JPH0468739B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a magnetic field detection device in a magnetic field type mass spectrometer.

B. Prior Art A magnetic field type mass spectrometer performs mass scanning by changing the magnetic field strength over time. In this case, when the mass scanning speed is increased, the distribution of the magnetic field between the magnetic poles becomes different from that in the static state due to the eddy currents induced in the magnetic poles, and the magnetic field at the center of the magnetic pole becomes more relative than in the static state. comes down to. When measuring a mass spectrum, the magnetic field strength is detected to obtain a mass scale signal (mass marker signal), but since the magnetic field detector is installed around the magnetic pole, increasing the scanning speed , the detected magnetic field strength is stronger than the magnetic field strength in the area where mass spectrometry is actually performed, and the mass scale is expressed larger than the actual mass. For this reason, the mass scanning speed could not be made very high. Conventionally, in order to increase the mass scanning speed, the distance between the magnetic poles was widened and the magnetic field detector was installed near the center of the magnetic pole, and the cross-sectional area of the magnetic pole was increased so that the magnetic field detector could be placed inside the periphery of the magnetic pole. things are being done.

However, increasing the magnetic pole spacing reduces the maximum magnetic field strength that can be obtained, narrowing the mass range that the mass spectrometer can measure, and the method of increasing the magnetic pole area has the disadvantage that the electromagnet becomes larger.

C. Purpose The purpose of the present invention is to prevent deviation of the mass scale signal from the actual amount when mass scanning is performed while the magnetic field detector is disposed around the magnetic pole.

D. Configuration The present invention provides an auxiliary magnetic pole on the outer edge of the main magnetic pole of an electromagnet that generates a magnetic field for mass spectrometry, electrically insulated from the main magnetic pole of the electromagnet, and a magnetic field detector is arranged between the auxiliary magnetic poles. This product provides a magnetic field detection device for mass spectrometers.Since the auxiliary magnetic pole is electrically insulated from the main magnetic pole, eddy currents flow independently of the main magnetic pole, and eddy currents due to temporal fluctuations in the magnetic field are prevented. Since the influence appears between the auxiliary magnetic poles, magnetic field detection can be performed that reflects the decrease in magnetic field strength at the center of the main magnetic pole, and a mass scale signal indicating the correct mass can be obtained even when mass scanning is performed.

E. Embodiment The drawings show an embodiment of the present invention. 1 is the iron core of the electromagnet that generates the magnetic field for mass spectrometry, 2 is the excitation coil of the electromagnet, 3 is the main pole piece, and 4 is the analysis tube placed in the magnetic field between the main pole pieces 3. .
Auxiliary pole pieces 5 and 6 are attached to the outside of the main pole pieces 3 and 3 with an electric insulating layer 7 interposed therebetween, and are opposed to each other, and a magnetic field detector 8 is provided between them.

FIG. 2 is a plan view of the magnetic pole pieces 3 and 5. When the excitation current is changed, eddy currents I and I flow in the same direction independently in the main magnetic pole piece 3 and the auxiliary magnetic pole piece 6, as shown by the arrows in the figure. ' occurs. Therefore, the effects of eddy currents on the central portions of the main magnetic pole and the auxiliary magnetic pole are similar.

Let B be the strength of the magnetic field generated between the main magnetic poles, which is due to the exciting current, Bo, and the eddy current.
When considered separately, eddy current is proportional to dB/dt, but if we consider the case where the exciting current increases linearly with time, dBo/dt is a constant, and the induced electromotive force is constant. Therefore, the eddy current is also constant over time and dB'/dt=o, so the eddy current is determined only by dBo/dt/. Bo is uniformly distributed in the cross section of the magnetic pole, and the eddy current is proportional to the temporal change in the total magnetic flux that passes within one closed curve along it.In the end, the eddy current is proportional to the area it surrounds, and from the center of the magnetic pole. It becomes excessive towards the outside. B′ is opposite in direction to Bo, and the influence of all eddy currents appears additively at the center of the magnetic pole.
The effect of the eddy current on the inside disappears as you move outward from the center, so the effect of the eddy current is greatest at the center of the magnetic pole, and the magnetic field is weaker at the center than at the outer periphery. Since the auxiliary magnetic pole itself generates an eddy current proportional to the time change of the excitation current and weakens the magnetic field caused by the excitation current, results equivalent to detecting the magnetic field at the center of the main magnetic pole can be obtained.

Effects According to the present invention, since there is no need to widen the gap between the magnetic poles, the measurable quality range is not narrowed, and there is no need to widen the cross section of the magnetic poles, so the electromagnet for generating a magnetic field for mass spectrometry can be made larger. No matter what speed the mass scan is performed, the mass scale signal obtained by the magnetic field detection device can always indicate the correct mass.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of an electromagnet that generates a magnetic field for mass analysis in a mass spectrometer according to an embodiment of the present invention, and FIG. 2 is a plan view of the magnetic pole surface of the same. 1... Iron core, 2... Excitation coil, 3... Magnetic pole piece, 4... Mass spectrometry tube, 5, 6... Auxiliary magnetic pole piece,
7... Electric insulating layer, 8... Magnetic field detector.

Claims (1)

[Claims] 1. Auxiliary magnetic poles are attached to the outer periphery of the opposing main magnetic poles of an electromagnet that generates a magnetic field for mass spectrometry, with an electric insulating layer interposed between them and the main magnetic poles, and the auxiliary magnetic poles are opposed to each other, and a mass scale is formed between these auxiliary magnetic poles. A magnetic field detection device in a mass spectrometer, characterized in that a magnetic field detector is arranged to obtain a signal.