Gas chromatography–mass spectrometry (GC-MS) is an analytical method that combines the features of gas-chromatography and mass spectrometry to identify different substances within a test sample.[1] Applications of GC-MS include drug detection, fire investigation, environmental analysis, explosives investigation, food and flavor analysis, and identification of unknown samples, including that of material samples obtained from planet Mars during probe missions as early as the 1970s. GC-MS can also be used in airport security to detect substances in luggage or on human beings. Additionally, it can identify trace elements in materials that were previously thought to have disintegrated beyond identification. Like liquid chromatography–mass spectrometry, it allows analysis and detection even of tiny amounts of a substance.[2] GC-MS has been regarded as a "gold standard" for forensic substance identification because it is used to perform a 100% specific test, which positively identifies the presence of a particular substance. A nonspecific test merely indicates that any of several in a category of substances is present. Although a nonspecific test could statistically suggest the identity of the substance, this could lead to false positive identification. However, the high temperatures (300°C) used in the GC-MS injection port (and oven) can result in thermal degradation of injected molecules,[3] thus resulting in the measurement of degradation products instead of the actual molecule(s) of interest.The first on-line coupling of gas chromatography to a mass spectrometer was reported in the late 1950s.[4][5] An interest in coupling the methods had been suggested as early as December 1954.

1. GC MASS SPECTROMETERY

2. Content
Introduction
History
Principle
Instrumentation
Working process
Application
Advantages
Disadvantages

4. Introduction
Gas chromatography-mass spectrometery is
the synergistic combination of two analytical
method to separate and identify different
substances within a test sample.
We obtain both qualitative and quantitative
information for our sample in a single run
within the same instrument.

5. Cont….
It is composed of two major building blocks:
1. The gas chromatography
2. The mass spectrometer
Gas chromatography separates the
components of mixture in time.
Mass spectrometer provides information that
aids in the identification and structural
elucidation of each components.

6. GC-Mass Spectrometer

7. HISTORY
Roland Gohlke and Fred McLafferty introduce
use of MS as detector of GC in 1950s.
In 1968, the Finnigan Instrument Corporation
delivered the first quadrupole GC/MS.
By the 2000s computerized GC/MS
instruments using quadrupole technology had
become essential.
2005 GC tandem MS/MS have been
introduced.

8. Principle
Gas Chromatography :- A separation
technique which separates organic or
inorganic compounds exploiting it’s physico
chemical properties such as polarity, boiling
point.
The interaction with the stationary phase with
the vapor pressure of the analyte ( due to
column temperature) is the key factor in
separating the molecules.

9. Cont….
Mass spectrometer :- MS is an analytical
device which measures the mass to charge
ratio (m/z) of a molecule.
MS requires charged molecules for analysis.
Charged molecules should be in gaseous state.

10. Instrumentation
Gas
chromatography
• It separates
components of the
sample
Interface
• Combines both
techniques by
removing pressure
incompatibility
problem between
GC and MS
Mass
spectrometery
• Ionise eluted
components and
separate, identify it
according to it’s
mass to charge
ratio

13. Gas chromatography
•Carrier gas
•Pneumatic control
•Injector
•Column
•Oven
Interface
•Jet interface
•Direct capillary
infusion interface
•Watson-Biemann
effusion separator
Mass spectrometer
•High vacuum system
•Ion source
•Mass analyzer
•Detector
Data system

14. Gas chromatography
Carrier Gas:
 Served as mobile phase supplied in the steel tank
under high pressure.
 At pressure of 40-80 psi this passes into flow
controllers.
 Example- Majorly Helium and Argon are used.
Pneumatic Control:
 Gas supply is regulated to the correct pressure
and then fed to the required part of instrument.

