This document provides a comprehensive overview of gas chromatography-mass spectrometry (GC-MS), detailing its principles, working mechanisms, and applications in chemical analysis. It explains sample preparation techniques, types of gas supplies, column designs, and various interfacing methods between GC and MS. The document also discusses the mass spectrometry process, ionization methods, and the advantages and disadvantages of GC-MS analysis.

1. 1
Gas Chromatography – Mass Spectrometry
GC/MS
Rajat Goel 20FET210
Punam Mukherjee 20FET209

2.  Introduction
 Principle
 Working
CONTENTS
GC
 Introduction
 Principle
 Working
MS
 Application
GC-MS
 Interface

3. Identifies (detects)
chemicals
based on their molecular
weight or mass
Analysis Technique
combining two
instruments to provide
for powerful separation
and identification
capabilities
Separates
mixture of
chemicals so each
can be identified
individually
Introduction GC-MS
Gas
Chromato
-graphy
Mass
Spectrom-
etry
GC- MS

4. • The sample solution is injected into the GC inlet where it is vaporized and
swept onto chromatographic column by the carrier gas (usually helium).
• The sample flows through the column and the compounds compromising the
mixture of inlet are separated by virtue of their relative interaction with the
coating of the column (stationary phase) and the carrier gas (mobile phase).
• The later part of the column passes through a heated transfer line and ends
at the entrance to ion source where compounds eluting from the column are
converted to ions.
Injected into GC
column
Separation of
compounds
Compound
get Ionized
Principle

5. GC
Gas Chromatography
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6. Sample Preparation for GC
GC is ideally suited to analysis of thermally stable volatile substances e.g.,
flavor compounds, many pesticides, etc
Types of sample Preparation
Headspace Methods: Direct injection of headspace vapors above a food
product is a simple method to isolate volatile compounds
Distillation Methods: Product moisture or outside steam is used to heat and
co-distill volatiles from food product
• Obtain dilute aqueous solution of volatiles, so must do solvent extraction
to concentrate volatiles
Direct Injection: Can analyze some foods by direct injection (use 2-3 ml
sample), detecting volatiles at >50 ppb

7. Solid-Phase Extraction: Liquid sample is passed through cartridge or filter
with chromatographic material (e.g., ion-exchange resins; reversed- or
normal-phase packings)
Solutes with affinity are retained on stationary phase
Stationary phase is rinsed with water or weak solvent, then with a stronger
solvent to elute the solutes of interest
Sample Derivatization: Some compounds can be injected directly, e.g.,
aroma compounds, pesticides, volatile contaminants
Some compounds must be derivatized (chemically modified; e.g., use silyl
reagents, esterifying reagents) before GC analysis, because of the following
Sample Preparation for GC

8. GC System
Gas Supply
2
1 4 Oven
3
5

9. • GC requires at least a carrier gas, usually gases for detector.
• Gases must be high purity
• Regulators, gas lines, and fittings must be of good quality
• Carrier gases: nitrogen, helium, hydrogen
• Carrier gas line should have traps to remove moisture and
contaminants
Gas Supply System
1

10. Injection port functions:
• Sample introduction
• Sample vaporization
• Possibility for sample
dilution and splitting
• Contains a soft septum
with gas-tight seal that can
be penetrated by syringe
needle
• Samples introduced using
either a manual syringe
technique (source of poor
precision) or automated
sampling system
• Commonly inject 1-3 ml
Injection Port
2

11. •Packed Columns
• Currently used very little, due to
resolution advantages of capillary
columns
• Made of stainless steel or glass
• 1.6–12.7 mm outer diameter, 0.5–5
m long
• Solid support commonly made of
diatomaceous earth, of definite
mesh size
• Liquid loading applied to solid
support at 1-10% by wt of solid
support
• Loading influences analysis time,
resolution, and column bleeding
(i.e., liquid coating volatilized and
lost at high temp.)
•Capillary Columns
• Hollow fused silica glass
• 5-100 m long; very thin walls
• Inner diameters the 0.1 mm
(microbore), 0.23 – 0.32 mm
(normal capillary), or 0.53 mm
(megabore)
• Stationary phase: Liquid
coating chemically bonded to
glass walls of column, and
internally crosslinked to
thickness of 0.1 – 5 mm
• Get more column bleeding with
thicker stationary phase film
Column
3

12. Capillary Column

13. • Oven controls temperature of column
• Temperature Programming:
• Injection is often made a temperature lower than oven, then
programmed to higher temp
• Commonly 2-10oC/min
• Higher temperature causes sample to elute faster, but at a cost to
resolution
• Capillary column can be heated directly with insulated heating wire
based on low thermal mass technology
• Makes total heating and cooling cycle much shorter
Oven
4

