Presentation on theme: "GC-MS Gas Chromatography-Mass Spectrometry. An Hybrid technique which couples the powerful separation potential of gas chromatography with the specific."— Presentation transcript:
GC-MS Gas Chromatography-Mass Spectrometry
An Hybrid technique which couples the powerful separation potential of gas chromatography with the specific characterization ability of mass spectroscopy. Development of GC (1941) by Martin and Synge Gas Chromatography-Mass Spectrometry
What is Gas Chromatography? The father of modern gas chromatography is Nobel Prize winner John Porter Martin, who also developed the first liquid-gas chromatograph. (1950) The father of modern gas chromatography is Nobel Prize winner John Porter Martin, who also developed the first liquid-gas chromatograph. (1950)
Separation of molecules by distribution between a stationary phase and a mobile phase. A stationary phase (absorbent) phase the material on which the separation takes place. can be solid, gel, or liquid. Also called matrix, resin, or beads. The mobile phase is the solvent transports the sample and it is usually a liquid, but may also be a gas. Also called eluting buffer The compounds to be separated are considered solutes
GC Step by Step Carrier Gas Injector Column – Capillary – Stationary Phase Detectors – Mass Spectrometer
Depending on its nature 1.Packed column: columns are available in a packed manner 2.Open tubular or Capillary column or Golay column Long capillary tubing M in length Uniform & narrow d.m of cm Made up of stainless steel & form of a coil Disadvantage: more sample cannot loaded
3.SCOT columns (Support coated open tubular column Improved version of Golay / Capillary columns, have small sample capacity Made by depositing a micron size porous layer of supporting material on the inner wall of the capillary column Then coated with a thin film of liquid phase
Column Types Packed Columns Length: <2m Diameter: 1/8” & ¼” OD Capillary Columns Length: 10m to 100m Diameter: 180um, 250um, 320um & 530um I.d
Columns Packed Capillary Cross section
Broadening can be minimized with: 1- decreasing particle size 2- decreasing column diameter
What Does GC/MS Data Look Like? Reviewing of Mass Spectra * m/z 78 * Abundance (Signal) Retention Time > mass/charge > 6.77 min. 1,1-dichloropropene/carbon tetrachloride
Example Chromatogram (Capillary) Time Inject Point Detector Response
DETECTORS Heart of the apparatus The requirements of an ideal detector are- Applicability to wide range of samples Rapidity High sensitivity Linearity Response should be unaffected by temperature, flow rate… Non destructive Simple & inexpensive
Flame Ionization Detector
Thermal Conductivity Detector
Electron Capture Detector
Application of GC
Analysis of Halogenated Pesticides 2ppb in Water
Schematic of a Gas Chromatography-Mass Spectrometry (GC-MS) Instrument
Ionization techniques - EI (electron impact) - CI (chemical ionization) - FAB (fast atom bombardment) - ESI (electrospray ionization) - MALDI (matrix assisted laser desorption ionization) - APCI (atmospheric pressure chemical ionization)
Electron Impact Ioniser In an electron-impact mass spectrometer (EI-MS), a molecule is vaporized and ionized by bombardment with a beam of high-energy electrons. The energy of the electrons is ~ 1600 kcal (or 70eV). The electron beam ionizes the molecule by causing it to eject an electron.
Quadrupole Mass Ion Filter Quadrupoles are four precisely parallel rods with a direct current (DC) voltage and a superimposed radio- frequency (RF) potential. The field on the quadrupoles determines which ions are allowed to reach the detector. Quadrupoles thus function as a mass filter.
Molecular ionThe ion obtained by the loss of an electron from the molecule Base peakThe most intense peak in the MS, assigned 100% intensity Radical cation+ve charged species with an odd number of electrons Fragment ionsLighter cations formed by the decomposition of the molecular ion. Isotope abundance Peak These often correspond to stable carbocations. “A” Element—an element that is monoisotopic “A + 1” an element with an isotope that is 1 amu above that of the most abundant isotope Definition of Terms
Mass Spectrum of Methane (CH 4 )
Mass spectrum of CO 2. Note that the molecular ion appears at m/z = 44 (C = 12, O = 16). Frag- ment ions appear at m/z values of 28, 16, and 12. These correspond to CO +, O +, and C +, resp- ectively. Mass to charge ratiom/z Relative abundance (%) a b c b b c b c The mass spectrum of naphthalene with electron impact ionization by 70 eV electrons. a, molecular ion and base peak(C 10 H + 8, 100%); b, 13 C isotope peak; c, fragment ion peaks.
Mass Spectrometry Theory In mass spectrometry, a small sample of a chemical compound is vaporized, bombarded with high energy electrons to ionize the sample, and the ions produced are detected based on the charge to mass ratio of the ions. Ionization process in mass spectrometry.
Fragments Produced by Benzamide
Interpretation of Mass Spectra(1)
Interpretation of Mass Spectra
Electron ionization (70 eV) mass spectra of molecular ion region of benzene (C 6 H 6 ) and biphenyl (C 12 H 10 ). Intensity of M+1 relative to molecular ion for C n H m : Intensity = n × 1.08% + m × 0.012% Contribution from 13 C Contribution from 2 H
GC-MS is increasingly used for detection of illegal narcotics marijuana, cocaine, opioids Clinicians oxycodone and oxymorphone Piperazines are not detectable by typical immunoassay testing, but they may be detectable via GC-MS Sports anti-doping analysis Applications of GC-MS
possible to test a newborn for over 100 genetic metabolic disorders by a urine test at birth based on GC-MS Foods and beverages contain numerous aromatic compounds (identification) Environmental monitoring and cleanup GC-MS is becoming the tool of choice for tracking organic pollutants in the environment Applications of GC-MS
Limitation Only compounds with vapor pressures exceeding about 10 –10 torr can be analyzed by gas chromatography-mass spectrometry (GC-MS). Determining positional substitution on aromatic rings is often difficult. Certain isomeric compounds cannot be distinguished by mass spectrometry (for example, naphthalene versus azulene), but they can often be separated chromatographically.