Respuesta :
The peak at 157 is due to M-C2H5+ . 128 from molecule and 29 from C2H5 ion formed from CH4.
What is Chemical Ionization?
Another ionisation method that is frequently utilised in GC MS applications is chemical ionisation, or CI. In CI, the process of ionising the target molecules is aided by a reagent gas. Ammonia, methane, and isobutene are typical reagent gases frequently employed in CI [30,38]. These reagent gases are used by CI as intermediates in the ionisation process, as opposed to EI, where the compounds of interest are immediately ionised by free electrons
Gases such isobutane, CH4 NH3, and others are needed for analyte onizing. Electron collision causes these gases to become ionised. The ion thus produced undergoes further self-reaction to produce various ions, and these ions subsequently interact with the analyte to produce more ions, which are then subjected to m/z ratio analysis.
The base peak in the spectra is caused by ions that are more abundant. The intensity is close.
The molecular weight of napthalene is 128. Higher ion abundance is shown by the base peak at 129. MH+ ion is the cause of this peak. It yields m/z = 129, (128-molecule and 1 from hydrogen of methane ion). This is an ionizing gas, CH4, characteristic.
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