3. INTRODUCTION
J. J. Thomson (1913) separated
the isotopes 20Ne and 22Ne
Atlantic Refining Company (1942),
first commercial use
This technique resolves ionic
species by their m/e ratio
Francis William
Aston won the
1922 Nobel Prize
in Chemistry for
his work in mass
spectrometry
Replica of an early mass
spectrometer
4. Some of the modern techniques of mass spectrometry were
devised by Arthur Jeffrey Dempster and F.W. Aston in 1918 and
1919 respectively.
In 1989, half of the Nobel Prize in Physics was awarded to Hans
Dehmelt and Wolfgang Paul for the development of the ion trap
technique in the 1950s and 1960s.
In 2002, the Nobel Prize in Chemistry was awarded to John
Bennett Fenn for the development of electrospray ionization (ESI)
and Koichi Tanaka for the development of soft laser desorption
(SLD) and their application to the ionization of biological
macromolecules, especially proteins.
The earlier development of matrix-assisted laser
desorption/ionization (MALDI) by Franz Hillenkamp and Michael
Karas has not been so recognized despite the comparable
(arguably greater) practical impact of this technique, particularly in
the field of protein analysis. This is due to the fact that although
MALDI was first reported in 1985, it was not applied to the
ionization of proteins until 1988,after Tanaka's report.
5. WHAT IS MASS
SPECTROMETRY
It is an analytical technique for
the determination of the
elemental composition of a
sample or molecule
6. MS is a powerful analytical technique
Identify Unknown Compounds
quantify known materials
Elucidation of structural and chemical properties
Requires minute Quantities (<Pg)
Identification of analyte molecules at very low
concentrations in complex matrices
High Sensitivity, Selectivity & Specificity- Provides
valuable information in various branches of science
Chemistry, Physics, Biology, Medicine, Material
Science, Environment, Forensic Science,
Geochemistry, Archeology, Astronomy etc.
7. Did you know that mass
spectrometry is used to...
Detect and identify the use of steroids in
athletes
• Monitor the breath of patients by
anesthesiologists during surgery
• Determine the composition of molecular
species found in space
• Determine whether honey is adulterated with
corn syrup
• Locate oil deposits by measuring petroleum
precursors in rock
8. • Monitor fermentation processes for the
biotechnology industry
• Detect dioxins in contaminated fish
• Determine gene damage from
environmental causes
• Establish the elemental composition of
semiconductor materials
9. principle
The MS principle consists of ionizing chemical
compounds to generate charged molecules
or molecule fragments and measurement of
their mass-to-charge ratios.
10. How the mass analyzer
works a sample is loaded onto the MS instrument, and
undergoes vaporization.
the components of the sample are ionized by one of a
variety of methods (e.g., by impacting them with an
electron beam), which results in the formation of
charged particles (ions)
the positive ions are then accelerated by an electric field
computation of the mass-to-charge ratio (m/z) of the
particles based on the details of motion of the ions as
they transit through electromagnetic fields, and
detection of the ions, which in step 4 were sorted
according to m/z.
13. Basic Components
1. Sample Introduction System
Volatilizes the sample and introduces it to the
ionization chamber under high vacuum
2. Ion Source
Ionizes the sample (fragmentation may occur)
and accelerates the particles into the mass
analyzer
3. Mass Analyzer (or Mass Separator)
Separates ionized particles based on their
mass-to-charge ratio (m/e-)
14. Basic Components cont…
4. Detector - Ion Collector
Monitors the number of ions reaching detector
per unit time as a current flow
5. Signal Processor
Amplifies the current signal and converts it to
a DC Voltage
6. Vacuum Pump System
A very high vacuum (10-4 to 10-7 torr) is
required so that the generated ions are not
deflected by collisions with internal gases
16. Electron ionization
chemical ionization
electrospray
ionization
matrix-assisted
laserdesorption/ioniza
tion
glow discharge
field desorption (FD)
fast atom
bombardment (FAB)
Thermospray
desorption/ionization
on silicon (DIOS)
Direct Analysis in
Real Time (DART)
atmospheric pressure
chemical ionization
(APCI) secondary
ion mass
spectrometry (SIMS)
spark ionization and
thermal ionization
(TIMS).
Ion source technologies
17. Mass analyzer technologies
○ Time-of-flight
○ Quadrupole
○ Quadrupole ion trap
○ Linear quadrupole ion trap
○ Fourier transform ion cyclotron resonance
○ Orbitrap
Detectors
○ electron multiplier
○ Faraday cups
○ Microchannel plate detectors
18. 1. Batch Inlet
Sample is volatilized externally and allowed to
“leak” into the ion source
Good for gas and liquid samples with boiling
points < 500 °C
2. Direct Probe
Good for non-volatile liquids, thermally
unstable compounds and solids
Sample is held on a glass capillary tube, fine
wire or small cup
Sample Introduction Systems
19. 3. Chromatography Interface (GC-MS)
The MS is used both quantitatively and
qualitatively
Major interface problem – carrier gas dilution
Jet separator (separates analyte from carrier gas)
4. Inductively Coupled Plasma (ICP)
Operates somewhat like a nebulizer in an AAS
Also ionizes the sample in argon stream (at very
high temperatures, >6000 °C)
Only a small amount of analyte is utilized (< 1%)
20. Electron ionization
Electron ionization (EI, formerly known
as electron impact) is an ionization
method in which energetic electrons
interact with gas phase atoms or
molecules to produce ions. This
technique is widely used in mass
spectrometry, particularly for gases and
volatile organic molecules
21. The following gas phase reaction describes
the electron ionization process :
where M is the analyte molecule being
ionized, e- is the electron and M+• is the
resulting ion.
