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Quantitative Analysis > Test 4 > Flashcards

Test 4 Flashcards

1
Q

Components of fluorescence, phosphorescence and scattering spectrophotometers

A

Source > wavelength selector > sample > detector > readout

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2
Q

Components of emission and chemiluminescence spectrophotometers

A

Source and sample > wavelength selector > detector > readout

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3
Q

Emittance (M)

A
  • measured in W/m^3
  • M = sigma T^4
  • sigma = Stefan Boltzmann constant = 5.6698 x 10^-8 Wm^-2K^-4
  • T= temperature
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4
Q

Laser defn

A

Light Amplification by Stimulated Emission of Radiation

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5
Q

Laser Properties

A
  • high intensity
  • monochromatic (1 color)
  • collimated (travels in a straight line)
  • coherent (emitted waves are in phase)
  • plane polarized (electric fields line up)
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6
Q

Laser characteristics

A
  • energy pump
  • spontaneous emission
  • stimulated emission
  • absorption
  • population inversion
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7
Q

Population Inversion

A

More species in excited (metastable) state than in the ground state

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8
Q

How laser works

A
  1. Pumping causes a population inversion

2. Lazing occurs when rate of stimulated emission exceeds the rate of absorption

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9
Q

Diffraction

A

Observation that light passing through a small aperture spreads out and does not travel in a straight line

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10
Q

Constructive interference

A

Electric field vectors are in the same direction

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11
Q

Destructive interference

A

Electric field vectors are in opposite directions

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12
Q

Components of absorption spectrophotometers

A

Source>wavelength selector> sample > detector > readout

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13
Q

Stray light

A

Radiation that reaches the detector without going through the sample or monochromator (unwanted radiation)

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14
Q

Detectors

A

Convert electromagnetic radiation into a measurable quantity (voltage, current, etc)

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15
Q

Photomultiplier tube (PMT)

A
  • very sensitive due to inherent amplification
  • easy to damage
  • Gains of 10^6 to 10^7 electrons/proton typical
  • fast response times
  • limited only by dark current. But thermal portion of this is gone at -30 degrees Celsius
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16
Q

Thermocouple

A

Junction between dissimilar metals generates potential difference which is temperature dependent

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17
Q

Thermopile

A

Group of thermocouples

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18
Q

Photoconductive

A

Semiconductor conductivity changed with infrared radiation

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19
Q

Fourier Transform Infrared Spectrometry (FTIS)

A
  • all frequencies measured simultaneously
  • spectrum computed by FFT
  • operated by generating a complex interference pattern as function of moving mirror distance
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20
Q

Advantages of FTIR

A
  • Fellgetts advantage
  • jacquinots advantage
  • wavelength accuracy
  • Stray light advantage
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21
Q

FTIR Advantage - Fellgetts Advantage

A

Signal-to-noise ratio increases with sq. root of number of scans added

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22
Q

FTIR Advantage Jacquinots advantage

A

High energy striking detector because slits not used

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23
Q

FTIR Advantage - wavelength accuracy

A

Laser fringe reference is best method of distance measurement. Wavelength accuracy +/- 0.01 cm^-1

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24
Q

FTIR Advantage - Stray Light Advantage

A

Only modulated radiation passing through interferometer detected. Stray light results in DC offset

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25
Q

Atomic absorbable width

A

0.2-0.5 nm wide

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26
Q

Molecular absorbance width

A

10-100nm

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27
Q

Absorption

A

Excite atoms with energy required for excitation transition

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28
Q

Emission

A

Source provides atomization and excitation - relaxation provides emission

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29
Q

Atomization

A

Process by which liquid samples are converted into aerosols, then molecules, and finally into atoms

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30
Q

Nebulizer

A

Device used to convert liquid samples into aerosols

31
Q

Laminar flow burner - Advantages

A
  • long (5-10 cm) flame path length

- quiet flame - stable/reproducible

32
Q

Laminar flow burner - disadvantages

A
  • low sampling efficiency (most goes down the drain)

- flashback (explosive mixtures)

33
Q

Non-Flame Atomizers -
Electro thermal (graphite furnace)
Advantages

A
  • no sample loss during nebulizing
  • longer residence time (secs)
  • large (>10 muL) volumes
  • lower detection limits (0.1-100 pg)
34
Q

Non-Flame Atomizers -
Electro thermal (graphite furnace)
Disadvantages

A
  • matrix interference problems (matrix diffusing into graphite)
35
Q

Blaze wavelength

A

Wavelength at which incidence angle = reflected angle.

36
Q

Grooves/mm

A

UV-VIS : 300-2000 (1500 typ.)

IR : 10-200 (100 typ.)

