GCMS Technique Gas Chromatography–Mass Spectrometry

1. GC- MS technique

2. GC- MS technique
 CREDIT
 HABIB UR REHMAN BPD02181285

3. CONTENT
 Introduction
 Gas chromatography
 Mass spectrometry
 MS as an detector
 interfacing GC with MS
 Interface & its types
 how GC/MS works

4.  Interpretation of results
 Advantages
 Disadvantage/ limitation
 applications

5. INTRODUCTION
 GS-MS is an Advance analytical instrumental technique that combines the physical
separation capability of GC with the mass analysing capability of MS.
 It is very versatile tool to separates ,quantify and identify unknown substances.
 GC separates the components of mixture.
 MS provides information that aids in the structural identification of each
component.

6. Gc-Ms diagram

7. GAS CHROMATOGRAPHY
 Used to separates the components of mixture.
 The principle of separation in GC is partition or adsorption depend upon which type
of stationary phase used.
 In gas chromatography, the sample is injected and vaporized in the injection port.
Elution is brought about by the flow of an inert gaseous mobile phase.
 The mobile phase does not interact with molecule of the analyte;its only function is to
transport the analyses through the column.
 Retention times are based on the polarity of the substance compared to the column.

9. Mass spectrometry
 It is a technique used for measuring the molecular weight and determining the
molecular formula.
 The spectra that obtained is called positive ion spectra .
 Apparatus
1. Sample inlet system
2. Ionization source
3. Ion accelerator chamber
4. Mass analyzer
5. Detector and readout

10. Principle and working
 In this technique ions are produce ,separate and detecte on the basis of
their mass to charge ratio.
 Sample Inlet system Convert the sample into vapours form either the
sample is liquid or solid.
 Ionization chamber produce ions by bombardment of high electron from
tungsten filament.The energy of the electron(70eV) cleave a typical bond
 In the ion Accelerator chamber the ions are gain some specific velocity
and move to the mass analyzer.

11. Cont...
 Mass analyzer deflects the ions down a curved tube in a magnetic field based
on their kinetic energy determined by the mass ,charge and velocity .
 Then these ions fall on the detector according to the their mass to charge
ratio and velocity.then readout device show the spectrum of analyte that is
represented by mass spectrum
 Mass spectrum is essentially a fingerprint for the molecule and can be used to
identify the compound

12. Mass spectrometer

13. Mass spectrometer as a detector
 The mass spectrometer is an universal detector for gas
chromatography,since any compound that can pass through a
gas chromatograph is converted into ions in the mass
spectrometer. Gas chromatography is an ideal separator ,
whereas mass spectrometry is excellent for identification.

14. Gc ms

15. Interfacing gas chromatography
with mass spectrometry
 The aim of an interfacing arrangement is to operate both techniques without
degrading the performance of either instrument .
 Problems
 Incompatibility
 GC operate at atmospheric presssure and the MS ion source at 10^-5 torr.
 Presence of much carrier gas and little sample in the elluent from the gas
chromatograph .

16. Interface
 A device to connect two techniques
 Transport the effluent from the gas chromatograph to the mass
spectrometer
 Analyte must not condense in interface
 Analyte may not decompose before entering the mass spectrometer
 It is play an important role in the overall efficiency of the instrument
 It remove the pressure incompatibility problem

17. Types of interface
 direct interface
 Jet separator
 Watson –biemann effusion separator

18. Direct interface
 Today most GC-MS system use capillary columns & fused
silica tubing permits an inert, high efficiency ,direct transfer
between the 2 systems .
 Flow rate is 2ml /min.

19. Jet separators(packed column)
 The separator consists of two glass tubes aligned with a small distance
between them .
 Carrier gas entering from the GC column is pumped away by a separate
vacumed system.
 The larger sample molecules maintain thei velocity and pass preferentially in
to the second jet.
 Sample enrichment occurs & the initial atmospheric pressure is reduced.

21. Watson –biemann effusion separator
 It consists of sintered glass tube .
 The carrier usually helium ,passes
preferentially through the sintered
glass tube , hence the analyte
enirchment occurs.

22. How GC Ms works
 The GC woks on the principle that a mixture will separate into
individual when heated .
 Sample introduced into GC inlet vaporized ,swept onto the column by
He carrier gas & separated on column .
 Sample components emerge from column ,flowing into the capillary
column interface connecting the GC column and the MS.
 Identification of a compound based on its mass spectrum relies on the
fact that every compound has a unique fragmentation pattern.

23. Cont...
 The computer drives the MS , records the data , and converts the electrical
impulses into visual displays and hard copy displays.
 As each solute exits the GC column , it is diverted into a mass spectrometer which
is capable of both monitoring the amount of and identifying the chemical nature
of the solute. In this way , both quantitative and qualitative information about the
mixture can be obtained .
 The sequence and relative intensity of the mass peaks give information about the
chemical identity of the solute .the absolute intensity of the peaks provides
information about the amount of solute

24. Interpretation of the result
 Through GC –a chromatogram is obtained
 Through MS-a spectrum is obtained .
 GC MS gives a 3D graph which has both chromatogram and a
spectrum to each separated component in chromatogram.

26. For example cocaine in urine sample

27. Advantages
 Easy to use
 Wide range of stationary phase
 Huge spectral libraries in the instrument that help with proper identifiation
 Used by many organization to monitor organic pollutant in environment.

28. Disadvantages/limitations
 It is expensive to buy a GC/MS machine
 It is difficult to measure and inject such small samples (approx 0.3 microlitres)
 Only compound with vapour pressure exceeding about 10 torr
 Determining positional substitution on aromatic ring is often difficult
 Certain isomeric compound cannot be distinguish by mass spectrometery.

29. General Applications
 Analysis of medicine
 Food, beverage & perfume analysis
 Criminal forensics
 Characterization & comparison of plant extract
 Envronmental monitoring

30. Pharmaceutical Applications
In the pharmaceutical industry, GC-MS is used in
 Research and Development
 Production and Quality control
 Identification of impurities in active pharmaceutical ingredients
 In medicinal chemistry
 In the synthesis and characterization of compounds
 In pharmaceutical biotechnology

32. Latest GC/MS