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Mass Spectroscopy - Coggle Diagram
Mass Spectroscopy
Mass Spectroscopy
How it works
Ionisation
bombarded with high-energy electrons
electrons run in stream
between anode and cathode
sample passes through stream
knock electrons out of sample
#
become cation
usually +1 charge
charge corresponds
1 more item...
electrons collide with sample
most common type
electro ionisation
electrical current
70 eV (electron volts)
sample enters + heated up
molecules move around
impact by electric/magnetic fields
Acceleration
ionised atoms placed
between 2 charged parallel plates
negative - slit
ions passed though
acceleration of ions
rapid movement of ions in chamber
gives all species
same kinetic energy
only charged particles
accelerated, deflected, detected
Deflection
pass through magnetic field
bend path/stream
deflect ions with charge
on mass (m) + charge (z)
force of deflection
larger mass/2+ charge +
deflected less
higher m/z
lower mass/1+ charge
deflected more
lower m/z
types of analysers
time-of-flight (TOF)
measure time taken
to reach detector
others
measure deflection by magnetic field
Detection
ion stream reach detector
hit wire
become neutralised
amplifier
amplifies signal
current wire + ion
computer detects signal
converts to m/z
spectrum produced
along with relative abundance
more ions hit certain spot
more abundance
heavier fragment
further right hit detector
lighter fragment
further left hit detector
chart
x/horizontal-axis
mass to charge (m/z)
relative mass of charged cations
y/vertical-axis
relative abundance %
Applications
organic chemistry
determine ionic formula
ions can be distinguished
based on masses
molecular formula
moleculale structure
structural rings + double bonds
structural formulas
fragmentation
deduce structural formulas
semi-empirical rules are known
pick peaks in spectrum
characteristic of particular chemical groups
isotopic labelling
which particular atoms in reaction
idea on fragmentation reactions
work
pharmaceutical
use of drugs
biomolecule characterisation
environmental analysis
pesticides
soil + ground water contamination
date geological samples
atomic masses
trace element analysis
space probes
leak detection - vacuum systems
ion-molecule reaction
Advantages
require small amount of material
sensitive (parts/million)
fast
differentiate isotopes
identify components in unknown sample
confirms presence
Disadvantages
not good at identifying
hydrocarbons with similar ion
unable to tell
optical + geometrical isomers apart
no structural information
can be worked out
needs pure component
difficult with non-volatile compounds
information can be determined
molecular mass of sample
molecular formula
structure + chemical properties - molecules
identification of isotopes
mass
relative abundance
protein sequence
strengths of chemical bonds
molar mass + elements present
what it is
produces cations
separated by mass + charge
neutral species not detected
measures relative abundance
separate components of sample
by mass and charge
sorting of gaseous ions
in electric/magnetic field
mass spectrometer
produce mass spectrum
plot mass to charge ratio (m/z)
compounds in mixtures
molecular ion
#
resultant particle
sample particle
after loss of electron/s
fragmentation
#
molecular ion
can break into smaller pieces
sometimes 2 parts
positive ion
seen on mass spectra
lines at different m/z
uncharged free radical
no line on mass spectra
fire of high-energy electrons
cause fragmentation
each has different molecular mass
particularly long molecules
single bond in molecular ion break
smaller + and neutral fragments
use of electrons
very little mass
no impact on mass
Interpreting mass spectra
alkanes
form most stable
carbocation
tertiary (stable) > secondary > primary
more substituted side
attached to most carbons
cation
less substituted side
radical
fragmentation
look for typical break
substituted each of carbons
lines with m/z 1 or 2 less
loss of 1+ H
play around with numbers
pentane (C4H9)
4C x 12 = 48
57- 48=9
peak at m/z 57
straight chain
molecular ion
faint
identifiable peak
alkane longer than 8 C
base peak
peak at m/z 57
C4H9 carbocation
surrounded by smaller peaks
separation of 14 mass units
loss of CH2 group
prominent peak
CmH2m+1
largest peak
loss of (CH2)CH3
base peak
indicate alkane
branched
molecular ion
almost always undetected
branching point
accompanied by H rearrangement
CnH2n peak prominent
over CnH2n+1
larger compound branched alkanes
peaks at
CmH2m+1
lack smooth exponential decay
C3 or C4
secondary over primary carbocation
C12 alkane
indicates branched alkane
fragments
C5
intensity peak m/z71
C9
m/z 127
methyl group (4th carbon)
another functional group
ethyl more unstable
than methyl radical
methyl occur less frequently
alkane proportion
becomes larger
prominent CnH2n+1
carboxylic acid
straight
molecular ion weak
usually present
short chain
gives prevalent peaks
longer
peaks = less prevalent
peaks
loss of OH
molecular ion <17
loss of COOH
molecular ion <45
cleavage of bonds
next to C=O
general
carbocation
#
C atom that is + charged
lost 1 valence electron
base peak
highest/most abundant
100% abundance
most stable
sometimes molecular ion is base
often not the case
other peaks
reasons
isotopes
little peaks
fragmentation
can be isomeric
plotted as
relative percentage to base peak
comparison to base peak
molecular ion peak
most important
gives molar mass of original compound
heaviest ion
furthest right
exception
furthest and 2nd furthest
have m/z of 1
furthest peak = m+1
2nd furthest = M+ peak
subtract other peak m/z
from molecular ion peak
= fragment broken off
each peak
shows component - unique m/z
height
= relative abundance of components
higher the peak
more stable it is
more of particular ion formed
isotopes
differ in # of neutrons
peak
position
relative isotopic mass
height
relative abundance
relative abundance
35Cl:37Cl
3:1
79Br:81Br
1:1
N, O, F
1:0
examples
2-methylbutane
isomer of putane
peak at m/z 43
secondary carbocation
2 alkyl group
attached to C+
distinguish pentan-2-one, pentane-3-one
produce ions on CO+
pentan-2-one
2 ions
peaks: m/z 43 + m/z 71
pentan-3-one
1 ion
strong peak: m/z 57
common fragments
Organic Compounds
alkanes
#
carbon chains
single bond between carbons
formula
straight-chain alkanes
look zig-zag
carbons arranged tetrahedrally
joined in 1 continuous string
naming
stem
give length of carbon chain
branched alkanes
longest continuous C chain
use name - corresponding alkane
substituents
other atoms/groups
attached to main chain
form branches
alkyl group
if C group
ethyl
methyl
example
3-ethyl
attached 3rd C
end in -ane
carboxylic acids
#
contain carboxyl functional group
carbonyl (C=O)
hydroxyl (-OH)
found end parent chain
molecular formula
naming
identify longest C chain
-COOH group
delete 'e' - parent alkane
add 'oic' acid
number C atoms of main chain
name alkyl groups
branched alkanes
isomers
structural isomers
compounds
different structural formula
same molecular formula
positional isomers
different placement of substituents
occur through
changing position of double/triple bonds
chain isomers
rearrangement of carbon skeleton
same number + type atom
differing structure