14. 5 Detector

15. INTERFACE
Interface
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16. • It mainly join GC and MS
• There are many interface like jet, Electrospray, Thermo Spray, Direct
electrical ionization, Moving wire or belt interface.
1) Jet interface
• It takes advantages of the differences in diffusibility between the carrier
gas and the organic compound
• These jet separators work well at the higher carrier gas flow rates(10-40
ml/min).
Interface

17. 2) Direct Interface-
• Most GC-MS interfacing is now done by simply inserting the
capillary column directly into the ion source.
• This gives a helium or hydrogen GC carrier gas velocity of 25-35
cm/sec or a flow of about 1-2 ml/min.
Interface

18. 3) Perm Selective Membrane
• The permselective membrane interface, developed by Llewellyn and
Littlejohn
• Made of a silicone-rubber membrane that transmits organic non-polar
molecules and acts as a barrier for (non-organic) carrier gases.
• Despite being a very effective enrichment procedure, it also suffers from
discrimination effects with more polar analytes
Interface

19. 4) Molecular Effusion
• The molecular effusion interface is based on the molecular filtering of the gas
effluent by means of a porous glass frit.
• The column effluent passes through a fritted tube situated in a vacuum
chamber. Small molecules traverse the microscopic pores in the tube walls
and are evacuated whereas high molecular mass molecules are transferred to
the ion source.
• Among the principal drawbacks of this interface are the high dead volume
added and its high surface area. Also, as in the case of the jet separator, this
interface shows discrimination effects in the case of smaller molecules.
Interface

20. MS
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Mass Spectroscopy

21. Mass Spectroscopy: Introduction
• Mass spectrometry (MS) works by placing a charge on a molecule, which
converts it to an ion (process is called ionization)
• Generated ions are then resolved according to their mass-to-charge ratio
(m/z) by subjecting them to electrostatic fields (mass analyzer), then
detected
• MS is most commonly interfaced with GC, but increasingly interfaced with
HPLC
• MS instrument performs 3 functions:
Ionize the molecules
Charged molecular
ion and its fragments
must be separated
according to their m/z
Separated, charged
fragments must be
monitored by a
detector

22. Typical – MS Working (Quadrupole)

23. Ionization
method
Typical
Analytes
Sample
Introduction
Mass
Range
Method
Highlights
Electron Impact (EI)
Relatively
small
volatile
GC or
liquid/solid
probe
to
1,000
Daltons
Hard
method
versatile
provides
structure
info
Chemical Ionization (CI)
Relatively
small
volatile
GC or
liquid/solid
probe
to
1,000
Daltons
Soft
method
molecular
ion peak
[M+H]+
Electrospray (ESI)
Peptides
Proteins
nonvolatile
Liquid
Chromatography or
syringe
to
200,000
Daltons
Soft
method
ions often
multiply
charged
Sample Ionization Method

24. Sample Ionization Method

25. Quadrap
ole
Time of
Flight
Fourier
Transform
Ion Trap
Isotope
Ratio
Mass filter, since it filters
ions that achieve stability
from those that do not
Ion trap: Stable ions are trapped; Unstable ions are ejected and detected
Quadrupole: Stable ions reach detector; Unstable ions hit rods and are pumped
away
Ions are pulsed from
source with same
kinetic energy, so ions
of different m/z ratios
acquire different
velocities, which
determines time to
reach detector
Multidimensional
quadrupole mass
analyzers that store
ions (trap), and eject
these trapped ions
according to their
m/z ratios
Deconvolutes image currents produced
by ion motion into mass spectra
Mass Analyzers

26. Graphs &
study
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Mass Spectroscopy

27. Fragment (m/z) that has highest abundance or
intensity (presented at 100% relative abundance,
for comparison to others)
Peak with highest mass number;
Positively charge intact molecule
with m/z = molecular mass
Smaller fragments, due to stepwise
cleavage of large fragments
Case Study

28. Example Application:
• Caffeine, theobromine, theophylline
• Catechins
• Compounds of concern: Melamine, Acrylamide,
Furans, Antibiotic residues
• Determine the compounds during kinetics
Application

29. Advantages
• High sensitivity
• excellent detection limits. Typically low ppb to high ppt
• High selectivity
• identification is based on two parameters not one
(retention time and mass spectrum must match standard)
selects analyte of interest with very high confidence
• Speed
• typical analysis takes from 1/2 hour to approx. 1 hour
analysis can contain upwards of 80 and more pollutants
Disadvantages
• Higher capital cost (approx. $ >85 K vs. $15 K for GC)
• Higher maintenance (time, expertise and money)
• Optimum results requires analyst knowledgeable inboth
• Chromatography and mass spectrometry
Advantages & Disadvantages

30. THANK YOU !!