JPH041990B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic field leading type double focus mass spectrometer suitable for analyzing high molecular weight substances.

Recently, the demand for mass spectrometry of high molecular weight substances has increased. When performing mass spectrometry in a high molecular weight region, it is necessary to increase the ion orbital radius am in the magnetic field using the following equation.

H _O am=143.9√・ Here, H _O : Magnetic field strength (Gauss) am: Radius of ion orbit in magnetic field (cm) M: Ion mass (a, m, a) Vac: Ion acceleration voltage (volts) However, Generally, in order to increase the radius of an ion's orbit in a magnetic field, it is necessary to increase the size of the electromagnet that generates the magnetic field, which increases the size and weight of the mass spectrometer as a whole. In view of this situation, the present invention has been made with the aim of downsizing a high-mass region double convergence type mass spectrometer.

Conventional commercially available mass spectrometers have a standard ion orbit radius of about 20 cm in a magnetic field. In this case, the maximum mass that can be analyzed is 4500 a.mu with an ion acceleration voltage of 1 KV and a magnetic field strength of 15000 Gauss.
The analytical mass range increases in proportion to the square of am, but
If am is increased, the weight of the electromagnet becomes extremely large if a conventionally used 90° deflection type electromagnet is used. Also, toroidal electrodes
Since it has to be made larger in proportion to am, the mass spectrometer as a whole becomes very large. In the present invention, by setting the deflection angle in the magnetic field to about 60°, the size of the electromagnet can be avoided even though am has been increased, and the ion orbital radius ae of the trodal electric field can be reduced.
By setting the am to about 0.65 x am, we succeeded in avoiding increasing the overall size even though we increased the am to make it suitable for analysis in the high mass range. If this is done, the device will be more compact than the conventional device.

However, by simply setting the deflection angle by the magnetic field to about 60°,
Although it is generally possible to achieve relative miniaturization by simply setting ae to 0.65×am, high resolution and high sensitivity are not necessarily guaranteed. The present invention pursues the relationships among the dimensions, angles, and shapes of each part to obtain even higher resolution and sensitivity under the above-mentioned setting conditions. As is already known, the performance (resolution R) of a double-focusing mass spectrometer is determined by the second-order aberration coefficients Aαα, Aαδ,
It is evaluated using the following formula using Aδδ, Ayy, Ayβ, and Aββ.

R=am・Ax/XiSi+Sc+△...(1) where Ax: Mass dispersion coefficient Xi: Image magnification Si: Ion source slit width Sc: Collector slit width Usually, in order to increase the resolution, the slit width Si,
I'm going to make the Sc narrower. However, if △ is large, the effect of narrowing Si and Sc will not be achieved. Here△
is called aberration and is given by the following equation using the second-order aberration coefficient.

△＝am(｜Aαα｜αo ² +｜Aαδ｜αo・δo +｜Aδδ｜δo ² ｜Ayy｜(yo/am) ² + ｜Ayβ｜(yo/am)・βo+｜Aββ｜βo ²
...(2) Here, αo: Divergence angle of the ion beam that exits the ion source slit in the orbital plane (usually about 1/200) δo: Energy of the ion beam ΔE with acceleration voltage Vac
amount divided by (usually about 1/1000) yo: Vertical direction of ion source slit (perpendicular to the orbital plane)
width (usually 2 to 3 mm) βo: Vertical divergence angle of the ion beam (usually about 1/200) In the present invention, each part is It defines the relationship between the dimensional ratio, angle, and shape of.

FIG. 1 is a plan view of an embodiment of the present invention, where M is an electromagnet that generates a deflection magnetic field, TE is a toroidal electrode, and the signs of parameters characterizing the shape and dimensions are determined as shown. S1 is an ion source slit, and the ion input end of the magnetic field forms an arc within the ion orbital plane (the paper plane of the figure), and the ion exit end forms an angle E2 with the ion orbit. The distance D2 between the electromagnet M and the toroidal electrode TE and the distance D3 from the toroidal electrode to the collector electrode are determined by determining the distance D1 from S1 to the incident end of the electromagnet M. Figure 2 is a perspective view of the toroidal electrode TE, and its ion input end face and exit end face are perpendicular to the ion orbital plane (containing the center orbit of the incoming and outgoing ions as shown in Figure 3). It forms an arc in the vertical (vertical) plane. The sign of each parameter is determined as shown in the figure.
In this example, ae=0.65×am φe=90° ae/Re1=-0.125 ae/Re2=-0.375 ae/R=0.4375 (here, R is R shown in Figure 2) φm=60° am/ Rm1=−1.45 E2=−22° D1=1.025am When determined as above, the secondary aberration coefficients were Aαα=0.002 Aαδ=0.021 Aδδ=0.166 Ayy=0.022 Ayβ=0.087 Aββ=0.399.

According to the present invention, it is possible to obtain a compact, high-resolution magnetic field-first type double-focus mass spectrometer suitable for analysis in the high molecular weight region.

[Brief explanation of drawings]

FIG. 1 is a plan view of an apparatus according to an embodiment of the present invention, and FIG.
The figure is a perspective view of the toroidal electrode in the same example.
FIG. 3 is a side view of the ion input/output end face. M...Electromagnet, TE...Troidal electrode.

Claims (1)

[Scope of Claims] 1. In the arrangement of a magnetic field-leading double-focusing mass spectrometer consisting of a series arrangement of a magnetic field that deflects an ion beam and a toroidal electric field that further deflects the ion beam passing through this magnetic field at right angles, the following A high mass region double convergence mass spectrometer characterized in that the parameters are 0.625ae/am0.675 85゜φe95゜ 55゜φm65゜ −20゜E2−25゜ 0.80D1/am1.20. Note ae: Radius of ion orbit in electric field am: Radius of ion orbit in magnetic field φe: Deflection angle of ion orbit due to electric field φm: Deflection angle of ion orbit in magnetic field E2: Inclination angle of magnetic field exit end face with respect to ion orbit D1: Ion source slit Distance from to the magnetic field incidence end face.