GC-MS principle instrumentation and working

1. GC-MS
Presented by
CHINNU SURESH
M PHARM 2ND SEMESTER

3. INTRODUCTION
• Gas chromatography mass spectrometry (GC-MS) is an analytical technique that combines two
powerful techniques. The analytical instrument consists of a gas chromatograph that is hyphenated
via a heated transfer line to the mass spectrometer, and the two techniques take place in series.
• GC-MS can be used with solid, gaseous, and liquid samples, GC-MS analysis is most often used
with volatile and semi-volatile compounds.
Reference:https://chemistnotes.com/analytical_chemistry/gas-chromatography-mass-spectrometry-
principle-instrumentation-advantages-and-10-reliable-applications/
Hyphenated
Technique

4. GC-MS Principle
 The sample solution is injected into the GC inlet where it is vaporized and
enter into a chromatographic column by the carrier gas (usually
helium, Helium is most commonly used because it is safer than, but
comprable to hydrogen in efficiency, has a larger range of flow rates and is
compatible with many detectors.).
 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 LAYOUT
Gas
Chromatography
• Carrier gas
• Pneumatic control
• Injector
• Colum
• oven
Interface
• Jet interface
• Direct
Capillary
Infusion
interface
• Watson-
Biemann
effusion
interface
Mass
Spectrometer
• Ion source
• High vacuum
system
• Mass analyzer
• Ion collector
Data System

8. GAS CHROMATOGRAPHY
 1. Carrier Gas:
• Served as mobile phase supplied in the steel tank under high
pressure.
• At pressure of 40-80 psi this passes into flow controllers.
• Example- nitrogen, helium; hydrogen and argon can also be used.

9. 2.Pneumatic Control
 Gas supply is regulated to the correct pressure and then fed to the required part of
instrument.
 Older instruments manual pressure control via regulators.
 Modern GC instruments Electronic Pneumatic pressure controller.
3. Oven:
 Temperature programmable, typically range from 5°C-400°C but can go as low as -25°C
with cryogenic cooling.

10. 4- Sample Injection Port
Sample is made to vaporized rapidly before entering to column.
Various kind of injectors:
• Packed column injectors
• Split injection
• Splitless injection
• Programmed Split/Splitless injection
• Programmed On-Column injector
5 Column:
Two kinds of column used:
✔ Packed column
✓ Capillary column
Gas chromatograph GC-MS utilizes capillary column.
Here, stationary phase has been chemically bonded to the fused silica, e.g., DB-5.

12.  Packed Column :
 -Less commonly used, having diameter of 2-
3 mm and length of 0.5-10 m.
 Manufactured from steel or glass, internal
wall is treated to avoid catalytic effect with
the sample.
 They can withstand a carrier gas flow rate
within range 10- 40ml/min.
 Capillary Column:
 Consist of long capillary 10-100 m in length.
 Made up from stainless steel & coil.
 Shorter columns for fast analysis
 Larger columns resolution separation for high

14. 6.Detectors:
✓ Simple and reliable
✓ Sensitive to electronegative groups (halogens)
 Non-destructive
o Thermal conductivity detector
o Electron capture detector
 Destructive
o Flame ionization detector
o Argon ionization detector
o Nitrogen Phosphorous detector

15. 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.
TYPES OF INTERFACES
 Watson-Biemann Effusion Separator
 Ryhage Jet Separator
 Direct capillary infusion interface

16. 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%.
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.

17. 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.
 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.

18. 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% .
 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.

19. 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.

20. 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
• An ion collector
• Data system

21. ION SOURCE

22. 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
Ion entering into the chamber Trapped by EMF Ions oscillate in Concentric trajectories

23.  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.

24. How does a GC-MS instrument work?
The sample mixture is first separated by the GC before the analyte molecules are eluted into the MS for detection. They are
transported by the carrier gas (1)), which continuously flows through the GC and into the MS, where it is evacuated by the
vacuum system (6).
1. The sample is first introduced into the GC manually or by an autosampler (2) and enters the carrier gas via the GC inlet
(3). If the sample is in the liquid form, it is vaporized in the heated GC inlet and the sample vapor is transferred to the
analytical column(4).
2. The sample components, the “analytes”, are separated by their differences in partitioning between the mobile phase (carrier
gas) and the liquid stationary phase (held within the column), or for more volatile gases their adsorption by a solid stationary
phase. In GC-MS analyses, a liquid stationary phase held within a narrow (0.1-0.25 mm internal diameter) and short (10-30 m
length) column is most common.
3. After separation, which for GC-MS analyses doesn’t require total baseline resolution unless the analytes are isomers, the
neutral molecules elute through a heated transfer line (5) into the mass spectrometer.

25.  4. Within the mass spectrometer, the neutral molecules are first ionized most commonly by electron ionization (EI). In
EI, an electron, produced by a filament, is accelerated with 70 electron volts (eV) and knocks an electron out of the
molecule to produce a molecular ion that is a radical cation. This high energy ionization can result in an unstable
molecular ion and excess energy can be lost through fragmentation. Bond breakage can lead to the loss of a radical or
neutral molecule and molecular rearrangements can also occur. This all results in a, sometimes very large, number of
ions of different masses, the heaviest being the molecular ion with fragment ions of various lower masses, depending
on:
• the molecular formula
• the molecular structure of the analyte
• where bond breakage has occurred
• which part has retained the charge
 5. The next step is to separate the ions of different masses, which is achieved based on their m/z by the mass analyzer
(8).

