Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

Instrumental Analysis > Test 3 > Flashcards

Test 3 Flashcards

(127 cards)

Start Studying
1
Q

What is atomization?

A

The process by which a sample is converted to gaseous atoms or elementary ions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

In optical atomic spectrometry, what is the purpose of the flame, plasma, electric arc, or spark?

A

To excite the electrons of the sample to higher orbitals

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What happens when an excited atom returns to the ground state?

A

A photon is emitted

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What causes line broadening in atomic line widths?

A

Uncertainty effect, Doppler effect, pressure effects, electric and magnetic field effects

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is the uncertainty effect?

A

It is the natural line width (10^-4 Angstrom) because spectral lines have fintire widths since the lifetime of transition states are finite

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What causes doppler broadening?

A

the atom is either moving toward incoming radiation that makes it absorb radiation that is higher in frequency or the atom is moving with the direction of radiation and absorbs lower frequency radiation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What results in maximum doppler shifts?

A

Atoms moving directly towards or away from transducers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What results in no doppler shifts?

A

atoms moving perpendicular to the transducer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What do doppler shifts depend on?

A

Atom speed and direction as the magnitude of the broadening increases with velocity of the emitting species

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is pressure broadening?

A

When the emitting species collides with other atoms or ions which causes small changes in the ground state energy levels and the range of the emitted wavelengths

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

How does temperature effect line width?

A

It affects the ratio between the number of excited and unexcited atomic particles and the magnitude of the effect is calculated using the Boltzmann equation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the value of Boltzmann constant?

A

1.28x10^-23 J/K

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the relationship between temperature and line broadening?

A

An increase in temperature results in increased line broadening

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What are the order of processes during atomization?

A

Nebulization, desolvation, volatilization, dissociation, ionization, and excitation (Occurs at every step past volatilization)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are the different types of atomizers??

A

Flame, electrothermal vaporization (ETV), inductively coupled argon plasma (ICP), direct current argon plasma (DCP), microwave-induced argon plasma (MIP), glow-dsicharge plasma (GD), electric arc, and electric spark

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What are pneumatic nebulizers?

A

It is a component that is used to introduce solution samples into the atomization region via high-pressure gas flow breaking apart the sample into smaller pieces

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is an ultrasonic nebulizer?

A

It is where a sample is placed on the surface of a piezoelectric crystal that has a frequency of 20 kHz-MHz that can introduce the sample to the atomization region

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is an electrothermal vaporizer?

A

A small liquid/solid sample is placed on a conductor (like C rod or Ta filament) and an electric current evaporates the sample into a chamber with inert argon gas that carries the vaporized sample to the atomizer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

How can solid samples be introduced in optical atomic spectroscopy?

A

directly into the atomizer, electrothermal vaporization, arc/spark or laser ablation, slurry nebulization, sputtering in a glow discharge device

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

How does glow discharge atomization work?

A

A potential is applied to a pair of electrodes which breaks apart argon gas into ions and electrons and the argon ions accelerate to the cathode surface that holds the sample. When the ions strike the sample, neutral sample atoms are ejected into the cell.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What can glow discharge be used for?

A

Metallic and conducting samples

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is the most common source for optical atomic spectrometry?

A

hollow cathode lamp

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is the main limitation of hollow cathode lamps?

A

The cathode must be coated with the same element as the analyte

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

How does a hollow cathode lamp work?

A

A potential of 300 V is applied across electrodes and the current generated ionizes the inert gas and the gas strikes the cathode surface and sputters the metal from the surface, which excites the metal atoms causing them to emit light

