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Instrumental Analysis > Test 2 > Flashcards

Test 2 Flashcards

1
Q

sig figs for 5

A

(any integer) 0

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2
Q

T eq

A

P/Po

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3
Q

A eq (not beers law)

A

A = -logT OR log(P0/P)

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4
Q

rule for log sig figs

A

log(x) = 1.x

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5
Q

P

A

Watts/cm^2

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6
Q

molar absorptivity units

A

1/cm*M

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7
Q

chemical deviations from beers law

A

epsilon changes for indicator reactions, intermolecular complexes created due to high conc

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8
Q

pKa

A

can give you Ka for ratio

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9
Q

instrumental deviation from beers law

A

stray light or polychromatic light

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10
Q

stray light eq and info

A

more stray decreases signal (A), A= log ((Po + Ps)/(P + Ps))

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11
Q

polychromatic light deviation

A

can be up or down from linear, add the initial powers of light over the other powers of both for T

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12
Q

light sources

A

H/D lamps visible light, Xenon peaks at 500 nm, W goes up to 2500 nm

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13
Q

Noise sources for spectrometer

A

source, absorption, intensity loss from wavelength selection, photoelectric transducer noise (all propagate)

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14
Q

silicon photodiode

A

silicon chip with a depleted layer (pn junction) that radiation can enter and go to the electrodes. used for low radiation, portable. more sensitive than a phototube but less than a photomultiplier tube

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15
Q

CCD vs multichannel photon detectors

A

CCD is 2d (grid is scanned) while multichannel is 1D (rows in a line)

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16
Q

double beam reduces..

A

fluctuation, deviation from source wavelength (simultaneous)

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17
Q

photodiode array

A

double beam, fast response (good for kinetics). multiple photodiodes form an array and circuit. they act as pixels, 1000ish together does the whole spectrum very quickly (simultaneously)

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18
Q

I and Io

A

dependent for double beam, independent for single beam

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19
Q

dependent values prop of error for A

A

A = log Io - log I

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20
Q

error in single and double beam

A

error compounds for single beam, it cancels to 0 for double

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21
Q

error canceling equation

A

sigmaA^2 = sigma(logIo)^2 + sigma(logI)^2 - 2sigma(ab) using the errors

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22
Q

error through spectrometry equation

A

Sf = Ilamp* L* Sample * Spt

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23
Q

calculating molar absorptivity

A

8.7x10^19(P)(A) where P is transitional probability (0-1), A is target cross sectional area for photon of whatever wavelength to interact with, around 10^-15 cm^2 for organic molecules

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24
Q

quantum jump

A

e- changing energy levels. prob determined by transitional prob, below 0.01 not happening, 0.1to 1ok

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25
Q

solvent effects

A

can make peaks more diffuse due to strong solvent interactions

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26
Q

why is absorption good for quantitative analysis

A

widely applicable, sensitive (10^-4-10^-7 M), fairly selective, 1-3% uncertainty, easy to do.

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27
Q

method for spectrometry

A

find lamba max, look at variables: solvent, pH, temp, electrolytes, interfering species, then clean cell before using

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28
Q

standard addition use

A

reduces matrix effects

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29
Q

standard addition procedure

A

usually 5 replicates, know volume and the amount of standard added to learn the initial concentration

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30
Q

beers law graph SHOULD

A

pass through 0

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31
Q

sig figs for error

A

should match the # for the value

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32
Q

deuterium vs hydrogen lamps

A

continuum, UV. deuterium creates a more intense light

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33
Q

filter vs monochromator

A

filters are cheaper and retain intensity, but are specific to a wavelength. monochromators can be adjusted but leads to a drop in intensity and more costly

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34
Q

photovoltaic cells

A

visible light range, common. copper or iron with semiconductor layer, and gold or silver outside that which e- liberated at semiconductor Flow through so current tells us # of e-. cheap, but low resistance and fatigue (current dec during continued use)

