Graduate
  1. Physical Chemistry  1.1. Thermodynamics  1.1.1. Laws of Thermodynamics  1.1.2. Enthalpy and heat capacity  1.1.3. Entropy and free energy  1.1.4. Phase Equilibrium  1.1.5. Statistical thermodynamics  1.1.6. Thermodynamic cycle  1.1.7. Fugacity and activity  1.2. Quantum Chemistry  1.2.1. Principles of quantum mechanics  1.2.2. Schrödinger Equation  1.2.3. Particle in a box  1.2.4. Operators and eigenvalues  1.2.5. Atomic orbitals  1.2.6. Molecular orbital theory  1.2.7. Perturbation theory  1.2.8. Valence bond theory  1.2.9. Hybridization and chemical bonding  1.3. Chemical kinetics  1.3.1. Rate laws and reaction mechanisms  1.3.2. Collision theory  1.3.3. Transition state theory  1.3.4. Enzyme Kinetics  1.3.5. Chain Reactions and Polymerization  1.3.6. Photochemical reactions  1.4. Statistical mechanics  1.4.1. Partitioning functions  1.4.2. Molecular distribution functions  1.4.3. Boltzmann Distribution  1.4.4. Bose–Einstein and Fermi–Dirac statistics  1.5. Spectroscopy  1.5.1. Rotational Spectroscopy  1.5.2. Vibrational Spectroscopy  1.5.3. Electronic Spectroscopy  1.5.4. Nuclear magnetic resonance spectroscopy  1.5.5. Mass Spectrometry  1.5.6. Raman Spectroscopy  1.5.7. Electron paramagnetic resonance spectroscopy  1.6. Surface and colloidal chemistry  1.6.1. Absorption isotherm  1.6.2. Surface tension and wetting  1.6.3. Colloidal Stability  1.6.4. Catalysis  1.6.5. Emulsions and micelles  1.7. Electrochemistry  1.7.1. Nernst equation  1.7.2. Electrochemical cells  1.7.3. Conductivity and mobility  1.7.4. War  1.7.5. Fuel cells  1.7.6. Electrolysis
  2. Organic chemistry  2.1. Reaction mechanism  2.1.1. Nucleophilic substitution reactions  2.1.2. Electrophilic addition reactions  2.1.3. Elimination reactions  2.1.4. Rearrangement reactions  2.1.5. Radical reactions  2.1.6. Pericyclic reactions  2.2. Spectroscopy and structural determination  2.2.1. UV-Vis Spectroscopy  2.2.2. IR Spectroscopy  2.2.3. NMR Spectroscopy  2.2.4. Mass Spectrometry  2.2.5. X-ray crystallography  2.3. Stereoscopic  2.3.1. Chirality and optical activity  2.3.2. Structural analysis  2.3.3. Geometrical isomerism  2.3.4. Dynamic Stereochemistry  2.4. Organometallic Chemistry  2.4.1. Organolithium and organomagnesium reagents  2.4.2. Palladium-catalyzed cross-coupling reactions  2.4.3. Transition Metal Complexes  2.4.4. Metal–carbon bond  2.5. Polymer chemistry  2.5.1. Polymerization mechanism  2.5.2. Polymer Characteristics  2.5.3. Biodegradable Polymer  2.5.4. Conducting polymer  2.5.5. Supramolecular polymers  2.6. Medicinal chemistry  2.6.1. Drug design and development  2.6.2. Pharmacokinetics and pharmacodynamics  2.6.3. Structure-activity relationships  2.6.4. Molecular docking and drug screening
