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Instrumental Analysis > Test 4 > Flashcards

Test 4 Flashcards

1
Q

how does mass spec find mass

A

forms ions, looks at mass to charge ratio and fragmentation (peak height comparison at diff masses

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2
Q

dalton

A

unit of MW. use as = to g/mol

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3
Q

1 AMU is =

A

mass of a proton

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4
Q

MS instrumentation order

A

inlet for sample, ion source (w vaccuum), mass analyzer, detector, processor/readout

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5
Q

vacuum pressure in MS

A

10-5 - 10-8 torr

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6
Q

TOF MS

A

accelerates ions from anode to cathode (detector) w no field, measures TOF (t = l/v)

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7
Q

quadrupole ms

A

4 metal rods, opposite rods have same charge, 2 + and 2 -, alternate between DC and AC. only ions that arent stuck to a side can pass through. can be low pass (light molecules can get through when the AC is applied to the negative rods), high pass (heavy molecules can get through with AC on the pos. rods - they are less moveable) and bandpass by varying these in tandem

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8
Q

double focus (ICP)

A

inductively coupled plasma. higher resolution than single, needs more amplification, uses 2 magnets or a magnet and electric field

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9
Q

single focus (magnetic sector)

A

uses magnetic field, ions move thru curved tube and those that match the curvature (within mass range) are able to exit. resolution limited by rate at which magnetic field can be changed.

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10
Q

ion trap analyzer

A

selects for ions by having heavier ones stay in orbit as radio frequency voltage on encircling electrode increases. to mass spec analyze, as this happens the destabilized species will fall to the detector in order of mass.

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11
Q

KE and m/z eq

A

1/2 mv^2 = zeV, so m/z = 2eVt^2/L^2

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12
Q

centripetal force eq

A

F = BzeV

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13
Q

centrifugal force eq

A

F = mv^2/r

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14
Q

electrospray ionization

A

at atomspheric temp and pressure, sample solvent moves thru needle with induced voltage, becomes charged, then is desolvated and as solvent leaves the analyte can become multiply charged.

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15
Q

m/z for FT MS equation (think for bonus)

A

= eB/2(pi)f

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16
Q

Faradays law in ion trap

A

spinning particle creates field

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17
Q

ICR-FT

A

uses ion cyclotron resonance. no collisions, measures freq of cycle to get the size of particle. directly measures time domain

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18
Q

orbitrap MS

A

type of ion trap with inner and outer electrode, ions spin around the inner part. holds few ions and needs very low pressure, but small and less expensive.

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19
Q

resolution for MS

A

m (avg) / delta m

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20
Q

external inlet system

A

aka batch. gas or liquid heated to 400 degrees, pressure 10-4 - 10-5 torr, moved in thru valve along with solvent gas.

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21
Q

LC and GC coupling with MS

A

inlet system, allows analyte components to enter MS already separated. in GC separating carrier gas from analyte uses jet separator where lighter gas sprays out and sample goes in straight line to inlet

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22
Q

electron impact source

A

bombarding sample with e- to cause ion formation. can cause too much fragmentation of sample

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23
Q

chemical ionization source

A

sample ionized using ions, less fragmentation

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24
Q

field ionization

A

sample gas is moved thru ion source, less fragmentation than chemical

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25
Q

field desorption

A

sample is dipped in electron source. very gentle, minimal fragmentation, can be used on thermally unstable compounds

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26
Q

MALDI

A

matrix assisted laser desorption/ionization. sample is mixed with laser-absorbing substance, this is bombarded w laser and the substance shares e- with the larger molecule sample, ionizing it. (molecules 100-100000 Da).

