Chemical Ionization
Chemical Ionization - Related Videos
01:21
Chemical Ionization (CI) Mass Spectrometry
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2024
The molecular ion peak of a molecule in the mass spectrum provides vital information for molecular identification. However, conventional electron impact ionization can lead to the rapid dissociation of some molecular ions before they reach the detector. A milder ionization method is required to increase the lifetime of such ionized analyte molecules. Chemical ionization (CI) is a gas-phase protonation reaction useful for mass-analyzing analyte molecules that are easily protonated to yield the...
03:12
Ionization Energy
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2020
The amount of energy required to remove the most loosely bound electron from a gaseous atom in its ground state is called its first ionization energy (IE1). The first ionization energy for an element, X, is the energy required to form a cation with 1+ charge: The energy required to remove the second most loosely bound electron is called the second ionization energy (IE2). The energy required to remove the third electron is the third ionization energy, and so on. Energy is always required...
02:37
Types of Chemical Bonds
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2020
Chemical bonding theories were pioneered by American chemist Gilbert N. Lewis. He developed a model called the Lewis model to explain the type and formation of different bonds. Chemical bonding is central to chemistry; it explains how atoms or ions bond together to form molecules. It explains why some bonds are strong and others are weak, or why one carbon bonds with two oxygens and not three; why water is H2O and not H4O. Ionic Bonds Ions are atoms or molecules bearing an electrical charge.
09:22
Gas Chromatography (GC) with Flame-Ionization Detection
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2023
Source: Laboratory of Dr. B. Jill Venton - University of Virginia Gas chromatography (GC) is used to separate and detect small molecular weight compounds in the gas phase. The sample is either a gas or a liquid that is vaporized in the injection port. Typically, the compounds analyzed are less than 1,000 Da, because it is difficult to vaporize larger compounds. GC is popular for environmental monitoring and industrial applications because it is very reliable and can be run nearly continuously.
06:21
Imaging of Biological Tissues by Desorption Electrospray Ionization Mass Spectrometry
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Cited by 21 •
2013
Desorption electrospray ionization mass spectrometry (DESI-MS) is an ambient method by which samples, including biological tissues, can be imaged with minimal sample preparation. By rastering the sample below the ionization probe, this spray-based technique provides sufficient spatial resolution to discern molecular features of interest within tissue sections.
FAQs
The reagent gas acts as an intermediate ion source rather than simply serving as a background gas. An electron beam first generates reagent ions from methane or ammonia. Those ions subsequently transfer charge or a proton to analyte molecules, or form adducts with them. This sequence enables ion formation through ion-molecule reactions.
Chemical ionization usually produces less fragmentation than electron ionization because the analyte is ionized through reagent-ion reactions rather than the electron-ionization approach used for comparison. The resulting spectrum often contains stronger molecular-related ions, so molecular mass remains easier to recognize even when fewer structural fragments are available.
Three pathways are identified in the process: proton transfer, charge exchange, and adduct formation. Each represents a different way for reagent ions to interact with analyte molecules in the gas phase. Considering these alternatives helps explain why the resulting spectrum can emphasize molecular-related ions rather than extensive fragmentation.
A typical workflow begins by introducing a reagent gas, such as methane or ammonia, and exposing it to an electron beam. The reagent ions formed in that step then encounter gas-phase analyte molecules and react with them. The resulting ions are analyzed by mass spectrometry, linking ion formation to molecular-mass information.
A typical setup requires a reagent gas, an electron beam to ionize that gas, and analyte molecules present in the gas phase. The reagent ions produced from methane or ammonia then react with the analyte, after which the resulting gas-phase ions enter mass-spectrometric analysis. Each component supports the ion-generation sequence.
Chemical ionization is useful in gas chromatography-mass spectrometry because it can analyze volatile substances while producing stronger molecular-related ions and less fragmentation. Those spectral features help researchers identify compounds and confirm molecular weights after chromatographic introduction. Its value is especially practical when recognizing molecular mass is more important than obtaining an extensively fragmented spectrum.