X Q in equation 3.8 is significantly smaller than Ca. [Pg.41]

Even if a method is more selective for an interferent, it can be used to determine an analyte s concentration if the interferent s contribution to Sjamp is insignificant. The selectivity coefficient, Ka,i> was introduced in Chapter 3 as a means of characterizing a method s selectivity. [Pg.202]

An interferent, therefore, will not pose a problem as long as the product of its concentration and the selectivity coefficient is significantly smaller than the analyte s concentration. [Pg.202]

In a particular analysis the selectivity coefficient, Xa.i, is 0.816. When a standard sample known to contain an analyte-to-interferent ratio of 5 1 is carried through the analysis, the error in determining the analyte is +6.3%. (a) Determine the apparent recovery for the analyte if Rj = 0. (b) Determine the apparent recovery for the interferent if Ra = 1 ... [Pg.229]

The amount of calcium in a sample of urine was determined by a method for which magnesium is an interferent. The selectivity coefficient, Rca.Mg> for the method is 0.843. When a sample with a Mg/Ca ratio of 0.50 was carried through the procedure, an error of-3.7% was obtained. The error was +5.5% when a sample with a Mg/Ca ratio of 2.0 was used. [Pg.229]

A sample contains a weak acid analyte, HA, and a weak acid interferent, HB. The acid dissociation constants and partition coefficients for the weak acids are as follows Ra.HA = 1.0 X 10 Ra HB = 1.0 X f0 , RpjHA D,HB 500. (a) Calculate the extraction efficiency for HA and HB when 50.0 mF of sampk buffered to a pH of 7.0, is extracted with 50.0 mF of the organic solvent, (b) Which phase is enriched in the analyte (c) What are the recoveries for the analyte and interferent in this phase (d) What is the separation factor (e) A quantitative analysis is conducted on the contents of the phase enriched in analyte. What is the expected relative erroi if the selectivity coefficient, Rha.hb> is 0.500 and the initial ratio ofHB/HA was lO.O ... [Pg.229]

Plot of cell potential versus the log of the analyte s concentration In the presence of a fixed concentration of Interferent, showing the determination of the selectivity coefficient. [Pg.477]

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. [Pg.496]

Creager and colleagues designed a salicylate ion-selective electrode using a PVC membrane impregnated with tetraalkylammonium salicylate. To determine the ion-selective electrode s selectivity coefficient for benzoate,... [Pg.535]

The equilibrium constant for this ion-exchange reaction, which is also called the selectivity coefficient, is... [Pg.592]

At equdibrium, the selectivity coefficient ) for B over A is determined from the fodowing equation ... [Pg.377]

Ion-exchange isotherms assume different shapes depending on the selectivity factor and the variations in with the level of exchange The rational selectivity coefficient includes the ionic charge and is given by... [Pg.450]

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