My Seminar title..

1. 1

2. Gas Chromatography Mass Spectrometry
(GC-MS)
Presented by :Ayesha Abdul Ghafoor
Student ID : MS (I)
(Analytical Chemistry section)
Session : 2011-13
2

3. Latest Advances in Chemistry
GAS CHROMATOGRAPHY
MASS SPECTROMETRY (GC-
MS)
3

4. GC-MS
 Introduction
 History
 Instrumentation
 Gas Chromatograph
 Interface
 Mass Spectrometer
 Data System
 GC-MS operation
 Analysis of Results
 Calibration of Instrument
 Applications
 Limitations
 Good Practise of GC-MS
 Conclusion
 Refrences
4

5. Hyphenated Techniques
term hyphenated techniques introduced by
Hirschfeld
―It refers to an on-line combination of a
chromatographic sepration technique with a
sensitive and element-specific Spectroscopic
detector‖ .
Chromatography + Spectroscopy = Hybrid Techniques
5

6. Hyphenated Techniques
Hybrid techniques exploit both qualitative and
quantitavie advantages .
Examples of Hyphenated techniques are
 LC-FTIR
 LC-NMR
 ICP-ES
 GC-MS
6

7. GC-MS
GC-MS is an integrated composite analysis Instrument
Combining GC which is excellent in its ability for separation
with mass spectrometry ideal in identification and elucidate
structure of separated component .
Gas Interface Mass spectrometry
Chromatography Combines both Ionise eluted
It seprates techniques by componet and
components of removing pressure seprate, identify it
sample incompatibility according to its
problem between mass to charge
GC and MS ratio
7

8. Introduction
 Gas chromatography-mass spectroscopy (GC-MS) is a hyphenated
analytical technique
 exquisitely sensitive but also specific and reliable
 GC can separate volatile and semi-volatile compounds with great
resolution, but it cannot identify them.
 MS provide detailed structural information on most compounds such that
they can be exactly identified, but can’t readily separate them.
8

9. Continued............
 Therefore, marriage of both instruments have been propsed
shortly after the development of GC in the mid-1950s.
 we obtain both qualitative and quantitative information of our
sample in a single run within the same instrument
 Today computerized GC/MS instruments are widely used in
environmental monitoring ,in the regulation of agriculture and
food safety , and in the discovery and production of medicine.
9

10. Historical Background of GC-MS
 Roland Gohlke and Fred McLafferty introduce use of MS as
detecot of GC in 1950s
 Miniaturized computers has helped in the simplification of
instrument
 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
 In 2005 GC tandem MS/MS have been intoduced
10

11. Principle of GC-MS
 The sample solution is injected into the GC inlet where it is
vaporized and swept onto a chromatographic column by the carrier
gas (usually helium).
 The sample flows through the column and the compounds
comprising the mixture of interest are separated by virtue of their
relative interaction with the coating of the column (stationary phase)
and the carrier gas (mobile phase).
 The latter 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 and detected according to
their mass to charge m/z ratio
11

12. Instrumental Layout
GC-MS comprise following major blocks
1. the gas chromatograph
2. Interface
3. the mass spectrometer
4. A data system is necessary to handle results
obtained during a sample run
12

13. GC-MS Instrument
Fig 1:The insides of the GC-MS, with the column of the gas chromatograph in the
oven on the right.
13

14. GAS CHROMATOGRAPHY
 Gas chromatography leads to Separation of
volatile organic compounds
 Separation occurs as a result of unique
equilibrium established between the solutes and
the stationary phase (the GC column)
 An inert carrier gas carries the solutes through
the column
14

15. 1. Gas Chromatograph
Basic Components:
 Carrier Gas
 Gas Controls
 The Injector
 The Column
Two Groups:
 Packed Column
 Capillary Column
 The Oven
 The Detector
(Mass Spectrometer)
15

16. Carrier Gas/Mobile Phase
Gas Requirements:
 Inert
 Column requirements
 Detectors
 Purity
 Better than 99.995%
 Better than 99.9995% for Mass Spec.
 Cost and Availability
16

17. Injector
 Packed column injectors
 Split Injection
 Splitless Injection
 Programmed Split/Splitless Injector
 Programmed On-Column Injector
17

18. Septum
purge Carrier gas in
Split vent
Cooling fins
Cooling fan
Liner
Split point Heater block
Capillary column
Fig 1.1:Programmed Split/Splitless Injector 18

19. Columns
 There are two kinds of columns used i.e. Packed
or capillary columns
 The gas chromatograph GCMS utilizes a
capillary column which
 most widely used columns for GC-MS are those
in which the stationary phase has been
chemically bonded to the fused silica
 DB-5 is a common trade name.
19