37
Q

AAS vs AES (flame)

A
  • AES requires no source but AAS source lines are so narrow that monochromator needs are not too demanding
  • necessary operator skill generally less for AAS
  • background correction usually easier for AES
  • precision/accuracy approximately equal for both
  • linear range typically wider for AES
  • interferences. AAS subject to less spectral. Chemical interferences are approximately the same for both.
  • detection limit depends on the element
38
Q

AES more sensitive than AAS (in these elements)

A

Al, Ba, Ca, Eu, Ga, Ho, In, K, La, Li, Lu, Na, Nd, Pr, Rb, Re, Ru, Sm, Sr, Tb, TI, Tm, W, Yb

39
Q

AAS vs AES (sensitivity about the same)

A

Cr, Cu, Dy, Er, Gd, Ge, Mn, Mo, Nb, Pd, Rh, Sc, Ta, TI, V, Y, Zr

40
Q

AAS vs AES (AAS more sensitive)

A

Ag, As, Au, B, Be, Bi, Cd, Co, Fe, Hg, Ir, Mg, Ni, Pb, Pt, Sb, Se, Si, Sn, Te, Zn

41
Q

Plasma defn

A

A plasma is a conducting, ionized gas

42
Q

AAS advantage

A

Cheaper, easier to operate, lower operating costs (compared to Plasma too)

43
Q

Plasma vs AAS

A
  • Compared to flame and electro thermal, much higher temperatures
  • high temperature minimizes interelement interferences
  • high temperature allows access to difficult metals and non-metals
  • emission allows for simultaneous multi-element analysis
  • generally complimentary
  • plasma emission has advantage due to higher operating temperatures
44
Q

Separation methods- Extraction

A

Using a solvent to selectivity remove the analyte

45
Q

Separation methods - Chromatography

A

Using a separation column to isolate mixture components

46
Q

Chromatography general principles

A
  • Mobile phase (gas, liquid, or supercritical fluid) flows over/through immiscible stationary phase (liquid, solid) held in a column or solid surface
  • sample introduced at the beginning of the column
  • sample components exhibit various affinities for stationary phase
  • sample components with strong affinities for stationary phase move slowly through the column. Those with weak affinities move rapidly
  • individual components elute in “bands”
47
Q

3 major components of chromatography

A
  • mobile phase: analyses “dissolve” in the mobile phase. Also, it serves as the transport medium
  • stationary phase: immobile phase to which the individual analyses have varying degrees of attraction
  • equilibrium: the nature of attraction of individual analysts can be described as equilibrium processes, such as adsorption and solvent-solvent partition
48
Q

Elution defn

A

Process by which analyzes are passed through the column

49
Q

Eluent defn

A

Mobile phase

50
Q

Partition coefficient (partition ratio)

A

For a given eluting species, A, the ratio of the concentration of A in the stationary phase to that in the mobile phase.

51
Q

HETP (H)

A

Height Equivalent to a Theoretical Plate

52
Q

Resolution defn

A

Ability of column to separate to analytes

53
Q

Qualitative analysis by chromatography

A

TR is characteristic of analyte under fixed chromatography conditions

54
Q

Quantitative analysis by chromatography

A

Both peak height and peak area are proportional to analyte concentration under fixed chromatography conditions

55
Q

mass spectrometry

A

Process for analysis of single ions. Basically, molecules are converted into gas phase ions, separated according to mass to charge ratio, and then detected by an ion sensitive detector

56
Q

Base peak

A
  • Largest peak in the mass spectrum
  • arbitrarily given an intensity of 100
  • represents the most favorable fragmentation pathway
57
Q

Exact mass

A

Involves particular isotopes of element or compound containing a particular set of isotopes

58
Q

Nominal mass

A

Referring to MS ion masses measured to the nearest whole number

59
Q

MS structural information

A
  • fragmentation pattern is representative of molecular structure
  • exact mass measurements give elemental composition of fragments and molecular ions
  • recognition of isotope abundance patterns
60
Q

Radical cation

A
  • radical cation know as the molecular ion
  • it’s usually the highest mass speak in spectrum
  • also called the “parent” ion
  • accurate mass analysis of the molecular ion can determine elemental composition
61
Q

M + 1 for H

A

0.015

62
Q

M+ 1 for C

A

1.08

63
Q

M+ 1 for N

A

0.37

64
Q

M+ 1 for O

A

0.04

65
Q

M+2 for O

A

0.20

66
Q

M+2 for Cl

A

32.5

67
Q

M+2 for Br

A

98.0

68
Q

Effects of rings and double bonds

A

More rings and double bonds means a more stable molecular ion

69
Q

Branching effects

A

More branching equals less stable molecular ion

Because branches are places of weakness and so places for molecules to work

70
Q

Basic instrumentation for mass spectrometry

A

Inlet>source>mass analyzer>detector

Source»detector vacuum (10^-5 - 10^-8)

71
Q

Sources for mass spec.

A
  • gas phase sources: sample volatilizations; then ionization
  • desorption sources: simultaneous volatilization and ionization
72
Q

Sources for mass spec. (Hard and soft)

A
  • hard sources; causes lots of fragmentation

- soft sources; causes little fragmentation

73
Q

Mass analyzers - features of a quadrupole mass analyzer

A
  • rapid scan (50msec/decade)
  • high transmission (good sensitivity)
  • low voltage (0-50 V)
  • no accelerating voltage dependence on trajectory
  • linear mass scan
  • low resolution (R
74
Q

Mass analyzers time of flight mass spectrometer features

A
  • Msec per scan
  • high mass analysis (> 10000 amu)
  • low resolution (R

Quantitative Analysis (2 decks)

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