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Analytical Chemistry > Atomic Spectroscopy > Flashcards

Atomic Spectroscopy Flashcards

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1
Q

Types of Atomic Spectroscopy (3)

A
  1. Atomic Absorption Spectroscopy
  2. Atomic Emission Spectroscopy
  3. Atomic Fluorescence Spectroscopy
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2
Q

Basic Instrumentation of Atomic Absorption Spectroscopy

A

Radiation Source > Focusing Lens > Atomizer and Sample > Focusing Lens > Wavelength Selector > Detector > Amplifier > Signal Processor

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3
Q

Radiation source that consists of a tungsten anode and a cylindrical cathode sealed in a glass tube containing an inert gas (e.g., Ar)

A

Hollow Cathode Lamp

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4
Q

Using Hollow Cathode Lamp, the cathode is fabricated from the analyte metal or serves as
_____ of that metal application of a potential of about +300 V across the electrodes causes ionization of ____ to ____

A

a support for coating

Ar to Ar+ & e-

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5
Q

Using Hollow Cathode Lamp, ionized Ar+ strikes that cathode with sufficient energy to ____ and _____

A

dislodge and excite some of metal atoms

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6
Q

In using Hollow Cathode Lamp, excited metal atoms emit their _____ as they return to ground state

A

characteristic wavelengths

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7
Q

Radiation source that has a lamp constructed from a sealed quartz tube, containing an inert gas (ex. Ar) at a pressure of few torr and a small quantity of the analyte metal (or its salt)

A

Electrodeless Discharge Lamp

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8
Q

In electrodeless discharge lamp, a ____ or _____ generates intense RF field, causing the ionization of Ar

A

coil of radiofrequency (RF) or microwave radiation

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9
Q

In electrodeless discharge lamp, the ions (ionized Ar) are accelerated by the RF field, thereby ______, whose emission spectrum is sought

A

colliding with and exciting the atoms of the metal

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10
Q

Radiation source where electric arc between two electrodes causes excitation of xenon filled in a quartz tube and xenon atoms/atoms upon deexcitation gives continuous spectrum

A

Xenon arc lamp

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11
Q

Radiation source that can emits continuous spectrum at high intensity and all the elements can be measured from 185-900 nm

A

xenon arc lamp

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12
Q

High intensity Xe lamp gives ___ and ____

A

better signal/noise ratio and detection limit

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13
Q

Atomization process that involves reduction to a fine spray by passing the solution through thin nozzle

A

nebulization

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14
Q

Atomization process that involves removal of solvent, leaving just the analyte and other matrix compounds

A

desolvation

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15
Q

Atomization process that involves converting solid analyte/matrix into gas phase

A

volatilization

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16
Q

Atomization process that involves break-up molecules into atoms

A

dissociation

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17
Q

Atomization process that involves light, heat, etc. for spectra measurement

A

excitation

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18
Q

Atomization process that causes atom to become charged

A

ionization

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19
Q

Sample -?-> mist -?-> solid/gas aerosol -?-> gaseous molecules -?-> atoms

A

Sample —nebulization—> mist —desolvation—> solid/gas aerosol —volatilization—> gaseous molecules —dissociation—> atoms

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20
Q

In flame atomization method, ideal flow rate is ____

A

flow velocity +burning velocity

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21
Q

In flame atomization method,

Too high flow rate = ____
Too low flow rate = _____

A

Too high flow rate = flame blows off
Too low flow rate = flashback occurs

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22
Q

In flame optimization, the maximum temperature is located _____

A

above the primary combustion zone

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23
Q

In flame optimization, beam from lamp has to be focused on the part of the flame where _____

As this is different for elements, the ____ has to be adjusted while aspirating a standard solution of the analyte

A

atomization efficiency of the analyte is greatest

burner height

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24
Q

In flame optimization, increasing the angle ____ the path length of the light beam through the flame and ___ the absorbance

This can be useful for the analysis of concentrated solutions which may give off-scale absorbance reading when _____ is use

A

shortens the path length
decreases the absorbance

a maximum path length (zero burner angle)

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25
Q

In flame optimization, the initial increase in absorbance as the _____ increases due to the longer exposure to the heat causing more _____ atoms to be formed

A

distance from the flame base

magnesium atoms

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26
Q

In flame optimization using magnesium, absorption _____ if the magnesium is exposed even longer because ______

A

decreases

oxides are formed which absorbs at a different wavelength

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27
Q

In flame optimization using ____, no stable oxides so a continuous increase in absorbance is seen

A

silver

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28
Q

In flame optimization using ____, forms very stable oxides so there is a continuous decrease in absorbance as it rises above the burner tip

