Mixed Solution Methods

Membrane phase, 2.7 x 10 3 M vallnomycin in diphenyl ether geometrical surface, —0.012cm3 First value, separate solution of the same concentration second value, separate solution with the same potential third value, mixed solution method Constant concentration of the interfering ion, / = 0.1 M... 

For the synthesis of a photopolymerizable receptor molecule that has a high selectivity for K+, we have modified the hemispherand synthesis according to Scheme 4. The final polymer membrane is represented by Figure 8. The response to a variation in K+ concentration (10 s - 10"1 M) in the presence of 0.1 M NaCl is given in Figure 9. The potentiometric selectivities (log K ) determined by the mixed solution method are -3.0 (Na+), -3.5 (Ca2+), -4.0 (Mg2+), and -0.7 (NH/). This renders this CHEMFET an excellent K+-sensor with a longterm stability t> 100 days). 

To be validated, the selectivity of the method must be measured using a mixed solutions method because this method reflects real-world conditions for sample measurement. The separate solutions method gives only the... 

Ion-selective membrane electrodes have as a main characteristic their selectivity. They are constructed to be utilized to determine an analyte directly in the solution without any prior separation from the matrix. This is achieved assuming a high selectivity of the electrode vs. the possible interfering ions. The selectivity is characterized through the potentiometric selectivity coefficient. The values of the coefficients that can be taken into account for validation are those obtained through the mixed solutions method at a ratio between analyte and interferent of 1 10. The method is... 

Mixed Solution Method. There are various measurement methods using mixed solutions of the two ions. The. fixed interference method is commonly used. Consider, for example, the testing of a lithium ion-selective electrode in the presence of sodium ion. A lithium calibration curve is prepared in the presence of a fixed concentration of sodium, for example, 140 mM as found in blood. A plot such as that given in Figure 13.16 results. In the upper portion of the curve, the electrode responds in a Nemstian manner to the lithium ion. As the lithium concentration decreases, the electrode potential is increasingly affected by the constant background of sodium ions, and in the lower portion of the curve the electrode exhibits a mixed response to both the lithium and the sodium. When the lithium concentration is very small, the response is due solely to sodium (the baseline potential). 

Mixed solution methods better represent conditions of actual samples. 

Figure 2.1 also demonstrates a common method of obtaining the selectivity coefficient, whereby the emf response is measured for solutions containing a fixed amount of interferent with varying activities of the primary ion. A, for which the electrode is designed. This is known as the mixed solution method with fixed amount of interferent and calculated from... 

An alternative mixed-solution method for expressing selectivity involves varying the interferent activity, ab> 3t constant primary ion activity, a. This method is normally used for expressing the pH range over which ion-selective electrodes are useful. 

The method based on using particulate/liquid hybrid mixtures has some of the advantages of the mixed-solution method, such as a better mixing of the carbon and silica as compared to the mixing of distinct powders. In addition, SiC with fine crystallite sizes can be produced. However, as one component has a particulate form, the mixing is not expected to be as good as the method of mixed solutions. 

Membrane number Selectivity coefficient, (mixed solution method) [MCI] = 0.05M [MCI2] = 5 X 1C r M ... 

Membrane number Selectivity coefficient, (mixed solution method) ... 

MgClj] = [NaCl] = 5 X 10 M, using mixed solution method Surface exudates observed on membrane surfaces... 

Separate solution method in 0.1 M unbuffered metal chlorides Mixed solution method in calcium buffer [NaCl = 0.094 M]... 

Mixed solution method in all four cases for 0.5 M unbuffered chlorides... 

Potentiometrie selectivity coefficients were evaluated by a mixed solution method, with an interference ion concentration of 10 M, and calculated using the following relationship ... 

Several methods have been proposed for the experimental determination of ion-selectivity coefficient. They can be listed in the two groups separate solution methods and mixed solution methods. Applying both methods, the cell voltages (emf) are measured in a cell when the reference electrodes and the ISEs are dipped in solutions of known composition. When the separate solution method is used, pure primary ion solutions or pure solutions of the tested interfering ion are introduced into the measuring cell, while in mixed solution methods, both the primary and the selected interfering ions are introduced. 

Indexes just indicate that the AE is measured in mV and S in mV/decade units. In reality, however, the two calibration curves are not parallel. The Nicolsky-Eisenmann equation is not rigorously followed. Therefore, depending on where the horizontal or vertical lines are drawn, different selectivity coefficient values can be obtained with the separate solution methods. Therefore, it is recommended that the selectivity coefficient be measured in the range of the ionic concentration of the samples using mixed solution methods. 

The other version of the mixed solution method is the d interference method. It is based on the... 

One of major changes for high performance polymer nanocomposites is to optimize the processing of CNT-reinforced polymer nanocomposites with low costs. Four processing techniques are in common use to fabricate the CNT/polymer nanocomposites direct mixing, solution method, in situ polymerization, and melt compounding [26-35]. Among these... 

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