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 → Physical Chemistry → Spectroscopy ↓


Mass Spectrometry


Mass spectrometry is a powerful analytical technique used in chemistry, particularly physical chemistry, to identify the amount and type of chemicals present in a sample by measuring the mass-to-charge ratio of ions. Despite the sophistication of the technology, the principles behind mass spectrometry are relatively simple. This technique allows chemists to detect and quantify specific molecules in a sample, estimate structures, assess purity, and even track the kinetics of chemical reactions. Through this process, mass spectrometry plays a vital role in both research and a variety of application areas.

Fundamentals of mass spectrometry

At its core, the principle of mass spectrometry is based on the motion of charged particles in electric and magnetic fields. The elementary steps in mass spectrometric analysis include sample ionization, ion acceleration, mass analysis, and ion detection. These steps are performed in a sequential manner:

  • Ionization: The sample is introduced and the chemicals are ionized, meaning they turn into charged particles or ions. This is important because only charged particles can be controlled by electric and magnetic fields.
  • Acceleration: The ions are accelerated to high speeds by an electric field, ensuring that they maintain a constant kinetic energy.
  • Deflection: In a magnetic field, these charged particles are deflected. The degree of deflection depends on the mass-to-charge ratio (m/z) of the ion. Lighter ions are deflected more than heavier ions.
  • Detection: The ions are detected, and a mass spectrum is produced. This spectrum shows the relative abundance of each ion as a function of its m/z.

Ionization technique

There are several ionization techniques used in mass spectrometry, the choice of which often depends on the type of sample and the information needed. Some of the most common methods include:

  • Electron ionization (EI): In this method, electrons are used to bombard the sample, causing ionization via electron ejection. EI is typically used for gaseous samples.
  • Chemical ionization (CI): Similar to EI, but involves ionization of the sample in the presence of a reagent gas.
  • Electrospray ionization (ESI): Particularly useful for large biomolecules such as proteins, ESI produces ions from liquid solutions.
  • Matrix-assisted laser desorption/ionization (MALDI): A gentle technique used for delicate molecules, using a laser to ionize the sample embedded in a matrix.

Understanding mass spectrum

The result of mass spectrometric analysis is a mass spectrum. This spectrum plots the m/z ratios of different ions on the x-axis against their relative abundances on the y-axis. The peak height or intensity of each m/z value in the spectrum indicates the abundance of the ion.

0 m/z 20 40 60 80 100 120 intensity

In the spectrum, each peak corresponds to an ion of a particular m/z ratio. For example, a peak at an m/z ratio of 44 may indicate the presence of CO2 in the sample because the molecular weight of CO2 is approximately 44. In cases where the compound forms fragments, additional peaks representing these fragments also appear in the spectrum.

Molecular ion peak

The molecular ion peak is one of the most important peaks in the mass spectrum. It represents an ion that has the same mass as the molecule being analyzed, from which one electron has been subtracted. This peak provides direct information about the molecular weight of the sample.

Molecular ion peak example:
- The molecular weight of methane (CH4) is about 16 amu.
- The molecular ion peak for methane will appear at m/z = 16.

Fragmentation pattern

When molecules absorb energy during ionization, they can break into smaller fragments, each of which also contributes to the mass spectrum. The pattern of fragmentation can be extremely useful for identifying the structure of the original molecule.

For example, alcohol may dissociate due to the loss of a water molecule (H2O), resulting in a maximum decrease of 18 amu in the mass spectrum.

Use of mass spectrometry

Mass spectrometry is used in many ways in different scientific fields. Let's take a look at some key examples:

Applications in chemistry

In synthetic chemistry, mass spectrometry is often used to confirm the identity and purity of synthesized compounds. Chemists rely on it to verify that their reactions have proceeded as planned by comparing the product's molecular ion peak with the expected mass.

Application example:
- Synthesis of aspirin (C9H8O4).
- Expected molecular ion peak at m/z = 180.

Biochemistry and medicine

In biochemistry and medical research, mass spectrometry is used to study proteins and other biomolecules. Identifying protein structures, analyzing their post-translational modifications, and measuring interactions between proteins becomes possible with specialized mass analyzers.

Environmental science

Environmental scientists use mass spectrometry to assess pollutants in air, water, and soil. For example, minute amounts of pesticides in agricultural water can be identified and quantified using mass spectrometric techniques.

Imagine a mass spectrometry analysis of a water sample that shows a molecular ion peak at m/z = 272, indicating the presence of a commonly used pesticide, DDT (C14H9Cl5).

Medicines

In the pharmaceutical industry, mass spectrometry plays a vital role in drug development, from the early discovery phase to quality control. Techniques such as liquid chromatography-mass spectrometry (LC-MS) integrate separation with mass analysis, making it easier to investigate complex biological samples.

Pharmaceutical example:
- Analyzing a biological sample with LC-MS can reveal various drug metabolites with specific m/z ratios, shedding light on the drug's metabolic pathway.

Tools and innovations

Technological advances have continued to advance the field of mass spectrometry. Although many types of mass spectrometers exist, they generally share key components: the ion source, the mass analyzer, and the detector. These components form the core of all mass spectrometric instruments, which range from simple bench-top models to sophisticated high-resolution instruments.

Mass analyzer

A mass analyzer is a component of a mass spectrometer that separates ions based on their m/z ratio. Different analyzers offer varying degrees of resolution, accuracy, and speed. Some common types include:

  • Quadrupole: Uses an oscillating electric field to filter ions by mass, ideal for separating complex mixtures.
  • Time-of-flight (TOF): measures the time it takes for ions to travel through a field-free region, and provides high speed and resolution.
  • Fourier-transform ion cyclotron resonance (FT-ICR): uses magnetic fields to trap ions and provide ultrahigh resolution measurements.

Technological integration

As computational and hardware technologies advance, integration with data analysis software and programs has become more prominent. Automated systems now easily process large datasets, interpret spectral patterns, and even perform in-depth analysis, leading to more informed and accurate scientific conclusions.

Conclusion

Mass spectrometry is one of the most versatile and indispensable tools in physical chemistry and beyond. From gathering intricate details about molecular structures to providing insights into biochemical processes, its ability to accurately determine the composition of samples has transformed scientific investigations and practical applications alike.


Graduate → 1.5.5


U
username
0%
completed in Graduate

← Prev (1.5.4)
Nuclear magnetic resonance spectroscopy
Next (1.5.6) →
Raman Spectroscopy

Comments 



Mass Spectrometry

https://www.chemistryelite.com/g/1.5.5?ceal=en