Plasma mass spectrometer

A mass spectrometer comprising:

• 1) means for generating ions from a sample introduced into a plasma;
• 2) nozzle-skimmer interface means for transmitting at least some of said ions from said plasma into a first evacuated chamber along a first axis;
• 3) diaphragm means comprising a focusing electrode with an aperture, said diaphragm means dividing said first evacuated chamber from a second evacuated chamber;
• 4) ion guiding means disposed in said first evacuated chamber for guiding ions from said nozzle-skimmer interface means to said aperture;
• and
• 5) ion mass-to-charge ratio analyzing means having an entrance axis and disposed to receive ions passing through said aperture and to produce a mass spectrum thereof;
• said ion guiding means including;
• 1) one or more multipole rod-sets, the or each set comprising a plurality or elongate electrode rods spaced laterally apart a short distance from each other about a second axis to define an elongate space therebetween extending longitudinally through such set;
• 2) means for applying an AC voltage between rods comprised in the or each set such that ions enter said set travel in said elongate space through said rod set;
• and
• 3) means for introducing into said ion guiding means an inert gas selected from the group consisting of helium, neon, argon, krypton, xenon and nitrogen so that the partial pressure of said inert gas in at least a portion of said elongate space inside said rod set(s) is at least 10−3 torr, wherein at least a portion of said ion guiding means is surrounded by a gas containment sleeve disposed wholly within said first evacuated chamber and disposed so that both the entrance and exit of the ion guiding means are outside of said sleeve, and said inert gas is introduced into said sleeve so that the partial pressure of said inert gas is at least 10−3 torr in at least a portion of the ion guiding means while the entrance and the exit of said ion guiding means are maintained at a lower pressure.

A method of mass spectrometric analysis of a sample comprising the following steps carried out sequentially:

• 1) introducing a said sample into a plasma made by an inductivley-coupled plasma source to generate ions therefrom;
• 2) passing at least some of said ions through nozzle skimmer interface means into a first evacuated chamber;
• 3) guiding at least some of said ions entering said first evacuated chamber to an aperture in a focusing electrode and a diaphragm which divides said first evacuated chamber from a second evacuated chamber;
• and
• 4) mass analyzing at least some of the ions passing into said second evacuated chamber to produce a mass spectrum thereof;
• said method being characterised in that:
• 1) the step of guiding said ions comprises passing said ions through ion guiding means disposed entirely upstream or said aperture comprising one or more multipole electrode rod sets which comprise a plurality of elongate rod electrodes spaced laterally apart a short distance from each other to define an elongate space therebetween which extends longitudinally through the set, and applying an AC voltage to said rod electrodes;
• and
• 2) introducing into a sleeve which surrounds a portion of the elongated space of said guiding means and is spaced from both an entrance and an exit of said guiding means, an inert gas selected from the group consisting of helium, neon, argon, krypton, xenon and nitrogen so that the partial pressure of said inert gas in at least the portion said elongate space is at least 10−3 torr while both the entrance and the exit of said guiding means are maintained at a lower pressure.

A mass spectrometer comprising:

• 1) an inductively-coupled plasma source for generating ions from a sample introduced into a plasma;
• 2) nozzle-skimmer interface means for transmitting at least some of said ions from said plasma into a first evacuated chamber along a first axis;
• 3) diaphragm means comprising a focusing electrode with an aperture, said diaphragm means dividing said first evacuated chamber from a second evacuated chamber and enabling said chambers to operate at different pressures;
• 4) ion guiding means disposed entirely upstream of said aperture in said first evacuated chamber for guiding ions from said nozzle-skimmer interface means to said aperture;
• and
• 5) ion mass-to-charge ratio analyzing means having an entrance axis and disposed to receive ions passing through said aperture and to produce a mass spectrum thereof;
• said ion guiding means including:
• 1) one or more multipole rod-sets, the or each set comprising a plurality of elongate electrode rods spaced laterally apart a short distance from each other about a second axis to define an elongate space therebetween extending longitudinally through such set;
• 2) means for applying an AC voltage between rods comprised in the or each set such that ions entering said set travel in said elongate space through said rod set;
• and
• 3) means for introducing into said ion guiding means an inert gas selected from the group consisting of helium, neon, argon, krypton, xenon and nitrogen so that the partial pressure of said inert gas in at least a portion of said elongate space inside said rod set(s) is at least 10−3 torr wherein at least a portion of said ion guiding means is surrounded by a gas containment sleeve disposed wholly within said first evacuated chamber and disposed so that both the entrance and exit of the ion guiding means are outside of said sleeve, and said inert gas is introduced into said sleeve so that the partial pressure of said inert gas is at least 10−3 torr in at least a portion of the ion guiding means while the entrance and the exit of said ion guiding means are maintained at a lower pressure.