GC MASS SPECTROMETERY

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.[1] Applications of GC-MS include drug detection, fire investigation, environmental analysis, explosives investigation, food and flavor analysis, and identification of unknown samples, including that of material samples obtained from planet Mars during probe missions as early as the 1970s. GC-MS can also be used in airport security to detect substances in luggage or on human beings. Additionally, it can identify trace elements in materials that were previously thought to have disintegrated beyond identification. Like liquid chromatography–mass spectrometry, it allows analysis and detection even of tiny amounts of a substance.[2]

GC-MS has been regarded as a "gold standard" for forensic substance identification because it is used to perform a 100% specific test, which positively identifies the presence of a particular substance. A nonspecific test merely indicates that any of several in a category of substances is present. Although a nonspecific test could statistically suggest the identity of the substance, this could lead to false positive identification. However, the high temperatures (300°C) used in the GC-MS injection port (and oven) can result in thermal degradation of injected molecules,[3] thus resulting in the measurement of degradation products instead of the actual molecule(s) of interest.The first on-line coupling of gas chromatography to a mass spectrometer was reported in the late 1950s.[4][5] An interest in coupling the methods had been suggested as early as December 1954.

1. GC MASS SPECTROMETERY

2. Content Introduction History Principle Instrumentation Working process Application Advantages Disadvantages

3. Introduction Gas chromatography-mass spectrometery is the synergistic combination of two analytical method to separate and identify different substances within a test sample. We obtain both qualitative and quantitative information for our sample in a single run within the same instrument.

4. Cont…. It is composed of two major building blocks: The gas chromatography The mass spectrometer Gas chromatography separates the components of mixture in time. Mass spectrometer provides information that aids in the identification and structural elucidation of each components.

5. GC-Mass Spectrometer

6. HISTORY Roland Gohlke and Fred McLafferty introduce use of MS as detector of GC in 1950s. In 1968, the Finnigan Instrument Corporation delivered the first quadrupole GC/MS. By the 2000s computerized GC/MS instruments using quadrupole technology had become essential. 2005 GC tandem MS/MS have been introduced.

7. Principle Gas Chromatography :- A separation technique which separates organic or inorganic compounds exploiting it’s physico chemical properties such as polarity, boiling point. The interaction with the stationary phase with the vapor pressure of the analyte ( due to column temperature) is the key factor in separating the molecules.

8. Cont…. Mass spectrometer :- MS is an analytical device which measures the mass to charge ratio (m/z) of a molecule. MS requires charged molecules for analysis. Charged molecules should be in gaseous state.

9. Instrumentation

10. Gas chromatography Carrier gas Pneumatic control Injector Column Oven Interface Jet interface Direct capillary infusion interface Watson- Biemann effusion separator Mass spectrometer High vacuum system Ion source Mass analyzer Detector Data system

11. Gas chromatography 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- Majorly Helium and Argon are used. Pneumatic Control: Gas supply is regulated to the correct pressure and then fed to the required part of instrument.

12. Cont…. Oven: Temperature programmable, typically range from 5°C - 400°C but can go as low as -25°C with cryogenic cooling. 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

13. Cont…. 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.

14. Cont…. 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 tubing 10-100 m in length. Made up from stainless steel & coil. Shorter columns used for fast analysis Larger columns for high resolution separation

15. Interface Pressure incompatibility problem between GC and MS was solved by inserting an interface. Mainly three types of interfaces are there commercially available: Jet/Orifice separator Direct capillary infusion interface Watson- Biemann effusion separator

16. Jet/Orifice separator The jet separator consist of two glass tubes aligned with a Small distance between them. Carrier gas entering from the GC column is pumped away by a separate vacuumed system. The larger sample molecules maintain their momentum &pass preferentially in to the second capillary. Sample enrichment occurs & the initial atmospheric pressure is reduced.

17. Direct capillary infusion interface GC-MS systems use capillary columns & fused silica tubing permits an inert, high efficiency, direct transfer between the 2 systems. Flow rates is 5ml/min.