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35
Q

phototubes

A

resistance is high so they can amplify. voltage of e- goes through wires to anode, when saturated the amount of current corresponds to light intensity. made for many ranges of light nm

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36
Q

photomultiplier tube

A

light hits a small area and disturbs e- which disturb surrounding e- in the material, amplifying the signal.con: cannot take intense light

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37
Q

time vs space double beam

A

time needs 1 detector, space needs 2

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38
Q

photometers vs spectrophotometers

A

photometers use filters, spectro use monochromators

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39
Q

multichannel spectrophotometers

A

very fast, use electronic rather than manual scanning

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40
Q

titration stages

A

in A + T gives P, at start all A, then A + P, then all P at endpoint and past endpoint T + P

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41
Q

inconsistencies with Einsteins calculations

A

atoms do not necessarily start with all atoms at ground state

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42
Q

eigenstate

A

value for an e- at which it can exist, only has specific quantities (stable)

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43
Q

scattering

A

energy goes in and instantly leaves

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44
Q

stimulated emission

A

light enters and emission occurs

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45
Q

virtue states

A

unstable values at which an e- can exist (leads to scattering)

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46
Q

phosphorescence is when..

A

singlet state moves to triplet.

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47
Q

singlet state

A

all e- paired, no split orbitals on magnetic contact (diamagnetic)

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48
Q

diamagnetic

A

0 net magnetic field, e- are stably repelled by their respective fields

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49
Q

paramagnetic

A

moment of attraction w magnetic field due to unpaired e-

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50
Q

spin multiplicity =

A

2S +1 (for e- of same spin)

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51
Q

triplet state

A

e- unpaired, spin multiplicity, more stable than singlet even when excited

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52
Q

delta S =

A

0 (magnetic QNs should add to 0)

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53
Q

lines on Jablonski diagram are..

A

Eigenstates

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54
Q

internal conversion

A

molecule dec energy state by intramolecular processes

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55
Q

singlet vs triplet radiation

A

singlet is very short(<10-5 s) triplet is longer (10-5 to full seconds)

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56
Q

fluorescence vs phosphorescence

A

f has high quantum yield, can work in most temperatures and 0 e- spin and singlet-singlet transition shorter than 10-5 sec, p has low quantum yield at low temp and +/-1 e- spin, singlet state moves to triplet (longer than 10-5 sec).

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57
Q

stokes shift measurement

A

distance between the max values for absorbance and emission

58
Q

quantum yield

A

luminescent molecules/# total excited molecules

59
Q

quantum yield approaches 0 as..

A

radiationless decay rate is much smaller than radioactive decay

60
Q

power of fluorescence eq

A

F =K’ (Io-I), K is related to QY, transforms to If = K’Io(1-10^-Ebc), if Ebc < 0.05, linear version If = logK’IoEbvc…. therefore Io inc fluorescence.

61
Q

T vs A

A

T is multiplied as more parts are added, A is additive

62
Q

external conversion

A

molecule dec energy state by intermolecular processes

63
Q

intersystem crossing

A

energy level change causes a change in electron spin, which changes multiplicity (usually triplet to singlet) but has a very similar energy

64
Q

excitation graph spectrum

A

one wavelength of emission shows peak at a wavelength of input(x axis is diff input wavelengths)

65
Q

rigidity and fluorescence

A

more rigid = higher quantum yield, more fluorescence

66
Q

power of fluorescence covaries with

A

K (includes quantum yield, emission lambda, initial intensity (from excitation lambda), b, a constant), and conc.