15. Cont….
Oven:
 Temperature programmable, typically range from 5°C -
400°C but can go as low as -25°C with cryogenic
cooling.
Sample Injection Port:
 Sample is made to vaporized rapidly before entering to
column.
 Various kind of injectors:
1. Packed column injectors
2. Split injection
3. Splitless injection
4. Programmed Split/Splitless injection
5. Programmed On-Column injector

16. Cont….
Column:
Two kinds of column used:
1. Packed column
2. Capillary column
Gas chromatograph GC-MS utilizes capillary
column. Here, stationary phase has been
chemically bonded to the fused silica.

17. Cont….
Packed column
 Less commonly used.
 having diameter of 2-3 mm
and length of 0.5-10 m.
 Manufactured from steel
or glass. internal wall is
treated to avoid. catalytic
effect with the sample.
 They can withstand a
carrier gas flow rate within
range 10 40ml/min.
Capillary column
 Consist of long capillary
tubing 10-100 m in
length.
 Made up from stainless
steel & coil.
 Shorter columns used for
fast analysis
 Larger columns for high
resolution separation

19. Interface
Pressure incompatibility problem between GC
and MS was solved by inserting an interface.
Mainly three types of interfaces are there
commercially available:
1. Jet/Orifice separator
2. Direct capillary infusion interface
3. Watson-Biemann effusion separator

20. Jet/Orifice separator
The jet separator consist of two glass tubes aligned with a Small
distance between them. Carrier gas entering from the GC
column is pumped away by a separate vacuumed system. The
larger sample molecules maintain their momentum &pass
preferentially in to the second capillary. Sample enrichment
occurs & the initial atmospheric pressure is reduced.

21. Direct capillary infusion interface
GC-MS systems use capillary columns & fused
silica tubing permits an inert, high efficiency,
direct transfer between the 2 systems. Flow
rates is 5ml/min.

22. Watson-Biemann effusion separator
It consists of a sintered glass tube. The carrier gas
usually helium passes preferentially through the
sintered glass tube and the effluent is
concentrated. The gas flow rates in the order of
20-60ml/min

23. Detector

24. Mass Spectrometer
Vacuum system
 All mass analysers operate under vacuum in order to minimise
collisions between ions and air molecules. At atmospheric pressure,
the mean free path of a typical ion is around 52 nm at 1mtorr.
 In most instruments, two vacuum pump types are used.
 Rotary vane pump:- This pump can be an oil pump to provide initial
vacuum. It is used to produce the main reduction in pressure.
(approximately 1torr).
 Turbomolecular pump:- It is also known as diffusion pump, provides
working high vacuum (1mtorr to 1ntorr). This is a high-speed gas
turbine with interspersed rotors (moving blades) and stators (i.e.
fixed or stationary blades) whose rotation forces molecules through
the blade system

25. Ion source or Ionization
Ionization means placing a charge on an
otherwise a neutral molecule.
Ions may be produced from a neutral molecule by
removing an electron to produce a positively
charged cation, or by adding an electron to form
an anion.
Both positive and negative-ion mass
spectrometry may be carried out.
Majorly two types of ionization are used in GC-
MS
1. Electron impact ionization 2. Chemical
ionization

26. Electron impact ionization (EI)
Here a beam of electrons with energy of 70
electron volts is made to interact with the sample
This interaction causes electron ejection in the
sample molecules thereby leading to ionization.
This method is suitable for small molecules of
molecular weights up to 400 Daltons only.
It is widely used for the analysis of metabolites,
pollutants and pharmaceutical compounds, for
example in drug testing programmes

27. Cont….

28. Chemical Ionization (CI)
Chemical Ionization (CI)
 Chemical ionization (CI) is used for a range of
samples similar to those for EI.
 It is particularly useful for the determination of
molecular masses, as high intensity molecular ions
are produced due to less fragmentation.

