What ionization method produces positive ions by causing a loss of electrons?

The method that produces positive ions by causing a loss of electrons is Electron Ionization. This technique is widely used in mass spectrometry to create ions from gaseous samples. It involves bombarding the sample molecules with high-energy electrons, which leads to the removal of an electron from the molecule, resulting in the formation of a positively charged ion. This process is effective because the high-energy electrons impart enough energy to overcome the ionization energy of the molecules, making it a reliable method for generating ions for analysis.

The other methods, while also capable of producing ions, operate on different principles. Chemical Ionization, for example, involves ion-molecule reactions that typically produce ions by adding protons, while Thermal Ionization relies on thermally generated ions from the sample. Field Ionization is based on strong electric fields to produce ions, but this also differs fundamentally from the simple electron loss mechanism that characterizes Electron Ionization.