Module 3c: Electro-analytical methods Flashcards
1
Q
concerned with the interplay between electricity & chemistry, electrical quantities like current, potential or charge and chemical parameters such as concentration
A
Electroanalytical techniques
2
Q
Advantages of electroanalytical methods over other analytical methods include:
A
- determination of different oxidation states, not just concentration
- exceptionally low detecrion limits
- abundance of characterisation information (chemical kinetics)
- low cost
3
Q
The relationship of Electrical potential to resitamce amd current
A
E = RI V = IR
4
Q
Term for the relationship E = RI
A
Ohm’s law
5
Q
5 types of electroanalytical techniques
A
- Potentiometry
- Coulometry/Amperometry (current)
- Voltammetry
- Polarography
- Osmometry
6
Q
cathode or anode:
deonoted by a positive sign
A
cathode
7
Q
cathode or anode:
electrons are liberated here
A
anode
8
Q
cathode or anode:
oxidation reaction occurs here
A
anode
9
Q
cathode or anode:
electrons are consumed here
A
cathode
10
Q
cathode or anode:
denoted by a negative sign
A
anode
11
Q
cathode or anode:
reduction reaction occurs here
A
cathode
12
Q
cathode or anode:
electrons move out
A
anode
13
Q
cathode or anode:
electrons move in
A
cathode
14
Q
Electrochemical Cells are made up of
A
two half cells consisting of electrode dipped in electrolyte, connected by a salt bridge
15
Q
The tendency of an electrode which is in contact with an electrolyte to lose or gain
electrons
A
electrode potential
16
Q
The standard or reference electrode used to measure electrode potentials
A
hydrogen electrode
17
Q
Cells in which the reactions are irreversible in nature, and made up of use-and-throw galavanic cells
A
Primary cells
18
Q
Here, the reactants are consumed for the generation of electrical energy and the cell stops producing an electric current once the reactants are completely depleted
A
Primary cells
19
Q
Electrochemical cells in which the cell has a reversible reaction, i.e. the cell can function as a Galvanic cell as well as an Electrolytic cell.
A
Secondary cell
20
Q
Secondary cells are also known as
A
rechargeable batteries
21
Q
Two primary types of electrochemical cells
A
- Galvanic cell (voltaic cell)
2. Electrolytic cell
22
Q
Galvanic or Electrolytic cell:
chemical energy –> electrical energy
A
galvanic
23
Q
Galavanic or Electrolytic cell:
electrical energy –> chemical energy
A
electrolytic
24
Q
Galvanic or Electrolytic cell:
spontaneous redox reactions
A
galvanic
25
Galvanic or Electrolytic cell:
| Input of energy is required for redox reaction to proceed/ non spontaneous
electrolytic
26
Galvanic or Electrolytic cell:
| positively charged anode
electrolytic
27
Galvanic or Electrolytic cell:
| anode is negatively charged
galvanic
28
Galvanic or Electrolytic cell:
| cathode is positively charged
galvanic
29
Galvanic or Electrolytic cell:
| cathode is negatively charged
electrolytic
30
Galvanic or Electrolytic cell:
| electrons originate from oxidizing species
Galvanic
31
Galvanic or Electrolytic cell:
| electrons originate from external source (such as battery)
electrolytic cell
32
Measures - change in electric potential
| Constant- current
Potentiometry
33
A form of potentiometry where the potential of the glass electrode is measured as a function of hydrogen ion concentration in the solution.
measurement of pH
34
An analytical technique which converts the activity of a specific ion (dissolved in a solution)
into a voltage (potential), which can be measured by a mV or Ion meter.