20. FIG 1.2 :PACKED AND CAPILLARY
COLUMN COMPARISON
Fig1.3 :( a) Uninstalled Capillary Columns (b)Installed capillary
Columns 20

21. INTERFACE
 The pressure incompatibility problem between GC
and MS was solved by Inserting an Interface.
 Interface join GC with MS. There are many
interfaces like jet ,Electrospray, thermospray, direct
electrical ionization, moving wire or belt interface.
Commercially available interface are:
1. Jet Interface
2. Direct Interface
21

22. 1. Jet Interface
 device takes advantage 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 to 40 mL/min)
 is sprayed through a small nozzle, indicated into a partially
evacuated chamber (about 10–2 torr).
 The carrier gas is almost always a small molecule with a high
diffusion coefficient, whereas the organic molecules have much
lower diffusion coefficients. 22

23. Fig:1.4: Jet Interface
JET SEPARATORS ARE MADE FROM GLASS BY DRAWING
DOWN A GLASS CAPILLARY, SEALING IT INTO A VACUUM
ENVELOPE, AND CUTTING OUT THE MIDDLE SPACING
23

24. 2. Direct Capillary Infusion Interface
 Most GC-MS interfacing is now done by simply
inserting the capillary column directly into the ion
source.
 Using a column that is 25 to 30 m long by 220 to
250 μm inner diameter gives an ion source pressure
of 10–6 to 10–5 torr
 This gives a helium or hydrogen GC carrier gas
velocity of 25 to 35 cm/sec or a flow of about 1 to 2
mL/min.
 Pumping Speed of Mass spectrometer should be
high
24

25. Capillary Column Interface
Fig1.5 :Direct Capillary Column Interface
25

26. 3.Mass spectrometer
―Mass spectrometry is a technique used for measuring
the molecular weight and determining the molecular
formula of an organic compound‖
In general a mass spectrometer consists of
 an ion source,
 High-vacuum system
 a mass-selective analyzer,
 and an ion collector
26

27. Ion Source
Electron Impact Ioniser
• In an electron-impact mass spectrometer (EI-MS),
a molecule is vaporized and ionized by
bombardment with a beam of high-energy
electrons.
• The energy of the electrons is ~ 1600 kcal (or
70eV).
• The electron beam ionizes the molecule by
causing it to eject an electron.
27

28. Electron
Impact Ionization
H H
H C C H
H H
H H H H
e- + H C C H H C C+ H
H H H H
H H
H C+ C H
H H
28

29. Chemical Impact Ionizer
 CI begins with ionization of methane, ammonia or
another gas,
 creating a radical cation (e.g. CH4•+ or NH3•+).
 sample molecule M will produce MH•+ molecular
ions.
 positively charged species will be detected.
 CI Used for determination of molecular ion while
EI for
 detailed structure Information. hence the two
methods are complementary.
29

30. Chemical Ionisation
• First - electron ionization of CH4:
– CH4 + e- CH4+ + 2e-
• Fragmentation forms CH3+, CH2+, CH+
• Second - ion-molecule reactions create stable
reagent ions:
– CH4+ + CH4 CH3 + CH5+
– CH3+ + CH4 H2 + C2H5+
• CH5+ and C2H5+ are the dominant methane CI reagent ions
30

31. Mass analyzers scan or select ions over a particular m/z range.
contribute to the accuracy, range and sensitivity of an instrument.
common types of mass analyzers are
quadrupole,
magnetic sector,
time-of-flight,
Mass Analyzers
Fourier transform-ion cyclotron resonance (FT-ICR).
31

32. Quadrupole Analyzer
 Quadrupoles are four precisely parallel rods with a direct current
(DC) voltage and a superimposed radio-frequency (RF) potential.
The field on the quadrupoles determines which ions are allowed to
reach the detector. Quadrupoles thus function as a mass filter.
1.6
the B 32

33. Time-of-flight
 The time-of-flight (TOF) analyzer uses an
 electric field to accelerate the ions through the
same potential,
 and then measures the time they take to reach the
detector.
 If the particles all have the same charge, the
kinetic energies will be identical, and their
velocities will depend only on their masses.
Lighter ions will reach the detector first.
33

34. 34

35. Data System
 GCMS system purchased with a powerful (but
small) computer acting as a data system.
 Data System of GC-MS used to identify and
measure the concentration of one or more
analytes in a complex mixture.
 Quantitation can be based on peak areas
 mass chromatograms
 from selected ion monitoring(SIM).
35