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
What are electroless discharge lamps?
A sealed quartz tube containing a small quantity of inert gas and metal
26
How do electroless discharge lamps work?
A radio or microwave frequency is applied and ionizes the inert gas that excites the metal atoms which emits a spectrum
27
What is the main interference that is present in AAS?
Interference from the emission of radiation by the flame
28
How do you remove the main source of AAS interference?
Monochromator and source modulation
29
What is source modulation?
Fluctuating the intensity of the output of the source at a constant frequency so the detector recieves two signals (alternating source and continuous flame)
30
What component is used to modulate a source?
Simple chopper
31
What are spectral interferences?
When absorption or emission of an interfering species overlaps/is very close to the analyte absorption/emission. Also when products like oxides are produced in the flame with diameters greater than the wavelength of light and scatter the beam
32
What are methods to correct spectral interferences?
Two line method, continuum source method, source self-reversal correction (Smith-Hieftje)
33
What is the two line method?
Use a line from the source as a reference close to the analyte line so any decrease in the reference line can be assumed to arise from absorption or scattering of matrix products
34
What is the continuum source method?
A D2 lamp source goes through a chopper and a hollow cathode lamp goes through a graphite tube atomizer and the absorbance of D2 radiation is subtracted from the analyte beam
35
What is source self-reversal correction?
A high current is used for a hollow cathode lamp which produces a large concentration of nonexcited atoms that absorb the radiation from the excited species. This produces a minimum at the center of a band
36
What are chemical interferences?
Come from the various chemical processes occurring during atomization and alter the absorption characteristic of the analyte
37
What type of AAS interference is more common?
Chemical interference
38
What is the most common type of chemical interference?
Formation of compounds with low volatility
39
How does formation of compounds of low volatility produce chemical interference?
Anions form compounds of low volatility with the analyte and reduce the rate of atomization of the analyte and gives low absorbance results
40
How can the formation of compounds of low volatility be minimized?
Using high temps, releasing agents, protective agents
41
What is dissociation equilibrium?
In the flame or furnace the analyte undergoes dissociation and association reactions and the molecular bands of metal oxides or hydroxides are more intense than the lines for atoms or ions
42
What is ionization equilibrium?
In high temp flames, ionization increases and produce high concentrations of free electrons in the flame.
43
What can decrease ionization equilibrium?
Use of an ionization suppressor which produces more electrons which shifts the equilibrium back
44
What are the three major techniques used for elemental analysis?
optical, mass, and x-ray spectrometry
45
What are the advantages of ICP?
Lower susceptibility to chemical interferences because of high temps, good emission spectra for most elements that can be recorded at the same time, can determine low concentrations of refractory compounds, can determine non-metals, has a larger linear range
46
What are the disadvantages of ICP?
Spectra are highly complex which increases probabiliy of interferences for quantitative work and need more expensive optical equipment which is more difficult to maintain
47
What is a plasma?
An electrically conducting gaseous mixture that contains a high concentration of cations and electrons
48
What is the ICP source called?
Torch which is three concentric quartz tubes and a water cooled induction coil
49
What types of samples can be used in ICP?
aerosols, vapor, or solid
50
How do you introduce samples to ICP?
Similar to AA, aspirate the sample into the plasma and use nebulization (liquid only) or electrothermal vaporization (liquid and solid), laser ablation (solid only)
51
What are the advantages of atomization of the sample in ICP?
More complete atomization in plasma, fewer chemical interferences, less oxide formation, more uniform temperature, larger linear range for calibration curves, and plasma produces significant ionization
52
What are the types of ICP instruments?
Sequential, simultaneous multichannel, Fourier transform
53
What are the desirable properties of an emission spectrometer (AAS and ICP)?
high resolution, rapid signal acquisition and recovery, low stray light, wide dynamic range, accurate and precise wavelength identification and selection, precise intensity readings, high stability with respect to environmental changes, and easy background corrections
54
What is a slew-scan spectrometer?
It scans quickly to region of interest then slows down to 0.01-0.001 nm steps
55
What is a scanning echelle spectrometer?
Move the PMT in x and y direction to scan an aperture plate with 300 slits
56
What are the advantages of Fourier transform spectrometers?
wide wavelength coverage, speed, high resolution, accurate measurements, accurate measurements, large dynamic range, compact size, large optical output
57
What is the disadvantage of FT spectrometers?
Very expensive
58
How are electrochemical solutions structured?
There is a compact inner layer where potential decreases lineraly with distance from the electrode surface and a diffuse layer where potential decreases exponentially
59
What are Faradaic processes?
Direct transfer of electrons by an oxidation or reduction reaction
60
What is nonfaradaic current?
background current
61
What is Faraday's law?
the amount of chemical reactant at an electrode is proportional to the current (faradaic current)
62
What are the types of cells?
galvanic and electrolytic
63
What is a galvanic cell?
Cells that produce electrical energy like a battery. Can store electrical energy and reactions at the electrodes proceed spontaneously
64
What is an electrolytic cell?
Cells that consume electrical energy. It consumes energy so you need an external source of electrolytic energy
65
What kind of electrode is used when the reaction doesn't contain a solid metal?
inert electrode
66
What is the electrode potential?
The potential difference between cathode and anode of the cell is a measure of the tendency of the reaction
67
When is the sign of the electrode potential (E0) positive?
When the half-cell behaves spontaneously as the cathode
68
When is the sign of the electrode potential (E0) negative?
When the half-cell behaves as an anode
69
What is standard electrode potential?
when it is referenced to standard hydrogen electrode
70
What are the limitations of standard electrode potential?
Uses concentrations not activities, is temperature dependent, other side reactions, formal potential where ratio of reactants and products must be in unity
71
What is ohmic potential or IR drop?
where cells resist the flow of charge
72
What leads to IR drop?
