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Air sampling methods

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deepak ravi

This document discusses air sampling methods and gas chromatography. It begins by describing various air sampling techniques for particulate and gaseous pollutants, including filtration, impingement, precipitation, absorption, adsorption and condensation. It then discusses gas chromatography, explaining the basic components and process. Key aspects covered are the carrier gas, column, stationary phase, detectors and how gas chromatography can be used to qualitatively analyze samples based on retention times and peak detection.

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AIR SAMPLING METHODS AND GAS CHROMATOGRAPHY SUBMITTED BY :-DEEPAK RAVI ROLL NO:-162509 ME(I&C) REGULAR 2016-18 SUBMITTED TO :- Dr. POONAM SYAL ASSOCIATE PROFESSOR ELECTRICAL ENGINEERING DEPARTMENT NITTTR CHANDIGARH
CONTENTS • AIR SAMPLING • TYPES OF CONTAMINANT • CONTAMINANT DEFINITIONS • AIR SAMPLING CALCULATION • AIR SAMPLING METHOD • SOME NEW METHODS OF AIR SAMPLING • RESEARCH PAPER • REFERENCES
AIR SAMPLING Air pollution sampling : Related to analysis of pollutants in a given volume of air. Air sampling: Capturing the contaminant from a known volume of air, measuring the amount of contaminant captured, and expressing it as a concentration The air is passed through a filter medium (normally a paper for solid & liquid contaminants and a sorbent for gases).  The volume of air is measured against the amount of contaminant captured. This gives the concentration, which is expressed either as milligrams per cubic metre (mg/m3 ) or parts per million (ppm). The volume of air is calculated by multiplying the flow rate through the filter medium by the time in minutes.
TYPES OF CONTAMINANT There are three types of contaminant according to their physical properties: Particulates  Vapours  Gases Particulates can be further subdivided into five types:  Aerosols  Dusts  Fumes  Smokes  Mists
CONTAMINANT DEFINITIONS Aerosol : Dispersion of solid particles of microscopic size in air. Dust: Solid particulate capable of temporary suspension in air. Fume: Solid particles produced by condensation from the gaseous phase. Fumes are usually derived from the heating of a solid to its melting point and the subsequent cooling of the gas produced.
CONTINUED…. Smoke: Particles resulting from the incomplete combustion of organic matter consisting predominantly of carbon and oxides of carbon. Mist: Dispersion in air of liquid droplets usually large enough to be seen by the naked eye. Vapour: Gaseous phase of a substance that usually exists as a liquid or solid at normal room temperature and pressure. Gas: A substance which does not normally exist as a liquid or solid at normal room temperature and pressure.
AIR SAMPLING CALCULATION An air sample requires three basic measurements: Amount of pollutant collected Flow of air through the medium The run time in minutes.  Flow×time(in minute)=volume through filter in cubic meter  Concentration in microgram per cubic meter or in ppm
AIR SAMPLING METHODS • Air pollutant sampling are of two types :- Air sampling based on the particulate pollutant Air sampling based on the gaseous and vapor pollutant
AIR SAMPLING BASED ON THE PARTICULATE POLLUTANTS Air sampling techniques for particulate pollutants SEDIMENTATION FILTRATION IMPINGEMENT PERCIPITATION  THERMAL PRECIPITAION  ELECTROSTATIC PRECIPITATION
SEDIMENTATION • Used to collect settle able particulate that settle out of the atmosphere as a result of the gravitation force • Particulate pollutant having size of 10 mirco meter can be collected with 99% efficiency • The sampler consists of simple dust jar fitted with a funnel • A liquid is added to collector to prevent the solids blown out from the jar by air • Collected dust is evaporated to dryness and then weighed in mg • Sampling period is 30 days
