Mass spectrometer
View Patent ↗An ion optical system to form a loop orbit is provided to sufficiently ensure required performance such as ion transmission efficiency while making it easy to design the system by alleviating a space-focusing condition. The loop orbit of the ion optical system is realized so as to satisfy (t|x)=(t|α)=(t|δ)=0 as the time-focusing condition and to satisfy −2<(x|x)+(α|α)<2, and −2<(y|y)+(β|β)<2 as the space-focusing condition. (x|x) and other similar terms are constants determined by the elements indicated in the parenthesis in a general expression format of the ion optical system. The conditions are substantially alleviated as opposed to the conventional space-focusing condition where each of (x|x), (α|α), (y|y) and (β|β) needs to be ±1. Thus, the parameters to decide the shape of electrodes by which the ion optical system is configured have higher degree of freedom.
1. A multi-turn time-of-flight mass spectrometer or a Fourier-transformation mass spectrometer including an ion optical system for generating electric fields, in which ions are made to fly along a closed loop orbit repeatedly by effects of the electric fields so as to separate the ions in accordance with their mass to charge ratios, wherein:
the ion optical system comprises a first sector-shaped electric field, a second sector-shaped electric field, a third sector-shaped electric field, and a fourth sector-shaped electric field, where
the first and third sector-shaped electric fields have a deflection angle of 23.8 degrees, and a C value of 0.0274, while the second and fourth sector-shaped electric fields have a deflection angle of 156.2 degrees, and a C value of 0.0274, where the C value is a value defined by C=r 0 /R, r 0 being a radius of a central orbit as an orbit of a reference ion having a specific energy, and R being a curvature radius of an equipotential surface within a plane orthogonal to the central orbit, and
a free flight space between the fourth sector-shaped electric field and the first sector-shaped electric field has a distance of 1.2854r 0 , and a free flight space between the first sector-shaped electric field and the second sector-shaped electric field has a distance of 2.064r 0 ; and
the ion optical system creates a loop orbit that satisfies the following equation as a time-focusing condition:
( t|x )=( t|α )=( t|δ )=0
where the ion orbit in the ion optical system are expressed by a following method:
it is assumed that ions are made incident from an incident plane, transported by the ion optical system, and emitted from an emission plane;
an ion made incident from the incident plane with an initial value different from that of the reference ion has a displacement from the central orbit on the emission plane; and
the displacement is expressed by following first-order approximation equations:
x= ( x|x ) x 0 +( x|α )α 0 +( x|δ )δ
α=(α| x ) x 0 +(α|α)α 0 +(α|δ)δ
y= ( y|y ) y 0 +( y|β )β 0
β=(β| y ) y 0 +(β|β)β 0
t= ( t|x ) x 0 +( t|α )α 0 +( t|δ )δ
using x 0 and α 0 as, respectively, an amount of deviation of a position in a direction orthogonal to the central orbit and an amount of deviation of an angle or flight direction to the central orbit within the loop orbit plane at the incident plane; y 0 and β 0 as, respectively, an amount of deviation of a position in a direction orthogonal to the central orbit and an amount of deviation of an angle to the central orbit within a plane perpendicular to the loop orbit plane at the incident plane; x and α as, respectively, an amount of deviation of a position in a direction orthogonal to the central orbit and an amount of deviation of an angle to the central orbit within the loop orbit plane at the emission plane; y and β as, respectively, an amount of deviation of a position in a direction orthogonal to the central orbit and an amount of deviation of an angle to the central orbit within a plane perpendicular to the loop orbit plane at the emission plane; δ as an amount of deviation of energy at the incident plane; t to express an amount of deviation in the flight distance of a given ion from the reference ion in a direction parallel to the central orbit which corresponds to a deviation from the reference ion in the time of flight; and
(x|x), (x|α), (x|δ), (α|x), (α|α), (α|δ), (y|y), (y|β), (β|y), (β|β), (t|x), (t|α) and (t|δ) as constants of the ion optical system, each determined by elements indicated in parenthesis, where the constants represent characteristics of the ion optical system.
2. The multi-turn time-of-flight mass spectrometer or a Fourier-transformation mass spectrometer according to claim 1 , wherein the ion optical system creates the loop orbit that further satisfies the following equations as a space-focusing condition:
0<|( x|x )+(α|α)|<2
0<|( y|y )+(β|β)|<2.