Method of increasing the dynamic range and sensitivity of a quadrupole ion trap mass spectrometer operating in the chemical ionization mode

Claim 1

A method of using an ion trap in a CI mode which comprises performing a prescan including the steps of introducing the analyte and reagent gas molecules into an ion trap having a three dimensional quadrupole field in which ions are stored, ionizing the mixture with an applied RF voltage chosen to selectively store primarily the reagent ions, allowing the reagent ions and analyte molecules to react and thereafter changing the three dimensional field to allow the products of reactions between the analyte molecules and the reactant ions to be trapped, ejecting and detecting these product ions to obtain a signal indicating the concentration of product ions, adjusting the ionization and/or reaction time to produce an optimum or suitable number of stored product or analyte ions for the following mass analysis step and performing a mass analysis including the steps of introducing analyte and reagent gas molecules into the ion trap having a three dimensional quadrupole field in which low mass ions are stored, ionizing the mixture with RF voltage applied to selectively store primarily the reagent ions for the amount of time determined during said prescan, allowing the reagent ions and analyte molecules to react for the amount of time determined during said prescan and thereafter changing the three dimensional field to allow the products of reactions between the analyte molecules and the reactant ions to be trapped and scanning the three dimensional field to successively eject the product ions and detecting the product ions to obtain a CI mass spectrum of the analyte.

Claim 2

A method of using an ion trap in a CI mode which comprises performing a prescan including the steps of introducing the analyte and reagent gas molecules into an ion trap having a three dimensional quadrupole field in which ions are stored, ionizing the mixture with an applied RF voltage chosen to selectively store primarily the reagent ions, allowing the reagent ions and analyte molecules to react and thereafter changing the three dimensional field to allow the products of reactions between the analyte molecules and the reactant ions to be trapped, ejecting and detecting these product ions to obtain a signal indicating the concentration of product ions, adjusting the ionization and/or reaction time to produce an optimum or suitable number of stored product or analyte ions for the following mass analysis step and performing a mass analysis including the steps of introducing analyte and reagent gas molecules into the ion trap having a three dimensional quadrupole field in which low mass ions are stored, ionizing the mixture with RF voltage applied to selectively store primarily the reagent ions for the amount of time determined during said prescan, allowing the reagent ions and analyte molecules to react for the amount of time determined during said prescan and thereafter changing the three dimensional field to allow the products of reactions between the analyte molecules and the reactant ions to be trapped and scanning the three dimensional field to successively eject the product ions and detecting the product ions to obtain a CI mass spectrum of the analyte.