FILTRATION Technique used in the collection of air pollutants of size smaller than 10 micro meter in diameter The particulates are removed from the air sample by suction apparatus through a porous filter where particulates are deposited The glass fiber filter of porous size less than 0.1 micro meter is used in high volume sampler Sampling period: 24 hours Air volume sucked: 2000 cubic meter Particulate concentration: micro gram per cubic meter
CONTINUED……
IMPINGEMENT Based on the inertial technique in which particles are collected from the high velocity air steam directed toward the obstacles placed across the path of air stream Particulates collide with the obstacle and air changes its direction If the obstacle are adhesive surface then particles are impacted on it and this is known as dry impingement If obstacle is wet by any liquid then it is called wet impingement
PRECIPITATION Precipitation are two types--- Thermal precipitation Electrostatic precipitation THERMAL PRECIPITATION :- Thermal precipitation is based on the principle that the particles move towards the lower temperature region when subjected to a strong temperature gradient  The temperature gradients are normally of the order of 3000 ° C per centimeter  This technique is used to collect the particle of size 0.001 micrometer with high efficiency
CONTINUED….. ELECTROSTATIC PRECIPITATION:-  Theses precipitators are an electrically charged to force radioactive particulates to migrate out the air steam onto a collection surface  In this precipitators two electrodes are used positive and negative  When the air stream with particulates pass through the electrodes particles pick up negative charge and migrate towards inner post of the precipitators where got discharged and deposited on the positive electrodes
AIR SAMPLING OF THE GASEOUS POLLUTANTS ABSORPTION SAMPLING ADSORPTION SAMPLING CONDENSATION SAMPLING
ABSORPTION SAMPLING Gaseous pollutants are absorbed in a solvent when both the pollutant and absorbent are in close contact Liquid react with the gaseous pollutant to form a non gaseous pollutant ALKALINE FOR ACIDIC GASES ACIDIC SOLUTION FOR ALKALINE GASES OILS FOR HYDROCARBONS
ADSORPTION SAMPLING Gaseous pollutants are adsorbed on the solid surface of activated carbon, silica gel, activated alumina and molecular sieve As the surface area increases the adsorption increases
CONDENSATION SAMPLING The conversion of a vapour or gas to a liquid Method used to collect the radioactive gases, hydrocarbons and non reactive vapors Air pollutant can be trapped by condensation reaction As the gaseous pollutant pass through the different temperature range of condensers where the temperature is below the boiling point the gaseous pollutant will trap in the liquid
SOME NEW METHODS OF AIR SAMPLING Bubble Sampling Air drawn into the impinger is forced through a nozzle, which is covered by a liquid such as high purity water. The pollutant dissolves in the liquid and is subsequently analysed, usually by colorimetric techniques. Sorbent Sampling Sorbents are normally contained in a small glass tube with sealed ends.  Air is drawn through the sorbent, which captures molecules of the gas or vapour to be sampled. The trapped contaminants are released using solvent washing or heat to a gas chromatograph (GC) for analysis. One of the best known sorbents is charcoal.
CONTENTS • CHROMATOGRAPHY • DIFFERENT TECHNIQUES OF CHROMATOGRAPHY • GAS CHROMATOGRAPHY • REQUIREMENT FOR GAS CHROMATOGRAPHY • BLOCK DIAGRAM OF GAS CHROMATOGRAPHY • QUALITATIVE ANALYSIS • ADVANTAGES AND DISADVANTAGES OF GAS CHROMATOGRAPHY • MODERN APPROACH
CHROMATOGRAPHY Laboratory technique for the separation of a mixture. The mixture is dissolved in a fluid called the mobile phase, which carries it through a structure holding another material called the stationary phase.  The various constituents of the mixture travel at different speeds, causing them to separate.  The separation is based on differential partitioning between the mobile and stationary phases. Chromatograph: equipment that enables a sophisticated separation, e.g. gas chromatographic or liquid chromatographic separation. Chromatogram: Visual output of the chromatograph.  In the case of an optimal separation, different peaks or patterns on the chromatogram correspond to different components of the separated mixture.
