PHD
  1. Inorganic chemistry  1.1. Coordination chemistry  1.1.1. Ligand field theory  1.1.2. Crystal field theory  1.1.3. Molecular Orbital Theory for Coordination Compounds  1.1.4. Stability of Coordination Compounds  1.1.5. Electronic spectra of coordination compounds  1.1.6. Isomerism in Coordination Compounds  1.1.7. Kinetics and mechanism of coordination reactions  1.2. Organometallic Chemistry  1.2.1. Metal Carbonyls  1.2.2. Metal alkyl and aryl  1.2.3. Fischer and Schrock carbonaceans  1.2.4. Oxidative Addition and Reductive Elimination  1.2.5. Metal Hydrides  1.2.6. Catalysis by organometallic compounds  1.2.7. Metallocenes and Sandwich Complexes  1.2.8. CH activation  1.3. Solid state chemistry  1.3.1. Crystal structures and lattices  1.3.2. Band theory and electrical properties  1.3.3. Defects in the crystal  1.3.4. Synthesis of solid state materials  1.3.5. Magnetic and optical properties of solids  1.3.6. Superconductivity  1.3.7. Solid state ionics  1.4. Bio-inorganic chemistry  1.4.1. Metalloproteins and enzymes  1.4.2. Metal ion transport and storage  1.4.3. The role of metals in medicine  1.4.4. Bioinspired catalysis  1.4.5. Metal–DNA interactions  1.4.6. Metal Complexes in Medical Science  1.5. Lanthanides and Actinides  1.5.1. Electronic configuration and oxidation states in lanthanides and actinides  1.5.2. Spectral and Magnetic Properties in Lanthanides and Actinides  1.5.3. Separation and Extraction of Lanthanides and Actinides  1.5.4. Coordination chemistry of f-block elements  1.6. Main Group Chemistry  1.6.1. Chemistry of boron compounds  1.6.2. Chemistry of Silicon and Germanium Compounds  1.6.3. Chemistry of Phosphorus and Sulfur Compounds  1.6.4. Organosilicon chemistry  1.6.5. Noble Gas Chemistry
  2. Organic chemistry  2.1. Reaction mechanism  2.1.1. Nucleophilic substitution reactions  2.1.2. Electrophilic addition and substitution reactions  2.1.3. Elimination reactions  2.1.4. Rearrangement reactions  2.1.5. Radical reactions  2.1.6. Pericyclic Reactions  2.1.7. Photochemical reactions  2.2. Stereoscopic  2.2.1. Chirality and optical activity  2.2.2. Structural analysis  2.2.3. Stereoelectronic effects  2.2.4. Asymmetric synthesis  2.2.5. Dynamic Stereochemistry  2.3. Organometallic Chemistry in Organic Synthesis  2.3.1. Organolithium and organomagnesium reagents  2.3.2. Transition metal catalyzed coupling reactions  2.3.3. Palladium-catalyzed reactions  2.3.4. Olefin Metathesis  2.3.5. Gold and silver catalysis  2.4. Natural products chemistry  2.4.1. Alkaloids and terpenoids  2.4.2. Steroids and Flavonoids  2.4.3. Total synthesis of natural products  2.4.4. Biosynthesis of natural products  2.5. Supramolecular Chemistry  2.5.1. Host-Guest Chemistry  2.5.2. Self-assembly and molecular recognition  2.5.3. Supramolecular Catalysis  2.5.4. Molecular Machines
  3. Physical Chemistry  3.1. Thermodynamics  3.1.1. Laws of Thermodynamics  3.1.2. Chemical Potential and Equilibrium  3.1.3. Statistical thermodynamics  3.1.4. Non-equilibrium thermodynamics  3.2. Quantum Chemistry  3.2.1. Schrödinger equation and its applications  3.2.2. Molecular orbital theory  3.2.3. Density functional theory  3.2.4. Post-Hartree–Fock methods  3.3. Chemical kinetics  3.3.1. Reaction rate theory  3.3.2. Mechanism and rate laws  3.3.3. Catalysis and enzyme kinetics  3.3.4. Reaction dynamics  3.4. Spectroscopy and molecular structure  3.4.1. Infrared Spectroscopy  3.4.2. UV-visible spectroscopy  3.4.3. Nuclear Magnetic Resonance Spectroscopy  3.4.4. Mass Spectrometry  3.4.5. Raman Spectroscopy  3.5. Surface and Colloid Chemistry  3.5.1. Absorption and Catalysis  3.5.2. Surfactants and micelles  3.5.3. Colloidal Stability  3.5.4. Nanomaterials and Interfaces
  4. Analytical chemistry  4.1. Chromatography  4.1.1. Gas Chromatography  4.1.2. High Performance Liquid Chromatography  4.1.3. Thin Layer Chromatography  4.1.4. Ion Chromatography  4.2. Electroanalytical techniques  4.2.1. Voltammetry and Polarography  4.2.2. Conductometry and potentiometry  4.2.3. Colometry  4.3. Spectroscopic Methods  4.3.1. Atomic absorption spectroscopy  4.3.2. Fluorescence Spectroscopy  4.3.3. X-ray diffraction  4.3.4. Electron paramagnetic resonance spectroscopy  4.4. Chemometrics  4.4.1. Data processing and statistical methods  4.4.2. Multidisciplinary analysis  4.4.3. Machine Learning in Analytical Chemistry
  5. Theoretical and Computational Chemistry  5.1. Molecular dynamics simulation  5.2. Quantum chemistry methods  5.3. Computational drug design  5.4. Machine Learning in Chemistry  5.5. Ab initio molecular dynamics
  6. Biophysics and Medicinal Chemistry  6.1. Drug discovery and design  6.2. Enzyme kinetics and inhibition  6.3. Chemical biology approach  6.4. Protein-ligand interactions  6.5. Bioorthogonal chemistry
  7. Materials chemistry  7.1. Polymer chemistry  7.1.1. Polymerization mechanism  7.1.2. Functional Polymers  7.1.3. Biodegradable Polymer  7.1.4. Conducting and semiconducting polymers  7.2. Nano Chemistry  7.2.1. Nanoparticles and nanostructures  7.2.2. Carbon-based nanomaterials  7.2.3. Quantum dots  7.3. Energy and Environmental Chemistry  7.3.1. Battery and Fuel Cell Chemistry  7.3.2. Green chemistry and sustainable materials  7.3.3. Photocatalysis