A

chromium

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29
Q

Type of burner which draws sample up and nebulizes by Venturi action

A

Turbulent Flow Burner

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30
Q

Turbulent flow burner consumes ____ amount of sample but with ____ path length, ____ problems, and ____

A

large amount of sample

short path length
clogging problems
noisy

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31
Q

Type of burner in which the sample is nebulized by flow of oxidant past a capillary tip

A

laminar flow burner

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32
Q

Using Laminar Flow Burner, the resulting aerosol is mixed with fuel and flows past a series of baffles that remove _____

The ___, ____, and ___ are fed into the burner

A

remove all but finest droplets

aerosol, oxidant, and fuel

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33
Q

Laminar Flow Burner has ___ drop size, ___ and ___ flame, and _____ path length,

but has ____ if Vburning>Vflow, ～____% of sample is lost, and ____ mixing volume

A

uniform drop size, homogenous and quiet flame, and long path length

flashback if Vburning>Vflow, ～90% of sample is lost, and large mixing volume

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34
Q

Meaning of the ff. acronyms:

FAAS
GFAAS
CVAA

A

Flame Atomic Absorption Spectroscopy
Graphite Furnace Atomic Absorption Spectroscopy
Cold-Vapor Atomic Absorption

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35
Q

Strengths of FAAS (7)

A
  1. Easy to use
  2. Very fast
  3. Lowest capital cost
  4. Relatively few interference
  5. Very compact instrument
  6. Good performance
  7. Robust interface
36
Q

Limitations of FAAS (4)

A
  1. Moderate detection limits
  2. Element limitations
  3. 1-10 elements per determination
  4. No screening ability
37
Q

____ is often used as a purge gas to remove excess material during the dry and ash phases after atomization

A

Argon

38
Q

External argon gas prevents _____ by reducing oxidation of the tube and provide a ____ during atomization since high temperature carbon will react with nitrogen to produce ____

Internal argon gas _____

A

tube destruction
protective blanket
cyanogen

circulates gaseous analyte

39
Q

Three stages of sample preparation for graphite furnace

A
  1. Dry: a fixed temperature and times is used to remove solvent (50-200 C)
  2. Ash: a second temperature used to decompose the matrix (200-800 C)
  3. Atomization: a rapid increase tot 2000-3000 C for just a few seconds
40
Q

Strengths of GFAAS (5)

A
  1. Very good detection limits
  2. Small sample size
  3. Moderate price
  4. Very compact instrument
  5. Few spectral interferences
41
Q

Limitations of GFAAS (6)

A
  1. Slower analysis time
  2. Chemical interferences
  3. Element limitations
  4. 1-6 elements per determination
  5. No screening ability
  6. Limited dynamic range
42
Q

It provides a method for introducing samples containing arsenic, antimony, tin, selenium, bismuth, and lead into an atomizer as a gas

A

Hydride generation

43
Q

Volatile hydrides can be generated by addition of an ____ of a sample to a small volume of a 1% aqueous solution of ____

A

acidified aqueous solution
sodium borohydride (NaBH4)

44
Q

The volatile hydride during hydride generation is swept into the atomization chamber by an ____ which enhances the ______ by a factor of 10 to 100.

A

inert gas
detection limits

45
Q

Determining volatile hydride at ____ levels is quite important because several of these species are highly toxic

A

low concentration

46
Q

Spectroscopy used for the determination of Hg

A

Cold-Vapor Atomic Absorption (CVAA) Spectroscopy

47
Q

In CVAA Spectroscopy, sample solution is treated with a _____ such as ____ which converts mercury ions to metallic mercury

A

reducing agent such as Sn(II)

48
Q

In CVAA Spectroscopy, the metallic mercury is then swept into a____ for absorption measurement

On the completion of the measurement, the mercury is flushed from the system by pumping the vapor through a ____

A

glass cell
mercury absorption solution (KMnO4)

49
Q

Sample Preparation for Atomic Spectroscopy (5)

A
  1. Wet Ashing
  2. Dry Ashing
  3. Fusion
  4. Solubilization
  5. Microwave
50
Q

performed in open reaction systems using Kjeldahl flask or autoclave using strongly oxidizing mineral acids (HNO3, HClO4, H2SO4)

A

wet ashing

51
Q

sample is placed in crucible (Pt or fused silica) dried at 105-110 C then ashed between 400 8800 C using a muffle furnace; ash is then dissolved in a variety of acids or mixtures of acids

A

dry ashing

52
Q

geological sample is mixed in a Pt crucible with a flux such as lithium metaborate, hashed in a furnace at 1000 C, then cooled to room temp dissolved in HNO3