TECHNIQUES BASED ON CHROMATOGRAPHIC BED SHAPE Column chromatography: Separation technique in which the stationary bed is within a tube. Planar chromatography: Separation technique in which the stationary phase is present as or on a plane. The plane can be a paper, serving as such or impregnated by a substance as the stationary bed (paper chromatography) or a layer of solid particles spread on a support such as a glass plate (thin layer chromatography)
TECHNIQUES BASED ON PHYSICAL STATE OF MOBILE PHASE Gas chromatography (GC): Also known as gas-liquid chromatography, (GLC), a separation technique in which the mobile phase is a gas. Gas chromatographic separation is always carried out in a column, which is typically "packed" or "capillary". Liquid chromatography (LC): Separation technique in which the mobile phase is a liquid. carried out either in a column or a plane
GAS CHROMATOGRAPHY Gas chromatography: Mobile phase a carrier gas, usually an inert gas such as helium or an nonreactive gas such as nitrogen. Hydrogen is preferred for improved separations. The stationary phase is a microscopic layer of liquid or polymer on an inert solid support, inside a piece of glass or metal tubing called a column. The instrument used to perform gas chromatography is called a gas chromatograph. The gaseous compounds being analysed interact with the walls of the column, which is coated with a stationary phase. This causes each compound to elute at a different time, known as the retention time of the compound. The comparison of retention times is what gives GC its analytical usefulness.
CONTINUED…. The function of the stationary phase in the column is to separate different components, causing each one to exit the column at a different time(retention time). As the carrier gas sweeps the analytic molecules through the column, this motion is inhibited by the adsorption of the analytic molecules either onto the column walls or onto packing materials in the column. The rate at which the molecules progress along the column depends on the strength of adsorption, which in turn depends on the type of molecule and on the stationary phase materials.
CONTINUED…… Since each type of molecule has a different rate of progression, the various components of the analytic mixture are separated as they progress along the column and reach the end of the column at different times(retention Time). Detector: used to monitor the out let stream from the column; thus, the time at which each component reaches the outlet and the amount of that component can be determined. Generally, substances are identified(qualitatively) by the order in which they emerge(elute) from the column and by the retention time of the analytic in the column.
REQUIREMENT FOR GAS CHROMATOGHRAPHY VOLATILITY:-Tendency of a substance to evaporate at normal temperatures POLARITY:-Substance comprised of molecules that contain unbalanced localized charges (dipoles) is a polar substance.  Polar substances tend to interact with other polar substances and rarely react to a significant degree with nonpolar substances When two atoms form a covalent bond, they each share an electron. Different atoms have different abilities to attract electrons quantified by their electronegativity values. When one atom in a covalent bond has a much higher electronegativity than the other, the electron is found closer to that atom than the weaker one. This creates a dipole effect with a slight negative charge at the atom the electron favours and a slight positive charge at the other
BLOCK DIAGRAM OF GAS CHROMATOGRAPHY
COMPONENT OF GAS CHROMATOGRAPH carrier gas flow regulator injector column stationary phase oven detectors display device
CARRIER GAS • he(common), • others:n2,h2 • safety; non-flammability, cost and efficiency are factors for gas selection • inertness • suitable for the detector • high purity • easily available
FLOW METER • Deliver the gas with uniform pressure/flowrate • Flowmeters:-Rotameter
INJECTOR • Transfers the sample into the column. • Provides the means to introduce a sample into a continuous flow of carrier gas. • Injectors are usually heated to ensure sample’s transfer to a gas phase. • Volatile liquid or gaseous sample is injected through a septum.
COLUMN Gas chromatography columns : packed and capillary. Packed columns :A glass or stainless steel coil(typically1-5m total length and 5mm inner diameter), filled with the stationary phase, or a packing coated with the stationary phase. Capillary columns: A thin fused-silica (purified silicate glass) capillary (typically10-100 m in length and 0.5 mm inner diameter) that has the stationary phase coated on the inner surface. Provides much higher separation efficiency than packed columns but are more easily overloaded by too much sample. The main chemical attribute regarded when choosing a column is the polarity of the mixture, The polarity of the sample must closely match the polarity of the column stationary phase to increase resolution and separation while reducing runtime.
TEMPERATURE CONTROL DEVICES Temperature Control Devices Preheaters: convert sample into its vapour form, present along with injecting devices Thermostatically controlled oven Temperature maintenance in a column is highly essential for efficient separation.
