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Instrumental Analysis > Test 3 > Flashcards

Test 3 Flashcards

1
Q

time spectrum vs space spectrum

A

both can be described by a frequency which corresponds to a wavelength of photons, and a specific amplitude also correlated to that wavelength. difference: time is expressed as a function of time, space uses a function of retardation as a measure of space, and time domain can be described by a higher frequency and therefore shorter tau than space domain

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2
Q

time domain vs frequency domain

A

can encode non electrical domain information (like number), belong to electrical domains and the time domain. differences: intensity as a function of time vs intensity as a function of frequency. and freq domain can be gotten from dispersive spectrometry but time cannot

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3
Q

inferogram time frequency for michelson interferometer (xray)

A

2(vm)/lambda aka 2(vm)v/c where vm is velocity of mirror

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4
Q

what does michelson inferometer measure directly in spectrophotometry

A

space measurement

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5
Q

retardation =

A

(delta) = 2(mirror drive distance)

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6
Q

tau

A

time for a freq (= 1/f)

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7
Q

delta and wavenumber in FTIR

A

every delta in space spectrum contains info for every wavenumber and vice versa

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8
Q

fourier transformation

A

info goes from space domain to frequency domain

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9
Q

resolution for FTIR eq

A

improves with inverse delta

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10
Q

overtones

A

first overtone = 2 and so on, just multiply eq by that number because we’re fools

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11
Q

time domain graph

A

x axis has time, with 0 at the center

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12
Q

FTIR advantages

A

high S/N (very fast), accurate, precise, source reaches detector in one pulse, “high throughput” (fast)

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13
Q

IR applications

A

qualitative distinction of functional groups and id of molecules, quantitative things like BAC and conc similarly based on intensity of peaks

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14
Q

Raman scattering

A

inelastic. has a delta E bc delta E = h(v1 - v2) and v1 and v2 are not equal due to vibration. Has antistokes and stokes lines at specific distance from the rayleigh line for specific species. polarizability (alpha) changes because distance btwn molecules changes.

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15
Q

Compton scattering

A

longer wavelengths due to energy lost in ionization (as opposed to vibration)

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16
Q

photoionization

A

adding radiation to species to induce ionization

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17
Q

Rayleigh scattering

A

the vast majority of scattering. elastic, v1 = v2

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18
Q

remember wavelength to freq conversion

A

c = v(lamba)

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19
Q

boltzmann eq

A

ratio of excited:ground state = e^(-deltaE/kT), T must be in K

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20
Q

Raman vs IR

A

based on polarizability vs change in dipole, quadratic eqs on character table vs translational symbols, IR has transition to eigenstate while raman goes to a virtual state. both measure light and matter interaction and molecular vibrations. the interactions differ (vibration vs scattering), IR transition is from ground to some excitation while Raman is from virtual state to ground.

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21
Q

stokes and anti-stokes magnitude

A

stokes have much larger magnitude than anti-stokes, the ratio is temp-dependent (Boltzmann eq) and magnitude is also based on the power of the excitation radiation

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22
Q

typical raman spectrum lines

A

only stokes lines usually

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23
Q

Raman wavelengths overlap with other processes

A

far from absorbance but often stokes overlap with fluorescence

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24
Q

Raman intensity eq

A

varies with source freq^4, also varies with concentration

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25
Q

raman original experiment setup

A

sun, lenses, blue-violet filter, sample, yellow-green filter, observer (at 90 degrees)

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26
Q

Raman equipment setup

A

laser source, sample, selector, detector (can be 180 or 90 degrees). usually HeNe laser

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27
Q

minimizing fluorescence interference with Raman

A

use FT instrument

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28
Q

FTIR vs FTRaman spec

A

both use michelson inferometer and give qualitative info on functional groups, energy for Raman is Excitation - deltaV where IR is just the delta V, and setup for Raman is more complex than IR also Raman sample is at 90 while IR is at 180

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29
Q

Raman advantages over IR for quantitation

A

water interferes with it less, machines are more compact for field work

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30
Q

Raman intensity eq

A

Ir = kv(Iex)C - slope, varies with excitation intensity

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31
Q

polarizability for Raman to be scattering produced

A

alpha varies based on r (distance btwn atoms)