67
Q

for better linear shape, this level of conc is best

A

LOWER (for luminescence)

68
Q

excitation spectrum uses

A

constant emission wavelength (they only look at one wavelength and how emission there changes as the excitation beam takes on different wavelengths)

69
Q

emission spectrum uses

A

constant excitation wavelength

70
Q

phosphorescence vs fluor energy

A

for the same (natural) molecule, lower energy and quantum yield

71
Q

fluorophotometer equipment setup

A

excitation monochromator, emission monochromator, can be sequential or double. can also be filters

72
Q

phosphorescence detector setup

A

excite radiation, chopper blocks light from hitting sample while it fluoresces, then detector gets phosphorescence

73
Q

measured variable in fluorometry

A

always emission

74
Q

sensors and fluorescence

A

have smth that binds to species of interest and then fluoresces

75
Q

chemiluminescence

A

luminescence from product of a reaction (emits when produced due to energy, no excitation is needed)

76
Q

fluorescence applications

A

detects GFP! can have fluorescent binding to DNA etc to detect it

77
Q

laser

A

light amplification by stimulated emission of radiation

78
Q

energy conservation for laser

A

must put in energy to get energy

79
Q

spontaneous emission examples

A

fluorescence and phosphorescence. they emit right after they have input

80
Q

stimulated emission

A

used in lasers, e- must be excited and get an additional input to give off twice the excitation beam w energy conserved

81
Q

metastable excited state

A

this is needed for a laser. population inversion allows the excited state to have a constant population (it is changing but there are always a similar number)

82
Q

parts for laser

A

power supply, pumping source, mirrors on both ends, lasing medium in middle

83
Q

pumping

A

excitation of the lasing medium (can be electric, heat, chemical)

84
Q

how does laser create coherent radiation

A

photon hits excited e- on lasing medium > 2 photons in phase with one another are produced

85
Q

absorption in laser

A

when non excited molecules pick up a photon and become excited, this competes with stimulated emission (takes photons from the source/previous emissions)

86
Q

wavelength amplified by laser is determined by

A

the cavity size

87
Q

population inversion

A

majority of molecules are excited (not ground state) and thus can emit coherent photons. required to sustain laser beam

88
Q

4 level laser

A

has 2 intermediate energy levels, one at which no e- can stay and a higher one that must be reached for pop. inversion, but the number only needs to be higher than the number in that transient state (0). so it is easier to sustain inversion, more widely used

89
Q

3 level laser

A

for pop inversion you need to have more in the intermediate than ground state and so many molecules are ground state that it is harder to achieve this

90
Q

first laser

A

solid state, ruby

91
Q

gas laser types

A

neutral atom, ion, molecular (gases like N2), eximer

92
Q

eximer laser

A

ion complex of a normal ion and a noble gas that is only stable when excited, this makes inversion very easy (any amount of pumping)

93
Q

solid vs gas lasers

A

solid lasers can be much more compact

94
Q

IR setup

A

same as absorbance, just reports in wavenumber

95
Q

IR given off by (in graphical form)..

A

the vibrational relaxation in Jablonski diagram

96
Q

how to tell if IR active

A

FIRST draw molecular shape. dipole must change (not net 0)

97
Q

selection rule - vibration

A

IR absorption occurs when there is vibration bc the emission matches the vibration and it is able to absorb (changes amplitude) so it wont absorb without a dipole change (IR active vibration)

98
Q

dipole moment eq

A

mu = qR, mu = dipole moment, q = charge, R = distance, so if distance changes non symmetrically it will change.

99
Q

frequency with force constant

A

f= 1/2pi sqrt(k/mu)

100
Q

wave number eq

A

v = 1/2pi(c) sqrt(k/mu)

101
Q

k (force/strength) and carbon-carbon bonds

A

high for single, drops for double, climbs a bit for triple

102
Q

v

A

the vibrational qn, can be 0 or more

103
Q

fundamental transition

A

moving 1 energy level (deltaV=1)

104
Q

anharmonic oscillators

A

transition plus of minus 2 or 3 = create overtones

105
Q

transition selection rule

A

only 1 peak for a molecular vibration due to energy level spacing (normal modes of harmonic are +/-1)