STATIONARY PHASES For every polar sample, polyethylene glycol(thickess 0.25mircometer) is commonly used as the stationary phase. Stationary Phases must have: 1.Low volatility 2.Thermal stability 3.Chemical inertness
SOME STATIONARY PHASE LIST
DETECTOR Placed at the exit of the column. Employed to detect and provide a quantitative measurement of the various constituents of the sample The choice of a particular type of detector is governed by the following factors: 1. High sensitivity, sufficient enough to provide adequate signal for even small sample 2. Response should be linear, unaffected by temperature and flowrate. 3. Non distorted shape of peak and non destructive. 4. Detector temperature must not condense the eluted vapours in it. 5. Simple & Inexpensive 6. Applicable to wide range of samples 7. Good reproducibility, rapidity and linearity.
COMMONLY USED DETECTOR Most commonly used types:- 1.Thermal Conductivity Detector TCD 2.Flame Ionization Detector FID 3.Electron Capture Detector ECD 4.Atomic-Emission Detector AED 5.Flame Photometric GC Detector FPD
QUALITATIVE ANALYSIS Chromatographic data is presented as a graph of detector response(y-axis) against retention time(x-axis), which is called a chromatogram. This provides a spectrum of peaks for a sample representing the analytics present in a sample eluting from the column at different times. The number of components in a sample is determined by the number of peaks. The amount of a given component in a sample is determined by the area under the peaks. The identity of components can be determined by the given retention times.
ADVANTAGES AND DISADVANTAGES OF GC ADVANTAGES:- High Resolution Very high sensitivity, detect down to 100 ppm. Very good precision and accuracy. Very good separation Time(analysis is short), fast analysis is possible. Small sample is needed-ml Good detection system Quantitatively analysis DISADVANTAGES :- Sample must be volatile Dirty sample choke the capillary
MODERN APPROACH GCMS:-Gas Chromatography Mass Spectrometry Mass spectrometry: Analytical technique that ionizes chemical species and sorts the ions based on their mass-to-charge ratio. Gas chromatography–mass spectrometry (GC- MS):Analytical method that combines the features of gas- chromatography and mass spectrometry to identify different substances within a test sample. Applications of GC-MS include drug detection, fire investigation, environmental analysis, explosives investigation, and identification of unknown samples
GCMS:-GAS CHROMATOGRAPHY MASS SPECTROMETRY
2014 IEEE International Conference on Liquid Dielectrics, Bled Slovenia, June 30 - July 3, 2014 Methanol Detection in Transformer Oils using Gas Chromatography and Ion Trap Mass Spectrometer S. Y. Matharagel, Q. Liul, E. Davenportl, G. Wilson2, D. Walker3 and Z.D. Wang The University of Manchester, Manchester, M13 9PL, UK 2The National Grid Company, Warwick, CV34 6DA, UK 3Scottish Power, Blantyre, G72 OHT, UK
Continued….. • Abstract-Paper ageing is an irreversible process, which has made paper insulation a lifetime determining factor for transformers. Chemical indicators in oil such as carbon oxide gases and 2-FAL, are used to indicate the ageing state of paper as it is difficult to obtain paper samples to measure DP or tensile strength. Methanol amount in oil was recently found to be an early-ageing indicator for paper. In this study, a heads pace gas chromatography mass spectrometry setup was developed to measure methanol in transformer oil. This setup consists of an auto sampler with a gas tight syringe, a gas chromatography unit with 60 m VF-624ms column and a quadrupole ion trap type mass spectrometer unit. Measurement of several laboratory-aged and service-aged oil samples were conducted with both external standard and internal standard calibration methods. Higher methanol values obtained from internal standard method confirmed that it is more suitable than external standard method.
