Please explain the principles, advantages, and disadvantages of CI

Please explain the principles, advantages, and disadvantages of CI.

CI (Chemical Ionization)

First, a reagent gas is ionized by the fast electrons from the filament. The reagent gas ions thus created then react with and ionize the sample molecules. Nearly all of the ions created show molecular weight and no fragment ions are produced. Therefore, while molecular weights are easy to determine from CI mass spectra, no structural information is obtained due to the lack of fragment ions.