36. SELECTED ION MONITORING
 With the selected ion monitoring technique, the mass
spectrometer is not scanned over all masses; instead, the
instrument jumps from one selected mass to another.
 the mass spectrometer spends much more time at a given mass
Difference b/w
SELECTED ION MASS CHROMATOGRAM
MONITORING all of the masses are scanned;
the responses from only a few thus, no preselection is
preselected masses are required
recorded
36

37. Fig 1.7 :Block Diagram of GC-MS
37

38. Sampling
 State
 compounds must be in solution form
 The solvent must be volatile and organic
 Amount
 1 to 100 pg per component are routine.
 Preparation
38

39. GC-MS Operation
1.START-UP PROCEDURE
 Turn on the computer, monitor, data transfer
module and the printer.
 Remove the MS detector from STAND-BY
and engage the pumping unit and heater.
 Turn on the gauge controller - depress the
power and degas buttons simultaneously.
 You are now ready to make a run.
39

40. 2.Operating Conditions:
of GC-MS
 Column Temp. Profile
Initial temp. = 110°C, 4 min. hold
 Ramp at 15°C/min to 140°C
Hold at 140°C for 2 min
 Sample: 1000 ppm acetic acid in water
40

41. 3.Working of GC-MS
 Vaporized Sample introduced into GC inlet
 swept onto the column by He carrier gas &
separated on column.
 Sample components eluted from column moved
to the MS (He removed).
 The computer drives the MS, records the data
 Identification based on it's mass spectrum
 A large library of known mass spectra is stored
on the computer and can be searched for
identification 41

42. interface
Fig1.8 : Schematic of a Gas Chromatography-Mass Spectrometry (GC-MS)
Instrument
42

43. Analysis Time
 In addition to sample preparation time, the
instrumental analysis time usually is fixed by the
duration of the gas chromatographic run,
typically between 20 and 100 min.
 Data analysis can take another 1 to 20 hr (or
more) depending on the level of detail necessary.
43

44. Analytical Information Obtained from
GC-MS
 There are three ways of examining GC-MS data.
 First, the analyst can go through the gas
chromatogram
 The second approach is to look at each mass
spectrum in turn, in essence stacking up the mass
spectra one behind the other and examining them
individually.
44

45. Continued..........
 The third approach is to look at the intensity of
one particular mass as a function of time i.e mass
chromatogram.
 This third approach makes use of the three-
dimensional nature of GC-MS data. Two of these
dimensions
 are the mass versus intensity of the normal mass
spectrum; the third dimension is the GC retention
plot of the intensity of one selected mass as a
function of time is called a mass chromatogram
45

46. Fig1.9 : Three dimensional view of Mass Chromatogram
46

47. Fig 1.10 :GC trace of a three component mixture.The mass spectrometer
gives a spectrum for each component 47

48. Definition of Terms
Molecular ion The ion obtained by the loss of an electron from the
molecule
Base peak The most intense peak in the MS, assigned 100% intensity
Radical cation +ve charged species with an odd number of electrons
Fragment ions Lighter cations formed by the decomposition of the
molecular ion.
These often correspond to stable carbocations.
―A‖ Element—an element that is monoisotopic
Isotope abundance Peak ―A + 1‖ an element with an isotope that is 1 amu above that
of the most abundant isotope 48

49. Consider the mass spectrum of CH4 below:
Fig1.11 : Mass Spectrum of Methane (CH4)
49

50. list of some of problems and their
Solutions in GC-MS Analysis
 contaminations from solvents ,glass ware ;solved by high-quality solvents, the
latter by heating the glassware to 450 °C after solvent and acid washing
 sample decompose before or after workup can be identified by spike recovery
 GC column or GC-MS interface is not working properly can be find out using
a mixture of standard compounds of varying polarities and acidities.
 either the mass spectrometer itself or the data system may not be working
properly can be determined these problems is to run an overall mass
spectrometer performance standard. The one recommended (mandated in many
cases) by the EPA is decafluorotriphenylphosphine .
50

51. Quality Assurance of GC-MS
results
 First, the mass spectra of the unknown compound and of the authentic compound must
agree over the entire mass range
 Second, the GC retention times of the unknown compound and of the authentic
compound must agree within about ±1 to 2 sec.
 Third, a compound cannot be considered fully identified in a mixture unless two other
questions are addressed:
 Is the identification plausible?
 Why is it present in a given sample?
51

52. Applications of GC-MS
 Petrochemical and hydrocarbons analysis
 Geochemical research
 Forensic (arson, explosives, drugs, unknowns)
 Environmental analysis
 Pesticide analysis, food safety and quality
 Pharmaceutical and drug analysis
 Clinical toxicology
 Food and fragrance
52