106
Q

normal modes for polyatomic molecule

A

3N-6

107
Q

normal modes for linear

A

3N -5

108
Q

vibrational coupling

A

an atom btwn two stretching bonds or bond btwn two atoms involved in bending or connecting 2 different motions couples the vibrations. must be close together and fairly close in energy - one peak (i think)

109
Q

IR radiation sources

A

inert solid heated up

110
Q

IR detectors

A

thermal, pyroelectric, photoconducting

111
Q

new tech in IR

A

lamp is also the wavelength selector

112
Q

fourier transform spectrometer

A

source > sample > selector > detector but all surrounded with mirrors, one moves and changes the lambda when needed. not dispersive, a lot of light reaches the detector. high resolution (you can see every tiny peak), and most importantly can read whole spectrum VERY FAST so potential S/N can be tiny. also records in time domain so graph is the wave of the radiation

113
Q

michelson interferometer

A

transducer in fourier spectroscopy, time domain to space domain, measures interference in time domain and modulates signal to be read in space bc it is usually too high freq and space is lower.

114
Q

quantum vibration eq (Energy)

A

E = (v+ (1/2)) (h/2(pi))sqrt(k/mu) where v is the qn.

115
Q

thermal IR detector

A

heats up, susceptible to thermal noise

116
Q

pyroelectric IR detector

A

dielectric materials have thermal and electrical effects. change in conductivity when radiation hits them. very fast

117
Q

photoconductor IR detector

A

absorbs radiation in non-conducting e- which become conducting, decreasing resistance in unit when radiation is detected

118
Q

dispersive IR spectrophotometers

A

usually have a chopper to discriminate noise, but same design as spectrophotometers

119
Q

mirror drive resolution eq for FTIR

A

delta v (diff btwn wavenumbers) = 1/delta , where delta is the retardation = 2x distance of mirror drive

120
Q

predissociation

A

an internal conversion releases vibrational energy large enough to break a bond, more likely in larger molecules

121
Q

dissociation

A

absorbed radiation excites an e- to a high enough energy level that a bond is broken

122
Q

why is fluorescence better that absorbance in detection

A

only intensity of source light can be inc and the measurement of intensity will inc for fluoro. for spectrophotometry since there is P and Po the ratio cannot be changed as much (= just light from a source vs being forced to measure transmission

123
Q

pi vs other transitions

A

n = non-bonding, pi = pi orbitals, sigma = sigma orbitals. so sigma sigma* is excitation of a single bond (out of UVVIS range), n to pi* is less energetic than pi to pi* (shorter distance), so the double bond is favored for more fluorescence compared to non bonding e- in same process.

124
Q

FTIR spectrometry is better for…

A

resolution, high absorption spp, weak absorption spp, kinetics (it is very fast), very small samples, IR emitting samples

125
Q

how to do refractive index

A

it is a percent transmittance basically, so multiplicative. %lost = og(n1-n2/n1+n2)^2

126
Q

retardation in FTIR

A

retardation (delta) = 2(movable mirror-fixed)

127
Q

mirror drive distance FTIR

A

1/delta = wavenumber, distance = delta/2

128
Q

inferogram time frequency for michelson interferometer

A

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

129
Q

tau in michelson interferometry

A

time for a wave, 1/f

130
Q

what is the fourier transformation

A

spatial information converting to frequency

131
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

132
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

133
Q

wagging

A

ligand moves out of the plane towards viewer

134
Q

scissoring

A

in non linear, central moves down and sides move up/out (2 bending vibrations)/ligands bend in opposite directions

135
Q

vm and tau

A

vm*tau = lamba/2

136
Q

twisting

A

one ligand moves into the plane the other out

137
Q

rocking

A

ligands bend (2 bonds attached to 1 A) in same direction

138
Q

laser eq

A

lambda = 2L/n where L is cavity length

139
Q

std dev for measurements eq

A

the RSD based on S/N (= 1/S/N) times 0.434 = std deviation

140
Q

reduced mass (mu)

A

m1*m2/(m1+m2) < all in kg.

Instrumental Analysis (4 decks)

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