GAS CHROMATOGRAPHY-Principle, Instrumentation Advantage and disadvantage applications.pptx

Gas chromatography its principle, instrumentation, advantages and disadvantages and application are widely covered in this presentation.

1. GAS CHROMATOGRAPHY By- Dipesh Adesh Gamare Principle, Instrumentation, Advantage and disadvantage, applications of Gas Chromatography

2. INTRODUCTION In gas chromatography, gas is the mobile phase and solid or liquid is the stationary phase . Two techniques:- Gas solid chromatography - Gas is used as the mobile phase and solid is used as the stationary phase. Adsorption process takes place. Rarely used . Gas liquid chromatography - Gas is used as the mobile phase and liquid, which is immobilized by supporting on some solid matrix, is used as the stationary phase. Partition process takes place. Widely used .

3. PRINCIPLE OF GLC The major role of the mobile phase is to push the solutes, which are desorbed from the stationary phase, out of the column. Hence, the mobile phase is usually referred to as a carrier gas. Sample should be in the form of vapor . Vapors of the sample is introduced at the head of the column. The solutes from the mixture interact with the stationary phase by dissolving in it. The solutes having greater solubility in the stationary liquid phase remain in the higher concentration in it, whereas solutes having lesser solubility in the stationary liquid phase remain in the smaller concentration in it. Thus, the solutes distribute themselves between the phases according to their distribution coefficients . The solutes having lesser interaction with the stationary phase are easily desorbed from it and are eluted out faster . The elution of the desorbed compounds is achieved by forcing an inert carrier gas such as nitrogen or helium through the column.

4. INSTRUMENTATION OF GLC 1) Carrier gas supply Soap bubble flow meter Soap bubbler flow meters are a classic method for measuring the gas flow rate for carrier gases in applications such as gas chromatography (GC). The unit is supplied with a rubber bulb which attaches to the bottom of the device. The outlet of the system to be measured is connected to the serrated hose connection (9 mm O.D. at the middle ring, 10 mm O.D. at the largest ring), and the bulb is partially filled with soapy water. To make the measurement, the user squeezes the bulb until the soapy water goes above the gas sidearm. This will cause a series of flat soap film bubbles to rise up the calibrated column. Simply time how long it takes for the bubble to travel a given volume to determine your flow rate. The column is open at the top and a clever projection at the top breaks the bubbles automatically. This item is available in 10 and 25 mL sizes. The 10 mL has 0.05 mL subdivisions and the 25 mL has 0.1 mL subdivisions. 10 mL dimensions: Overall length (without bulb): ~12-5/8" (322 mm). Width at sidearm: ~3" (76 mm). Tube diameter: 7/16" (11 mm). Helium (He), nitrogen (N 2 ), hydrogen (H 2 ), and argon (Ar)  are often used. Helium and nitrogen are most commonly used and the use of helium is desirable when using a capillary column. Although expensive, it is safe and has a relatively wide optimum linear velocity range.

5. INSTRUMENTATION OF GLC 2) Sample injection system A sample of the suitable size should be introduced as a ‘plug’ of vapor i.e. it should be introduced at once. The slow injection or the oversized samples- poor resolution. For injecting the sample into a heated sample port located at the head of the column, a microsyringe is used. The sample port is usually maintained at about 50 ℃ above the boiling point of an analyte . Sample size- few tenths to 10 μ L. Sample splitters.

6. INSTRUMENTATION OF GLC 3) Columns Capillary columns/ Open tubular columns:- Capillary tubing of internal diameter- 0.3- 0.5 mm . Inner walls are coated with a very thin film of the liquid which acts as the stationary phase. It offers negligible resistance to the flow of the mobile phase hence pressure drop across the two ends of the capillary column is negligible . Therefore, columns as long as 10-100 m or more can be used consists of several hundred thousand theoretical plates . Vs / Vm = 100- 300- high efficiency . Limited amount of the stationary phase = very low sample loading capacity . Can be increased by coating inner walls with porous material such as graphite, metal oxide or silicate. This will increase the surface area for coating of the stationary phase which increases loading capacity.

7. INSTRUMENTATION OF GLC Packed columns:- Glass or tubes of stainless steel, copper or aluminium , with the internal diameter 1- 8 mm. They are filled with solid supports, which adsorb liquid used as the stationary phase for the separation. The packed stationary phase offers some resistance to the flow of the mobile phase hence there is some pressure drop across the two ends of the column. Therefore not as long as the capillary columns; length is 2- 20 m . Vs / Vm = 10- 20 . More amount of the stationary phase = high sample loading capacity. Low efficiency due to less number of theoretical plates (100-10000). 4) Thermostats/ temperature programming Sample in the form of vapor = column is operated at high temperature. Variation in temp. results in the change in the retention time of a compound. The optimum column temp . depends upon the B.P. of the sample to be analyzed and also on the degree of separation required.