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27
Q

MALDI-TOF

A

time of flight used to analyze samples ionized via maldi. most common tool for maldi

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28
Q

isotopes changing peaks

A

peaks of isotopes have spec ratios to main molecule, differentiates diff compounds of same mw

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29
Q

eq for isotopic peak ratio

A

n!/(k!(n-k)!)*relative abundance^k (where n is number of that atom in molecule, and k is diff in mw of isotope) (1 1) is = 1. n is truly all possible numbers, must multiply (chance inc when there are more of an atom in a molecule)

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30
Q

product rule of probability for isotopes

A

multiply the ratios for multiple isotopes in 1 molecule

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31
Q

mass spec applications

A

finding structure and mass, amino acid sequence, drug tests, tests for pesticides, archaelogical dating

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32
Q

GC/MS steps

A

separation, fragmentation, detection

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33
Q

tandem MS (MS/MS)

A

first selects for an ion with a minimally fragmented substance passing through, then ionized and fragmented more just that part and mass speced a second time.

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34
Q

chromatography

A

separating mixture using mobile phase and stationary phase, mobile is solvent that parts with analyte based on ratio of affinity for solvent vs the stationary phase

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35
Q

LC and GC mean..

A

the mobile phase is gas or liquid respectively

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36
Q

supercritical fluid

A

dense but compressible like gas. can be used as a mobile phase

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37
Q

chromatogram

A

results for chromatography, signal over time,

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38
Q

how does chromatography fight entropy

A

separation dec entropy so it must be encouraged by washing (dilution) which inc entropy

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39
Q

balance of peak resolution

A

we want narrow and separate peaks, but they widen and separate over time, so must get as narrow as possible while having distinct peaks

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40
Q

distribution constant

A

affinity for stationary phase over affinity for mobile phase (based on c), like rate constant is K.

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41
Q

tm

A

retention time of mobile phase - how fast a substance with no affinity for stationary moves through the column

42
Q

tr

A

total time for eluent to pass thru column

43
Q

solute velocity in column

A

= L/tr

44
Q

retention factor and eqs

A

KVs/Vm = (tr-tm)/tm = k, represents migration rate given a solvent, mobile and stationary phase under any conditions.

45
Q

selectivity factor

A

alpha, always >1, = K (more retained ) /K (less retained)

46
Q

plate height eq

A

H = L/N

47
Q

plate height meaning

A

more plates with less distance = more efficient

48
Q

plate height also =

A

sigma^2/L = W^2L/16t^2r base of peak

49
Q

van deemter eq

A

H = A + B/v + (Cs+Cm)*v, speed has a big impact on this and leads to zone broadening. A represents eddy diffusion, B is longitudinal diffusion, C is mass-transfer coefficients

50
Q

longitudinal diffusion

A

diffusion in either direction of band, messes up resolution

51
Q

resolution for chromatography eq

A

R = sqrt(N)/4 * (a-1)/a * (kb/(kb+1)) OR 2(tr-tr)/W+W

52
Q

plate height for a column w multiple analytes

A

take the average

53
Q

GC advantages and requirements

A

low DL, fast, accurate, good resolution. molecules must be volatile, small, thermally stable

54
Q

GC instrument setup

A

gas source, inlet valve, column (with oven), detector

55
Q

mobile phase in gc

A

carrier gas, doesnt interact. inc. Ar, He, H2, N2, O2, CO2, H2O vapor

56
Q

elution

A

movement of mobile phase along stationary phase via more liquid dilution being added at the top

57
Q

retention time

A

tx, time btwn injection and reaching the detector

58
Q

fast atom bombardment

A

solid or liquid matrix of larger molecules bombarded by charged atoms to ionize them, comparable to CI for fragmentation

59
Q

SCF chromatography

A

mobile phase is supercritical fluid, stationary is organic solid bound to walls

60
Q

GLC

A

gas-liquid chrom. gas mobile phase, liquid bound to solid stationary

61
Q

partition chromatography

A

liquid-liquid (immiscible), stationary attached to wall

62
Q

adsorption chromatography

A

liquid-solid, liquid mobile phase adsorbs to solid

63
Q

ion exchange chromatography

A

type of LC where liquid exchanges ions with the stationary phase

64
Q

affinity chromatography

A

liquid-liquid where the stationary phase is specific to the analyte and is bound to surface

65
Q

flow rate vs H graphs for GC and LC

A

LC has much smaller plate heights bc the L is always smaller, GC has higher speeds and taller plate height bc of this. also GC has more diffusion which contributes

66
Q

capacity factor

A

same as retention factor, (k), he might call it this.

