instrumentation of Mass spectroscopy

1. Instrumentation of Mass spectroscopy
 Imran Laiq
 Roll No. 12
 M.Sc. (Analytical Ch) Part II
 Semester IV (2021 )
 CKT College New Panvel
 Date: 07/06/2021

2. Contents
 Introduction
 Components of mass spectrometer
 Working of Mass spectrometer
 Inlet system
 Ion sources
 FAB
 Mass analyzers
 Quadrupole analyzer
 Time of flight analyzer
 Detectors
 References

3. Introduction
Mass Spectroscopy:
Involves the production and separation of ionized molecules.
The complete process involves the conversion of the sample into gaseous ions, with
or without fragmentation, which are then characterized by their mass to charge
ratios (m/z) and relative abundances.
It is a destructive technique in which the sample is consumed during analysis.
Mass spectra is used in two general ways:
1) To prove the identity of two compounds.
2) To establish the structure of a new compound.

4. Instrumentation
Components of a mass spectrometer:
 A sample inlet (inlet system)
 An ionization source
 A mass analyzer
 An ion detector
 Data system
Figure: Components of a Mass Spectrometer

5. Working of
Mass
spectrometer

6. Inlet system:
 Inlet transfers analyte into the source as a gas phase molecule.
 Liquids and solids are usually heated to increase the vapor pressure for analysis.
 Liquid samples are handled by hypodermic needles injection through a silicon rubber
dam.
 If the analyte is thermally labile (it decomposes at high temperatures) or if it does not
have a sufficient vapor pressure, the sample must be directly ionized from the condensed
phase.

7. Ion sources:
 The ion source ionizes the sample.
 Molecular ions are formed when energy of the electron beam reaches to 10-15 eV.
 Fragmentation of the ion reaches only at higher bombardment energies at 70 eV.
 The ions are then transported by magnetic or electric fields to the mass analyzer.
• a. Electrospray Ionization (ESI).
• b. Matrix assisted laser desorption Ionization (MALDI).
• c. Fast Atom Bombardment (FAB).
• d. Field Desorption (FD).
• e. Plasma desorption (PD).
1. Desorption Sources
• a. Atmospheric pressure chemical ionization (APCI)
• b. Atmospheric pressure photoionization (APPI)
2. Atmospheric pressure ionization
• a. Electron Impact Ionization (EI).
• b. Chemical Ionization (CI).
• c. Field Ionizations (FI).
3. Gas Phase Sources

8. FAB (Fast Atom Bombardment) :
 The analyte is dissolved in a viscous liquid, typically glycerol
and ionization is achieved by bombardment of the sample
matrix by a beam of fast moving neutral atoms.
 The bombarding atoms are usually rare gases, either xenon or
argon.
 Common matrices include glycerol, thioglycerol, 3-nitrobenzyl
alcohol (3- NBA), triethanolamine etc.
 After acceleration, the fast moving ions enter into a chamber
containing further gas atoms and collision of ions and atoms
leads to charge exchange.
Xe•+ (fast) + Xe (thermal) Xe (fast) + Xe+• (thermal)
 The fast atoms formed in this process retain the original kinetic
energy of the fast ions and proceed towards the analyzer.

9. Mass analyzers
Mass analyzer is the heart of mass spectrometer. It separates the ions in vapor phase on
the basis of their mass to charge ratio (m/z). There are two types widely used mass
analyzers
1- Quadrupole mass analyzer:
 Consists of four rods with a hyperbolic cross section that are accurately positioned
parallel in a radial array.
 The quadrupole rods are typically constructed using molybdenum alloys because of
their inherent inertness and lack of activity.
 Quadrupole mass spectrometers ~QMSs’ are widely used in both industry and
research for fast accurate analysis of gas and vapors.
 The QMS contains basically three elements; i) ion source, ii) mass filter, and
iii) ion detector.

10. Working of Quadrupole mass analyzer

11. 2-Time of flight analyzer:
TOF is a non-scanning mass
analyzer that emits pulses of ions (or
transients) from the source.
These ions are accelerated so that
they have equal kinetic energy
before entering a field free drift
region, also known as the flight tube.
A time-of-flight (TOF) instrument
consists of a pulsed ion source, an
accelerating grid, a field-free flight
tube, and a detector.

12. sensitive.
1000 times
greater than
faraday cup.
Least
sensitive.
Cup will
capture the
ion.
Most
sensitive.
Used for
high
resolution.
Photomultiplier
detector
Faraday Cup
detector
12
Photographic
detector
Detectors

13. References
1. Willard, Merritt, Dean, andd Settle. Instrumental Methods of Analysis, 7th edition,
(1986).
2. Douglas A. Skoog, F. James Holler, and Stanley Crouch Principles of Instrumental
Analysis - 6th Edition by (ISBN 0-495-01201-7).
3. Dar. Bashir Ahmed, Dar. Ayaz Mahmood Instrumental Methods of Chemical
Analysis, 1st edition, Mamta publication (2020).
4. Organic spectroscopy by William kemp.
5. Spectroscopic identification of organic compounds by Silverstein