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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