Method of operating tandem ion traps

Abstract

A method is provided comprising accumulating ions in a first ion trap at a first time; transmitting a first plurality of ions out of the first ion trap through a timed-ion selector; applying a pulsed DC voltage to the timed-ion selector; transmitting the first portion of selected ions into a second ion trap at a second time; retaining a second plurality of ions in the first ion trap at the second time; transmitting the first portion of selected ions out of the second ion trap at a third time; transmitting the second plurality of ions out of the first ion trap through a timed-ion selector; applying a pulsed DC voltage to the timed-ion selector transmitting a second portion of selected ions into the second ion trap at a fourth time; and transmitting the second portion of selected ions out of the second trap.

1 . A method of operating a mass spectrometer system having a first ion trap and a second ion trap, the method comprising:
 a) accumulating ions in the first ion trap at a first time;   b) transmitting a first plurality of ions out of the first ion trap through a timed-ion selector;   c) applying a pulsed DC voltage to the timed-ion selector for deflecting a first group of unwanted ions from the first plurality of ions, leaving a first portion of selected ions having masses within a first mass range;   d) transmitting the first portion of selected ions out of the timed-ion selector and into the second ion trap at a second time;   e) retaining a second plurality of ions in the first ion trap at the second time, the second plurality of ions having masses within a second mass range different from the first mass range;   f) transmitting the first portion of selected ions out of the second ion trap at a third time; and,   g) transmitting the second plurality of ions out of the first ion trap through a timed-ion selector;   h) applying a pulsed DC voltage to the timed-ion selector for deflecting a second group of unwanted ions from the second plurality of ions, leaving a second portion of selected ions having masses within a second mass range;   i) transmitting a second portion of selected ions out of the timed-ion selector and into the second ion trap at a fourth time; and   j) transmitting the second portion of selected ions out of the second trap.   
     
     
         2 . The method of  claim 1 , wherein the steps of (b) and (g) comprise transmitting ions out of the first ion trap during a first sliding transmission window, the ions transmitted during the first sliding transmission window having masses within a first variable mass range, the first variable mass range corresponding to different mass ranges at different operating times, such that the first variable mass range corresponds to the first mass range at the second time and the second mass range at the third time;
 wherein step (c) comprises transmitting the first variable mass range through the timed-ion-selector to select a portion of the first variable mass range;   wherein step (d) comprises transmitting the portion of the first variable mass range into the second ion trap; and   wherein step (f) comprises transmitting the portion of the first variable mass range out of the second trap during a second sliding transmission window, the ions transmitted during the second sliding transmission window having masses within a second variable mass range, the second variable mass range corresponding to different mass ranges at different operating times, such that the second variable mass range corresponds to the first mass range at the third time.   
     
     
         3 . The method of  claim 2  further comprising, over an operating time interval, scanning the first variable mass range and the second variable mass range over an operating mass range. 
     
     
         4 . The method of  claim 3 , wherein over the operating time interval, the second sliding transmission window is time delayed relative to the first sliding transmission window by a delay time interval such that the first variable mass range at any operating time substantially corresponds to the second variable mass range at the operating time plus the delay time interval. 
     
     
         5 . The method of  claim 3 , wherein over the operating time interval, the second sliding transmission window is time delayed relative to the first sliding transmission window by a delay time interval such that the first variable mass range at any operating time equals the second variable mass range at the operating time plus the delay time interval. 
     
     
         6 . The method of  claim 4 , wherein the first variable mass range is changed at a first scan rate, and the second variable mass range is changed at a second scan rate, the first scan rate and the second scan rate being substantially equal. 
     
     
         7 . The method of  claim 6  further comprising controlling the first scan rate using a first RF voltage provided to the first ion trap and controlling the second scan rate using a second RF voltage provided to the second ion trap, such that during the operating time, the first RF voltage at any operating time substantially corresponds to the second RF voltage at the operating time plus the delay time interval. 
     
     
         8 . The method of  claim 7 , wherein the first and second RF voltages are independently provided to the first and second ion traps. 
     
     
         9 . The method as defined in  claim 6 , comprising controlling the first scan rate using a first RF voltage and a first auxiliary AC voltage provided to the first ion trap, and controlling the second scan rate using a second RF voltage and a second auxiliary AC voltage provided to the second ion trap, such that during the operating time a ratio of the first RF voltage to the second RF voltage is substantially constant. 
     
     
         10 . The method as defined in  claim 9 , wherein the first and second ion traps are capacitively coupled using one or more coupling capacitors, and ratio of the first RF voltage to the second RF voltage is controlled by selecting the capacitances of the one or more coupling capacitors. 
     
     
         11 . The method as defined in  claim 10 , wherein the first auxiliary AC voltage and the second auxiliary AC voltage are determined, based on the ratio of the first RF voltage to the second RF voltage, such that the first scan rate substantially equals the second scan rate. 
     
     
         12 . The method as defined in  claim 9 , wherein the first and second RF voltages are independently provided to the first and second ion traps. 
     
     
         13 . The method as defined in  claim 4 , further comprising selecting a second space charge level for the second ion trap; and then determining a cooling time interval for retaining ions in the second ion trap to provide the space charge level, wherein the delay time interval substantially equals the cooling time interval. 
     
     
         14 . The method as defined in  claim 6 , wherein,
 the ions in the first ion trap have a starting mass range;   the ions in the second ion trap have a variable operating mass range, the variable operating mass range at any operating time after the delay time interval being substantially equal to the first scan rate multiplied by the delay time interval; and   the variable operating mass range is less than half of the starting mass range.   
     
     
         15 . The method as defined in  claim 16  wherein the variable operating mass range is less than a fifth of the starting mass range. 
     
     
         16 . The method as defined in  claim 16  wherein the variable operating mass range is less than a tenth of the starting mass range.