REFERENCES A text book of environmental chemistry by “BALRAM PANI” “https://en.wikipedia.org/wiki/Gas_chromatography%E2%80%93mas s_spectrometry https://en.wikipedia.org/wiki/Gas_chromatography https://www.youtube.com/watch?v=p3_WtEYIhTo https://www.youtube.com/watch?v=gU2st5-T1Go
Air sampling methods

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Air sampling methods

  • 1. AIR SAMPLING METHODS AND GAS CHROMATOGRAPHY SUBMITTED BY :-DEEPAK RAVI ROLL NO:-162509 ME(I&C) REGULAR 2016-18 SUBMITTED TO :- Dr. POONAM SYAL ASSOCIATE PROFESSOR ELECTRICAL ENGINEERING DEPARTMENT NITTTR CHANDIGARH
  • 2. CONTENTS • AIR SAMPLING • TYPES OF CONTAMINANT • CONTAMINANT DEFINITIONS • AIR SAMPLING CALCULATION • AIR SAMPLING METHOD • SOME NEW METHODS OF AIR SAMPLING • RESEARCH PAPER • REFERENCES
  • 3. AIR SAMPLING Air pollution sampling : Related to analysis of pollutants in a given volume of air. Air sampling: Capturing the contaminant from a known volume of air, measuring the amount of contaminant captured, and expressing it as a concentration The air is passed through a filter medium (normally a paper for solid & liquid contaminants and a sorbent for gases).  The volume of air is measured against the amount of contaminant captured. This gives the concentration, which is expressed either as milligrams per cubic metre (mg/m3 ) or parts per million (ppm). The volume of air is calculated by multiplying the flow rate through the filter medium by the time in minutes.
  • 4. TYPES OF CONTAMINANT There are three types of contaminant according to their physical properties: Particulates  Vapours  Gases Particulates can be further subdivided into five types:  Aerosols  Dusts  Fumes  Smokes  Mists
  • 5. CONTAMINANT DEFINITIONS Aerosol : Dispersion of solid particles of microscopic size in air. Dust: Solid particulate capable of temporary suspension in air. Fume: Solid particles produced by condensation from the gaseous phase. Fumes are usually derived from the heating of a solid to its melting point and the subsequent cooling of the gas produced.
  • 6. CONTINUED…. Smoke: Particles resulting from the incomplete combustion of organic matter consisting predominantly of carbon and oxides of carbon. Mist: Dispersion in air of liquid droplets usually large enough to be seen by the naked eye. Vapour: Gaseous phase of a substance that usually exists as a liquid or solid at normal room temperature and pressure. Gas: A substance which does not normally exist as a liquid or solid at normal room temperature and pressure.
  • 7. AIR SAMPLING CALCULATION An air sample requires three basic measurements: Amount of pollutant collected Flow of air through the medium The run time in minutes.  Flow×time(in minute)=volume through filter in cubic meter  Concentration in microgram per cubic meter or in ppm
  • 8. AIR SAMPLING METHODS • Air pollutant sampling are of two types :- Air sampling based on the particulate pollutant Air sampling based on the gaseous and vapor pollutant
  • 9. AIR SAMPLING BASED ON THE PARTICULATE POLLUTANTS Air sampling techniques for particulate pollutants SEDIMENTATION FILTRATION IMPINGEMENT PERCIPITATION  THERMAL PRECIPITAION  ELECTROSTATIC PRECIPITATION
  • 10. SEDIMENTATION • Used to collect settle able particulate that settle out of the atmosphere as a result of the gravitation force • Particulate pollutant having size of 10 mirco meter can be collected with 99% efficiency • The sampler consists of simple dust jar fitted with a funnel • A liquid is added to collector to prevent the solids blown out from the jar by air • Collected dust is evaporated to dryness and then weighed in mg • Sampling period is 30 days
  • 11. FILTRATION Technique used in the collection of air pollutants of size smaller than 10 micro meter in diameter The particulates are removed from the air sample by suction apparatus through a porous filter where particulates are deposited The glass fiber filter of porous size less than 0.1 micro meter is used in high volume sampler Sampling period: 24 hours Air volume sucked: 2000 cubic meter Particulate concentration: micro gram per cubic meter
