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 ↓


Thin Layer Chromatography


Thin-layer chromatography (TLC) is a technique used in chemistry to separate, identify, and analyze the components of a mixture. It is an essential tool in analytical chemistry that provides qualitative information and is commonly used in a variety of applications due to its simplicity, speed, and cost-effectiveness.

Introduction to Thin Layer Chromatography

TLC is a type of planar chromatography in which the stationary phase is a thin layer of a solid substance, usually silica gel, alumina or cellulose, coated on a flat, inert substrate called a plate. The mobile phase is a liquid solvent or mixture of solvents that moves through the stationary phase by capillary action, allowing the mixture to be separated based on differential adsorption.

Root system

The TLC process involves several major steps:

  1. Preparation of TLC plate:

    TLC plates are prepared by coating a thin layer of an adsorbent on an inert backing such as glass, plastic or aluminium. This material serves as the stationary phase. The adsorbent is usually a fine powder of silica gel, alumina or cellulose.

  2. Sample application:

    A small dot or line of the sample mixture is placed on the baseline (near the bottom) of the TLC plate.

  3. Development of Plate:

    The plate is then placed in a developing chamber containing a shallow pool of solvent, known as the mobile phase. The solvent moves to the top of the plate by capillary action, carrying the components of the mixture with it.

  4. Visualization:

    Once the solvent has traveled a sufficient distance through the stationary phase, the plate is removed, dried, and the separated spots are viewed under UV light or using a suitable chemical reagent.

  5. Analysis:

    The distances travelled by the different components are measured and compared. The retention factor (Rf value) is calculated for each component to facilitate the analysis.

Retention Factors

The retention factor (Rf value) is an important numerical descriptor in TLC that indicates the relative distance traveled by a substance during the development of a chromatogram. It is calculated using the formula:

    Rf = (Distance traveled by the compound) / (Distance traveled by the solvent front)

For example, consider a compound that moves 3 cm upward on the TLC plate, and the solvent front moves 6 cm forward. Rf value would be 0.5.

This simple calculation allows scientists to characterize and compare compounds in different TLC experiments.

Development Techniques

TLC plate development can be done through several techniques, such as:

  • Ascending Development:

    The most common approach where the solvent moves upward due to capillary action.

  • Descending development:

    In this less common method, the solvent moves downward under the influence of gravity.

Materials used in thin layer chromatography

TLC involves a combination of materials designed to facilitate the separation and identification of components in a mixture.

Stationary Phase

The stationary phase in TLC is a thin layer of adsorbent material. The selection of the adsorbent depends on the properties of the compounds being analyzed. Commonly used adsorbents include:

  • Silica Gel (SiO2):

    It is the most widely used adsorbent due to its effectiveness and versatility.

  • Alumina (Al2O3):

    It is used to separate non-polar compounds and compounds sensitive to acidic or alkaline conditions.

  • Cellulose:

    Less common but useful for certain specific applications, especially in biological studies.

silica gel

Mobile Phase

The selection of the solvent or solvent mixture in the mobile phase is important because it affects the separation efficiency. The polarity of the solvent affects its interaction with the components being analyzed. Some common solvents include:

  • Hexane:

    A nonpolar solvent that is often used for nonpolar compounds.

  • Ethyl acetate:

    A polar solvent suitable for more polar compounds. It is often used in mixtures with other solvents to control polarity.

  • Methanol:

    An extremely polar solvent used for the separation of extremely polar compounds.

Applications of Thin Layer Chromatography

TLC is widely used in various fields of science and industry. Its applications include:

Medicines

In pharmaceutical research and manufacturing, TLC is used for the following:

  • Active Pharmaceutical Ingredients (APIs) Identification and Related Substance Analysis.
  • Determining the purity of a product.
  • To analyse the stability and degradation of drugs under different conditions.

Food & Beverage Industry

In the food industry, TLC is used for the following:

  • Analyzing additives and preservatives in food products.
  • Detection of contaminants and toxins, ensuring food safety.

Environmental Analysis

In environmental chemistry, TLC helps in:

  • Analyzing pollutants and residues in water, soil and air samples.
  • Detection of pesticides and herbicides in agricultural sites.

Advantages and Limitations of Thin Layer Chromatography

Benefit

  • Simplicity and low cost:

    TLC does not require sophisticated equipment, making it accessible and affordable.

  • Pace:

    The TLC process is relatively quick, producing prompt results.

  • Resilience:

    Capable of analyzing a wide range of compounds.

Boundaries

  • Limited resolution:

    The resolution of TLC is limited compared to other chromatographic methods such as HPLC.

  • Sample Loading:

    Only small amounts of the sample can be analyzed, which may not be sufficient for some analyses.

  • Qualitative analysis:

    TLC provides mainly qualitative data and other methods are required for quantitative analysis.

Conclusion

Thin-layer chromatography is a valuable method in analytical chemistry, offering simplicity, speed, and versatility. With its ability to separate and identify compound components in a variety of fields ranging from pharmaceuticals to environmental analysis, TLC maintains its importance in the scientific community. While TLC has limitations, when integrated with other methods, it can provide robust analytical solutions. Continued research and advancements in TLC methods will likely continue to expand its applications and utility in chemistry and beyond.


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