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Gas Chromatography Mass Spectrometry (GC-MS)

Presented by :Ayesha Abdul Ghafoor

Student ID : MS (I)

(Analytical Chemistry section)

Session : 2011-13

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GAS CHROMATOGRAPHY MASS SPECTROMETRY

(GC-MS)

Latest Advances in Chemistry

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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

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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” .

+ =

Hybrid TechniquesChromatography Spectroscopy

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Hyphenated Techniques

Hybrid techniques exploit both qualitative and quantitavie advantages .

Examples of Hyphenated techniques are LC-FTIR LC-NMR ICP-ES GC-MS

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Gas Chromatography

It seprates components of sample

Interface

Combines both techniques by removing pressure incompatibility problem between GC and MS

Mass spectrometry

Ionise eluted componet and seprate, identify it according to its mass to charge ratio

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 .

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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.

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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.

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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

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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

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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

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GC-MS Instrument

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

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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

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1. Gas Chromatograph

Basic Components: Carrier Gas Gas Controls The Injector The ColumnTwo Groups:

Packed Column Capillary Column

The Oven The Detector

(Mass Spectrometer)

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Carrier Gas/Mobile PhaseGas Requirements:

Inert Column requirements Detectors Purity

Better than 99.995% Better than 99.9995% for Mass Spec.

Cost and Availability

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Injector

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

18Fig 1.1:Programmed Split/Splitless Injector

Septumpurge Carrier gas in

Split vent

Split point

Capillary column

Liner

Cooling fins

Heater block

Cooling fan

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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.

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FIG 1.2 :PACKED AND CAPILLARY COLUMN COMPARISON

Fig1.3 :( a) Uninstalled Capillary Columns (b)Installed capillary Columns

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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

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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.

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JET SEPARATORS ARE MADE FROM GLASS BY DRAWING DOWN A GLASS CAPILLARY, SEALING IT INTO A VACUUM ENVELOPE, AND CUTTING OUT THE MIDDLE SPACING

Fig:1.4: Jet Interface

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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

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Fig1.5 :Direct Capillary Column Interface

Capillary Column Interface

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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

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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.

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Electron Impact Ionization

e- + H C

H

H

C

H

H

H

H C

H

H

C

H

H

H

H C

H

H

C

H

H

+ H

H C

H

H

C

H

H

H

+

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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 fordetailed structure Information. hence the two

methods are complementary.

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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

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Mass Analyzers

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,

Fourier transform-ion cyclotron resonance (FT-ICR).

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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.

the B

1.6

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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.

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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).

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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 MONITORING the responses from only a few preselected masses are recorded

MASS CHROMATOGRAM all of the masses are scanned; thus, no preselection is required

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Fig 1.7 :Block Diagram of GC-MS

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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

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GC-MS Operation1.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.

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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

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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

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

interface

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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.

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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.

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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

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Fig1.9 : Three dimensional view of Mass Chromatogram

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

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Definition of TermsMolecular 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. 

Isotope abundance Peak

These often correspond to stable carbocations.“A” Element—an element that is monoisotopic“A + 1” an element with an isotope that is 1 amu above that

of the most abundant isotope

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Consider the mass spectrum of CH4 below:

Fig1.11 : Mass Spectrum of Methane (CH4)

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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 .

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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?

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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

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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.

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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

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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.

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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.

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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

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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.

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Food, beverage and perfume analysis

Foods and beverages contain numerous aromatic compounds identification and in Foodpairing

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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.

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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.

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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

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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).

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Conclusions

Gass Chromatography mass spectrometry is

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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.

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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.

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THANK YOU HAVE A NICE DAY

Questions ???