  • 13. IMPINGEMENT Based on the inertial technique in which particles are collected from the high velocity air steam directed toward the obstacles placed across the path of air stream Particulates collide with the obstacle and air changes its direction If the obstacle are adhesive surface then particles are impacted on it and this is known as dry impingement If obstacle is wet by any liquid then it is called wet impingement
  • 14. PRECIPITATION Precipitation are two types--- Thermal precipitation Electrostatic precipitation THERMAL PRECIPITATION :- Thermal precipitation is based on the principle that the particles move towards the lower temperature region when subjected to a strong temperature gradient  The temperature gradients are normally of the order of 3000 ° C per centimeter  This technique is used to collect the particle of size 0.001 micrometer with high efficiency
  • 15. CONTINUED….. ELECTROSTATIC PRECIPITATION:-  Theses precipitators are an electrically charged to force radioactive particulates to migrate out the air steam onto a collection surface  In this precipitators two electrodes are used positive and negative  When the air stream with particulates pass through the electrodes particles pick up negative charge and migrate towards inner post of the precipitators where got discharged and deposited on the positive electrodes
  • 16. AIR SAMPLING OF THE GASEOUS POLLUTANTS ABSORPTION SAMPLING ADSORPTION SAMPLING CONDENSATION SAMPLING
  • 17. ABSORPTION SAMPLING Gaseous pollutants are absorbed in a solvent when both the pollutant and absorbent are in close contact Liquid react with the gaseous pollutant to form a non gaseous pollutant ALKALINE FOR ACIDIC GASES ACIDIC SOLUTION FOR ALKALINE GASES OILS FOR HYDROCARBONS
  • 18. ADSORPTION SAMPLING Gaseous pollutants are adsorbed on the solid surface of activated carbon, silica gel, activated alumina and molecular sieve As the surface area increases the adsorption increases
  • 19. CONDENSATION SAMPLING The conversion of a vapour or gas to a liquid Method used to collect the radioactive gases, hydrocarbons and non reactive vapors Air pollutant can be trapped by condensation reaction As the gaseous pollutant pass through the different temperature range of condensers where the temperature is below the boiling point the gaseous pollutant will trap in the liquid
  • 20. SOME NEW METHODS OF AIR SAMPLING Bubble Sampling Air drawn into the impinger is forced through a nozzle, which is covered by a liquid such as high purity water. The pollutant dissolves in the liquid and is subsequently analysed, usually by colorimetric techniques. Sorbent Sampling Sorbents are normally contained in a small glass tube with sealed ends.  Air is drawn through the sorbent, which captures molecules of the gas or vapour to be sampled. The trapped contaminants are released using solvent washing or heat to a gas chromatograph (GC) for analysis. One of the best known sorbents is charcoal.
  • 21. CONTENTS • CHROMATOGRAPHY • DIFFERENT TECHNIQUES OF CHROMATOGRAPHY • GAS CHROMATOGRAPHY • REQUIREMENT FOR GAS CHROMATOGRAPHY • BLOCK DIAGRAM OF GAS CHROMATOGRAPHY • QUALITATIVE ANALYSIS • ADVANTAGES AND DISADVANTAGES OF GAS CHROMATOGRAPHY • MODERN APPROACH
  • 22. CHROMATOGRAPHY Laboratory technique for the separation of a mixture. The mixture is dissolved in a fluid called the mobile phase, which carries it through a structure holding another material called the stationary phase.  The various constituents of the mixture travel at different speeds, causing them to separate.  The separation is based on differential partitioning between the mobile and stationary phases. Chromatograph: equipment that enables a sophisticated separation, e.g. gas chromatographic or liquid chromatographic separation. Chromatogram: Visual output of the chromatograph.  In the case of an optimal separation, different peaks or patterns on the chromatogram correspond to different components of the separated mixture.
