Test 4 Flashcards
how does mass spec find mass
forms ions, looks at mass to charge ratio and fragmentation (peak height comparison at diff masses
dalton
unit of MW. use as = to g/mol
1 AMU is =
mass of a proton
MS instrumentation order
inlet for sample, ion source (w vaccuum), mass analyzer, detector, processor/readout
vacuum pressure in MS
10-5 - 10-8 torr
TOF MS
accelerates ions from anode to cathode (detector) w no field, measures TOF (t = l/v)
quadrupole ms
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
double focus (ICP)
inductively coupled plasma. higher resolution than single, needs more amplification, uses 2 magnets or a magnet and electric field
single focus (magnetic sector)
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.
ion trap analyzer
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.
KE and m/z eq
1/2 mv^2 = zeV, so m/z = 2eVt^2/L^2
centripetal force eq
F = BzeV
centrifugal force eq
F = mv^2/r
electrospray ionization
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.
m/z for FT MS equation (think for bonus)
= eB/2(pi)f
Faradays law in ion trap
spinning particle creates field
ICR-FT
uses ion cyclotron resonance. no collisions, measures freq of cycle to get the size of particle. directly measures time domain
orbitrap MS
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.
resolution for MS
m (avg) / delta m
external inlet system
aka batch. gas or liquid heated to 400 degrees, pressure 10-4 - 10-5 torr, moved in thru valve along with solvent gas.
LC and GC coupling with MS
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
electron impact source
bombarding sample with e- to cause ion formation. can cause too much fragmentation of sample
chemical ionization source
sample ionized using ions, less fragmentation
field ionization
sample gas is moved thru ion source, less fragmentation than chemical
field desorption
sample is dipped in electron source. very gentle, minimal fragmentation, can be used on thermally unstable compounds
MALDI
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).
MALDI-TOF
time of flight used to analyze samples ionized via maldi. most common tool for maldi
isotopes changing peaks
peaks of isotopes have spec ratios to main molecule, differentiates diff compounds of same mw
eq for isotopic peak ratio
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)
product rule of probability for isotopes
multiply the ratios for multiple isotopes in 1 molecule
mass spec applications
finding structure and mass, amino acid sequence, drug tests, tests for pesticides, archaelogical dating
GC/MS steps
separation, fragmentation, detection
tandem MS (MS/MS)
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.
chromatography
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
LC and GC mean..
the mobile phase is gas or liquid respectively
supercritical fluid
dense but compressible like gas. can be used as a mobile phase
chromatogram
results for chromatography, signal over time,
how does chromatography fight entropy
separation dec entropy so it must be encouraged by washing (dilution) which inc entropy
balance of peak resolution
we want narrow and separate peaks, but they widen and separate over time, so must get as narrow as possible while having distinct peaks
distribution constant
affinity for stationary phase over affinity for mobile phase (based on c), like rate constant is K.
tm
retention time of mobile phase - how fast a substance with no affinity for stationary moves through the column
tr
total time for eluent to pass thru column
solute velocity in column
= L/tr
retention factor and eqs
KVs/Vm = (tr-tm)/tm = k, represents migration rate given a solvent, mobile and stationary phase under any conditions.
selectivity factor
alpha, always >1, = K (more retained ) /K (less retained)
plate height eq
H = L/N
plate height meaning
more plates with less distance = more efficient
plate height also =
sigma^2/L = W^2L/16t^2r base of peak
van deemter eq
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
longitudinal diffusion
diffusion in either direction of band, messes up resolution
resolution for chromatography eq
R = sqrt(N)/4 * (a-1)/a * (kb/(kb+1)) OR 2(tr-tr)/W+W
plate height for a column w multiple analytes
take the average
GC advantages and requirements
low DL, fast, accurate, good resolution. molecules must be volatile, small, thermally stable
GC instrument setup
gas source, inlet valve, column (with oven), detector
mobile phase in gc
carrier gas, doesnt interact. inc. Ar, He, H2, N2, O2, CO2, H2O vapor
elution
movement of mobile phase along stationary phase via more liquid dilution being added at the top
retention time
tx, time btwn injection and reaching the detector
fast atom bombardment
solid or liquid matrix of larger molecules bombarded by charged atoms to ionize them, comparable to CI for fragmentation
SCF chromatography
mobile phase is supercritical fluid, stationary is organic solid bound to walls
GLC
gas-liquid chrom. gas mobile phase, liquid bound to solid stationary
partition chromatography
liquid-liquid (immiscible), stationary attached to wall
adsorption chromatography
liquid-solid, liquid mobile phase adsorbs to solid
ion exchange chromatography
type of LC where liquid exchanges ions with the stationary phase
affinity chromatography
liquid-liquid where the stationary phase is specific to the analyte and is bound to surface
flow rate vs H graphs for GC and LC
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
capacity factor
same as retention factor, (k), he might call it this.
GLC stationary phase making
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.
,
j
correction factor. = 3/2 ((Pi/Po)^2)-1)/((Pi/Po)^3-1)
Po
outlet pressure
Pi
inlet pressure. always > outlet.
Pw
vapor pressure of water in column
temperature in GC calcs
always convert to K
average flow rate eq
F = j(Fo)(Tc/To)((Po-Pw)/Po). SAME EQ for v and corrected v (soap bubble meter)
Vg and eq
specific retention volume; retention volume per gram of the stationary phase. Vg = (Vr-Vm)/ms * 273/Tc =KVs/ms * 273/Tc
head pressure (Pg)
diff btwn Po and Pi
column support types
packed column - large capacity, used for prep work. capillary (open) is faster, for analytical use, smaller sample sizes.
temperature programming
changing temp linear or in increments at spec times to improve resolution
Flame ionization detectors
destructive, mostly detects C. ions generate current. 10^7 linear range, low noise, not impacted by flow rate
NP / thermoionic detectors
only useful for N and P but really good for pesticide eval bc of this. (basically FID)
e- capture detectors
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.
atomic emission detectors
element-selective detectors, work well, good ranges, but destructive and expensive
peak area eq
A = k(amt) = kCFt, k is response factor, Ft = volume
GSC
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
soap bubble flowmeter
shows gas vol thru soap membrane moving up measurement
Thermal conductivity detectors (GC)
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
Flame photometric detectors GC
S and P detecting, but have worse DL and range than sulfur chemiluminescence detector for S, destructive.
carrier gas impacts on measurement
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
eddy diffusion
molecules reach detector at diff times due to taking diff paths thru a packed column
eluent
the mobile phase added to move the analyte
zone broadening causes
large stationary phase particles, high temps, very fast or slow elution, thick stationary phase, large column diameter
B variable in MS
magnetic field strength, Teslas
mass for MS (in all eq)
use kg!!
Resolution and N for chrom.
R1/R2 = sqrt(N1/N2)
retention volume
trflow rate, for “corrected” do j(tr)F
signal averaging rules
add up signals and get (n)S + sqrt(n)e, take average of the same signal and get S + e/sqrt(n)
single beam vs double beam
single is 2 measurements (1 blank) double is simultaneous,uses beamsplitter or mirror.
mass analyzers
all the components ie ion trap, quadrupole, TOF etc.
why is the sky blue
Rayleigh scattering
std dev from s/n
multiply 1/S by 0.434
