Gas chromatography-mass spectrometry (GC-MS)-an introduction

Gas chromatography-mass spectrometry (GC-MS)-an introduction

1. Gas Chromatography/Mass Spectrometry (GC/MS) Environmental biotechnology Division Raj K umar Regar (PhD Student) CSIR-Indian Institute of toxicology Research Supervisor: Dr. N. Manickam 1

2. Introduction Principle Instrumentation Working Applications Content

3. 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

4. Gas Chromatography Mass Spectrometry Gas Chromatography - Mass Spectrometry  = Identifies (detects) chemicals based 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)

5. 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

6. 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

7. 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

8. 6 . Ion Source 7. Mass Analyser 8. Detector 9. Vacuum System 10. Control Electronics 1. Pneumatic controls 2. Injector 3. Oven 4. Column 5. Interface Instrumentation

9. Image of GC-MS

10. A GC syringe penetrates a septum to inject sample into the vaporization camber Instant vaporization of the sample, 280  C Carrier gas transports the sample into the head of the column Purge valve controls the fraction of sample that enters the column Injector

11. Splitless (100:90) vs. Split (100:1) Injector Syringe Injector Syringe Purge valve open Purge valve closed GC column GC column He He

12. Packed Capillary Cross section Columns

13. GC Detectors

14. (Operational Description) Introduction System - Gas Chromatography Ionization Mass Separation Mass Detection Data System Mass Spectrometer Ionization Source Mass Analyzer Dedicated Data System Vacuum System - approx. 10 -6 torr Particle Detector Gas Chromatography Mass Spectrometry

15. Operational Description

16. Sample ionization

17. 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

18. 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 - + e - + + 2e - + . Mass Analysis can only work for charged species - not for neutrals. + 2e - + .

19. Quadrupole Mass Ion Filter

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21. Total Ion Chromatogram (TIC)   Definition:  A plot of the total ion current vs. retention time obtained from a chromatography experiment with mass detection.

22. 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

23. Environmental monitoring and cleanup Criminal forensics Law enforcement Sports anti­doping analysis Security Chemical warfare agent detection Food , beverage and perfume analysis Astrochemistry Medicine Applications of GC­MS

24. Advantages - high sensitivity excellent detection limits. Typically low ppb to high ppt - high selectivity identification is based on two parameters not one (retention time and mass spectrum must match standard) selects analyte of interest with very high confidence - Speed typical analysis takes from 1/2 hour to approx. 1 hour analysis 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

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