Patent ID: 7202470

Claim:
A mass spectrometer comprising: means ( 1 ) for generating ions from a sample introduced into a plasma; a sampling aperture ( 2 ) for transmitting some of the ions into an evacuated expansion chamber ( 3 ) along a first axis ( 9 ) to form an ion beam; a second aperture ( 5 ) for transmitting some of the ion beam into a first evacuated chamber ( 6 ); a first pump ( 7 ) for maintaining the first evacuated chamber ( 6 ) at high vacuum; a first ion optical device ( 17 ) located in the first evacuated chamber ( 6 ) for containing the ion beam wherein the first ion optical device ( 17 ) is a mass selective device; a third aperture ( 19 ) for transmitting the ion beam into a second evacuated chamber ( 20 ); a second pump ( 21 ) for maintaining the second evacuated chamber ( 20 ) at a lower pressure than the first evacuated chamber ( 6 ); a collision cell ( 24 ) having an entrance aperture ( 27 ) and an exit aperture ( 28 ) and pressurized with a target gas ( 26 ), the collision cell ( 24 ) being disposed in the second evacuated chamber ( 20 ); a second ion optical device ( 25 ) located in the collision cell ( 24 ) for containing the ion beam; a fourth aperture ( 32 ) for transmitting the ion beam into a third evacuated chamber ( 33 ) containing mass-to-charge ratio analyzing means ( 37 ) disposed along a second axis ( 36 ), wherein the mass-to-charge analyzing means is configured to mass analyze the ion beam to produce a mass spectrum of the ion beam such that both the first ion optical device ( 17 ) and the mass-to-charge ratio analyzing means ( 37 ) operate at the same mass to charge ratio, so as substantially to minimize the formation in the collision cell of interfering ions having the said mass to charge ratio; a third pump ( 39 ) for maintaining the third evacuated chamber ( 33 ) at lower pressure than the second evacuated chamber ( 20 ).