29. Mass analyzer or Mass selective analyzer
They deflects ions down a curved tubes in
magnetic field based on their kinetic energy
determined by the mass charge and velocity.
The magnetic field is scanned to measure
different ions.
They may be three types-
1. Quadrupole
2. Ion trap
3. TOF

30. Quadrupole analyzer
 Also known as 'Hewlett-Packard‘ Detector.
 In quadrupole mass analyzer a set of four rods are arranged parallel
to the direction.
 Only m/z is been determined and stable oscillation takes place.
 lons travels in quadrupole axis with cork screw type of trajectory.
 It functions as a mass filter.

31. Ion trap mass analyzer
The ion trap mass analyzer operates by similar principle where it
consists of circular ring electrode and two end caps that form a
chamber.
AC or DC power along RF potential is applied between the cups and
the ring electrode.
Ions entering Trapped by Ions oscillate in
into chamber electromagnetic field concentric trajectories

32. Time-of-flight Analyzer :
The time-of-flight (TOF) analyzer uses an electric
field to accelerate the ions through the same
potential. . Then it measures the time take to
reach the detector.
If the particles all have the same charge, the
kinetic energies will be identical and their
velocities will depend upon only on their masses.

33. detector
Detector is used for detection of ions.
Electron and photomultiplier conversion dynode
is used.

34. Electron multiplier
In electron multiplier-electrons released by the
first dynode when the ion impinges on it are
dragged to the second dynode because it has a
higher potential. Let us call these electrons
primary. These primary electrons strike the
second dynode with a force and the collision
releases even more secondary electrons which
too are dragged to the third dynode resulting in
release of even more electrons and so on.
Typical amplification of an electron multiplier is
one million.

35. Photomultiplier
 photomultiplier is similar to the electron
multiplier in that the ions strike a dynode
resulting in the emission of electrons. However,
these electrons are now made to strike a
phosphorus screen. This screen releases photons
when electrons strike it. These photons are now
detected by a photomultiplier.
The primary advantage of this setup is that the
photomultiplier tube is housed in vacuum. This
removes the possibility of any contamination
from the internal environment.

36. Work of dynodes

37. Data system
Data handling
Mass spectrometers employ computer control
of same functions and also use a
computerised display and output.It is used to
identify and measure the concentration of one
or more analytes in a complex mixture.
Advantages - Amount of data generated is
very large and It stores every sec for upto 90
min.

38. Graph of CO2 gas

40. Working of GC-MS
 The separation occurs in the gas chromatographic column
(such as capillary) when vaporized analytes are carried
through by the inert heated mobile phase (so-called carrier
gas such as helium).
 The analytes spend different time (called retention time) to
come out of (elute from) the GC column due to their
different adsorption on the stationary phase (of a packed
column in gas-solid chromatography).
 As the eluted substances emerge from the column opening,
they flow further into the MS through an interface.
 This is followed by ionization, mass-analysis and detection
of mass-to-charge ratios of ions generated from each
analyte by the mass spectrometer.
 The combination of the gas chromatograph and mass
spectrometer in a GC-MS allows a much accurate chemical
identification than either technique used separately.

42. Application
 Petrochemical and hydrocarbons analysis
 Geochemical research.
 Forensic (arson, explosives, drugs, unknowns)
 Environmental analysis
 Pesticide analysis
 Food safety and quality control
 Pharmaceutical and drug analysis
 Clinical toxicology
 Application to human dosimetery
 GC-MS is increasingly used for detection of illegal narcotics
marijuana, cocaine, opioids Clinicians oxycodone and
oxymorphone Sports anti-doping analysis

43. Advantages
Robust, mature technology
Relatively inexpensive
Quantitative (with calibration)
Small sample volume (50 ul.)
Good sensitivity (100 nM)
Large body of software and databases for
metabolite ID
Detects most organic and someinorganic
molecules.
Excellent separation reproducibility

44. Disadvantages
Sample not recoverable
Requires sample derivatization
Requires separation Relatively slow (2-3 hr to
collect data and analyze sample)
Cannot be used in imaging Novel compound
ID is difficult.