A

fusion

53
Q

biological sample is dissolved in quaternary ammonium hydroxide (tetramethylammonium hydroxide)

A

solubilization

54
Q

sample is mixed with acid and placed in a sealed vessel within the microwave digestion system

A

microwave

55
Q

Cations like LaCl3 from Ca, Mag, Sr that preferentially reacts with a species that would otherwise react with the analyte causing a chemical interference

A

Releasing agents

56
Q

prevent interferences by forming stable and volatile products with the analyte (example: EDTA)

A

Protection agents

57
Q

atoms that are more easily ionized than the analyte and provides a high concentration of electrons in the flame, thus suppress the ionization of the analyte

A

ionization suppressors

58
Q

substance added in excess to both sample and standards which swamps the effect of the sample matrix on the analyte

A

radiation buffer

59
Q

Result of any chemical process (formation of compounds of low volatility) which decreases or increases the absorption of analyte

A

chemical interference

60
Q

Remedy for chemical interference (3)

A
  1. Use higher temperature flame
  2. Use of releasing agent
  3. Use of protection agents
61
Q

Spectral lines that occur at different λ than atomic lines

A

ionization interference

62
Q

Causes of ionization interference (3)

A
  1. decrease in AAS signal
  2. ionization decrease at high concentration
  3. competition between atoms for available energy
63
Q

Remedy for ionization interference (3)

A
  1. Use of low temperature flame
  2. Use of high concentration of analyte
  3. Use of ionization suppressor
64
Q

Caused by the physical nature of matrix enhancing or depressing sensitivity

A

matrix interference

65
Q

Remedy for matrix interference (3)

A
  1. Use of standard addition technique
  2. Use of solvent extraction to isolate the analyte
  3. Use of radiation buffer
66
Q

interference with overlapping of spectra (analyte and matrix absorb at the same wavelength)

A

spectral interference

67
Q

Remedy for spectral interference (3)

A
  1. Chemical separation prior to analysis
  2. Modulation of the detector
  3. Background correction
68
Q

Basic instrumentation of Atomic Emission Spectroscopy

A

Excitation source > Sample holder > Lens > Wavelength Selector > Detector

69
Q

Sequential spectrometer- uses ____

Simultaneous spectrometer- uses ____

A

sequential = monochromator
simultaneous = polychromator

70
Q

Sources of Excitation in Atomic Emission Spectroscopy (6)

A
  1. Flame
  2. Plasma
  3. Electrothermal
  4. Laser Ablation
  5. Spark or arc ablation
  6. glow-discharge sputtering
71
Q

The same source of thermal energy used for atomization usually serves as the ____.

A

excitation source

72
Q

_____ is an electrically conducting gaseous mixture containing enough cations and electrons to maintain the conductance

A

Plasma

73
Q

Plasma Sources in Atomic Emission Spectroscopy (4)

A
  1. Inductively coupled Plasma (ICP)
  2. Microwave-induced plasma (MIP)
  3. Direct current plasma (DCP)
  4. Laser-induced Plasma
74
Q

Atomization method for solution (2)

A
  1. pneumatic nebulization (solution or slurry)
  2. ultrasonic nebulization (solution)
75
Q

Atomization method for solid, liquid or solution sample

A

electrochemical vaporization

76
Q

Atomization method for solution of certain elements

A

hydride generation

77
Q

Atomization method for solid and powder samples (2)

A
  1. direct insertion
  2. laser ablation
78
Q

Atomization method for conducting solid (2)

A
  1. spark or arc ablation
  2. glow-discharge sputtering
79
Q

In principle, line absorption should only affect a very unique wavelength but in reality, also _____ are absorbed called ___

A

slightly different wavelengths
line broadening

80
Q

Line broadening because of uncertainties in the transition times

A

Uncertainty effect

81
Q

Uncertainty effect results from the ____ principle postulated in 1927 by _____

A

uncertainty principle
Werner Heisenberg

82
Q

Line broadening because of rapid movement of atoms; emitted or absorbed wavelength changes as a result of atom movement relative to detector

A

Doppler effect

83
Q

Wavelength _____ if atom moves toward a photon detector

Wavelength _____ if atom moves away from a photon detector

A

Wavelength decreases if atom moves toward a photon detector

Wavelength increase if atom moves away from a photon detector

84
Q

Line broadening due to collision between atoms of the same kind and with foreign atoms

A

Pressure effect

85
Q

Pressure effect is ____ in high pressure conditions

A

worse

86
Q

line broadening that affects the number of atoms in ground and excited state

A

temperature effect

87
Q

Since temperature changes number of atoms in ground and excited state, ____ is needed

A

good temperature control

Analytical Chemistry (13 decks)

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