67
Q

GLC stationary phase making

A

diatomeceous earth (Si-rich) mixed with a solvent and the stationary phase, packed and solvent evaporated off to form liquid w/the solid support. may bleed off. OR can do “bonded/crosslinked-phase” where stationary is covalently attached to support = no bleeding.

68
Q
A

,

69
Q

j

A

correction factor. = 3/2 ((Pi/Po)^2)-1)/((Pi/Po)^3-1)

70
Q

Po

A

outlet pressure

71
Q

Pi

A

inlet pressure. always > outlet.

72
Q

Pw

A

vapor pressure of water in column

73
Q

temperature in GC calcs

A

always convert to K

74
Q

average flow rate eq

A

F = j(Fo)(Tc/To)((Po-Pw)/Po). SAME EQ for v and corrected v (soap bubble meter)

75
Q

Vg and eq

A

specific retention volume; retention volume per gram of the stationary phase. Vg = (Vr-Vm)/ms * 273/Tc =KVs/ms * 273/Tc

76
Q

head pressure (Pg)

A

diff btwn Po and Pi

77
Q

column support types

A

packed column - large capacity, used for prep work. capillary (open) is faster, for analytical use, smaller sample sizes.

78
Q

temperature programming

A

changing temp linear or in increments at spec times to improve resolution

79
Q

Flame ionization detectors

A

destructive, mostly detects C. ions generate current. 10^7 linear range, low noise, not impacted by flow rate

80
Q

NP / thermoionic detectors

A

only useful for N and P but really good for pesticide eval bc of this. (basically FID)

81
Q

e- capture detectors

A

selective for halogens, nitro, conjugated, sulfur. highly sensitive, non-destructive, but 10^2 linear range. based on radioactive decay. detects e- from ions created by radioactive part, when they are interrupted by electronegative elements from the sample that change is detected.

82
Q

atomic emission detectors

A

element-selective detectors, work well, good ranges, but destructive and expensive

83
Q

peak area eq

A

A = k(amt) = kCFt, k is response factor, Ft = volume

84
Q

GSC

A

gas-solid chromatography. not as often used bc it is actual adsorption not dissolution, harder to abstract ions and polar molecules from solid. peaks become non symmetrical. work well for permanent gases, geometrical isomers

85
Q

soap bubble flowmeter

A

shows gas vol thru soap membrane moving up measurement

86
Q

Thermal conductivity detectors (GC)

A

10^5 linear range, non-destructive, work for organic and inorganic, but bad sensitivity (10-7). change in thermal conductivity btwn mobile phase and solute generates current. cannot use H2, sensitive to flow rate

87
Q

Flame photometric detectors GC

A

S and P detecting, but have worse DL and range than sulfur chemiluminescence detector for S, destructive.

88
Q

carrier gas impacts on measurement

A

MW of gas (lower causes larger diffusion, higher is better separations), detector-specific gases needed, stability of other things in the column (H2 or O2 might react with them

89
Q

eddy diffusion

A

molecules reach detector at diff times due to taking diff paths thru a packed column

90
Q

eluent

A

the mobile phase added to move the analyte

91
Q

zone broadening causes

A

large stationary phase particles, high temps, very fast or slow elution, thick stationary phase, large column diameter

92
Q

B variable in MS

A

magnetic field strength, Teslas

93
Q

mass for MS (in all eq)

A

use kg!!

94
Q

Resolution and N for chrom.

A

R1/R2 = sqrt(N1/N2)

95
Q

retention volume

A

trflow rate, for “corrected” do j(tr)F

96
Q

signal averaging rules

A

add up signals and get (n)S + sqrt(n)e, take average of the same signal and get S + e/sqrt(n)

97
Q

single beam vs double beam

A

single is 2 measurements (1 blank) double is simultaneous,uses beamsplitter or mirror.

98
Q

mass analyzers

A

all the components ie ion trap, quadrupole, TOF etc.

99
Q

why is the sky blue

A

Rayleigh scattering

100
Q

std dev from s/n

A

multiply 1/S by 0.434

Instrumental Analysis (4 decks)

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