GAS CHROMATOGRAPHY-MASS SPECTROSCOPY HYPHENATION GC-MS HYPHENATION TECHNIQUE GAS CHROMATOGRAPHY MASS SPECTROSCOPY

1. GC-MS
SANDEEP BINDRA
MPHARM 2ND SEMESTER
KH.PH.P2MPC22001

2. INTRODUCTION
Spectroscopic + chromatographic hyphenation Hyphenated technique
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.
Gas chromatography is a technique capable of separating, detecting, and partially
characterizing organic compounds particularly when present in small quantities.
 Mass spectrometry provides some definite structural information in small quantities.
 The separation and identification of the components of complex natural and synthetic
mixtures are achieved more quickly than any other technique with less sample

3. Gas Chromatography/Mass Spectrometry
(GC/MS)
Gas
Chromatography
Mass
Spectrometry
Gas
Chromatography
- Mass
Spectrometry
Separates mixture of chemicals
so each can be identified
individually
Identifies (detects) chemicals
based on their molecular weight
or mass
A Chemical Analysis Technique
combining two instruments to
provide powerful separation
and identification capabilities

4. PRINCIPLE
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.

5. INSTRUMENTATION

6. SAMPLE
NATURE:- Samples should be organics, must be volatile or Semi-volatile
thermally stable
STATE:- Organic compounds must be in solution for injection into the gas
chromatograph. The solvent must be volatile and organic (for example, hexane or
dichloromethane).
AMOUNT:- Depending on the ionization method
PREPARATION:- Sample preparation can range from simply dissolving some
of the samples in a suitable solvent to extensive. Clean-up procedures using
various forms of liquid chromatography.

7. GC-MS Components
Flow controller assembly
Compressed gas cylinder
Pressure Regulator (Soap Bubble meter)
Valve
Filter
Injection system
Injection Port
Direct injection system
Flash vaporization technique

8. Column
Temperature Programming
Detectors
Non-destructive
oThermal conductivity detector
oElectron capture detector
Isothermal
Gradient
Destructive
o Flame ionization detector
o Argon ionization detector
o Nitrogen Phosphorous
detector

9. GC-MS INTERFACE
The interface must provide the link between the two instruments.
The high pumping speeds used in mass spectrometers may permit the total
effluent from capillary GC columns to be transported to the ion source of the
mass spectrometer.
When the chemical ionization reagent gas is used as the carrier gas ,the effluent
can be introduced directly into the mass spectrometer.

10. TYPES OF INTERFACES
Watson-Biemann Effusion Separator
Ryhage Jet Separator
Llwellyn-Littlejohn membrane Separator

11. EFFUSION SEPARATOR
Since the carrier gas molecules are usually much lighter than those of the
sample, they can be removed preferentially by an effusion chamber.
Effluent from the gas chromatography passes through a tube constructed of
ultrafine porosity sintered glass.
The porous barrier is surrounded by a vacuum chamber.
The lighter carrier gas (assumed to be helium) permeates the effusion barrier in
preference to the heavier organic molecules.
Enrichment is typically five to sixfold and the yield is about 27%.

12. ADVANTAGE
Relatively simple and inexpensive approach.
DISADVANTAGE
High dead volume added.
High surface area.
Rate of diffusion is molecular weight dependent.
Selectivity based on molecular weight.

13. JET ORIFICE SEPARATOR
A precisely aligned, supersonic jet orifice system is effective in removing the
carrier gas by effusion.
Effluent from the gas chromatography is removed through a fine orifice, where
it rapidly expands into a vacuum chamber.
During this expansion, the faster diffusion rate of helium results in a higher
sample concentration in the core of the gas stream, which is directed towards a
second jet or orifice aligned with the first jet.
Alignment and relative spacing of the expansion and collector orifices are very
critical.

14. The distance between jets must be changed for a change in flow rates.
Yields are about 25%.
An all-glass jet separator is frequently used for packed column operation.
The short path through the interface to the ion source reduces dead volume,
which gives better peak separation.
ADVANTAGES
Versatile ,inert and efficient.
DISADVANTAGE
Reduced efficiency with more volatile compounds.
Potential plugging problem at the capillary restrictor.