  • 23. TECHNIQUES BASED ON CHROMATOGRAPHIC BED SHAPE Column chromatography: Separation technique in which the stationary bed is within a tube. Planar chromatography: Separation technique in which the stationary phase is present as or on a plane. The plane can be a paper, serving as such or impregnated by a substance as the stationary bed (paper chromatography) or a layer of solid particles spread on a support such as a glass plate (thin layer chromatography)
  • 24. TECHNIQUES BASED ON PHYSICAL STATE OF MOBILE PHASE Gas chromatography (GC): Also known as gas-liquid chromatography, (GLC), a separation technique in which the mobile phase is a gas. Gas chromatographic separation is always carried out in a column, which is typically "packed" or "capillary". Liquid chromatography (LC): Separation technique in which the mobile phase is a liquid. carried out either in a column or a plane
  • 25. GAS CHROMATOGRAPHY Gas chromatography: Mobile phase a carrier gas, usually an inert gas such as helium or an nonreactive gas such as nitrogen. Hydrogen is preferred for improved separations. The stationary phase is a microscopic layer of liquid or polymer on an inert solid support, inside a piece of glass or metal tubing called a column. The instrument used to perform gas chromatography is called a gas chromatograph. The gaseous compounds being analysed interact with the walls of the column, which is coated with a stationary phase. This causes each compound to elute at a different time, known as the retention time of the compound. The comparison of retention times is what gives GC its analytical usefulness.
  • 26. CONTINUED…. The function of the stationary phase in the column is to separate different components, causing each one to exit the column at a different time(retention time). As the carrier gas sweeps the analytic molecules through the column, this motion is inhibited by the adsorption of the analytic molecules either onto the column walls or onto packing materials in the column. The rate at which the molecules progress along the column depends on the strength of adsorption, which in turn depends on the type of molecule and on the stationary phase materials.
  • 27. CONTINUED…… Since each type of molecule has a different rate of progression, the various components of the analytic mixture are separated as they progress along the column and reach the end of the column at different times(retention Time). Detector: used to monitor the out let stream from the column; thus, the time at which each component reaches the outlet and the amount of that component can be determined. Generally, substances are identified(qualitatively) by the order in which they emerge(elute) from the column and by the retention time of the analytic in the column.
  • 28. REQUIREMENT FOR GAS CHROMATOGHRAPHY VOLATILITY:-Tendency of a substance to evaporate at normal temperatures POLARITY:-Substance comprised of molecules that contain unbalanced localized charges (dipoles) is a polar substance.  Polar substances tend to interact with other polar substances and rarely react to a significant degree with nonpolar substances When two atoms form a covalent bond, they each share an electron. Different atoms have different abilities to attract electrons quantified by their electronegativity values. When one atom in a covalent bond has a much higher electronegativity than the other, the electron is found closer to that atom than the weaker one. This creates a dipole effect with a slight negative charge at the atom the electron favours and a slight positive charge at the other
  • 29. BLOCK DIAGRAM OF GAS CHROMATOGRAPHY
  • 30. COMPONENT OF GAS CHROMATOGRAPH carrier gas flow regulator injector column stationary phase oven detectors display device
  • 31. CARRIER GAS • he(common), • others:n2,h2 • safety; non-flammability, cost and efficiency are factors for gas selection • inertness • suitable for the detector • high purity • easily available
  • 32. FLOW METER • Deliver the gas with uniform pressure/flowrate • Flowmeters:-Rotameter
  • 33. INJECTOR • Transfers the sample into the column. • Provides the means to introduce a sample into a continuous flow of carrier gas. • Injectors are usually heated to ensure sample’s transfer to a gas phase. • Volatile liquid or gaseous sample is injected through a septum.
  • 34. COLUMN Gas chromatography columns : packed and capillary. Packed columns :A glass or stainless steel coil(typically1-5m total length and 5mm inner diameter), filled with the stationary phase, or a packing coated with the stationary phase. Capillary columns: A thin fused-silica (purified silicate glass) capillary (typically10-100 m in length and 0.5 mm inner diameter) that has the stationary phase coated on the inner surface. Provides much higher separation efficiency than packed columns but are more easily overloaded by too much sample. The main chemical attribute regarded when choosing a column is the polarity of the mixture, The polarity of the sample must closely match the polarity of the column stationary phase to increase resolution and separation while reducing runtime.
  • 35. TEMPERATURE CONTROL DEVICES Temperature Control Devices Preheaters: convert sample into its vapour form, present along with injecting devices Thermostatically controlled oven Temperature maintenance in a column is highly essential for efficient separation.