18. Watson- Biemann effusion separator It consists of a sintered glass tube. The carrier gas usually helium passes preferentially through the sintered glass tube and the effluent is concentrated. The gas flow rates in the order of 20-60ml/min

19. Detector

20. Mass Spectrometer Vacuum system All mass analysers operate under vacuum in order to minimise collisions between ions and air molecules. At atmospheric pressure, the mean free path of a typical ion is around 52 nm at 1mtorr. In most instruments, two vacuum pump types are used. Rotary vane pump :- This pump can be an oil pump to provide initial vacuum. It is used to produce the main reduction in pressure. (approximately 1torr). Turbomolecular pump :- It is also known as diffusion pump, provides working high vacuum (1mtorr to 1ntorr). This is a high-speed gas turbine with interspersed rotors (moving blades) and stators (i.e. fixed or stationary blades) whose rotation forces molecules through the blade system

21. Ion source or Ionization Ionization means placing a charge on an otherwise a neutral molecule. Ions may be produced from a neutral molecule by removing an electron to produce a positively charged cation, or by adding an electron to form an anion. Both positive and negative-ion mass spectrometry may be carried out. Majorly two types of ionization are used in GC-MS 1. Electron impact ionization 2. Chemical ionization

22. Electron impact ionization (EI) Here a beam of electrons with energy of 70 electron volts is made to interact with the sample This interaction causes electron ejection in the sample molecules thereby leading to ionization. This method is suitable for small molecules of molecular weights up to 400 Daltons only. It is widely used for the analysis of metabolites, pollutants and pharmaceutical compounds, for example in drug testing programmes

23. Cont….

24. Chemical Ionization (CI) Chemical Ionization (CI) Chemical ionization (CI) is used for a range of samples similar to those for EI. It is particularly useful for the determination of molecular masses, as high intensity molecular ions are produced due to less fragmentation.

25. Mass analyzer or Mass selective analyzer They deflects ions down a curved tubes in magnetic field based on their kinetic energy determined by the mass charge and velocity. The magnetic field is scanned to measure different ions. They may be three types- Quadrupole Ion trap TOF

26. Quadrupole analyzer Also known as 'Hewlett-Packard‘ Detector. In quadrupole mass analyzer a set of four rods are arranged parallel to the direction. Only m/z is been determined and stable oscillation takes place. lons travels in quadrupole axis with cork screw type of trajectory. It functions as a mass filter.

27. Ion trap mass analyzer The ion trap mass analyzer operates by similar principle 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. Ions entering Trapped by Ions oscillate in into chamber electromagnetic field concentric trajectories

28. 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 take to reach the detector. If the particles all have the same charge, the kinetic energies will be identical and their velocities will depend upon only on their masses.

29. detector Detector is used for detection of ions. Electron and photomultiplier conversion dynode is used.

30. Electron multiplier In electron multiplier-electrons released by the first dynode when the ion impinges on it are dragged to the second dynode because it has a higher potential. Let us call these electrons primary. These primary electrons strike the second dynode with a force and the collision releases even more secondary electrons which too are dragged to the third dynode resulting in release of even more electrons and so on. Typical amplification of an electron multiplier is one million.

31. Photomultiplier photomultiplier is similar to the electron multiplier in that the ions strike a dynode resulting in the emission of electrons. However, these electrons are now made to strike a phosphorus screen. This screen releases photons when electrons strike it. These photons are now detected by a photomultiplier. The primary advantage of this setup is that the photomultiplier tube is housed in vacuum. This removes the possibility of any contamination from the internal environment.

32. Work of dynodes

33. Data system Data handling Mass spectrometers employ computer control of same functions and also use a computerised display and output.It is used to identify and measure the concentration of one or more analytes in a complex mixture. Advantages - Amount of data generated is very large and It stores every sec for upto 90 min.

34. Graph of CO2 gas

35. Working of GC-MS The separation occurs in the gas chromatographic column (such as capillary) when vaporized analytes are carried through by the inert heated mobile phase (so-called carrier gas such as helium). The analytes spend different time (called retention time) to come out of (elute from) the GC column due to their different adsorption on the stationary phase (of a packed column in gas-solid chromatography). As the eluted substances emerge from the column opening, they flow further into the MS through an interface. This is followed by ionization, mass-analysis and detection of mass-to-charge ratios of ions generated from each analyte by the mass spectrometer. The combination of the gas chromatograph and mass spectrometer in a GC-MS allows a much accurate chemical identification than either technique used separately.

36. Application Petrochemical and hydrocarbons analysis Geochemical research. Forensic (arson, explosives, drugs, unknowns) Environmental analysis Pesticide analysis Food safety and quality control Pharmaceutical and drug analysis Clinical toxicology Application to human dosimetery GC-MS is increasingly used for detection of illegal narcotics marijuana, cocaine, opioids Clinicians oxycodone and oxymorphone Sports anti-doping analysis

37. Advantages Robust, mature technology Relatively inexpensive Quantitative (with calibration) Small sample volume (50 ul .) Good sensitivity (100 nM ) Large body of software and databases for metabolite ID Detects most organic and someinorganic molecules. Excellent separation reproducibility

38. Disadvantages Sample not recoverable Requires sample derivatization Requires separation Relatively slow (2-3 hr to collect data and analyze sample) Cannot be used in imaging Novel compound ID is difficult.