Ion selective electrode
35
The sensing part of an ion seoecrive electrode is made up of
ion specific membrane coupled with reference electrode
36
There is a voltage change in the ion selective electrode when
there is change in potential after ions comes in contact with electrode
37
The strength of the net charge measured is _______ to the concentration of the selected ion
directly proportional
38
The high degree of selectivity of Ion specific electrode is due to
the high specificity of membrane for one ion
39
The ion selective electrode works on the principle of :
galvanic cell
40
Three main components of n ISE
reference electrode
ion selective membrane
voltmeter
41
Three main components of ISE measurement
inner reference or standard solution
outer analyte or sample solution
thin membrane
42
Ion selective membrane formed from special ionically conducting glass.
Glass membrane electrode
43
Two most common glass membrane ion selective electrode
pH electrode
| sodium selective electrode
44
Ion selective membrane made from relatively insoluble ionically conducting inorganic salts, where only ions that cn introduce themselves to the lattice can interfere
Crystalline or solid state membrane electrodes
45
Two examples of Crystalline or solid state electrodes
```
Fluoride electrode (doped LaF3 crystal)
Chrploride electrode (silver chloride powder)
```
46
Ion selective membrane based on special organic polymer membranes which contain various ion-exchange ionophores incorporated into an inert matrix.
Polymer membrane electrodes
47
Polymer membrane elctrodes are used in measurement of
K, Ca, N
48
Ion selective electrodes thag have gas permeable membranes and an internal solution, where gas molecules diffuse across the membrane and react with the solution causing a pH change
Gas sensing electrodes
49
Common gas sensing electrodes include:
ammonia and Carbon dioxide
50
Ion selective electrodes based on the reaction of an enzyme reacting with a specific
substrate, and the resultant product of this reaction (usually H+ or OH-) is detected by an
electrode such as a pH electrode.
Enzyme electrodes
51
Example of enzyme electrode
Glucose electrode
52
universally used ISE in the clinical laboratory
pH electrode (sensitive to H+)
53
Components of a pH meter
1. indicator electrode
2. reference electrode
3. liquid junction
4. readout meter
54
commonly used reference electrode in pH meter
calomel electrode
Mercurous chloride
AgCl
55
Commonly used filling solution for liquid junction due to same mobilities
KCl
56
Analytical method converting analyte from one oxidation state to another to measure the flow of electrons per unit of time.
constant: potential
Coulometry
57
Coulometry operates on the principle of
Faraday's Law
58
Soultion which has chloride ions interacts with electrode that releases silver ions which attach to Cl. What happens next?
Chloride ions are used up = change in electricity
59
measure: concentration of reducible elements through differences in current
increase at a constant rate: voltage
polarography
60
Polarography is based on the principle of
Ilkovic Equation
61
Similar to polarography except that electrical potential is varied over time.
Voltameter
62
defined as the concentration of solutes dissolved in a solvent
osmolality
63
Major osmotic substances are:
```
sodium (half)
chloride
glucose
urea
proteins
ethyl alcohol
```
64
as osmolality increases, osmotic pressure ________
increases
65
as osmolality increases, freezing point ________
decreases
66
as osmolality increases, boiling point ________
increases
67
as osmolality increases, vapor pressure ________
decreases
68
describes the migration of a charged particle under the influence of an electric field.