15. MEMBRANE SEPARATOR
The membrane separator takes advantage of large differences in permeability
between most organic molecules and the carrier gas when both are confronted by
a membrane.
Effluent from a gas chromatography enters a cavity that is separated from the
mass spectrometer vacuum system by a dimethyl silicone rubber membrane,
usually about 0.025-0.040 mm thick.
Helium has a low permeability, whereas the organic molecules pass through the
membrane and directly into the high vacuum of the mas spectrometer system.
Enrichment values are 10-20 fold; the yield may be 30-90% .

16. Major problems with this type of separator are the temperature limits(80-220ºC)
and temperature optimization.
The upper temperature limit is a serious disadvantage that cuts out a segment
of GC-MS work.
Each compound has an optimum temperature for membrane enrichment,and
thus sample discrimination occurs.
There is also a time lag of about 0.1 sec by the sample molecules pass through
the membrane.
DISADVANTAGE
Membrane selectivity based on polarity and molecular weight
Slow to respond.

17. The most extensively used interfaces for a GC-MS are electron impact
ionization (EI) and chemical ionization (CI) modes.
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 30m long by 220 to 250 µm Inner diameter gives
an ion source pressure of 10-6 to 10-5torr.
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 the Mass spectrometer should be high.

18. Mass spectrometer Components
ION SOURCE
IONIZATION
METHOD
TYPICAL ANALYTES SAMPLE
INTRODUCTION
MASS RANGE
CHEMICAL
IONIZATION
Relatively
small,volatile
GC or liquid or solid
probe
Upto 1000Daltons
ELECTRON IMPACT
IONIZATION
Relatively
small,volatile
GC or liquid or solid
probe
Upto 1000 Daltons
ELECTROSPRAY
IONIZATION
Peptides,Proteins,n
onvolatile
Liquid
chromatography
Upto 200000
Daltons
FAST ATOM
BOMBARDMENT
Carbohydrates,orga
nometallics,peptide
s,nonvolatile
Sample mixed in
viscous matrix
Upto 600 Daltons
MATRIX ASSISTED
LASER DESORPTION
IONIZATION
Peptides,proteins,n
ucleotides
Sample mixed in
solid matrix
Upto 500000
Daltons

19. MASS ANALYZERS
Quadrupole Mass Analyzer:
Also known as Hewlett-Packard or Mass Selective Detector.
In quadrupole mass analyzer a set of four rods are arranged in parallel direction.
Ions travels in quadrupole axis with cork screw type of trajectory.
It functions as a mass filter.
Ion Trap Mass Analyzer
The ion trap mass analyzer operates by similar principles 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.

20. 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 takes to reach the detector.
If the particles all have the same charge, kinetic energies will be identical and
their velocities will depend upon only on their masses.
Detector
Data Handling
Mass spectrometers employ computer control of the same functions and also
use a computerized display and output.
It is used to identify and measure the concentration of one or more analytes in a
complex mixture.

21. ADVANTAGES OF GC-MS
High sensitivity excellent detection limits.
Speed-typical analysis takes from ½ hour to approx.1 hour.
DISADVANTAGES
Determining positional substitution on aromatic ring is often difficult.
Certain isomeric compounds cannot be distinguished by mass spectrometry.

22. APPLICATIONS OF GC-MS
Elucidation of the structure of organic and biological molecule.
Identification of drugs of abuse and metabolites of drugs in blood,urine and
saliva.
Impurity profiling of pharmaceuticals.
Determination of pesticide residue in food.
Perfume analysis.
Criminal forensics-sports antidoping analysis.

23. REFERENCE
AH Beckett, J.B Stenlake, Pharmaceutical chemistry 4 th Edition-Part two (Pg.No 474-477).
Skoog, Holler, Lrouch, Instrumental-Analysis. (Pg.No 606-629).
GurdeepR.Chatwal, K.Anand, Instrumentalmethodsof chemicalanalysis(Pg.No2.272,2.673)