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32
Q

temp change of stokes vs antistokes

A

stokes - heating, anti-stokes = cooling (vibrations need to release or get energy somehow)

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33
Q

lasers for Raman

A

HeNe is less likely to produce fluorescence than Ar or Kr (these are higher energy), diode lasers are better than elemental to have high power with low interference from fluorescence. near-IR (Nd:YAG) used for FTRaman, high power again but cannot make e- transitions happen

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34
Q

lifetime of virtual state/Raman

A

1x10^-15 seconds

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35
Q

SERS

A

surface enhanced Raman spec. detects for molecules adsorbed to a surface, can be as sensitive as fluorescence due to enhancement of the EM waves by the metal.

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36
Q

atomic spectroscopy applications

A

lead detection, shifting of celestial bodies based on composition and red shift

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37
Q

the sun emits..

A

black body radiation

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38
Q

transition rules**

A

delta S = 0, delta L = 0 or +-1, delta I = +-1, delta J = 0 or +-1 (most of these are angular momentum), spin is S

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39
Q

singlet excited state

A

e- are in diff levels but still have opposite spins

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40
Q

triplet state value

A

is +- 1 until change occurs bc split could be resolved by move of either e- in the system (diff levels, same spin)

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41
Q

why cant triplet be in ground state

A

pauli exclusion principle - no same spins in 1 orbital

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42
Q

how is atomic spectra generated (atom)

A

outermost e- specifically homo-lumo gap unique to each element

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43
Q

thermal excitation

A

spark, heat (non radiative energy) can be added causing excitation and emission of radiation. this is why elements have spec colors in flame

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44
Q

boltzmann eq for atomic spectra

A

excited/ground = (Pj/Po) e^(-deltaE/kT) where P are number of electrons that go in higher energy over the lower energy orbital

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45
Q

why is atomic line width so thin

A

no vibrations to interfere

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46
Q

atomic line is broadened by…

A

uncertainty, doppler effect, high pressure, electrical and magnetic fields

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47
Q

heisenberg uncertainty energy and time eq

A

delta v * delta t greater than or = 1

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48
Q

delta t in atomic spec

A

lifetime of the excited state

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49
Q

derived eq for heisenberg uncertainty calc

A

delta lamba = lamba^2*deltav/c

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50
Q

think about derivatives. c/x

A

-c/x^2

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51
Q

doppler effect and eq

A

wavelength inc as object moves away, dec as it approaches. observed freq = (c + observer v)/(c+source v) (actual freq)

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52
Q

doppler broadens atomic lines eq

A

due to deviation in wavelength. change/initial = v/c where v is relative velocity of object

53
Q

thermal doppler broadening calculation

A

maxwell distribution (we dont do this)

54
Q

high pressure broadening why

A

more atomic collisions

55
Q

stark effect

A

electric field broadening

56
Q

zeeman effect

A

magnetic field broadening (due to e- energy levels splitting)

57
Q

temp and atomic spectra

A

as shown in boltzmann eq, it excites. so constant temp is important for these measurements.

58
Q

UV vs IR

A

UV has noise in the radiation source, IR has it in the detector

59
Q

resolution for inferometer

A

delta wavenumber = 1/delta

60
Q

1 angstrom

A

0.1 nm

61
Q

why is emission effected by temp change more than fluor or absorbance

A

the pop measured is excited state where for the others it is ground state, temp changes the fraction that are excited which really impacts emission but it is still a tiny proportion compared to ground for fluor and abs.

62
Q

three types of atomic spectroscopy

A

emission, fluorescence, absorbance

63
Q

atomization

A

sample is turned into atomic vapor, very crucial for error (causes the error in the process for the most part)

64
Q

continuous vs discrete atomizers

A

continuous is often nebulizer feeding soln into plasma or flame= steady population of excited atoms, while discrete is a specific amt of sample in chamber being atomized, such as electrothermal atomizer

65
Q

higher temperature in atomization can cause..