Diagram representing an electron
ionization ion source
22. Chemical Ionization (CI) Ion
Source
A modified form of EI
Higher gas pressure in ioniation cavity (1 torr)
Reagent gas (1000 to 10000-fold excess) added; usual
choice is methane, CH4
Reagent gas is directly ionized instead of analyte
Gentle; little fragmentation; even-electron ions
produced more stable than odd-electron ions
produced in EI
Excess energy of excited ions removed by many
ion-reagent gas collisions
24. Fast Atom Bombardment
Ion source for
biological molecules
Ar ions passed
through low pressure
Ar gas to produce
beam of neutral ions
Atom-sample collisions
produce ions as large as 25,000
Daltons
25. glow discharge
Sputtering of the
cathode material (the
sample) by an argon
plasma.
Ionisation of the
elements of the sample
in the plasma.
Extraction and
acceleration of ions.
Ions separation with a
magnetic sector
(Mattauch Herzog
configuration).
Ions detection by a
Faraday cup or an
electron multiplier
26. Matrix-Assisted Laser
Desorption/Ionization (MALDI)
Analyte mixed with
radiation-absorbing
material and dried
Sample ablated with
pulsed laser
Often coupled to
time-of-flight (TOF)
detector
Excellent for larger
molecules, e.g.
peptides, polymers
27.
28. MASS ANALYZERS
Quadrupole Analyzer
Ions forced to wiggle
between four rods whose
polarity is rapidly
switched
Small masses pass
through at high frequency
or low voltage; large
masses at low frequency
or high voltage
Very compact, rapid (10
ms)
R = 700-800
29. TOF Time of Flight Mass
Analyzer
Separates ions
based on flight time
in drift tube
Positive ions are
produced in pulses
and accelerated in
an electric field (at
the same frequency)
All particles have the
same kinetic energy
Lighter ions reach
the detector first
Typical flight times
are 1-30 µsec
30. Time of Flight Mass
Analyzer
Separation Principle
All particles have the same kinetic
energy
In terms of mass separation principles:
Vparticle = Her/m
Hold H,e, and r constant
Vparticle = 1/m (constant)
Vparticle is inversely proportional to mass
31. Quadrupole Ion Trap
Ions follow complex
trajectories between
two pairs of
electrodes that
switch polarity
rapidly
Ions can be ejected
from trap by m/z
value by varying the
frequency of end
cap electrodes
33. Electron multiplier
Continuous dynode electron multiplier
An electron multiplier (continuous dynode electron
multiplier) is a vacuum-tube structure that multiplies incident
charges.
In a process called secondary emission, a single electron
can, when bombarded on secondary emissive material,
induce emission of roughly 1 to 3 electrons.
If an electric potential is applied between this metal plate and
yet another, the emitted electrons will accelerate to the next
metal plate and induce secondary emission of still more
electrons.
This can be repeated a number of times, resulting in a large
shower of electrons all collected by a metal anode, all having
been triggered by just one.
34. Faraday cup
A Faraday cup is a metal
(conductive) cup designed
to catch charged particles
in vacuum.
The resulting current can
be measured and used to
determine the number of
ions or electrons hitting the
cup.
The Faraday cup is named
after Michael Faraday who
first theorized ions around
1830.
Schematic of a Faraday cup
35. Faraday cup cont..
When a beam or packet of Ions hits
the metal it gains a small net charge
while the ions are neutralized.
The metal can then be discharged to
measure a small current equivalent to
the number of impinging ions.
Essentially the faraday cup is part of
a circuit where ions are the charge
carriers in vacuum and the faraday
cup is the interface to the solid metal
where electrons act as the charge
carriers (as in most circuits).
Faraday cup with an electron-
suppressor plate in front
• By measuring the electrical current (the number of
electrons flowing through the circuit per second) in the
metal part of the circuit the number of charges being
carried by the ions in the vacuum part of the circuit can be
determined.
36. Micro-channel plate (MCP)
It is a planar component used for
detection of particles (electrons or
ions) and impinging radiation
(ultraviolet radiation and X-rays).
It is closely related to an electron
multiplier, as both intensify single
particles or photons by the
multiplication of electrons via
secondary emission.
However, because a micro channel
plate detector has many separate
channels, it can additionally provide
spatial resolution.
37. A micro-channel plate is a slab
made from highly resistive
material of typically 2 mm
thickness with a regular array of
tiny tubes or slots
(microchannels) leading from
one face to the opposite,
densely distributed over the
whole surface.
•The microchannels are typically approximately 10
micrometers in diameter (6 micrometer in high resolution
MCPs) and spaced apart by approximately 15
micrometers; they are parallel to each other and often
enter the plate at a small angle to the surface (~8° from
normal).