  • 36. STATIONARY PHASES For every polar sample, polyethylene glycol(thickess 0.25mircometer) is commonly used as the stationary phase. Stationary Phases must have: 1.Low volatility 2.Thermal stability 3.Chemical inertness
  • 38. DETECTOR Placed at the exit of the column. Employed to detect and provide a quantitative measurement of the various constituents of the sample The choice of a particular type of detector is governed by the following factors: 1. High sensitivity, sufficient enough to provide adequate signal for even small sample 2. Response should be linear, unaffected by temperature and flowrate. 3. Non distorted shape of peak and non destructive. 4. Detector temperature must not condense the eluted vapours in it. 5. Simple & Inexpensive 6. Applicable to wide range of samples 7. Good reproducibility, rapidity and linearity.
  • 39. COMMONLY USED DETECTOR Most commonly used types:- 1.Thermal Conductivity Detector TCD 2.Flame Ionization Detector FID 3.Electron Capture Detector ECD 4.Atomic-Emission Detector AED 5.Flame Photometric GC Detector FPD
  • 40. QUALITATIVE ANALYSIS Chromatographic data is presented as a graph of detector response(y-axis) against retention time(x-axis), which is called a chromatogram. This provides a spectrum of peaks for a sample representing the analytics present in a sample eluting from the column at different times. The number of components in a sample is determined by the number of peaks. The amount of a given component in a sample is determined by the area under the peaks. The identity of components can be determined by the given retention times.
  • 41. ADVANTAGES AND DISADVANTAGES OF GC ADVANTAGES:- High Resolution Very high sensitivity, detect down to 100 ppm. Very good precision and accuracy. Very good separation Time(analysis is short), fast analysis is possible. Small sample is needed-ml Good detection system Quantitatively analysis DISADVANTAGES :- Sample must be volatile Dirty sample choke the capillary
  • 42. MODERN APPROACH GCMS:-Gas Chromatography Mass Spectrometry Mass spectrometry: Analytical technique that ionizes chemical species and sorts the ions based on their mass-to-charge ratio. Gas chromatography–mass spectrometry (GC- MS):Analytical method that combines the features of gas- chromatography and mass spectrometry to identify different substances within a test sample. Applications of GC-MS include drug detection, fire investigation, environmental analysis, explosives investigation, and identification of unknown samples
  • 44. 2014 IEEE International Conference on Liquid Dielectrics, Bled Slovenia, June 30 - July 3, 2014 Methanol Detection in Transformer Oils using Gas Chromatography and Ion Trap Mass Spectrometer S. Y. Matharagel, Q. Liul, E. Davenportl, G. Wilson2, D. Walker3 and Z.D. Wang The University of Manchester, Manchester, M13 9PL, UK 2The National Grid Company, Warwick, CV34 6DA, UK 3Scottish Power, Blantyre, G72 OHT, UK
  • 45. Continued….. • Abstract-Paper ageing is an irreversible process, which has made paper insulation a lifetime determining factor for transformers. Chemical indicators in oil such as carbon oxide gases and 2-FAL, are used to indicate the ageing state of paper as it is difficult to obtain paper samples to measure DP or tensile strength. Methanol amount in oil was recently found to be an early-ageing indicator for paper. In this study, a heads pace gas chromatography mass spectrometry setup was developed to measure methanol in transformer oil. This setup consists of an auto sampler with a gas tight syringe, a gas chromatography unit with 60 m VF-624ms column and a quadrupole ion trap type mass spectrometer unit. Measurement of several laboratory-aged and service-aged oil samples were conducted with both external standard and internal standard calibration methods. Higher methanol values obtained from internal standard method confirmed that it is more suitable than external standard method.
  • 46. REFERENCES A text book of environmental chemistry by “BALRAM PANI” “https://en.wikipedia.org/wiki/Gas_chromatography%E2%80%93mas s_spectrometry https://en.wikipedia.org/wiki/Gas_chromatography https://www.youtube.com/watch?v=p3_WtEYIhTo https://www.youtube.com/watch?v=gU2st5-T1Go