Method of separating ions

1. A method of separating ions according to their ion mobility, comprising:

(i) accumulating a first population of ions in a first region of an ion mobility separator;

(ii) separating said first population of ions according to their ion mobility in said first region of said ion mobility separator; and

(iii) accumulating a second population of ions in said first region of said ion mobility separator whilst said first population of ions are being separated according to their ion mobility in said ion mobility separator,

wherein said ion mobility separator comprises a second region downstream of said first region, and step (ii) comprises separating said first population of ions according to their ion mobility in said first and second regions of said ion mobility separator; and

wherein said first region of said ion mobility separator switches between a trapping mode, in which the first region is configured such that ions are substantially trapped within said first region and not caused to separate according to their ion mobility, and an ion mobility separation mode, in which the first region is configured such that ions are separated according to their ion mobility within said first region.

2. A method as claimed in claim 1 , wherein step (ii) comprises accumulating said second population of ions in an accumulation region upstream of said first region, whilst said first population of ions are being separated according to their ion mobility in said first and second regions of said ion mobility separator.

3. A method as claimed in claim 2 , wherein step (iii) comprises transferring said second population of ions from said upstream accumulation region and into said first region, and continuing to pass ions through said upstream accumulation region and into said first region so as to accumulate said second population of ions in said first region.

4. A method as claimed in claim 3 , wherein step (iii) comprises accumulating said second population of ions in said first region of said ion mobility separator whilst said first population of ions are being separated according to their ion mobility in said second region of said ion mobility separator, and after said first population of ions have exited said first region of said ion mobility separator.

5. A method as claimed in claim 1 , further comprising:

(iv) separating said second population of ions according to their ion mobility in said ion mobility separator; and

(v) accumulating a third population of ions in said first region of said ion mobility separator whilst said second population of ions are being separated according to their ion mobility.

6. A method as claimed in claim 5 , further comprising:

repeating steps (ii) to (v) for said third and further populations of ions, such that subsequent populations of ions are accumulated in said first region of said ion mobility separator whilst preceding populations of ions are being separated according to their ion mobility.

7. A method as claimed in claim 1 , further comprising directing a beam of ions continuously into the upstream accumulation region.

8. A method as claimed in claim 1 , wherein said ion mobility separator comprises an RF-confined ion mobility separator.

9. A method as claimed in claim 8 , wherein said ion mobility separator comprises a plurality of electrodes stacked adjacent to one another, wherein alternate phases of an RF voltage are applied to adjacent electrodes.

10. A method as claimed in claim 9 , wherein each of said plurality of electrodes comprise apertures through which ions travel in use.

11. A method as claimed in claim 9 , wherein said plurality of electrodes comprises a plurality of pairs of electrodes stacked adjacent to one another, wherein alternate phases of an RF voltage are applied to adjacent pairs of electrodes.

12. A method as claimed in claim 11 , wherein each of said pair of electrodes comprises a first plate electrode opposite a second plate electrode, wherein in use ions travel through the gap between said first and second plate electrodes.

13. A method as claimed in claim 2 , wherein said first region, said second region, and said accumulation region comprise RF-confined regions.

14. A method as claimed in claim 1 , wherein step (i) comprises accumulating said first population of ions in said first region when in the trapping mode such that within the first region the first population of ions are not caused to separate according to their ion mobility and has a relatively small spatial spread in the intended direction of ion mobility separation during the ion mobility separation mode, and a relatively large spatial spread in the direction orthogonal to the intended direction of ion mobility separation during the ion mobility separation mode.

15. A method as claimed in claim 2 , wherein said accumulation region of said ion mobility separator is arranged and adapted to trap or accumulate a population of ions and then transfer the population of ions from the accumulation region into the first region.

16. An ion mobility spectrometer or separation device comprising:

an ion mobility separator comprising a first region arranged and adapted to accumulate consecutive populations of ions, and a second region downstream of said first region; and

a control system arranged and adapted:

(i) to accumulate a first population of ions in said first region of said ion mobility separator;

(ii) to separate said first population of ions according to their ion mobility in said first region of said ion mobility separator; and

(iii) to accumulate a second population of ions in said first region of said ion mobility separator whilst said first population of ions are being separated according to their ion mobility in said ion mobility separator,

wherein, in step (ii), said control system is arranged and adapted to separate said first population of ions according to their ion mobility in said first and second regions of said ion mobility separator;

wherein said first region of said ion mobility separator switches between a trapping mode, in which the first region is configured such that ions are substantially trapped within said first region and not caused to separate according to their ion mobility, and an ion mobility separation mode, in which the first region is configured such that ions are separated according to their ion mobility within said first region.

17. An ion mobility spectrometer or separation device as claimed in claim 16 , further comprising an accumulation region upstream of said first region, wherein said control system is arranged and adapted:

to accumulate said second population of ions in said accumulation region whilst said first population of ions are being separated according to their ion mobility in said first and second regions of said ion mobility separator.

18. A method of separating ions in a device, wherein the device comprises a first region, an accumulation region upstream of the first region and a second region downstream of the first region, wherein said first region, said second region, and said accumulation region comprise RF-confined regions, and the method comprises the steps of:

(i) driving a first population of ions through the first and second regions so as to separate a first population of ions according to their ion mobility, whilst accumulating a second population of ions in the accumulation region;

(ii) after the first population of ions has exited the first region, but prior to the first population of ions exiting the second region, transferring the second population of ions into the first region and trapping the second population of ions within the first region without causing the second population of ions to separate according to their ion mobility; and then

(iii) driving the second population of ions through the first and second regions so as to separate the second population of ions according to their ion mobility, whilst accumulating a third population of ions in the accumulation region;

(iv) repeating steps (ii) and (iii) for the third and further populations of ions so as to successively separate the third and further populations of ions; and

wherein said first region of said ion mobility separator switches between a trapping mode, in which the first region is configured such that ions are substantially trapped within said first region and not caused to separate according to their ion mobility, and an ion mobility separation mode, in which the first region is configured such that ions are separated according to their ion mobility within said first region.

19. A method as claimed in claim 18 , wherein:

step (ii) comprises accumulating said second population of ions in said first region when in the trapping mode such that within the first region the second population of ions are not caused to separate according to their ion mobility and has a relatively small spatial spread in the intended direction of ion mobility separation during the ion mobility separation mode, and a relatively large spatial spread in the direction orthogonal to the intended direction of ion mobility separation during the ion mobility separation mode.