Time-of-flight mass spectrometer
View Patent ↗An embodiment with a dual-stage reflectron is as follows: (1) On the assumption that a reflector has a base potential X A (U) created by uniform electric fields, its design parameters are adjusted so as to cancel the first and second order derivatives at energy E=E 0 of a total time of flight T(E), and a second-order focusing position on a central axis at which the potential value becomes zero is determined (Mamyrin solution). (2) A correcting potential X C (U) to be superposed on X A (U), beginning from the second-order focusing position, is calculated so that T(E) of ions reflected in a region deeper than the second-order focusing position will be constant. (3) Voltage values of the reflector electrodes are determined so that a real potential X R (U)=X A (U)+X C (U) is created on the central axis.
1. A time-of-flight mass spectrometer including an ion ejector for accelerating target ions by imparting a certain amount of energy to the ions, an ion reflector for reflecting ions ejected from the ion ejector and turning the ions around by an effect of an electric field, an ion detector for detecting the ions reflected by and exiting from the ion reflector, and a reflector driver for driving the ion reflector so as to create a reflecting electric field inside the ion reflector, wherein:
with X denoting a coordinate along a central axis of the ion reflector, the reflector driver applies a voltage to the ion reflector so as to create, inside an inner hollow area of the ion reflector and along the central axis of the ion reflector, a predetermined potential distribution U A (X) in which the potential monotonously changes over the entire ion reflector and therefore an inverse function X A (U) can be uniquely obtained, thus creating an N-th order focusing position at a position with coordinate X 0 and potential E 0 inside the ion reflector; and
the reflector driver also applies a voltage to the ion reflector within a space having the N-th order focusing position with coordinate X 0 as a starting point and extending into a deeper region, so as to superpose, on the predetermined potential X A (U), a predetermined correcting potential X C (U) which can be approximated by a formula proportional to {U(X)−E 0 } N+3/2 in a vicinity of the coordinate X 0 and which is expressed as a smooth function continuing from the coordinate X 0 into the deeper region.
2. The time-of-flight mass spectrometer according to claim 1 , wherein:
a forward ion drift region for making the ions ejected from the ion ejector fly forward is provided between the ion ejector and the ion reflector, the ion reflector subsequently reflects the ions passing through the forward ion drift region and turns the ions around by the effect of the electric field; and
a backward ion drift region for making the ions reflected by and exiting from the ion reflector fly in a direction opposite to the forward ion drift region is provided between the ion reflector and the ion detector.
3. The time-of-flight mass spectrometer according to claim 1 , wherein:
either the ion ejector and the ion reflector, or the ion reflector and the ion detector, or both are connected to each other with no drift region or similar space provided in between.
4. The time-of-flight mass spectrometer according to claim 1 , wherein:
the electric field which is to be the predetermined potential distribution X A (U) is a uniform electric field at least in a vicinity of the coordinate X 0 .
5. The time-of-flight mass spectrometer according to claim 1 , wherein:
a grid electrode is provided inside an inner hollow area of the ion reflector, the grid electrode dividing the ion reflector into a plurality of stages.
6. The time-of-flight mass spectrometer according to claim 1 , wherein:
a grid-less structure with no grid electrode provided inside an inner hollow area of the ion reflector is adopted.
7. The time-of-flight mass spectrometer according to claim 1 , wherein:
the ion reflector is a single-stage system, a first-order focusing position inside the ion reflector is selected as the starting point, and a correcting potential for N=1, which is proportional to {U(X)−E 0 } 2.5 , is superposed on a region in a vicinity of a boundary of the starting point.
8. The time-of-flight mass spectrometer according to claim 1 , wherein:
the ion reflector is a dual-stage system, a second-order focusing position inside the ion reflector is selected as the starting point, and a correcting potential for N=2, which is proportional to {U(X)−E 0 } 3.5 , is superposed on a region in a vicinity of a boundary of the starting point.
9. The time-of-flight mass spectrometer according to claim 1 , wherein:
the ion reflector is a dual-stage system, a first-order focusing position inside the ion reflector is selected as the starting point, and a correcting potential for N=1, which is proportional to {U(X)−E 0 } 2.5 , is superposed on a region in a vicinity of a boundary of the starting point.
10. The time-of-flight mass spectrometer according to claim 1 , wherein:
the ion ejector is an orthogonal acceleration type.
11. The time-of-flight mass spectrometer according to claim 1 , wherein:
the ion ejector is a MALDI ion source.
12. The time-of-flight mass spectrometer according to claim 2 , wherein:
an accelerating or decelerating region is provided in a portion of the forward ion drift region and/or the backward ion drift region.
13. The time-of-flight mass spectrometer according to claim 2 , wherein:
a focusing lens is provided in a portion of the forward ion drift region.
14. The time-of-flight mass spectrometer according to claim 1 , wherein:
The ion ejector has a function of a focusing lens.
15. The time-of-flight mass spectrometer according to claim 1 , wherein:
an aperture or slit for limiting a passing area of the ions is provided between the ion ejector and the ion reflector.
16. The time-of-flight mass spectrometer according to claim 1 , wherein:
the ion ejector or a portion of electrodes of the ion reflector has the function of limiting a passing area of the ions.
17. The time-of-flight mass spectrometer according to claim 1 , wherein:
the ion reflector includes a plurality of thin electrodes arranged along an ion beam axis.
18. The time-of-flight mass spectrometer according to claim 1 , wherein:
the ion reflector includes a resistance element having an electric resistance adjusted along the ion beam axis.
19. The time-of-flight mass spectrometer according to claim 1 , wherein:
the ion reflector is constructed by using a printed circuit board or a microfabricated substrate.
20. The time-of-flight mass spectrometer according to claim 1 , which is designed as a multi-reflection time-of-flight mass spectrometer including a plurality of ion reflectors arranged opposite to each other so that ions are reflected a plurality of times between the plurality of ion reflectors, wherein:
at least one of the plurality of ion reflectors is the aforementioned ion reflector in which a predetermined correcting potential X C (U) is superposed on the predetermined potential X A (U).