Gas chromatography

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GAS CHROMATOGRAPHY (GC)Gas chromatography is a chromatographic technique that can be used to separate volatile organic compounds. GLC( or) GC is a type of partition chromatography.It consists of a flowing mobile phase (carrier gas)an injection porta separation column (the stationary phase)an ovena detector. BASIC GC SYSTEMOne or more high purity gases are supplied to the GC. One of the gases (called the carrier gas) flows into the injector, through the column and then into the detector. A sample is introduced into the injector usually with a syringe or an exterior sampling device. The injector is usually heated to 150-250C which causes the volatile sample solutes to vaporize. The vaporized solutes are transported into the column by the carrier gas. The column is maintained in a temperature controlled oven. The solutes travel through the column at a rate primarily determined by their physical properties, and the temperature and composition of the column.

The various solutes travel through the column at different rates. The fastest moving solute exits (elutes) the column first then is followed by the remaining solutes in corresponding order. As each solute elutes from the column, it enters the heated detector. An electronic signal is generated upon interaction of the solute with the detector. The size of the signal is recorded by a data system and is plotted against elapsed time to produce a chromatogram.

TYPES OF GCTwo types of gas chromatography 1. Gas-solid chromatography (GSC) 2. Gas-liquid chromatography(GLC)Gas-solid chromatography Is based upon a solid stationary phase on which retention of analytes is the consequence of physical adsorption. Gas-liquid chromatography Is useful for separating ions or molecules that are dissolved in a solvent.


The GC principle involves separationofcomponentsofthe sampleunder test due topartitionin between gaseousmobile phase and stationary liquid phase. Gas chromatographyruns on the principle of partition chromatography forseparationof components. In terms of stationary and mobile phases it iscategorizedundergas-liquid type ofchromatography.The organic compounds are separated due to differences in their partitioning behavior between the mobile gas phase and the stationary phase in the column.


Process Flow SchematicCarrier gas (nitrogen or helium)Sample injectionLong Column (30 m)Detector (flame ionization detector or FID)HydrogenAir

Gas Chromatograph Components

Flame Ionization DetectorColumnOvenInjection Porttop viewfront viewINSTRUMENTAL COMPONENTS

CARRIER GAS The carrier gas must be chemically inert. Commonly used gases include nitrogen, helium, argon, and carbon dioxide. SAMPLE INJECTION PORT The most common injection method is where a micro syringe is used to inject sample through a rubber septum into a flash vaporizer port at the head of the column. The temperature of the sample port is usually about 50C higher than the boiling point of the least volatile component of the sample. The carrier gas enters the chamber and can leave by three routes. The sample vaporizes to form a mixture of carrier gas, vaporized solvent and vaporized solutes.

COLUMNS There are two types of column, 1.Packed column 2. capillary column(also known asopen tubular).PACKED COLUMNS It contain a finely divided, inert, solid support material coated with liquid stationary phase. Most packed columns are 1.5 - 10m in length and have an internal diameter of 2 - 4mm.CAPILLARY COLUMNS 1. wall-coated open tubular(WCOT) 2. support-coated open tubular(SCOT)Both types of capillary column are more efficient than packed columns.

These have much thinner walls than the glass capillary columns, and are given strength by the polyimide coating. They have the advantages of physical strength, flexibility and low reactivity.

PREPARATION OF SAMPLE Polar compounds are not directly applied. polar groups (-OH, -COOH) into non-polar derivatives increases the volatility of these compounds. Silanization, methylation and perfluoroacylation are common conversion methods for CHO, fatty acids & amino acids. Non-polar organic compounds need any such conversion and they can be directly applied.APPLICATION OF SAMPLE The sample for GLC is dissolved in a suitable solvent such as acetone or methanol and is injected into the column using a micro syringe in the injecting port.SEPARATION PROCEDURE The most commonly used carrier gases are nitrogen, helium & argon. The gases are passed at a flow rate of 40 to 80 ml. Two types of temperature control techniques: 1. Isothermal analysis 2. Temperature programmingDETECTORs

