JPH0636741A - Magnetic field type mass spectrometer - Google Patents

Abstract

PURPOSE:To further stabilize the coil action for negating the fluctuation of the external magnetic field by coaxially arranging two same toroidal coils apart by the coil radius, and feeding the same current to both coils in the same direction. CONSTITUTION:The controller C of an external magnetic field negating device and an external magnetic field negating coil 4 are connected with a cable 6. A Helmholtz type coil is used for the coil 4, two same toroidal coils are coaxially arranged apart by the coil radius, and the same current is fed to both coils in the same direction. After the position of the controller C is determined, ions having the proper mass are guided into a mass spectrometer M, the magnetic field of the mass spectrometer M is set to detect the ions of the mass, and the ion detected output is stored. The regulating resistor is adjusted to eliminate the fluctuation of the ion detected output. The position susceptibility is eliminated, the negating action is stabilized, and the high-resolution, high- precision mass analysis can be performed even in the adverse magnetic environment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic field type mass spectrometer.

[0002]

2. Description of the Related Art Since an ion beam is bent by the action of a magnetic field, if a magnetic field type mass spectrometer is used in a place where the magnetic field fluctuates drastically, the resolution is lowered due to the influence of an external magnetic field and precise mass measurement cannot be performed. . Wiring of a commercial power supply, transformers, motors, etc. are also the causes of the fluctuating external magnetic field, but the fact that it has a large effect is a magnetic field fluctuation of a lower frequency of about 10 Hz, and the cause is passing outdoors There are trains.

As a countermeasure against the fluctuation of the external magnetic field as described above, a coil for canceling the external magnetic field has been installed on the ion orbit. Conventionally, a single ring coil having a winding wire wound several tens times. Was used.

[0004]

When a monocyclic coil is used as the magnetic field generating coil for canceling the external magnetic field, there are the following problems. The magnetic field generated by the monocyclic coil has a large rate of change in the magnetic field strength depending on the distance from the coil even on the coil axis, and a large rate of change in the magnetic field strength in the plane orthogonal to the coil axis. When canceling a magnetic field, its action is extremely sensitive to the position of the coil, and it is inconvenient to handle because it is affected by even a slight vibration.
Therefore, an object of the present invention is to make the action of the coil for canceling the fluctuation of the external magnetic field more stable.

[0005]

A magnetic field generation coil for canceling an external magnetic field is a Helmholtz type coil.

[0006]

As shown in FIG. 1, the Helmholtz type coil is a coil in which two identical annular coils are coaxially spaced apart by the radius of the coil so that the same current flows in the same direction in both coils. In such a coil, the magnetic field strength hardly changes in the vertical direction on the coil axis between the upper and lower coils, and the magnetic field strength B is given by B = 4 Nμi / 5√5r. Here, r is the radius of the coil, i is the coil current, and N is the number of turns of each single ring. In this Helmholtz type coil, the change in the magnetic field strength on the axis is small, which means that the magnetic field lines near the axis are in equilibrium with the axis and the bending is small, which means that the magnetic field is also perpendicular to the axis. This means that the change is small, and the parallel magnetic field with almost the same intensity is formed at any position at the intermediate position between the upper and lower coils. Therefore, the position sensitivity of the coil is eliminated, and stable external magnetic field cancellation is possible.

[0007]

FIG. 2 shows an embodiment of the present invention. M is the main body of the mass spectrometer, and C is the controller of the external magnetic field canceling device. In the mass spectrometer, 1 is an ion source, 2 is a magnetic field for mass dispersion, 3 is an ion detector, and 4 is a coil for canceling an external magnetic field according to the present invention, which is a Helmholtz type coil as described above. Reference numeral 5 is an analysis tube made of non-magnetic stainless steel, through which the ion beam passes. The mass-dispersing magnetic field disperses mass in a horizontal plane, which is a plane perpendicular to the paper surface in the figure. The external magnetic field canceling coil 4 is installed on the inlet side of the mass-dispersing magnetic field so that the vertical axis, that is, the vertical direction in the figure is the axial direction, and the analysis tube 5 is sandwiched by the upper and lower single rings.

The control section C of the external magnetic field canceling apparatus and the external magnetic field canceling coil 4 are connected by a cable 6, and the control section C of the external magnetic field canceling apparatus is placed at an appropriate place in the room. In the control unit, 7 is a magnetic sensor, 8 is a preamplifier, 9 is a variable resistor for adjustment, and 10 is a power amplifier.
The output current of the power amplifier is supplied to the external magnetic field canceling coil 4.

The usage of the above-mentioned external magnetic field canceling device is as follows. First, C is placed in an appropriate place away from an electric device such as a transformer without being influenced by the magnetic field for mass dispersion of the mass spectrometer M. As described above, the cause of the magnetic field fluctuation around 10 Hz is that it is considerably separated outdoors, so it can be considered that the fluctuation magnetic field is uniform indoors, and the control unit C is about 5 m away from the main body M of the mass spectrometer. The fluctuation of the external magnetic field can be sufficiently canceled. After deciding the position of device C,
Ions of appropriate mass are introduced into the mass spectrometer M, the magnetic field of the mass spectrometer is set to detect ions of that mass, and the ion detection output is recorded. Since the external magnetic field fluctuates,
This recording changes in response to changes in the external magnetic field. Therefore, the adjusting resistor 9 is adjusted so that the fluctuation of the ion detection output is eliminated. When the installation position of the device C is changed or the direction of the magnetic sensor is changed, the position of the adjusting knob of the adjusting resistor 9 must be changed, but the position of the device C and the direction of the magnetic sensor have the best stable ion detection output. It is best to find the best location and orientation. Once such a setting is made, there is almost no need to change the location of the control unit C thereafter.
The external fluctuating magnetic field to be canceled by the mass spectrometer is a magnetic field component in the direction perpendicular to the mass dispersion plane. Since this component is proportional to the magnetic field strength at that location, the magnetic sensor 7 changes the magnetic field detection direction to the external magnetic field. It is not necessary to be parallel to the axis of the canceling coil 4.

[0010]

According to the present invention, since the Helmholtz type coil is used as the coil for canceling the external magnetic field, the position sensitivity is eliminated, the canceling action becomes stable, and high resolution is achieved even in a bad magnetic environment. ， Highly accurate mass spectrometry is possible.

[Brief description of drawings]

FIG. 1 is a perspective view of a Helmholtz coil.

FIG. 2 is a block diagram of an embodiment of the present invention.

[Explanation of symbols] M mass spectrometer main body C control unit of external magnetic field cancellation device 1 ion source 2 mass dispersion magnetic field 3 ion detector 4 external magnetic field cancellation coil 5 analysis tube 6 cable 7 magnetic sensor 9 adjustment variable resistance

Claims (1)

[Claims] 1. A Helmholtz type coil is arranged so as to sandwich an ion beam passage at an entrance or an exit of a magnetic field for mass dispersion, or both, and a magnetic field sensor is arranged at a proper place where the influence of the magnetic field for mass dispersion does not reach. A magnetic field type mass spectrometer characterized in that the current of the coil is controlled by the output of the magnetic field sensor to cancel the external magnetic field on the center line of the coil.