8. INSTRUMENTATION OF GLC A temperature programming facilitates controlled increase of even temperature during an analysis. Thus, latter peaks also become sharp and emerge quickly. Thus in temp. programming the components of a wide boiling range mixture may be resolved efficiently. Requirements for temp. programming:- Dual column system- compensates for bleeding of liquid phase from columns during increase of temp. Separate heaters for injector, column, oven, detectors. Differential flow controllers. Thin walled columns. Pure dry carrier gas. 5 ) Detectors 6) Recorders

9. Electron capture detector Principle :- A beam of electrons is generated from an electron emitter . These electrons generate a standing current in the circuit, which remains constant in absence of an organic compound. If an organic comp. comes in the path of this electron beam, suddenly the number of electrons decreased, and it results in the change in the current in the circuit. This gives indication about the presence of an organic compound in the eluate and also about its conc. in it. Advantages:- It is selective in its response. Highly sensitive towards the organic compounds possessing electronegative functional groups such as halogens, peroxides, nitro, so on. Used for determination and detection of chlorinated insecticides. It does not alter the sample significantly. Disadvantages:- Response is non- linear.

10. Electron capture detector

11. Flame ionization detector CONSTRUCTION:- FID makes use of an oven, wherein flame is produced by burning hydrogen gas in presence of oxygen or air. A continuously moving wire loop is provided to transport a portion of the eluate in the furnace. Two electrodes, anode (A) and cathode (C) are placed on either side of a flame. A definite potential difference is maintained across the two electrodes with the help of a series of batteries. A amplifier and a recorder are included in the circuitry for recording chromatograms.

12. Flame ionization detector WORKING:- A continuously moving wire loop transports a portion of the eluate coming out from the column into the furnace, where the solvent is evaporated first. Most organic compounds get pyrolyzed at the temp. provided by hydrogen- air or hydrogen- oxygen flame. Certain compounds are able to form ions after pyrolysis. These ions are attracted either towards an anode or a cathode, depending on the charge present on them. The attraction of ions by the electrode results in the change in the potential difference across the electrodes, which in turn results in the change in the current in the circuit. The electrical resistance of a flame is very high and resulting current is therefore, minuscule. An electrometer must be employed to measure small magnitude of current accurately.

13. Flame ionization detector Advantages :- Detects minute quantities of solutes hence very sensitive. It produces linear response over a wide range of concentration. Disadvantages :- Complicated/ expensive. Destruction of the sample.

14. Thermal conductivity detector Principle :- Based upon the changes in the thermal conductivity of the gas stream. Whetstone’s bridge , which consists of four resistances in the circuit, the magnitude of 3 resistances remains constant and the fourth one varies as per the change in the temperature of the resistance wire. The change in the temperature of the resistance wire is because of the difference in the thermal conductivities of the solute and the carrier gas when they are passed over the heated element. This results in the change in the current in the circuit. Advantages:- Simple, rugged, inexpensive, broadly applicable detection system, non- destructive to the sample, accurate results. Disadvantages:- Non- selective detector, not very sensitive.

15. Thermal conductivity detector

16. ADVANTAGES OF GAS CHROMATOGRAPHY Gas chromatography (GC) is a widely used analytical technique in chemistry and related fields. It is a powerful separation method that separates and analyzes mixtures of volatile compounds. Gas chromatography analysis offers several advantages over other separation techniques, making it a popular choice for researchers and scientists.  Some of the advantages of gas chromatography analysis. 1.    High sensitivity: One of the significant advantages of gas chromatography is its high sensitivity. GC can detect even trace amounts of compounds in a mixture, making it a powerful tool in analytical chemistry. The high sensitivity of GC is due to the use of small sample sizes and the efficient separation of compounds. 2.   High resolution: GC can separate complex mixtures of compounds with high resolution. The resolution is the ability to distinguish between two adjacent peaks in a chromatogram. The high resolution of GC is due to the use of narrow-bore capillary columns and the ability to control the carrier gas flow rate. 3.   Rapid analysis: GC is a relatively fast analysis method, allowing for the analysis of multiple samples in a short time. This speed is due to the use of narrow-bore columns that have a high surface area-to-volume ratio, allowing for the efficient separation of compounds.

17. 4.   Quantitative analysis: GC can be used to perform quantitative analysis of compounds in a mixture. The area under a peak in a chromatogram is proportional to the amount of the compound present in the sample, allowing for accurate quantification of compounds in a mixture. 5.   Minimal sample preparation: GC requires minimal sample preparation compared to other analytical techniques, such as liquid chromatography. This advantage is due to the volatile nature of the compounds analyzed by GC, which do not require complex extraction or purification steps. 6.   Cost-effective: GC analysis is a relatively cost-effective technique compared to other analytical methods, making it accessible to many researchers and scientists. The low cost of GC analysis is due to the availability of inexpensive equipment and consumables.

