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Introduction to Electroanalytical Chemistry - Derived from Ningsi Analytical Instruments Co., Ltd.
1 , Salt Bridge:
Composition and characteristics: high concentration electrolyte solution
Positive and negative ion migration rate is almost the same
(Saturated KCl solution + 3% agar gel)
The role of salt bridge:
1) Prevent the mixing of the two electrolyte solutions, eliminate the potential of the liquid, and ensure accurate measurement.
2) Provide ion transfer channels (transport electrons).
2, the electrode potential of the test electrode: standard hydrogen electrode as a negative electrode, a positive electrode composed of the electrode test battery, the battery of the measured electromotive force.
3 , indicating and reference electrode applications:
The electromotive force is measured to calculate the activity or concentration of the ion to be measured; it is mainly used to determine the system in which the bulk concentration of the solution does not change.
4 , metal - metal ion electrode
(Silver, copper, zinc, mercury) √
(Iron, Cobalt, Nickel, Chrome) ×
5 , reference electrode - calomel electrode:
Features:
a. Simple to produce and widely used;
b. The use temperature is lower and the temperature is more affected;
c. When the temperature changes, the electrode potential balance time is longer;
d. Hg (II) reacts with some ions.
6 , membrane electrode:
Features (differs from the above three - first, second and third types of electrodes ):
1) No electron transfer, rely on ion diffusion and ion exchange membrane potential
2) Responsive to specific ions, with good selectivity
7, the neutral carrier membrane electrode:
Neutral carrier: An electrically neutral, macromolecular compound with a close-packed structure of the central cavity. Examples: valinomycin, antibiotics, crown ethers, etc.; typical composition: ion carrier 1%, non-polar solvent 66%, PVC 33%
8, the enzyme electrode: indicating electrode surface is covered with a substance activity, the enzyme catalyzed reaction to occur.
Application: Very high selectivity for organic and biological material analysis
Disadvantages: Difficult to purify enzymes and have a short life
9 , the advantages of direct potential method:
(1) The equipment is simple and easy to operate;
(2) The electrode responds quickly and directly shows the ion concentration;
(3) The sample does not require pretreatment;
(4) For micro analysis;
(5) to achieve continuous and automatic analysis.
10 , the shortcomings of the direct potential method:
(1) The error is large;
(2) The selectivity of the electrode is not ideal;
(3) The variety of electrodes is small;
(4) Poor reproducibility.
11, potentiometric titration: the use of projecting electrode potential jump indicated titration end point titration analysis. Key: Select indicator electrode
Compare the similarities and differences between AAS and UV-VIS.
The same point is the type of spectrum , and the essence is also the absorption spectrum.
However, AAS contains ultraviolet and visible bands, and emits light at a specific wavelength through a sharp-line light source to allow the material to absorb. UV-VIS emits light of a continuous wavelength using a xenon lamp or a tungsten lamp, and one of the wavelengths is absorbed by the object to be measured.
AAS: Atomic Spectroscopy, Line Spectroscopy UV-VIS: Molecular Spectroscopy, Band Spectroscopy
1. According to the instrumental analysis method, the following objects were analyzed: (1) Hg in fish (~x ug/mL); (2) Fe, Mn, Al, Ni, Co, Cr in waste water (10 -6 ~ 10) -3 ); (3) Ion content in water for power plants; (4) Electrochemical processes in living organisms; (5) Naphthalene and methylnaphthalene; (6) Quinoline and isoquinoline; (7) Fruits Residual organophosphorus pesticides.
1, (1) cold vapor atomic method; (2) ICP-AES; (3) conductimetry or ion exchange; (4) voltammetry; (5) Liquid-liquid partition chromatography or liquid chromatography; (6 Liquid-Solid Chromatography; (7) Gas Chromatography-Flame Spectrophotometer, at 2500K, the Na resonance line 589.3nm for the 3s → 3p transition, calculated its ratio of the excited state and the number of ground state atoms. It is known that k=1.38*10-23 JK −1 and h=6.626*10 −34 Js.
2. Determine trace lead in a calcium chloride solution by polarography. Take 5 mL of test solution and dilute to 50 mL with water. Pour out a portion of the solution in an electrolytic cup, pass nitrogen gas for 10 minutes, and then record the polarogram between -0.2 and -0.6V with a wave height of 50 cells. In addition, take 5 mL of test solution, dilute it with water to 50 mL, add 1.00 mL of 0.50 mg/mL standard lead solution, and obtain a wave height of 80 cells. Calculate the lead content in the sample.
3. Fractions A and B were separated on a 30 cm long column with retention times of 16.40 and 17.63 min, respectively, and peak widths were 1.11 and 1.21 min, respectively. It takes 1.30 min to pass through the column without retaining the components. Calculate: (1) the degree of separation; (2) the number of effective plates for component A (3) the length of column required for a resolution of 1.5.
E J =1.986×10 -23 J. Cm/(5893 Å × 10 -8 cm.Å -1 ) = 3.37 × 10 -19 J
In the 3s and 3p energy levels, there are 2 and 6 quantum levels respectively, so there is P J /P 0 =6/2=3
Substituting the above equation into the formula N J /N 0 =(P J /P 0 )exp(-E J /kT),
N J /N 0 =3exp[-3.37×10 -19 J/(1.38×10 -23 JK -1 ×2500K)]
=3 x 5.725 x 10 -5 = 1.72 x 10 -4
answer:
Let the concentration of the sample be x and the equations in the column:
50=K(5x)/50
80=K(5x+0.5*1.0)/51
Solve the equations to get x = 0.167 mg/mL.
answer:
( 1 ) Resolution = 1.06
(2)=2960
(3)=, find L 2 = 60.1cm
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