53. Applications of GC-MS
 Criminal forensics
 GC-MS can analyze the particles from a human body in
order to help link a criminal to a crime.
 accelerant is significant evidence in a fire investigation
because it suggests that the fire was set intentionally.
53

54. Law enforcement
 GC-MS is increasingly used for detection of illegal
narcotics marijuana, cocaine, opioids Clinicians
oxycodone and oxymorphone
 Piperazines are not detectable by typical immunoassay
testing, but they may be detectable via GC-MS
 Sports anti-doping analysis
54

55. Astrochemistry
Several GC-MS have left earth. Two were
brought to Mars by the Viking program. Venera
11 and 12 and Pioneer Venus analysed the
atmosphere of Venus with GC-MS.
55

56. Petrochemical and hydrocarbons
analysis
 PONA is an acronym for Paraffins, Olefins,
Naphthenes and Aromatics.
 Environmental monitoring and cleanup
 GC-MS is becoming the tool of choice for
tracking organic pollutants in the environment.
56

57. Medicine
 Inborn error of metabolism are now detectable by
newborn screening tests, especially the testing
using gas chromatography–mass spectrometry.
 possible to test a newborn for over 100 genetic
metabolic disorders by a urine test at birth based
on GC-MS
57

58. Security
 Thermo Detection (formerly Thermedic
explosive detection systems have become a part
of all US airports. These systems run on a host of
technologies, many of them based on GC-MS.
58

59. Food, beverage and perfume
analysis
 Foods and beverages contain numerous
aromatic compounds identification and in
Foodpairing
59

60. Cost
 The major factor influencing the cost
 ionization methods available on the
instrument and the
 mass range of the mass spectrometer.
 only electron impact ionization and have a mass
range of 20 to 700 cost about $50,000.
 Those capable of both CI and EI and with mass
ranges of 20 to 2000 cost about $200,000.
 Operating costs In most laboratories are about
5% of the instrument cost per year.
60

61. Limitation
 Only compounds with vapor pressures exceeding
about 10–10 torr can be analyzed by gas
chromatography-mass spectrometry (GC-MS).
 Determining positional substitution on aromatic
rings is often difficult.
 Certain isomeric compounds cannot be
distinguished by mass spectrometry (for
example, naphthalene versus azulene), but they
can often be separated chromatographically.
61

62. Good Practise
 Always wear clean, lint-free, nylon gloves when
handling parts which will come in contact with the
sample stream.
 Before login, please check the standard spectrum to
make sure the machine is in good condition for the
day.
 to avoid possible carryover from previous sample,
run a blank .
 Don’t overload the machine with too concentrated
sample
 Concentration >0.001mg/mL may carryover.
 If there is a problem, please notify respective
company for help 62

63. Required Level of Training and
Maintenance
 The required level of training and expertise
varies as a function of the level of data
interpretation and instrument maintenance
 For interpretation of the data, some chemistry
training is needed, particularly organic chemistry
 Refreshable courses specific in mass
spectrometry through 1- to 2-week offered
through professional societies (such as the
American Chemical Society or the American
Society for Mass Spectrometry). 63

64. Conclusions
 Gass Chromatography mass spectrometry is
64

65. References
 McLafferty, F. W.Hertel, R. H. and Villwock, R. D.
(1974), "Probability based matching of mass spectra.
Rapid identification of specific compounds in
mixtures". Organic Mass Spectrometry 9 (7): 690–
702
 Amirav, A.Gordin, A. Poliak, M. Alon, T. and
Fialkov, A. B. (2008), "Gas Chromatography Mass
Spectrometry with Supersonic Molecular Beams".
Journal of Mass Spectrometry 43: 141–163.
 R. A. Hites and K. Biemann (1968), Analytical
Chemistry, 40 ,1217–21.
 McMaster, C.McMaster, Marvin C. (1998). GC/MS:
a practical user's guide. New York: Wiley. 65

66. References
 R. S. Gohlke (1959), Analytical Chemistry, 31 535–41.
 J. T. Watson and K. Biemann (1965), Analytical
Chemistry, 37 , 844–51.
 R. Ryhage (1964), Analytical Chemistry, 36, 759–64.
 T. E. Jensen and others (1982) , Analytical
Chemistry, 54, 2388–90.
 Giannelli, Paul C. and Imwinkelried, Edward J. (1999).
Drug Identification: Gas Chromatography. In Scientific
Evidence 2, pp. 362.
 R. A. Hites and K. Biemann, Analytical Chemistry, 42
(1970), 855–60.
66

67. THANK YOU
HAVE A NICE DAY
Questions ???
67