12/31/2023 0 Comments Negative ions wiki![]() ![]() The CI source design for a mass spectrometer is very similar to that of the EI source. CI is thus useful as an alternative technique in cases where EI produces excessive fragmentation of the analyte, causing the molecular-ion peak to be weak or completely absent. In addition to some characteristic fragment ion peaks, a CI spectrum usually has an identifiable protonated molecular ion peak +, allowing determination of the molecular mass. ![]() The amount of fragmentation, and therefore the amount of structural information produced by the process can be controlled to some degree by selection of the reagent ion. The chemical ionization process generally imparts less energy to an analyte molecule than does electron impact (EI) ionization, resulting in less fragmentation and usually a simpler spectrum. Samples to be analyzed must be in vapour form, or else (in the case of liquids or solids), must be vapourized before introduction into the source. CI mass spectrometry finds general application in the identification, structure elucidation and quantitation of organic compounds as well as some utility in biochemical analysis. Negative chemical ionization (NCI), charge-exchange chemical ionization, atmospheric-pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI) are some of the common variants of the technique. Reagent gas molecules (often methane or ammonia) are ionized by electron ionization to form reagent ions, which subsequently react with analyte molecules in the gas phase to create analyte ions for analysis by mass spectrometry. This technique is a branch of gaseous ion-molecule chemistry. This was first introduced by Burnaby Munson and Frank H. A schematic diagram of chemical ionization sourceĬhemical ionization ( CI) is a soft ionization technique used in mass spectrometry. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |