Molecular razor blades

In FI, a high-potential electric field is applied to an anitter with a sharp surface, snch as a razor blade or a filament from which tiny whiskers have formed. This results in a very high electric field, which can result in ionization of gaseous molecules of the analyte. Mass spectra produced by FI have little or no fragmentation. They are dominated by molecular radical cations M or, less often, by protonated molecules [M + Hf". 

Field ionization occurs when gas-phase sample molecules are inteijected in a strong electrical field that is on the order of 10 Vcm The field distorts the electron cloud around the sample molecule and lowers the barrier for the removal of an electron. The quantum mechanical tunneling of this electron from the molecule to the conduction bands of the emitter produces M+ ions [10]. The heart of the FI ion source is an emitter electrode made fi om a sharp metal object such as a razor blade or thin wire. The emitter electrode is placed approximately 1 mm away from the cathode. The field is produced by applying a high potential (10 to 20 kV) to the tip of the emitter electrode. FI is a very soft ionization technique that produces primarily a molecular ion signal. It is applicable to volatile samples only. 

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