Gas Chromatography


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Gas Chromatography

  1. 1. GAS CHROMATOGRAPHY DETECTORS Presented By : Amul Chahar
  2. 2. CONTENTS <ul><li>Introduction </li></ul><ul><li>Principle of Gas Chromatography </li></ul><ul><li>Classification of Detectors </li></ul><ul><li>Ideal Characteristics of Detectors </li></ul><ul><li>Different Detectors Used in GC </li></ul><ul><li>Comparison of Sensitivity & Selectivity of Detectors </li></ul><ul><li>Application </li></ul><ul><li>References </li></ul>
  3. 3. INTRODUCTION <ul><li>Chromatography comprises a group of methods for the separating molecular mixtures that depend on the differential affinities of the solutes between two immiscible phases. </li></ul>
  4. 4. Cont…. <ul><li>Gas Chromatography is a technique for separation of volatile substances by percolating gas stream over a stationary phase. </li></ul><ul><li>Gas chromatography is one of the most versatile of all the chromatographic techniques, was first describes by James & Martin in 1952. </li></ul><ul><li>If the stationary phase is a solid, we speak of Gas-Solid Chromatography . This depends upon the adsorption properties of the column packing to separate samples, primarily gases. </li></ul><ul><li>Common packing used are silica gel, molecular sieves & charcoal. </li></ul>
  5. 5. Cont…. <ul><li>If the stationary phase is a liquid, we speak of Gas-Liquid Chromatography. </li></ul><ul><li>Gas chromatography is valuable technique for analyzing compounds of pharmaceutical interest. </li></ul><ul><li>The great sensitivity & specificity of GLC are outstanding characters. </li></ul><ul><li>Because of the high sensitivity of the detectors available nano gram quantities of the sample are sufficient. </li></ul><ul><li>It is used to analyze gases, liquids & solids. </li></ul>
  6. 6. PRINCIPLE OF GAS CHROMATOGRAPGY <ul><li>The principle of separation in GC is partition. </li></ul><ul><li>Gas is used as a mobile phase & liquid which is coated on to a solid support is used as a stationary phase. </li></ul><ul><li>The mixture of component to be separated is converted to vapour and mixed with gaseous mobile phase. </li></ul><ul><li>The component which is more soluble in stationary phase travel slower & eluted later. The component which is less soluble in stationary phase travel faster & eluted out first. </li></ul><ul><li>No two components has same partition co-efficient for fixed combination of stationary phase, mobile phase and other condition. </li></ul><ul><li>So the components are separated according to their partition co-efficient. </li></ul><ul><li>Partition co-efficient is the ratio of solubility of a substance distributed between two immiscible liquids at a constant temperature. </li></ul>
  7. 7. Instrumentation
  8. 8. DETECTORS <ul><li>It is the brain of GC. Its function is to detect & quantify the different components of the sample as they emerge out from the column. </li></ul><ul><li>The choice of the detector depends upon the type of analysis being performed. </li></ul><ul><li>Requirement of an Ideal Detectors : </li></ul><ul><li> High sensitivity </li></ul><ul><li> Physically suitable </li></ul><ul><li> Capable of operable upto a maximum column </li></ul><ul><li>temperature. E.g. – 350 o C </li></ul><ul><li> Ease of operation </li></ul><ul><li> No response to undesirable compounds. </li></ul><ul><li> Response to compounds for which analysis is required. </li></ul><ul><li> Non destructive to sample in case of preparative work </li></ul><ul><li> Inexpensive </li></ul>
  9. 9. CLASSIFICATION OF DETECTORS <ul><li>Detectors can be classified into two types , </li></ul><ul><ul><li>The Bulk Property Detectors measure some bulk physical property of the eluent (such as dielectric constant or refractive index) </li></ul></ul><ul><ul><li>The Solvent Property Detector , measures some physical or chemical property that is unique to the solute (such as heat of combustion or fluorescence). </li></ul></ul><ul><li>Detectors can also be classified as </li></ul><ul><ul><li>Concentration Sensitive Devices such as the katharometer or </li></ul></ul><ul><ul><li>Mass Sensitive Devices such as the flame ionization detector (FID). </li></ul></ul>