A

more ions in sample

66
Q

flame atomization

A

used for atomic spec of gases, sample is misted to the flame, and this yields atoms, molecules and ions

67
Q

flame hot zone

A

above the primary combustion zone

68
Q

highest temperature atomization method

A

electric spark (40000)

69
Q

glow discharge device

A

introduces and atomizes sample. low voltage is applied to argon in chamber with cathode coated in sample, these molecules are sputtered and some are excited, leading to glow (sample emission).

70
Q

electrothermal atomizers

A

milliseconds, high temp 2000-3000. temp increases from low for evaporation, ashing, and then inc. of current rises temp rapidly to atomize

71
Q

plasma

A

electrically conducting gas phase with lots of cations and e-, up to 10000 K

72
Q

types of plasma sources

A

ICP (inductively coupled), microwave induced, direct current

73
Q

getting atomization from solid sample

A

high voltage electric spark

74
Q

electrodeless discharge lamp sources

A

magnitudes more intense lines than hollow cathode, but need different lamp for each element

75
Q

two line correction method

A

source reference line close to analyte line but not absorbed by analyte, should be constant to correct for matrix interference

76
Q

continuum source background correction

A

deuterium and hollow cathode lamps alternate, deuterium giving background noise and hc the total signal, the computer subtracts these.

77
Q

Zeeman effect correction

A

atomic lines split by tiny portion of nm due to magnetic field splitting, this can be used to combat background interference. source can be split.

78
Q

chemical interference

A

formation of compounds of low volatility, ionization, dissociation during the atomization process. leads to diff analyte properties.

79
Q

combating compounds of low volatility

A

releasing agents or high temps

80
Q

internal standard

A

adding same amount of another species to each standard addition sample that contains sample, this will also have a response we can measure, and the ratio of unknown/internal standard will be constant to combat fluctuations

81
Q

calcs with internal standard

A

ratio of unknown/standard is the signal

82
Q

x-ray source range

A

0.1-25 A

83
Q

types of x-ray spectroscopy

A

fluorescence, absorbance, diffraction, photoelectron spectroscopy

84
Q

eq for thickness of sample in x-ray

A

ln(Po/P)=mu(x) where mu is linear abs. coefficient and x is thickness, OR ln(Po/P)=mu(density)x where mu is “mass absorption coefficient” (cm^2/g)

85
Q

bragg’s law

A

for x ray diffraction scattered rays. n(lambda)=2dsin(theta) where d is distance btwn atomic layers

86
Q

karat

A

purity measure (gold), 24 = 100%

87
Q

carat

A

weight measure (diamonds), 1C=200mg

88
Q

Geissler

A

discovers x-ray with his tube

89
Q

1st picture

A

using x-ray, roentgens wife’s hand

90
Q

Siegbahn

A

relates x ray to atomic structure > boom, analysis

91
Q

Siegbahn notation

A

shows how e- jump btwn orbitals = K and L series for p and d orbitals

92
Q

x-ray instrumentation steps

A

source, selector (can be crystal diffraction), sample, detector, processor and readout

93
Q

x-ray sources

A

tubes, secondary fluorescent x-rays, radioisotopes, synchotron radiation

94
Q

cyclotron sources

A

EM radiation can be generated when charged particles are accelerated radially = synchotron radiation (ie CERN)

95
Q

short wavelength limit (eq)/duane-hunt law

A

Ve = hc/lambda, so lambda (in A) = 12,398/voltage

96
Q

x-ray detector types

A

gas-filled transducer, scintillation counters, semiconductors, film

97
Q

scintillation detector

A

NaI crystal (often) fluoresces when hit with radiation from sample. pmt counts the light

98
Q

semiconductor x ray detector

A

energy dispersive, multiple layers to disturb e- and carry signal to amplifyer

99
Q

calculating mass absorption coefficient for a compound

A

%element*mass abs coefficient

100
Q

releasing agent

A

cations that bond to atoms that would otherwise form non-volatile complexes with the analyte, preventing analysis

101
Q

protective agents

A

form volatile compounds with the analyte so it can be measured in spite of the presence of other spp

102
Q

ionization suppressors

A

reduce ionization by providing a source of e- so the species will go back to elemental form