electrophoresis
69
two main types of gel electrophoresis
horizontal gel electrophoresis
| vertical gel electrophoresis
70
vertical or horizontal gel electrophoresis:
| buffer system is dicontinuous
vertical
71
vertical or horizontal gel electrophoresis:
| contijuous running buffer
horizontal
72
vertical or horizontal gel electrophoresis:
| has a single separating gel layer only
horizontal
73
vertical or horizontal gel electrophoresis:
| has two layers: upper stacking gel and lower running/resolving gel
vertical
74
vertical or horizontal gel electrophoresis:
| uses acrylamide gel
vertical
75
vertical or horizontal gel electrophoresis:
| uses agarose gel
horizontal
76
vertical or horizontal gel electrophoresis:
| used mainly in spearating mixtures of DNA and RNA
horizontal
77
vertical or horizontal gel electrophoresis:
| idelly used in separating proteins
vertical
78
positive electrode
anode
79
negative electrode
cathode
80
Usual pH of medium
pH 8.6
81
charge of proteins in 8.6 pH
negatively charged
82
proteins move towards what electrode at 8.6 pH
anode
83
five factors affecting the velocity of migration
- net charge of particle
- size and shape of the particle
- strength of electrical field
- chemical and physical properties of the supporting medium
- electrophoretic temperature
84
Three main components of an electrophoresis machine
1. power supply
2. buffers
3. support materials
85
Should be able to provide constant current for constany migration rate
power supply
86
Molecules, such as protein, whose net charge can be either positive or negative
ampholytes
87
two buffer properties that affect the charge of ampholytes
pH
| ionic strength
88
buffer: more acidic than isoelectric point of ampholyte, more H+
ampholyte: binds H+
charge of analyte :
migrates toward:
positively charged, cathode
89
buffer: more basic than pl, less H+
ampholyte: loses H+
charge of ampholyte:
migrates toward:
negatively charged
| anode
90
4 types of support materials
1. cellulose acetate
2. agarose gel
3. polyacrylamide gel
4. starch gel
91
Support material not commonly used anymore due to dryness and brittleness. it should be soaked to soften which uses more time and more resources
Cellulose acetate
92
How cellulose acetate is made
cellulose is acetylated to by treating wuth acetic anhydride
93
Support material that has big pores so almost all proteins can pass through. It also has neutral charge so it does not produce electroendosmosis.
agarose gel
94
size of molecules allowed in agarose gels
>10nm
95
amount of sample required in agarose gel
2 mL
96
Support medium usually used for common proteins only (albumin, globulin) with a small pore separation at the bottom, followed by large pore spacer and with a neutral charge
polyacrylamide gel
97
First ever support media that is not commonly used anymore due to technical difficulty in uniform consistency
starch gel
98
Support media which involves separation of protein on the basis of charge and molecular size
polyacrylamide gel
99
Support media which involves separation of protein on the basis of charge only
agarose gel
100
Support media which involves separation of protein on the basis molecular size only
cellulose acetate
101
Support media which involves separation of protein on the basis of surface charge and molecular size
starch gel
102
Used to visualize the separated fractions in gel electrophoresis
Dyes
103
Dye used for serum proteins in generap
Amido Black
| Ponceau S
104
Dye used for lipoprotein zones
Fat red 7B
| Sudan Black B
105
the amount of dye taken up by the sample is affected by :
typee of protein
| degree of denaturation
106
The result of zone electrophoresis and consists of sharply separated zones of a macromolecule.
electrophoretogram
107
A detergent with a strong protein-denaturing effect and binds to the protein backbone at a constant molar ratio, unfolding protein into linear chains with negative charge proportional to peptide chain length
SDS (sodium dodecyl sulfate) and reducing agent
108
Electrophoresis that eliminates the influence of the structure and charge, and proteins are separated solely based on polypeptide chain length.
SDS- PAGE ( sodium dodecyl sulfate- polyacrylamide gel)
109
DNA or RNA molecules separated based on their size, through the movement of negatively charged nucleic acid molecules. Molecules with smaller size move faster and migrate farther compared to longer ones.
Agarose gel electrophoresis
110
Refers to the bulk flow of liquid toward the cathode upon application of an electric field and it is superimposed on electrophoretic migration.
electro-osmotic flow
111
All positive and negative ions are pulled through in the same direction by electroosmotic flow, and the analytes separate as they migrate due to their electrophoretic mobility.
Capillary electrophoresis
112
Separates protein based on isoelectric points and molecular weights.
two-dimensional electrophoresis (2D)
113
Defined as the pH of a solution at which the net charge of the protein becomes zero.
isoelectric point
114
First dimension of 2D electrophoresis
Isoelectric focusing (separation based on charge)
115
Second dimension of 2D electrophoresis
SDS-PAGE (based molecular weight)