  3. Inorganic chemistry  3.1. Coordination chemistry  3.1.1. Crystal field theory  3.1.2. Ligand field theory  3.1.3. Spectrochemical Series  3.1.4. Chelation and stability  3.2. Organometallic Chemistry  3.2.1. Metal Carbonyls  3.2.2. Catalysis by organometallic complexes  3.2.3. Metallocenes  3.3. Bio-inorganic chemistry  3.3.1. Metalloproteins and enzymes  3.3.2. The role of metals in biological systems  3.3.3. Metal ion transport and storage  3.4. Solid state chemistry  3.4.1. Crystal Structures  3.4.2. Band theory of solids  3.4.3. Superconductors  3.4.4. Defects in the crystal  3.5. Lanthanides and Actinides  3.5.1. Electronic configuration in lanthanides and actinides  3.5.2. Coordination chemistry of the lanthanides  3.5.3. Magnetic Properties of Lanthanides
  4. Analytical chemistry  4.1. Chromatography  4.1.1. Gas Chromatography  4.1.2. High Performance Liquid Chromatography  4.1.3. Thin Layer Chromatography  4.2. Spectroscopic Techniques  4.2.1. Atomic absorption spectroscopy  4.2.2. X-ray diffraction  4.2.3. Inductively coupled plasma spectroscopy  4.3. Electroanalytical methods  4.3.1. Potentiometry  4.3.2. Voltammetry  4.3.3. Colometry  4.4. Mass Spectrometry  4.4.1. Ionization Technique  4.4.2. Fragmentation Pattern  4.5. Chemometrics  4.5.1. Multidisciplinary analysis  4.5.2. Machine Learning in Chemistry
  5. Theoretical and Computational Chemistry  5.1. Molecular dynamics simulation  5.1.1. Force fields and energy minimization  5.1.2. Monte Carlo simulation in molecular dynamics simulations  5.2. Quantum chemical methods  5.2.1. Hartree–Fock theory  5.2.2. Density functional theory  5.2.3. Semi-empirical methods  5.3. Computational drug design  5.3.1. Molecular Docking  5.3.2. QSAR Modeling  5.3.3. Virtual Screening
  6. Biochemistry  6.1. Enzyme Kinetics  6.1.1. Michaelis-Menten kinetics  6.1.2. Inhibition mechanism  6.2. Metabolism and Bioenergetics  6.2.1. Glycolysis  6.2.2. Citric acid cycle  6.2.3. Electron transport chain  6.3. molecular Biology  6.3.1. DNA replication and repair  6.3.2. Protein synthesis  6.3.3. Gene Regulation  6.4. Structural Biochemistry  6.4.1. Protein Folding  6.4.2. Membrane Biophysics
  7. Environmental Chemistry  7.1. Atmospheric Chemistry  7.1.1. Greenhouse gases  7.1.2. Ozone depletion  7.1.3. Air pollutants and smoke  7.2. Water Chemistry  7.2.1. pH and water hardness  7.2.2. Wastewater treatment  7.2.3. Aquatic Chemistry  7.3. Soil Chemistry  7.3.1. Heavy metal contamination  7.3.2. Soil pH and Buffering  7.3.3. Nutrient cycling  7.4. Toxicology and Chemical Safety  7.4.1. Toxicokinetics  7.4.2. Risk Assessment in Toxicology and Chemical Safety in Environmental Chemistry  7.4.3. Effects of pollutants on the environment

Graduate → Analytical chemistry ↓


Chromatography


Chromatography is an important analytical technique widely used in scientific research and industry to separate and analyze complex mixtures of chemicals. The word chromatography derives from the Greek words chroma, meaning "color," and graphein, meaning "to write." It historically referred to the process used to separate plant pigments and appeared as different colored bands on a column. Over time, the technique has evolved into a powerful tool that extends far beyond color-analyzed compounds to include colorless analytes found in solid, liquid, and gaseous states.

Fundamentals of chromatography

The basic principle of chromatography involves two phases: the stationary phase and the mobile phase. The separation of various components within a mixture depends on the differential partitioning between these two phases.

1. Stationary phase: This phase remains stationary either in the column or as a layer, like a thin film, on the plate. The stationary phase may be a solid, a liquid-coated solid, or a gel.

2. Mobile phase: The mobile phase moves through or across the stationary phase and may be a liquid or gas carrying the components of the mixture to be analyzed.

Separation occurs due to differences in the rate at which the different components of a mixture pass through the stationary phase. These differences are influenced by the molecules of each component and by specific interactions between the phases, such as adsorption, solubility, and ion exchange.

Types of chromatography

Chromatography may be broadly classified based on the nature of the mobile phase or the system of separation:

1. Gas chromatography (GC)

Gas chromatography is used to separate and analyze compounds that can be vaporized without decomposition. The mobile phase is a carrier gas (usually an inert gas such as helium or nitrogen), and the stationary phase is a microscopic layer of liquid or polymer on an inert solid support inside a column. Components are separated based on their volatility and interaction with the stationary phase.

Imagine a GC setup consisting of a column with a liquid stationary phase. A mixture containing compounds A, B, and C is introduced. Compound A elutes first because it interacts less with the stationary phase and is more volatile. Compound B follows, and finally compound C, which has the strongest interaction with the stationary phase, elutes last.

GC Column Inert gas

2. Liquid chromatography (LC)

Liquid chromatography involves a liquid mobile phase that passes through a column filled with a solid stationary phase. Separation is based on differential partitioning between the mobile liquid and stationary solid phases, using differences in polarity, molecular size, or ion exchange.

High performance liquid chromatography (HPLC)

It is a highly advanced form of liquid chromatography in which high pressure is used to force the liquid mobile phase through the column. HPLC offers high resolution and sensitivity and is extensively used for quantitative and qualitative analysis of complex mixtures.

HPLC system is used to separate mixtures containing compounds X, Y, Z. As the mobile phase travels under high pressure, it carries the compounds at different rates. Compound X has a strong affinity for the stationary phase and is the last to elute, while compound Z is the first to elute due to its weaker interaction.

3. Thin layer chromatography (TLC)

In this method, the stationary phase is a thin layer of an adsorbent material such as silica gel or alumina, coated on a flat surface such as glass or plastic. The mobile phase is a solvent that moves by capillary action.

TLC Plate mobile phase

In TLC, compounds are separated as they move up the plate at different speeds. The retention factor, R f, is a measure of how far a compound travels along the solvent front.

R f = (distance traveled by the compound) / (distance traveled by the solvent front)

4. Ion-exchange chromatography

This type of chromatography uses a charged stationary phase to separate ions and polar molecules based on their affinity for the ion exchanger. It is particularly useful in bioanalysis for separating proteins, peptides, and nucleotides.

An ion-exchange column filled with positively charged resins attracts negatively charged ions from the sample. The ions are then eluted by gradually changing the ionic strength of the mobile phase or its pH.

5. Size-exclusion chromatography

Also known as molecular sieve chromatography, this technique separates molecules based on their size. Larger molecules escape first because they cannot penetrate the smaller pores of the stationary phase and thus pass through the column more quickly.

This technique is valuable for purifying proteins, polymers, and other large molecules.

Applications of chromatography

Chromatography is indispensable in a variety of fields because of its ability to separate minute quantities of substances. Here are some of its many applications:

1. Pharmaceutical industry

Analysis of purity, active ingredients and stability testing of pharmaceutical drugs rely heavily on chromatography. Techniques such as HPLC ensure the quality and safety of drugs.

2. Environmental monitoring

Gas chromatography is used to detect and measure volatile organic compounds (VOCs) and persistent organic pollutants (POPs) in air, water, and soil. It is important for pollution assessment and control.

3. Food and beverage industry

Chromatographic techniques ensure the quality and authenticity of food products by analyzing additives, pesticides, and flavors. For example, LC techniques determine the amount of caffeine in beverages or vitamins in dietary supplements.

4. Biological and biomedical research

In this field, chromatography plays a vital role in separating and analyzing biomolecules such as proteins, peptides, nucleic acids, and metabolites. This information is vital for drug discovery and disease analysis.

Conclusion

In conclusion, chromatography is an extremely versatile and essential tool for qualitative and quantitative analysis in analytical chemistry. It enables scientists to separate complex mixtures into individual components, facilitating further analysis and application. As technology advances, the precision and application of chromatography continues to expand, solidifying its role as a cornerstone in scientific analysis.


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Chromatography

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