Time of flight mass analyzer having improved detector arrangement and method of operating same

Abstract

A time-of-flight mass analyzer having an improved ion detector arrangement is disclosed. The analyzer includes an ionizer that generates the ions that are to be analyzed. A flight tube accepts the ions provided from the ionizer and constrains the ions to a generally helical ion flight path using a generally static electric field. An ion detector is disposed in the flight tube to intercept ions as the ions travel along the substantially helical ion flight path. At least one timer is provided to determine the flight times of the ions along an ion path that comprises at least the generally helical ion path. The timer is responsive to the impingement of ions on the ion detector.

1 . A time-of-flight mass analyzer comprising: 
 an ionizer adapted to provide ions of a sample substance to be analyzed;    a flight tube accepting ions provided from the ionizer, said flight tube adapted to constrain said ions to a generally helical ion flight path using a generally static electric field;    an ion detector disposed in the flight tube to intercept ions as said ions travel along said generally helical ion flight path;    at least one timer adapted to determine the flight time of said ions along an ion path that comprises at least said generally helical ion path, said timer being responsive to impingement of ions on said ion detector.    
     
     
         2 . A time-of-flight mass analyzer as claimed in  claim 1  wherein said generally helical ion path is disposed about a linear axis, said ions being provided to said flight tube at an entrance angle to generate a velocity component in the direction of said linear axis, said entrance angle being within a predetermined tolerance range.  
     
     
         3 . A time-of-flight mass analyzer as claimed in  claim 2  wherein said ion detector comprises an ion detection surface that is generally aligned with said linear axis.  
     
     
         4 . A time-of-flight mass analyzer as claimed in  claim 2  wherein said ion detector comprises an ion detection surface that is disposed at an angle with respect to said linear axis.  
     
     
         5 . A time-of-flight mass analyzer as claimed in  claim 2  wherein said ion detector comprises an ion detection surface that is shaped so that ions having the same mass-to-charge ratio impinge thereon at substantially identical times of flight for entrance angles within said predetermined tolerance range.  
     
     
         6 . A time-of-flight mass analyzer as claimed in  claim 1  wherein said flight tube comprises: 
 an inlet portion having an ion inlet, said inlet portion being substantially free of electric fields;    an ion deflection portion having a substantially static electric field, said ion deflection portion being adapted to direct ions received from said inlet portion along said generally helical ion flight path.    
     
     
         7 . A time-of-flight analyzer as claimed in  claim 6  and further comprising: 
 at least one power supply connected to said flight tube to generate a first generally static electric field in said ion deflection portion, said power supply further being alternately operable between at least a first state in which said inlet portion is substantially free of electric fields, and a second state in which a second generally static electric field is generated in said inlet portion.    
     
     
         8 . A time-of-flight mass analyzer as claimed in  claim 7  wherein said first and second generally static electric fields have substantially the same magnitude.  
     
     
         9 . A time-of-flight mass analyzer as claimed in  claim 1  wherein said flight tube comprises: 
 a first electrode having a generally cylindrical electrode surface facing an interior portion thereof, said first electrode further having an ion inlet disposed through a side thereof;    a second electrode having a generally cylindrical electrode surface facing an exterior portion thereof, said second electrode being concentrically disposed with said first electrode, said generally helical ion flight path being defined within an interstitial region between said first and second electrodes.    
     
     
         10 . A time-of-flight mass analyzer as claimed in  claim 9  wherein said ion detector comprises an ion detection surface extending into said interstitial region and in electrical contact with the generally cylindrical internal electrode surface of said first electrode.  
     
     
         11 . A time-of-flight mass analyzer as claimed in  claim 10  and further comprising an ammeter connected to detect current through said first electrode in response to ion impingement on said ion detection surface.  
     
     
         12 . A time-of-flight mass analyzer as claimed in  claim 10  wherein said generally helical ion path is disposed about a linear axis, said ions being provided to said flight tube at an entrance angle to generate a velocity component in the direction of said linear axis, said entrance angle being within a predetermined tolerance range.  
     
     
         13 . A time-of-flight mass analyzer as claimed in  claim 12  wherein said ion detection surface is generally aligned with said linear axis.  
     
     
         14 . A time-of-flight mass analyzer as claimed in  claim 12  wherein said ion detection surface is disposed at an angle with respect to said linear axis.  
     
     
         15 . A time-of-flight mass analyzer as claimed in  claim 12  wherein said ion detection surface is shaped so that ions having the same mass-to-charge ratio impinge thereon at substantially identical times of flight for entrance angles within said predetermined tolerance range.  
     
     
         16 . A flight tube arrangement for use in a time-of-flight mass analyzer comprising: 
 a first electrode having a generally cylindrical electrode surface facing an interior portion thereof, said first electrode further having an ion inlet disposed through a side thereof;    a second electrode having a generally cylindrical electrode surface facing an exterior portion thereof, said second electrode being concentrically disposed with said first cylindrical electrode, said generally cylindrical electrode surfaces of said first and second electrodes defining a generally helical flight path for ions entering said ion inlet at an entrance angle within a predetermined tolerance range, said generally helical ion path is disposed about a linear axis, said ions being provided through said ion inlet at an entrance angle to generate a velocity component in the direction of said linear axis, said entrance angle being within a predetermined tolerance range;    an ion detector having an ion detection surface extending into said generally helical flight path and positioned to intercept selected ions traveling along said generally helical flight path.    
     
     
         17 . A flight tube arrangement as claimed in  claim 16  wherein said ion detection surface is in electrical contact with the generally cylindrical internal electrode surface of said first electrode.  
     
     
         18 . A flight tube arrangement as claimed in  claim 17  and further comprising an ammeter connected to detect current through said first electrode in response to ion impingement on said ion detection surface.  
     
     
         19 . A time-of-flight mass analyzer as claimed in  claim 16  wherein said ion detection surface is generally aligned with said linear axis.  
     
     
         20 . A time-of-flight mass analyzer as claimed in  claim 16  wherein said ion detection surface is disposed at an angle with respect to said linear axis.  
     
     
         21 . A time-of-flight mass analyzer as claimed in  claim 16  wherein said ion detection surface is shaped so that ions having the same mass-to-charge ratio impinge thereon at substantially identical times of flight for entrance angles within said predetermined tolerance range.  
     
     
         22 . A flight tube for use in a time-of-flight mass analyzer comprising: 
 an inlet portion adapted to direct ions received thereat to a region that is substantially free of electric fields;    an ion deflection portion having a substantially static electric field, said ion deflection portion being adapted to direct ions received from said inlet portion along a generally helical ion flight path defined by said substantially static electric field;    an ion detector disposed in said ion deflection portion to intercept ions as said ions travel along said generally helical ion flight path.    
     
     
         23 . A flight tube as claimed in  claim 22  wherein said generally helical ion path is disposed about a linear axis, said ions being provided to said inlet portion at an entrance angle to generate a velocity component in the direction of said linear axis, said entrance angle being within a predetermined tolerance range.  
     
     
         24 . A flight tube as claimed in  claim 23  wherein said ion detector comprises an ion detection surface that is generally aligned with said linear axis.  
     
     
         25 . A flight tube as claimed in  claim 23  wherein said ion detector comprises an ion detection surface that is disposed at an angle with respect to said linear axis.  
     
     
         26 . A flight tube as claimed in  claim 23  wherein said ion detector comprises an ion detection surface that is shaped so that ions having the same mass-to-charge ratio impinge thereon at substantially identical times of flight for entrance angles within said predetermined tolerance range.