  10. 10. Detectors used in Gas Chromatography <ul><li>Thermal conductivity Detector (Katharometer) (TCD) </li></ul><ul><li>Flame Ionisation Detector (FID) </li></ul><ul><li>Electron Capture Detector (ECD) </li></ul><ul><li>Flame Photometric Detector (FPD) </li></ul><ul><li>Argon Ionisation Detector (AID) </li></ul><ul><li>Nitrogen-phosphorus Detector (NPD) or Flame Thermionic Detector </li></ul>
  11. 11. Thermal Conductivity Detector
  12. 12. <ul><li>The thermal conductivity detector is based upon change in thermal conductivity of the gas stream. </li></ul><ul><li>Because the thermal conductivity of different gases are different, a change in composition of the gas causes the thermal conductivity to change. </li></ul><ul><li>The detector is a hot wire through which a current is allowed to flow. As the thermal conductivity of the gas environment changes, the temperature of the wire also changes. </li></ul><ul><li>The resistance of the wire or thermistor gives a measure of the thermal conductivity of the gas. </li></ul><ul><li>Advantages : </li></ul><ul><li> Simple </li></ul><ul><li> Rugged </li></ul><ul><li> Inexpensive </li></ul><ul><li> Non-selective </li></ul><ul><li> Accurate </li></ul><ul><li> Non-destructive to sample </li></ul>
  13. 13. <ul><li>Disadvantage : </li></ul><ul><li> Low sensitivity </li></ul><ul><li> Affected by fluctuation in temp. & flow rate </li></ul><ul><li> Response is only relative & not absolute </li></ul><ul><li> Biological samples can not be analyzed </li></ul><ul><li>Application : </li></ul><ul><li>These detectors have considerable application apart from gas chromatography but one of the most extensive applications of these detectors is in the determination of CO 2 in gases. </li></ul>
  14. 14. Flame Ionisation Detectors (FID)
  15. 15. <ul><li>Flame Ionization Detector (FID) is the most useful GC detector. </li></ul><ul><li>The FID has a very wide dynamic range, a high sensitivity & will detect all substances that contain carbon. </li></ul><ul><li>FIDs are mass sensitive rather than concentration sensitive. </li></ul><ul><li>Working : </li></ul><ul><li>The effluent from the column is mixed with hydrogen & air, & ignited at a small jet. </li></ul><ul><li>Organic compounds burning in the flame produce ions & electrons which can conduct electricity through the flame. </li></ul><ul><li> Surrounding the flame is a cylindrical electrode & a relatively high voltage is applied between the jet & the electrode to collect the ions that are formed in the flame. </li></ul>
  16. 16. <ul><li>The current resulting from the Pyrolysis of any organic compounds is amplified by a high impedance amplifier & the output fed to a data acquisition system or a potentiometric recorder. </li></ul><ul><li>Advantages : </li></ul><ul><li> Respond to most organic compounds </li></ul><ul><li> Linearity is good </li></ul><ul><li> High sensitive </li></ul><ul><li> Stable & insensitive to change in flow rate </li></ul><ul><li>Disadvantages : </li></ul><ul><li>The presence of &quot;Heteroatom&quot; in a molecule, such as oxygen, decreases the detector's response. </li></ul><ul><li>Methane response (CH 4 ) is fabulous but formaldehyde's (CH 2 O) is quite poor. </li></ul>
  17. 17. Electron Capture Detector (ECD)
  18. 18. <ul><li>The ECD uses a radioactive  emitter (electrons) to ionize some of the carrier gas & produce a current. </li></ul><ul><li>The ECD is sensitive to compounds with high electron affinities (halogen-containing compounds). </li></ul><ul><li>Gas entering the detector is ionized by a high energy radioactive source that gives off electrons (often 63 Ni). </li></ul><ul><li>When organic molecules that contain electronegative functional groups, such as halogens, phosphorous, & nitro groups pass by the detector, they capture some of the electrons & reduce the current measured between the electrodes. </li></ul><ul><li>Advantages : </li></ul><ul><li> Simple & reliable </li></ul><ul><li> Sensitive to electronegative groups </li></ul><ul><li> Non-destructive </li></ul><ul><li> Does not have any effect on sample </li></ul>
  19. 19. <ul><li>Disadvantages : </li></ul><ul><li> Insensitive to amine, alcohol & hydrocarbons </li></ul><ul><li> Limited dynamic range </li></ul><ul><li> Compounds which have more electron affinity groups </li></ul><ul><li>can only used. </li></ul><ul><li>Application : </li></ul><ul><li> Used for detection and measurement of trace environmental pollutants. </li></ul><ul><li> Due to high sensitivity for halogenated compound, used for detection of pesticides, herbicides & polynuclear aromatic carcinogens. </li></ul>