When a higher potential than the thermodynamic potential must be applied in order to generate a current in the cell
73
What are the two types of polarization?
Concentration and kinetic
74
What is concentration polarization?
electron transfer occurs at the interface of an electrode, leaving only a thin film of solution in contact with the electrode and the transfer of the molecules is slow
75
What are the three types of mass transfer?
Convection, migration, and diffusion
76
What is convection?
Mechanical motion of the solution
77
What is migration?
Movement of ions by electrostatic attraction
78
What is diffusion?
Motion of species due to concentration gradient
79
How does migration work?
Negative ions migrate toward positive electrode and positive ions migrate toward the negative electrode
80
How is kinetic polarization increased and decreased?
It is increased by catalysts and decreased by evolved gases and polymeric films on the electrode
81
What is mass transfer?
For faradaic current to continue, the species must be continuously transferred from the bulk of the solution to the electrode surface
82
What can be said about the rate of diffusion?
It is proportional to the concentration difference
83
What happens as the electrode potential at the cathode becomes more negative?
The concentration decreases and the rate of diffusion and current increases
84
What happens as the rate of migration increases?
The electrode energy (E) increases
85
What occurs with forced convection?
It decreases the thickness of the diffusion layer and decreases the concentration polarization
86
What is voltammetry?
Measurement of current as a function of applied potential using working electrode
87
What is an excitation signal?
A variable potential signal applied to an electrochemical cell and has a distinctive waveform
88
What is chronoamperometry?
Current as a function of time with respect to applied potential
89
What is chronocoulometry?
Charge as a function of time with respect to applied potential
90
What is differential pulse voltammetry?
Small pulses added to a linear ramp to measure current changes
91
What is linear sweep voltammetry?
Current as a function of time and applied potential
92
What is cyclic voltammetry?
Current as a function of applied potential in two directions
93
What is anodic stripping voltammetry?
Current as a function of applied potential after deposition
94
What is a potentiostat?
An instrument capable of applying a controlled potential to a working electrode and measuring the resulting current from a redox reaction
95
What is a working electrode?
Potential varies linearly with time, usually very small
96
What is a reference electrode?
Potential is constant with time
97
What is a counter (auxiliary) electrode?
Conducts current from source through the solution
98
What is a main feature of working electrodes?
It has a potential window which determines the range of potentials in which the working electrode can be used which is limited on the positive side by oxidation of water to dioxide gas and on the negative side by the reduction of water to dihydrogen gas.
99
What are common materials for working electrodes?
Ag, Au, Pt, Ni, carbon, mercury
100
What is polarography?
Voltammetry using a dropping Hg electrode
101
What are the important features of cyclic voltammetry?
Current response in unstirred solution is excited by triangular waveform, potential varies linearly, scan direction is reversed
102
What potentials does oxidation and reducation happen at?
Oxidation happens at more positive potentials and reduction at more negative potentials
103
What are the three mobile phase types of chromatography?
liquid, gas, and supercritical fluid
104
What is normal-phase chromatography?
A non-polar mobile phase with a polar stationary phase (LC)
105
What is reversed-phase chromatography?
A polar mobile phase with a nonpolar stationary phase (LC)
106
What are the different separation mechanisms of chromatography?
adsorption, partition, ion-exchange, size exclusion, affinity, and micellar or pseudophase
107
What is adsorption?
solute and mobile phase molecules compete for active sites on the surface of the solid stationary phase
108
What is partition?
Partitioning of a solute between two immiscible liquids but one liquid is held stationary on a solid support. A solute in contact with two immiscible liquids will distribute itself between them according to the distribution coefficient (K)
109
What is size exclusion?
A physical sieving process
110
What is affinity?
stationary phase is a bioactive liquid bonded to solid support
111
What does the sharpness of the peak of a chromatogram represent?
The efficiency of the chromatographic column
112
What is plate theory?
Movement of analyte and mobile phase is viewed as a series of transfers from one plate to the next. The efficiency of a column increases as the number of equilibrations (theoretical plates) increases
113
What is rate theory?
Focuses on the contributions of various kinetic factors to zone or band broadening
114
In rate theory, what does A, B, and C stand for?
A is the contribution to zone broadening by eddy diffusion, B is the contribution of longitudinal diffusion, C is the contribution of resistance to mass transfer in both the stationary and mobile phases
115
What is eddy diffusion?
Results from the inhomogeneity of flow velocities and path lengths around the packing particles
116
What is longitudinal diffusion?
Arises from the random molecular motion of analyte molecules in the mobile phase. Diffusion along the axis of the column results in zone broadening
117
What is obstructive factor?
Unity for coated capillary columns and longitudinal diffusion is hindered by packing
118
In rate theory, what does the diffusion rate depend on?
Temperature and pressure of the mobile phase
119
What causes the solute diffusion coefficient to decrease?
Decreasing temperature and increasing pressure
120
What kind of gas is favored as a mobile phase and why?
Has a higher molecular weight since diffusion is lower
121
What are processes that contribute to band broadening in chromatography?
multiple flow paths, longitudinal diffusion, mass transfer to and from stationary phase, and mass transfer in mobile phase
122
What does mu stand for in rate theory?
Average linear mobile phase velocity
123
For stationary phases, what is C?
C is small for solid phases, for liquids it depends on the thickness of the film and the diffusion coefficient of the analyte in the stationary phase and the geometric nature of the packing
124
For the mobile phase, what is C?
Depends on the capacity factor of the analyte and the particle diameter of the stationary phase or internal diameter of the column. Efficiency increases as particle size or column diameter decreases
125
What are qualitative applications of chromatography?
Confirm presence or absence of compounds in samples
126
What are quantitative applications of chromatography?
Establish the amount of individual components in a sample by comparing with standards used for quality control
127
What are preparative applications of chromatography?
Purifying samples

Instrumental Analysis (2 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions