Undergraduate
  1. General chemistry  1.1. Introduction to Chemistry  1.2. Atomic Structure  1.2.1. Subatomic particles  1.2.2. Atomic Model  1.2.3. Quantum numbers  1.2.4. Electron Configuration  1.2.5. Periodic trends  1.2.6. Isotopes and their applications  1.3. Chemical bond  1.3.1. Ionic bond  1.3.2. Covalent bonds  1.3.3. Metal Bond  1.3.4. Hybridization  1.3.5. Molecular geometry and VSEPR theory  1.3.6. Bond polarity and dipole moment  1.4. Stoichiometry  1.4.1. Mole concept  1.4.2. Empirical and molecular formula  1.4.3. Limiting reactant and excess reactant  1.4.4. Percent Yield and Purity  1.4.5. Dilution calculation  1.5. States of matter  1.5.1. Gas Laws  1.5.2. Matter and Intermolecular Forces  1.5.3. Solid and Crystal Structures  1.5.4. Phase diagram  1.5.5. Plasma and supercritical fluid  1.6. Chemical reactions  1.6.1. Types of Chemical Reactions  1.6.2. Balancing Chemical Equations  1.6.3. Thermochemical reactions  1.6.4. Reaction energy profiles  1.7. Solutions and Mixtures  1.7.1. Concentration units  1.7.2. Syndrome properties  1.7.3. Solubility and Solubility Rules  1.7.4. Henry's Law and Raoult's Law  1.7.5. Partition coefficient  1.8. Chemical equilibrium  1.8.1. Law of mass action  1.8.2. Le Chatelier's principle  1.8.3. Reaction quotient  1.8.4. To use this online calculator for Equilibrium Constant, enter Equilibrium Constant (Eq.) and hit the calculate button. Here is how the Equilibrium Constant calculation can be explained with given input values -> 0.05 = 0.05/0.  1.8.5. Acid-base balance  1.9. Acids and bases  1.9.1. Arrhenius, Brønsted–Lowry, and Lewis definitions  1.9.2. pH and pOH  1.9.3. Acid-base titration  1.9.4. Buffer Solution  1.9.5. Acid-base indicator  1.9.6. Polyprotic Acids and Bases  1.10. Electrochemistry  1.10.1. redox reactions  1.10.2. Galvanic and Electrolytic Cells  1.10.3. Nernst equation  1.10.4. Electrolysis  1.10.5. Faraday's laws of electrolysis  1.11. Thermodynamics  1.11.1. Laws of Thermodynamics  1.11.2. Enthalpy, entropy and Gibbs free energy  1.11.3. Spontaneity of reactions  1.11.4. Thermodynamic cycles (Hess's law, Carnot cycle)  1.12. Kinetics  1.12.1. Rate law and reaction order  1.12.2. Activation Energy and Catalyst  1.12.3. Collision theory  1.12.4. Reaction mechanism  1.12.5. Transition state theory
  2. Organic chemistry  2.1. Structure and relationships  2.1.1. Hybridisation in Carbon Compounds  2.1.2. Resonance and aromatization  2.1.3. Molecular orbitals  2.1.4. Inductive and mesomeric effects  2.2. Hydrocarbons  2.2.1. Hydrocarbons  2.2.2. Alkene  2.2.3. Alkynes  2.2.4. Aromatic compounds  2.2.5. Cycloalkanes and Conformation  2.3. Functional Group  2.3.1. Alcohols and phenols  2.3.2. Ethers and epoxides  2.3.3. Aldehyde and ketone  2.3.4. Carboxylic acids and derivatives  2.3.5. Amin  2.3.6. Esters and amides  2.3.7. Thiols and sulfides  2.4. Stereoscopic  2.4.1. Isomerism in Stereochemistry  2.4.2. Chirality and optical activity  2.4.3. Structural analysis  2.4.4. Diastereomers and Enantiomers  2.5.1. Substitution reactions  2.5.2. Elimination reactions  2.5.3. Addition reactions  2.5.4. Radical reactions  2.5.5. Rearrangement reactions  2.5.6. Pericyclic Reactions  2.6. Spectroscopy and structural analysis  2.6.1. Infrared Spectroscopy  2.6.2. Nuclear magnetic resonance spectroscopy  2.6.3. Mass Spectrometry  2.6.4. UV-visible spectroscopy  2.6.5. X-ray crystallography  2.7. Polymer chemistry  2.7.1. Addition and Condensation Polymers  2.7.2. Polymerization mechanism  2.7.3. Biodegradable Polymer  2.7.4. Conducting and smart polymers
  3. Inorganic chemistry  3.1. Coordination chemistry  3.1.1. Ligands and coordination compounds  3.1.2. Crystal field theory  3.1.3. Molecular Orbital Theory in Coordination Compounds  3.1.4. Jahn–Taylor distortion  3.2. Main Group Chemistry  3.2.1. Alkali and alkaline earth metals  3.2.2. Halogens and Noble Gases  3.2.3. Transition metals and their complexes  3.2.4. Lanthanides and Actinides  3.3. Solid state chemistry  3.3.1. Crystal lattices and unit cells  3.3.2. Defects in solids  3.3.3. Electrical and magnetic properties  3.3.4. Superconductivity  3.4. Bio-inorganic chemistry  3.4.1. Metal ions in biology  3.4.2. Enzymatic reactions with metals  3.4.3. Metal poisoning and detoxification  3.4.4. Metalloproteins and Metalloenzymes
  4. Physical chemistry  4.1. Quantum Chemistry  4.1.1. Wave–particle duality  4.1.2. Schrödinger Equation  4.1.3. Quantum Numbers and Orbitals  4.1.4. Atomic and molecular spectroscopy  4.2. Statistical mechanics  4.2.1. Maxwell–Boltzmann distribution  4.2.2. Partitioning functions  4.2.3. Bose–Einstein and Fermi–Dirac statistics  4.3. Chemical thermodynamics  4.3.1. Gibbs Free Energy  4.3.2. Phase transition  4.3.3. Thermodynamic efficiency  4.4. Surface chemistry  4.4.1. Absorption and Catalysis  4.4.2. Colloids and Emulsions
  5. Analytical Chemistry  5.1. Classical methods  5.1.1. Gravimetric Analysis  5.1.2. titrimeter  5.2. Instrumental methods  5.2.1. Chromatography  5.2.2. Spectroscopy  5.2.3. Electroanalytical methods  5.2.4. X-ray diffraction
  6. Industrial Chemistry  6.1. Petrochemistry  6.2. Chemical engineering principles  6.3. Green Chemistry  6.4. Pharmaceuticals and Drug Synthesis
  7. Biochemistry  7.1. Carbohydrates  7.2. Proteins and enzymes  7.3. Lipids and membranes  7.4. Nucleic acids  7.5. Metabolism and Bioenergetics  7.6. Enzyme kinetics and mechanism

Undergraduate → Analytical Chemistry → Instrumental methods ↓


Chromatography


Chromatography is a laboratory technique for separating mixtures into their individual components. This technique is important because it provides a way to identify and quantify each component within a mixture. Chromatography is widely used in a variety of fields including chemistry, biology, and even in the food industry for testing purity and quality.

History of chromatography

The concept of chromatography was first developed in the early 20th century by a Russian botanist named Mikhail Tsvet. He discovered that when plant pigments are passed through a column filled with calcium carbonate, they separate into bands of color. This observation laid the foundation for chromatographic science, which has evolved considerably since then.

Principles of chromatography

At its core, chromatography involves two phases: the mobile phase and the stationary phase. The stationary phase is the material that stays stationary inside the column or on a flat surface, while the mobile phase is a solvent or gas that moves the mixture through the stationary phase.

The basic principle is differential partitioning between these two phases. Different components of the mixture will interact with these phases differently, leading to their separation. Let us explain these two major phases in more detail:

  1. Stationary phase: It may be solid or viscous liquid. Its job is to temporarily adsorb the molecules of the sample mixture. This interaction depends on the physico-chemical properties such as polarity, affinity for hydrogen bonding, van der Waals forces, etc.
  2. Mobile phase: This is the solvent system that moves through the stationary phase, carrying the components of the mixture with it. Components that interact weakly with the stationary phase will move faster or farther than components with stronger interactions.

Types of chromatography

There are several types of chromatography, each of which uses different principles and methods for separation. Here are some of the most common types:

1. Paper chromatography

Paper chromatography is one of the simplest forms of chromatography. The stationary phase is a strip of paper, usually filter paper, and the mobile phase is a solvent that moves up the paper by capillary action. This technique is often used to separate pigments such as inks and plant components.

Paper Chromatography

2. Thin layer chromatography (TLC)

TLC is similar to paper chromatography, but uses a thin layer of an adsorbent, such as silica gel, coated on a flat, inert carrier sheet. The mixture is spotted at one end, and a solvent is used as the mobile phase. This is a quick and easy method for analyzing components.

Thin Layer Chromatography

3. Gas chromatography (GC)

In gas chromatography, the mobile phase is a gas that carries the vaporized mixture through a long column containing a liquid or solid stationary phase. GC is particularly useful for separating and analyzing compounds that can be vaporized. It is commonly used in environmental testing and forensics.

  - Mobile phase: carrier gas (e.g., helium)
  - Stationary phase: a microscopic layer of liquid or polymer on an inert solid

4. Liquid chromatography (LC)

Liquid chromatography involves separating mixtures with a liquid mobile phase. One of the most commonly applied techniques within LC is high-performance liquid chromatography (HPLC).

  - Mobile phase: liquid solvent
  - Stationary phase: solid packed column

High performance liquid chromatography (HPLC)

HPLC is a powerful and widely used form of liquid chromatography that uses high pressure to push the solvent through the column. This process enables very fine particles and provides high-resolution separation of components.

The efficiency of HPLC can separate complex mixtures into their components, allowing the analysis and purification of biomolecules such as proteins and nucleotides.

Inlet Shop Column

Components and operation of chromatographic systems

Regardless of the type of chromatography being performed, a typical chromatographic setup includes several key components:

  • Column: The heart of the chromatographic operation, where the separation takes place. For liquid and gas chromatography, different packing materials are used depending on the type of analysis.
  • Detector: After separation, the detector identifies the separated components. Common types include ultraviolet (UV) detectors and mass spectrometers.
  • Sample injector: It introduces the sample mixture into the mobile phase without any disturbance.
  • Recorder: Provides a readout for viewing the separation, often producing a chromatogram.
                - Chromatogram: A graph showing the detector response versus time.

Interpreting chromatograms

The chromatogram is a valuable output where peaks represent the different components in the mixture. It is necessary to identify and quantify these peaks:

  1. Retention time (t_R): It is the time from injection to peak. It helps to identify the component based on previous data.
  2. Peak area: The area under the peak is proportional to the concentration of the component within the mixture. This property is often used in quantitative analysis.
  3. Peak height: Although not as accurate as peak area, it still provides a quick estimate of concentration.
t_R t_R

Applications of chromatography

Given its precision and effectiveness, chromatography has applications in a wide variety of areas:

  • Pharmaceuticals: Ensuring the purity of pharmaceuticals by separating and quantifying active ingredients.
  • Environmental testing: Analyzing pollutants or chemicals in the air, water, or soil.
  • Forensic science: Identifying substances in biological samples to aid criminal investigations.
  • Food industry: Testing food products for adulteration, contaminants and ensuring quality control.

Benefits and limitations

Benefits:

  • High sensitivity and specificity in detection of components.
  • The ability to separate complex mixtures.
  • Adaptability to many analytical applications.

Limitations:

  • Skilled personnel are required for operation and analysis.
  • Equipment and setup can be costly.
  • Some methods require sample preparation, which can introduce errors.

Conclusion

Chromatography represents a cornerstone technique in analytical chemistry, providing a versatile platform for separation, identification, and quantification. Although many types of chromatography serve different purposes, all rely on the basic principles of partitioning between stationary and mobile phases. Understanding chromatography helps expand both theoretical knowledge and practical skills needed for a variety of scientific analyses.


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Chromatography

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