Basic Concepts
Mass Spectrometry (MS) is an analytical technique used to determine the molecular mass and structure of a compound. |
It involves ionizing a sample, separating the ions based on their mass-to-charge ratio (m/z), and detecting them to generate a mass spectrum. |
Mass Detectors
Electron Multiplier: Converts ions into electrons, amplifying the signal for detection. |
Faraday Cup: Collects and measures the current generated by ions striking a metal surface. |
Photomultiplier Tube (PMT): Converts ions into photons, which are then amplified and detected. |
Applications
Identification of Unknown Compounds: MS can be used to determine the elemental composition and structure of an unknown compound. |
Quantitative Analysis: MS can measure the abundance of specific compounds in a sample using techniques like Selected Ion Monitoring (SIM) or Multiple Reaction Monitoring (MRM). |
Proteomics: MS is extensively used to analyze proteins, peptides, and post-translational modifications. |
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Ionization Techniques
Electron Ionization (EI): Involves bombarding the sample with high-energy electrons, resulting in the formation of radical cations (M+•). |
Electrospray Ionization (ESI): Suitable for polar and large molecules. It involves the formation of charged droplets from a nebulized sample, which subsequently undergo desolvation to form ions. |
Matrix-Assisted Laser Desorption/Ionization (MALDI): Suitable for large biomolecules. Involves co-crystallizing the sample with a matrix compound and using a laser to ionize the analyte. |
Tandem Mass Spectrometry (MS/MS)
MS/MS involves performing multiple stages of mass spectrometry, usually involving precursor ion selection, fragmentation, and product ion analysis. |
Common techniques include Collision-Induced Dissociation (CID) and Electron Transfer Dissociation (ETD). |
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Mass Analyzers
Time-of-Flight (TOF): Measures the time taken for ions to reach the detector based on their m/z ratio. |
Quadrupole: Uses a combination of direct current (DC) and radio frequency (RF) voltages to selectively transmit ions of a specific m/z ratio. |
Ion Trap: Uses an electric field to trap and store ions, allowing their m/z ratios to be selectively scanned. |
Data Interpretation
Molecular Ion (M+•): Represents the intact molecule after ionization. |
Base Peak: The most intense peak in a mass spectrum, assigned a relative abundance of 100%. |
Fragmentation: The process of breaking down the molecular ion into smaller fragments, providing structural information. |
Isotopes: Different forms of an element with varying numbers of neutrons, resulting in peaks at different m/z values. |
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Created By
https://biologynotesonline.com
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