Chemical ionization 

CI uses a reagent ion to react with the analyte molecules to form ions by either a .....

Chemical ionization (CI)

CI uses a reagent ion to react with the analyte molecules to form ions by either a proton or hydride transfer:

MH + C₂H₅⁺ --> MH₂⁺ + C₂H₄

MH + C₂H₅⁺ --> M⁺ + C₂H₆

The reagent ions are produced by introducing a large excess of methane (relative to the analyte) into an electron impact (EI) ion source. Electron collisions produce CH₄⁺ and CH₃⁺ which further react with methane to form CH₅⁺ and C₂H₅⁺:

CH₄⁺ + CH₄ --> CH₅⁺ + CH₃

CH₃⁺ + CH₄ --> C₂H₅⁺ + H₂

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Periodic Table of the Elements

The periodic table was invented by the Russian chemist Dmitri Mendeleyev (1834-1907), which he published in Principles of Chemistry in 1869. His periodic table arranged the 63 known chemical elements in order of their atomic mass. Today, the elements in the periodic table are ordered by their atomic number. The 18 columns of

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TLC is a simple, quick, and inexpensive procedure that gives the chemist a quick answer as to how many components are in a mixture. TLC is also used to support the identity of a compound in a mixture when the Rf of a compound is compared with the Rf of a known compound (preferrably both run on the same TLC plate). A TLC plate is a sheet of glass, metal, or plastic which is coated with a thin layer of a solid adsorbent (usually silica or alumina). A small amount of the mixture to be analyzed is spotted near the bottom of this plate. The TLC plate is then placed in a shallow pool of a solvent in a developing chamber so that only the very bottom of the plate is in the liquid. This liquid, or the eluent, is the mobile phase, and it slowly rises up the TLC plate by capillary action. As the solvent moves past the spot that was applied, an equilibrium is established for each component of the mixture between the molecules of that component which are adsorbed on the solid and the molecules which are in solution. In principle, the components will differ in solubility and in the strength of their adsorption to the adsorbent and some components will be carried farther up the plate than others. When the solvent has reached the top of the plate, the plate is removed from the developing chamber, dried, and the separated components of the mixture are visualized. If the compounds are colored, visualization is straightforward. Usually the compounds are not colored, so a UV lamp is used to visualize the plates. (The plate itself contains a fluor which fluoresces everywhere except where an organic compound is on the plate.) The procedure for TLC, explained in words in the above paragraphs, is illustrated with photographs on the TLC Procedure page.

 

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