26.  There are numerous different mass analyzer types, and this is where the vast differences in mass
resolution (and hence instrument price) is seen. Mass resolution is the ability of the mass analyzer to
separate ions with very small differences in m/z. Unit mass resolution instruments can only separate
nominal masses or those down to a single decimal place, whereas high mass resolution (HRMS)
instruments can separate them to four or five decimal places.
 The most common type of unit mass instrument is the quadrupole, which is a scanning instrument
and varies the voltage to allow only ions of a certain m/z to have a stable trajectory through the four
poles to reach the ion detector. Quadrupole instruments are used in two different modes of operation:
• Full scan mode, where all ions are acquired across a mass range, useful for identification of
unknowns, method development and qualitative and quantitative analysis for higher concentration
analytes.
• Selected ion monitoring (SIM) mode, where only selected ions that represent the target compound
are acquired, useful for trace analysis, as higher sensitivity is obtained, but only of target analytes.

27.  6. After the ions have been separated by the mass analyzer based on their m/z, they reach the Ion
detector (9) where the signal is amplified by an electron multiplier (for most low resolution MS) or
a multi-channel plate (for most HRMS instruments). The signal is recorded by the acquisition
software on a computer (10) to produce a chromatogram and a mass spectrum for each data point.

28. Application of GC-MS
• Medicine: Several congenital metabolic illnesses can be detected with the help of GC-MS screening
techniques. Patients with hereditary metabolic abnormalities can be diagnosed by testing their urine for
the presence of trace chemicals. Oils in ointments, creams, and lotions are also detectable by this
instrument.
• Biological and pesticide detection: Blood and urine can be tested for the presence of drugs using GC-
MS. This includes anesthetics, anticonvulsants, antihistamines, sedative-hypnotics, opioids, and anti-
epileptic medications.
• Pharmaceutical industries: The pharmaceutical industry makes extensive use of GC-MS in the areas
of analytical development, quality control, quality assurance, production, and pilot plants for API, bulk
medicines, and formulations.
• Clinical toxicology: GC-MS is extensively employed in clinical toxicology to identify toxins and
venoms.
• Environmental monitoring: The gas chromatograph-mass spectrometer (GC-MS) is now widely used
as a method for detecting organic contaminants in the environment.

29. • Forensic Applications: The American Society for Testing Materials (ASTM) specifies that GC-
MS be used for fire debris analysis. GC-MS is commonly employed in anti-doping laboratories to
detect performance-enhancing drugs like anabolic steroids, and in forensic toxicology to detect
poison and steroids in biological materials.
• Industries: Common applications of GC-MS include regular analysis in the food, environmental,
forensics, anti-doping, and consumer products industries to detect volatile compounds with
molecular weights typically below 700 amu.
• Food and Fragnance applications: The fatty acids, aldehydes, esters, alcohols, and terpenes
present in food and drink can be easily analyzed using gas chromatography-mass spectrometry. It
also has the ability to detect spoilage and contamination in food.
• Chemical Welfare: The GC-MS method is utilized by explosive detection systems installed in
public locations for the purpose of conducting analyses and locating chemical warfare chemicals.
• Academic research: The GC-MS is an advanced technique that allows for the characterization
and identification of newly synthesized or derivatized compounds.

30. Limitation of GC-MS
• The fundamental drawback of GC is that it can only be used to distinguish compounds that are
either volatile or thermally stable.
• High cost
• Complex sample preparation: In order to properly prepare samples for GC-MS analysis,
including extraction and cleanup steps, it can take a while and call for specialized tools and
knowledge.
• Limited sensitivity: Although some GC-MS may have excellent sensitivity, the technology might
not be enough for the analysis of complicated materials or the detection of trace pollutants.
• Interferences: Some compounds in the sample may affect how accurately the analysis is
performed and cause false positives or false negatives.
• Limited structural information: While GC-MS can offer comprehensive details on a compound’s
molecular weight and elemental composition, it might not be able to offer details about the
molecular structure or particular functional groups that are present.

31. • Matrix effects: The precision and dependability of the GC-MS analysis might
be impacted by the presence of additional substances in the sample, collectively
referred to as the matrix. Careful sample preparation and the use of internal
standards can help reduce these matrix effects, although they still may introduce
some errors.
• Limited selectivity: Although GC-MS has a high degree of sensitivity and
specificity, it may not be able to differentiate between isomers or structurally
similar molecules. Issues with GC-MS can make it difficult to identify and
quantify certain compounds.
• Limited linear range: GC-MS can only reliably detect concentrations of a drug
within a particular range due to its limited linear range. If the compound
concentration is outside of this range, the results may not be correct.
• Recovery of the sample’s individual components is not possible.

32. 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)
 https://www.slideshare.net/DauRamChandravanshi1/gas-chromatography-mass-spectrometry-
gcms
 https://www.technologynetworks.com/analysis/articles/gc-ms-principle-instrument-and-
analyses-and-gc-msms-362513


33. THANK YOU

34. Gas Chromatography and Mass Spectrometry
(GC-MS)
Gas
Chromatography
Mass
Spectrometry
Gas Chromatography
and Mass Spectrometry
(GC-MS)
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