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Gas Chromatography/Mass Spectrometry (GC/MS)
Environmental biotechnology Division
Raj Kumar Regar (PhD Student)
CSIR-Indian Institute of toxicology Research
Supervisor: Dr. N. Manickam
Introduction
Principle
Instrumentation
Working
Applications
Content
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 the organic compounds particularly when present in small quantity.
Mass spectroscopy provides some definite structural information from in small quantity.
The separation and identification of the components of complex natural and synthetic mixture are achieved more quickly than any other technique with less sample
Introduction
GasChromatography
MassSpectrometry
Gas Chromatography -Mass Spectrometry =
Identifies (detects) chemicalsbased on their molecular weight or mass
A Chemical Analysis Technique combining two instruments to provide for
powerful separation and identification capabilities
Separates mixture of chemicals so each can be identified individually
Gas Chromatography/Mass Spectrometry (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.
Principle of GC-MS
Nature :- Samples should be organics must be volatile or semivolatile 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, analytical sensitivities of 1 to 100 pg per component are routine.
Preparation :- Sample preparation can range from simply dissolving some of the sample in a suitable solvent to extensive. Clean up procedures using various forms of liquid chromatography.
Samples
Classification of Organic Compounds
Boiling Point Polarity * Technique
Ionic high high HPLC, HPLC/MS
NonVolatiles high high HPLC, HPLC/MS
SemiVolatiles medium low-medium GC; GC/MS; HPLC
Volatiles low low-medium GC; GC/MS
* Increasing polarity = Increasing solubility in water
6. Ion Source7. Mass Analyser8. Detector9. Vacuum System10. Control Electronics
1. Pneumatic controls2. Injector3. Oven4. Column5. Interface
Instrumentation
Image of GC-MS
A GC syringe penetrates a septum to inject sample into the vaporization camberInstant vaporization of the sample, 280 CCarrier gas transports the sample into the head of the columnPurge valve controls the fraction of sample that enters the column
Injector
Splitless (100:90) vs. Split (100:1)
Injector
Syringe
Injector
Syringe
Purge valveopen
Purge valveclosed
GC column GC column
HeHe
• Packed
• Capillary
Cross section
Columns
GC Detectors
(Operational Description)
Introduction System - Gas Chromatography Ionization Mass Separation Mass DetectionData System
Mass Spectrometer
Ionization Source
Mass Analyzer
DedicatedData System
Vacuum System - approx. 10-6 torr
ParticleDetector
Gas Chromatography
Mass Spectrometry
Operational Description
Sample ionization
Sample introduction / ionization method:
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
Fast Atom Bombardment (FAB)
Carbohydrates Organometallics
Peptides nonvolatile
Sample mixed in viscous
matrix
to 6,000 Daltons
Soft method but harder than ESI or
MALDI
Matrix Assisted Laser Desorption (MALDI)
Peptides Proteins
Nucleotides
Sample mixed in solid matrix
to 500,000
Daltons
Soft method very high
mass
Molecular‘Ion’
The Ionization Process(Electron Impact) Neutral molecules are converted into Ions (charged particles)
(70 Electron Volts)
Neutral Molecule
Fragment Ion 1
Fragment Ion 2, etc.
e- +
CCCCC
C H
HH
HH
He- +CCCCC
C H
HH
HH
H + 2e-
+.
* Mass Analysis can only work for charged species - not for neutrals.
+ 2e-+ .
Quadrupole Mass Ion Filter
01/05/2023 SAMADANA PRABHU 21
Total Ion Chromatogram (TIC)
Definition: A plot of the total ion current vs. retention time obtained from a chromatography experiment with mass detection.
•Identify unknown compounds from EI (GC/MS) and MS/MS spectra, using library searching.
Identify unknown compounds from EI (GC/MS) and MS/MS spectra, using library searching.
Mass Spectral Library search
Environmental monitoring and cleanup Criminal forensics Law enforcement Sports anti doping analysis Security Chemical warfare agent detection Food, beverage and perfume analysis Astrochemistry Medicine
Applications of GC MS
Advantages
- high sensitivityexcellent detection limits. Typically low ppb to high ppt
- high selectivityidentification is based on two parameters not one(retention time and mass spectrum must match standard)selects analyte of interest with very high confidence
- Speedtypical analysis takes from 1/2 hour to approx. 1 houranalysis 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)- for optimum results requires analyst knowledgeable in both chromatography and mass spectrometry
Thank You
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