  20. 20. Flame Photometric Detector (FPD)
  21. 21. <ul><li>The determination of sulfur or phosphorus containing compounds is the job of the flame photometric detector (FPD). </li></ul><ul><li>This device uses the chemiluminescent reactions of these compounds in a Hydrogen/Air flame as a source of analytical information that is relatively specific for substances containing these two kinds of atoms. </li></ul><ul><li>In order to selectively detect one or the other family of compounds as it elutes from the GC column, an interference filter is used between the flame & the photomultiplier tube (PMT) to isolate the appropriate emission beam. </li></ul><ul><li>The final component necessary for this instrument is a thermal filter to isolate only the visible & UV radiation emitted by the flame. </li></ul>
  22. 22. <ul><li>Disadvantages : </li></ul><ul><li> Its selectivity </li></ul><ul><li> Poor commercial availability. </li></ul><ul><li> the filter must be exchanged between chromatographic runs if the other family of compounds is to be detected. </li></ul><ul><li>Application : </li></ul><ul><li> Use to detect heavy metals (Fe, Sn, Pb) in organometallic compounds, with nanogram (nm) sensitivity. </li></ul>
  23. 23. Argon Ionisation Detector (AID)
  24. 24. <ul><li>This type of detector depends on the excitation of argon atoms to a metastable state by using radioactive energy. </li></ul><ul><li>This can be achieved by irradiating the carrier gas with either alpha particles or beta particles. </li></ul><ul><li>Alpha particles can be obtained from radium-D. </li></ul><ul><li>Beta particles can be obtained from 90 Sr or tritium. </li></ul><ul><li>These high energy particles ionize the argon atoms and hence they are exited to metastable state. </li></ul><ul><li>These molecule collide with the effluent molecules and ionize them. </li></ul><ul><li>These ions when they reach the detector will cause an increase in current. </li></ul><ul><li>Thus the compounds can be detected. </li></ul><ul><li>Argon Argon e - Metastable state of argon </li></ul><ul><li>Increase in Ionization </li></ul><ul><li>current </li></ul>Irradiation Collision Collision of Substances
  25. 25. <ul><li>Advantages : </li></ul><ul><li> Responds to most of the organic compounds. </li></ul><ul><li> High sensitivity </li></ul><ul><li>Disadvantages : </li></ul><ul><li> Response is not absolute & it is relative </li></ul><ul><li> Sensitivity is affected by water and much reduced for </li></ul><ul><li>halogenated compounds </li></ul><ul><li> The response varies with the temperature of the detector </li></ul>
  26. 26. Nitrogen-phosphorus Detector (NPD)
  27. 27. <ul><li>Also known as Flame Thermionic Detector </li></ul><ul><li>The NPD is a specific type of FID that is particularly sensitive for compounds that contain N or P. </li></ul><ul><li>It may also be termed as a nitrogen detector, sulphur detector, phosphorus detector and halogen detector. </li></ul><ul><li>It is widely known as NP-FID because it is employed for carrying out the analysis of N- or P- containing organic compounds. </li></ul><ul><li>Alkali metal salt like Ruthenium silicate beads in flame increase sensitivity of compound containing halogen ,nitrogen ,phosphorus </li></ul><ul><li>(500 factor). </li></ul>
  28. 28. Detectors Type Support gases Selectivity Sensitivity Dynamic range Flame ionization (FID) Mass flow Hydrogen & air Most organic compounds Highly sensitive 10 7 Thermal conductivity (TCD) Concentration Reference Universal Low sensitive 10 7 Electron capture (ECD) Concentration Make-up Halides, nitrates, nitriles, peroxides, anhydrides, organometallics Sensitive to electronegative group 10 5 Flame photometric (FPD) Mass flow Hydrogen & air possibly oxygen Sulphur, phosphorus, tin, boron, arsenic, germanium, selenium, chromium High sensitive 10 3 Argon Ionisation Detector (AID) Concentration Make-up Organic compound Highly sensitive 10 7
  29. 29. References <ul><li>Text book of Pharmaceutical Analysis by Ravi Shankar. </li></ul><ul><li>Principles of Instrumental Analysis by Skoog.D.A; Holler.F.J. </li></ul><ul><li>Quantitative Analysis of drug-III edition by P.D.Sethi. </li></ul><ul><li>Pharmaceutical analysis- vol II by Dr. A.V.kasture </li></ul><ul><li> </li></ul>
  30. 30. THANK U