18. DISADVANTAGES OF GAS CHROMATOGRAPHY Gas chromatography is limited to volatile compounds. Non-volatile compounds don't vaporize. Analyte can decompose at high temperature. Analyte can also react with stationary phase. It is limited to low to medium molecular weight. It is incompatible with aqueous samples. Thermal stability is required during separation through gas chromatography. It is not suitable for high-boiling compounds. It is not sutable for polar analytes. 

19. APPLICATIONS OF GAS CHROMATOGRAPHY Gas chromatography offers many advantages, but what is it primarily used for? As we’ve said, gas chromatography’s versatility makes it a favorite across many industries and applications, from food testing to meteorite analysis. 1) Food Analysis Food analysis and quality control are one of the most common applications for gas chromatography due to their component quantification, accuracy, and speedy process. Gas chromatography is used in the food industry both for quality control and for accurate quantification of compounds and contaminants in food, such as: Carbohydrates Proteins Vitamins Lipids Steroids Pesticides Trace elements With gas chromatography, food producers can accurately quantify the elements in their food, and the FDA ensures that it's of sufficient quality and safety. Thanks to gas chromatography, consumers can purchase food at a grocery store with confidence that it's been thoroughly tested for safety and that the food labels are accurate. 2) Environmental Monitoring Gas chromatography is also a popular method for ensuring that the air and water we breathe are safe for consumption. A huge industry of scientists study our environment, and gas chromatography is a favored technique for detecting contaminants in the environment—particularly those in the air.

20. With gas chromatography, researchers can accurately determine the quality of the air and identify potentially harmful chemicals in the air and where they might come from. Environmental regulators and organizations like the EPA commonly use gas chromatography to ensure air and water sources aren’t contaminated. 3) Drug Testing Gas chromatography is also useful in identifying chemical compounds within the human body through the analysis of bodily fluids. Gas chromatography is a quick and accurate drug testing method, which makes it a favored technique for things like law enforcement; in fact, it’s been used to detect blood alcohol levels since the ‘50s. Gas chromatography can accurately identify and quantify alcohol or drug use in athletes. Sporting bodies like the Olympics and With gas chromatography, forensic analysts can more accurately determine the circumstances of a person’s death and provide that information to law enforcement. 4) Manufacturing Quality Control Another industry where gas chromatography is common in manufacturing. From automotive plants to pharmaceuticals, many manufacturers use gas chromatography to test the quality and safety of their products. Pharmaceuticals must test the purity of the compounds within their drugs to ensure every batch is safe for consumption. Automotive plants use gas chromatography to ensure there is no harmful chemicals leftover from the manufacturing process that can harm humans within the vehicle.

21. 5) Forensics Gas chromatography provides the capable identification of compounds in bodily fluids, so it's also a favored method in forensic analysis. Many forensic analysts use gas chromatography to determine a person's death by concluding whether they were poisoned, intoxicated, or overdosed on a banned substance. With gas chromatography, forensic analysts can more accurately determine the circumstances of a person's death and provide that information to law enforcement. 6) Environmental Research As we mentioned, environmental researchers use gas chromatography often, but it’s also favored by scientists examining things from outside our world. Gas chromatography has even been commonly used to analyze and research meteorites that have fallen to earth. With gas chromatography, scientists can accurately identify and quantify chemicals within objects from space, deepening our understanding beyond our planet.

22. REFERENCES Chatwal, G.R. and Anand, S.K.J. (2018) Instrumental Methods of Chemical Analysis. Himalaya Publishing House, Mumbai . Kaur, G., & Sharma, S. (2018). Gas Chromatography -A brief review. ResearchGate. https://www.researchgate.net/publication/344042922_Gas_Chromatography_-A_Brief_Review Libretexts . (2023, August 29). Gas chromatography. Chemistry LibreTexts . https://chem.libretexts.org/Bookshelves/Analytical_Chemistry/Supplemental_Modules_%28Analytical_Chemistry%29/Instrumentation_and_Analysis/Chromatography/Gas_Chromatography GenTech . (2023, March 27). Common Applications of Gas Chromatography | GenTech Scientific. GenTech Scientific. https://gentechscientific.com/6-common-applications-of-gas-chromatography/ Advantages and Disadvantages of Gas Chromatography (GC). ( 2023 .). https://www.pharmastuff4u.com/2023/03/advantages-and-disadvantages-of-gas.html Kumar, V. (2023, May 15). Advantages of gas chromatography Analysis. Infinita Lab. https://infinitalab.com/blogs/advantages-of-gas-chromatography-analysis/ Soap Bubble Flowmeter. (2020). Safety Emporium. https://www.safetyemporium.com

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