PHD → Analytical chemistry → Chromatography ↓


Gas Chromatography


Gas chromatography (GC) is an essential tool in analytical chemistry. It allows scientists to separate and analyze compounds that can vaporize without decomposition. The process of gas chromatography is widely used in the fields of environmental analysis, pharmaceuticals, forensic science, and the food and flavor industries due to its versatility and high efficiency.

Principle of gas chromatography

The basic principle of gas chromatography involves a mobile phase and a stationary phase. In GC, the mobile phase, or carrier gas (usually helium or nitrogen), is an inert gas that carries the vaporized sample through the column. The stationary phase is either a liquid or polymer on an inert solid support inside a glass or metal column. As the sample travels through the column, different compounds in the mixture interact differently with the stationary phase and are separated based on their boiling points and affinities.

Carrier gas (mobile phase) Stationary phase

Components of a gas chromatograph

A typical gas chromatograph has several major components:

  • Carrier gas: The carrier gas forms the mobile phase that transports the sample through the column.
  • Injector: The injector ensures that the sample enters the gas chromatograph as a vapor. It is heated to help vaporize liquid samples.
  • Column: The heart of the gas chromatograph, the column contains the stationary phase and separates the components of the sample.
  • Detector: The detector provides a signal whenever a compound leaves the column. Common detectors include flame ionization detectors (FID) and mass spectrometry (MS).
  • Data system: This records and analyzes the detector response, allowing identification and quantification of compounds.

Detailed procedure of gas chromatography

The gas chromatography process begins with sample injection. The sample, which can be liquid or gas, is inserted into the injector at the inlet of the chromatograph. The following steps describe the separation and detection of the sample components:

1. Injection

The injection process is important because it affects the accuracy and reproducibility of the analysis. A small volume of liquid sample is injected using a micro-syringe through a septum into a heated port, where it evaporates. Automated systems often use an autosampler to introduce samples at regular intervals to improve accuracy.

2. Separation in the column

As the vaporized sample enters the column, it collides with the stationary phase. Separation occurs as a result of the interaction between the sample components and the stationary phase—usually a liquid or solid. Different compounds pass through the column at different rates depending on their physical and chemical properties.

Component A Component B Component C

3. Detection

Once the separated components leave the column, they are detected, and their presence is recorded as a peak on the chromatogram. The time it takes for each component to reach the detector is known as the retention time, which characterizes a compound under prescribed conditions.

4. Analysis of the results

By comparing the retention times and shapes of peaks in the chromatogram with known standards, the identity and quantity of compounds can be estimated. Advanced data systems help to interpret and quantify the results efficiently.

Gas chromatography detector

There are several detectors used in gas chromatography, each suited to a specific type of analysis.

  • Flame ionization detector (FID): Sensitive to hydrocarbons, the FID detects ions formed during combustion at the flame tip.
  • Mass spectrometry (MS): Provides detailed information about molecular structure based on fragmentation patterns.
  • Thermal conductivity detector (TCD): Measures the change in thermal conductivity of the carrier gas due to various compounds.
  • Electron capture detector (ECD): Ideal for detecting halogenated compounds, this measures how electrons are absorbed by different substances.

Applications of gas chromatography

Gas chromatography has wide applications in a variety of fields, including:

  • Environmental analysis: monitoring of pollutants and toxins in air, water, and soil.
  • Pharmaceuticals: Quality control and analysis of raw materials, intermediates and final products.
  • Forensic science: Detection of drugs, explosives, and poisons in biological samples during criminal investigations.
  • Food and beverage industry: Quality control and taste analysis of food products, essential oils and perfumes.

Advantages and limitations of gas chromatography

Gas chromatography is preferred because of its accuracy, high resolution, and speed. However, it also has limitations.

Benefit:

  • High sensitivity and selectivity for a variety of compounds.
  • Capable of analyzing complex mixtures.
  • Efficient separation with accurate and reproducible results.

Boundaries:

  • Not suitable for analysis of heat-sensitive compounds that may decompose.
  • The compounds must be volatile, or capable of being vaporized.
  • Analysis may be limited by the availability of suitable detectors and the cost of equipment.

Future prospects and innovations

Advances in technology continue to enhance the capabilities and applications of gas chromatography. Innovations in column materials, detector sensitivity, and data analysis algorithms are paving the way for more efficient and versatile GC systems. Future developments may include miniaturization and integration with other analytical techniques to overcome current limitations and broaden its applicability.

Conclusion

Gas chromatography remains an important analytical technique. Its ability to separate, identify, and quantify compounds with high accuracy continues to benefit a variety of scientific fields. Through ongoing research and technological advancements, gas chromatography is set to become even more powerful, efficient, and accessible in the pursuit of chemical analysis.


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Gas Chromatography

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