Selection and application of ion electrodes

Selection and application of ion electrodes

Measuring principle

An ion selective electrode is an electrochemical sensitive element whose potential is linear with the logarithm of the ion activity in a given solution. It is a type of electrochemical sensor that uses the membrane potential to measure the ion activity or concentration in a solution. The component is a sensing film at the tip of the electrode. Ion-selective electrodes are also called membrane electrodes. These electrodes have a special electrode film. The electrode film has a selective response to specific ions. The relationship between the potential of the electrode film and the ion content to be measured conforms to the Nernst formula. Such electrodes have the characteristics of good selectivity and short balance time, and are the most used indicator electrodes for potential analysis.

The ion selective electrode method is a branch of potential analysis and is generally used for direct potentiometry or potentiometric titration. Its characteristics are: the concentration of specific ions in the solution can be determined; the application range is wide; it is not affected by the color and turbidity of the reagent.

Measuring structure

The sensitive membrane of the electrode is fixed at the top end of the electrode tube, and the tube is filled with an internal filling solution, wherein an internal reference electrode (usually an Ag│AgCl electrode) is inserted, and the internal filling solution functions to maintain the stability of the inner surface of the membrane and the internal reference electrode potential.

The ion-selective electrode is a half-cell (except gas-sensitive electrode). Its potential cannot be measured separately. It must be combined with a timely external reference electrode to form a complete electrochemical cell. Then, the electromotive force of the battery is measured. It includes the following items:

E=Em+En+E1-Ew where En is the potential of the internal reference electrode;

Ew and E1 are the potential of the external reference electrode and the liquid junction potential of the liquid junction portion.

In the general measurement, the above three items are required to remain unchanged, so there is only one constant term between the electromotive force E and Em, and its change can fully reflect the change of Em.

Application of ion selective electrodes

Ion-selective electrodes are widely available for analysis. The correct ion measurement method, ion meter, and electrode can be used to measure the concentration of the corresponding ion. It has been successfully applied in the fields of environmental monitoring, water quality monitoring, soil analysis, food testing, and drug analysis.

Ion electrode applications in various industries

Introduction of actual product application: (For more questions, please consult http://, 4008617021)

1. Determination of fluoride ion content in water using fluoride ion selective electrode

Equipment (Shanghai Lei Magnetic)

Experimental instrument: PXSJ-216F or other type ion meter, Dalong MS-H280-Pro LED digital display heating type magnetic stirrer

Experimental electrode: PF-1-01 fluoride ion selective electrode, 232-01 reference electrode (cabbage electrode)

2. Determination of choline chloride content

First, the experimental principle

The choline chloride contained in the sample was dissolved in water, and the filtrate was filtered. Chloride ions are dissolved in the filtrate.

The content of choline chloride is determined by the silver amount method.

The silver electrode can be judged at the end point depending on the potential.

Second, the instrument

ZDJ-5 automatic potentiometric titrator

216-01 Silver ion selective electrode 217-01 type reference electrode

Third, the reagent

(1) 0.1 mol/l silver nitrate standard titration solution

(2) Since the ultrapure water is used, the blank is 0.

(3) Sample 1 (50% silicon powder), sample 2 (50% corn core powder)

Fourth, the experimental steps

Accurately weigh 0.7g sample (accurate to 0.0001g), place it in a 100ml volumetric flask, dilute to the mark with water, place it for 20min and filter. Accurately transfer 25 ml into a 100 ml beaker and titrate. Each group is paralleled twice.

The content of choline chloride expressed by mass fraction

Calculation formula:

C(V-V0)×0.13963×4

X= ———————————— × 100 (1)

M

C——actual concentration of silver nitrate standard solution (0.1mol/L)

V——volume consumption of silver nitrate standard solution

V0 - blank test consumes the volume of silver nitrate standard solution ml

Because ultrapure water is used, the blank is V0=0

M——the mass of the sample (g)

0.13963 - the mass of choline chloride expressed in grams equivalent to a 1.00 ml silver nitrate standard titration solution. ,

4 - dilution factor

V. Results calculation

Sample 1 (50% silicon powder) Sample quality: 0.7045 g

(1) End point potential: 282.2 mV Consumption volume: 6.384 ml

X=50.61%

Sample 2 (50% corn cob powder) Sample quality: 0.7250 g

(1) End point potential: 287.1 mV Consumption volume: 6.573 ml

X=50.64%

Six, discussion

1 It can be seen from the titration curve that the choline chloride is determined by the pre-titration mode, the titration curve potential is large, and the end potential corresponding to the volume of the titrant added is obvious.

2 titration data showed that the content of choline chloride was determined by automatic potentiometric titration, and the reproducibility of the measured results was good. Mainly this method avoids the error of the human eye in determining the color change of the indicator.

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