GCdetectorsdetect the isolatedcomponentsand helps in identification and quantification of the sample. TYPES OF GC DETECTORS 1.Thermal conductivity detector 2.Flame ionization detector 3.Electron capture detector 4.Flame photometric detector 5.Photo-ionization detector 6.Hall electrolytic conductivity detector


The effluent from the column is mixed with hydrogen and air. Organic compounds burning in the flame produce ions and electrons which can conduct electricity through the flame. A large electrical potential is applied at the burner tip, and a collector electrode is located above the flame.The current resulting from the pyrolysis of any organic compounds is measured. The FID is a useful general detector for the analysis of organic compounds, it has high sensitivity, a large linear response range, and low noise. It is also easy to use, but unfortunately, it destroys the sample.

Flame Ionization DetectorHydrogenAirCapillary tube (column)Platinum jetCollectorSintered diskTeflon insulating ringFlameGas outletCoaxial cable to Analog to Digital converterIonsELECTRON CAPTURE DETECTORThecomputerto recordthe analysed readings. This is connected with the detector and hence records the detector changes in reference tothe flowof separatedcomponentsfrom the exit of the column. Therecordis calledgas chromatograph.

Thethermal chamberto fix or maintain fixedtemperature.

Further improvement in GCapparatus is fixed with Mass spectroscopy system (GC-MS)for better analysis of components.

GAS CHROMATOGRAPH OUTPUTtime (s)detectoroutput

Peak area proportional to mass of compound injectedPeak time dependent on velocity through columnUSES OF GCWidely used for the qualitative and quantitative analysis of a large number of compoundsThis technique provides a high speed and resolutionVery good reproducibility and high sensitivity1000 of volatile organic compounds can be separated by GCNon-volatile substance can also separated if converted in to volatile one by oxidation, acylation, alkylation, etc.Concentration of individual elements such as carbon and hydrogen can be determined very accuratelyAlcohols, esters, fatty acids and amines present in biological samples are often separated by GC.APPLICATION OF GCGas chromatography (GC) continues to play an important role in the identification and quantification of ubiquitous pollutants in the environment. GC in the analysis of various classes of persistent organic contaminants in air, water, soils, sediments. Special attention is given to sample-preparation techniques. The organic pollutant groups are: volatile organic compounds (VOCs) , polycyclic aromatic hydrocarbons (PAHs) , pesticides and halogenated compounds. Trends and future perspectives of capillary GC in the field of environmental analysis.

Refinery SolutionsGas Chromatographs are uniquely designed to provide extended analysis in the most extreme of plant condition. Emerson gas chromatograph offers: Better control of the process Environmental monitoring Billing and cost accounting for product transfers 1) REFINERY SOLUTIONS


chemical and petrochemical plants keep operating efficiently. Maintain proper chemical ratios Monitor for unconverted carbons Monitor purge gas rates and track BTU usage& variations in product feed composition Measure impurities in product Minimize product loss Chemical/Petrochemical Solutions

3) GAS PROCESSING SOLUTIONS For gas processing plants, gas chromatograph product and service offerings reduce installation and maintenance costs, while improving process quality. We offer a complete range of gas plantapplications that demonstrate an advanced combination of innovative technology and hardened instrumentation Gas Processing Solutions

4) ENVIRONMENTAL MONITORING SOLUTIONS There are numerous gases found inindustrial process plants thatare harmful should a gas leak occur, such as sulfur dioxide, hydrogen sulfide, and others. Analytical process gas chromatographs provides reliable, accurate analysis of gases. A Analytical process gas chromatograph offers a sensitivity of 100% humidity, and even samples will not deter accurate analysis.Environmental Monitoring Solutions22

Gas chromatograph with a headspace samplerREFERENCESBiomedical instrumentation- V.ArumugamPalanivelu. P. Analytical biochemistry and separation techniques.Webster. J.G. Bioinstrumentation.B