Time of flight mass spectrometer with selectable drift length

A mass spectrometer comprising:

• a) an ion source;
• b) a collisional focusing gas cell for collimating ions generated by said ion source and equalizing their kinetic energies;
• c) a drift region having an axis, an entrance and an exit;
• d) an ion packet generator for injecting packets of ions into said drift region at said entrance from a beam of ions by intermittent application of an electrostatic field such that said packets of ions enter said drift region in an initial direction which is inclined to the direction of said beam of ions;
• e) a first ion reflector disposed at said exit to reflect back towards said entrance packets of ions which are travelling towards said first ion reflector in said drift region, with ions in each of said packets being temporally separated according to their mass-to-charge ratios while travelling through said drift region;
• f) a second ion reflector disposed in juxtaposition to said first ion reflector to reflect back towards said first ion reflector packets of ions which are travelling in said drift region towards said second ion reflector through at least a portion of said drift region, so that the packets of ions may be reflected to and fro between said first and said second ion reflectors and undergo a number n of reflections at said second ion reflector;
• and
• g) at least one ion detector disposed to detect at least some of the ions reflected by said first ion reflector which do not enter said second ion reflector, wherein the number n of reflections at said second ion reflector is selected by adjustment of an inclination of said initial direction to said axis.

A tandem mass spectrometer comprising:

• a) an ion source;
• b) a first mass filter for transmitting ions having mass-to-charge ratios in a predetermined range;
• c) a collisional focusing gas cell for receiving ions transmitted by said first mass filter, fragmenting the ions by collisions with neutral molecules of gas, collimating said fragmented ions and equalizing kinetic energies of the fragmented ions;
• d) a drift region having an axis, an entrance and an exit;
• e) an ion packet generator for injecting packets of ions into said drift region at said entrance from a beam of ions by intermittent application of an electrostatic field such that said packets of ions enter said drift region in an initial direction which is inclined to the direction of said beam of ions;
• f) a first ion reflector disposed at said exit to reflect back towards said entrance packets of ions which are travelling towards said first ion reflector in said drift region, with ions in each of said packets being temporally separated according to their mass-to-charge ratios while travelling through said drift region;
• g) a second ion reflector disposed in juxtaposition to said first ion reflector to reflect back towards said first ion reflector packets of ions which are travelling in said drift region towards said second ion reflector through at least a portion of said drift region, so that the packets of ions may be reflected to and fro between said first and said second ion reflectors and undergo a number n of reflections at said second ion reflector;
• and
• h) at least one ion detector disposed to detect at least some of the ions reflected by said first ion reflector which do not enter said second ion reflector wherein the number n of reflections at said second ion reflector is selected by adjustment of an inclination of said initial direction to said axis.

A method of determining a mass-to-charge ratio of ions in an original direction traveling in a beam by measuring their time-of-flight through a drift region having an axis, an entrance and an exit, said method comprising the followings steps:

• 1) intermittently applying an electrostatic field to packets of ions in said beam to inject the ions into said drift region at said entrance in an initial direction inclined to the original direction of travel in said beam;
• 2) when said ions reach said exit, reflecting the ions back into said drift region towards said entrance by means of a first ion reflector;
• 3) when said ions reach said entrance, reflecting the ions back into said drift region towards said first ion reflector by means of a second ion reflector so that the ions may be reflected to and fro between said first and second ion reflectors and undergo a number n of reflections at said second ion reflector;
• 4) controlling the number of reflections at said second ion reflector by adjusting the inclination of said initial direction of said axis;
• and
• 5) detecting at least some of the ions reflected by said first ion reflector which do not enter said second ion reflector.