103
Q

hollow-cathode lamp

A

most common AAS source. light is produced by metal atoms that have been excited by inert gas from electrical stimulation

104
Q

sputtering

A

process within hollow cathode lamp where the metal produces an atomic cloud

105
Q

self-absorption

A

process in hollow-cathode lamp where unexcited sputtered atoms absorb the radiation from excited atoms (this radiation is now not reaching the sample)

106
Q

spectral interference

A

very close interference that cannot be resolved with the peak of the analyte

107
Q

radiation buffer

A

when some of an interfering substance is present, this is adding a bunch of it so that the presence of that small interference becomes insignificant. This measurement can be controlled for.

108
Q

solute-volatilization interference

A

changes in solute volatility based on presence or absence of another species.

109
Q

source modulation

A

the source output is modulated periodically (ie with a chopper) to eliminate interference from the portion of the flame light that is at the same wavelength as the result we want to measure

110
Q

plasma advantages over flame

A

high temp, versatile for many elements at just 1 temp setting while flame must be adjusted, works for very low conc of compounds that can take high heat and form refractory compounds, and works for nonmetals, also doesnt ionize much bc of the e- in the plasma

111
Q

arc vs spark spectra

A

arc is low temp (4000) and has atomic lines, spark is very high (40000) and has ionic lines

112
Q

sequential vs simultaneous multichannel

A

sequential can only measure 1 sample accurately in short time, must do one at a time, simultaneous takes that amt of time to do many many samples.

113
Q

energy dispersive x-ray fluorescence spectroscopy

A

uses multi-channel detector, measures radiation of diff spp using monochromator (DCC) before sample. worse resolution than WD.

114
Q

wavelength dispersive x-ray fluorescence spectroscopy

A

has 2 DCCs (before and after sample), focuses to spec wavelength. leads to higher resolution

115
Q

DCC

A

doubly curved crystal, monochromator for x-ray spec

116
Q

applications of ED-XRF and WD-XRF

A

ED for things in space bc it is more compact and the readings are still workable, WD for biological detection bc it works so well

117
Q

hkl in problems

A

given as peak XXX (hkl)

118
Q

extended x-ray absorption fine structure

A

tells configuration of atoms

119
Q

x-ray absorption near edge structure

A

probes oxidation state (valence)

120
Q

gas filled transducer

A

x-ray detection method where when gas is ionized by x-rays it conducts`

121
Q

semiconductor x ray detectors

A

are electric. can use CCD (charge coupled) or lithium-drifted silicon

122
Q

eq for lattice edge length

A

d = a/sqrt(h^2+k^2+l^2). a is lattice constant = cube edge length

123
Q

natural width of atomic emission line

A

10^-5 nm (only due to uncertainty principle)

124
Q

excitation for as

A

for flour it is wavelength, for AES it is thermal

125
Q

k and l emission lines

A

When an electron beam source collides with atoms in a sample, the incoming electron is decelerated and X-ray
energy is produced. Only atomic number atoms larger than 23 produce K and L emission lines; smaller ones
produce only the K series. K series spectral lines are produced when the high-energy electrons from the
cathode remove electrons from those orbitals nearest the nucleus of the target atom. As the outer orbital
electrons relax to replace the missing electron, X-ray radiation is given off. L series lines come when the
electron initially lost is from the second principal quantum level orbital.

126
Q

working with mass coefficients for x ray

A

can add them to use the weight fraction of a molecule ie double it for % of N2, calculate u for a solvent like ethanol by adding the weight % and u of each (meta-math)

127
Q

atomic emission vs atomic fluor

A

Similarities: Both use wavelength selectors after sample; line widths from broadening effects; quantitatively determine elemental intensity; photon generated during excited -> ground state transition
AES: ICP/flame/etc. thermally excites the sample; more popular than AFS
AFS: wavelength source for excitation; smaller useful concentration range, but for some elements like Hg lower LODs can be determined; measured at 90° from source path; for environmental samples; lamp sources

128
Q

for x ray crystal edge questions

A

dont forget it’s VOLUME!!

Instrumental Analysis (4 decks)

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