235. ion-pairing reagent A mobile phase additive used in ion-pairing chromatography to selectively increase the retention and improve the peak shape of charged analytes. Typically, an ion-pairing reagent contains both a hydro phobic region and an ionizable group whose charge is opposite that of the analyte. The resulting neutral complex shows improved chromatographic properties and peak resolution. Such reagents can be used in reversed phase systems with silica-based columns, which may be used to modify a hydrophobic stationary phase, adding ionic character.
236. ion source A device at the front end of the mass spectrometer that forms atomic and molecular ions and initiates their separation from the eluent. In some cases the source will be external to the mass spectrometer vacuum. Such sources are referred to as atmospheric pressure ionization sources.
237. ion suppression Reduced detector response in mass spectrometry as a result of competition for ionization between the analyte of interest and matrix or analytical components or excipients.
