JPH0332745B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic field strength setting device for a magnetic field type mass spectrometer, and particularly to a magnetic field strength setting device suitable for performing mass fragment graphing in a magnetic field type mass spectrometer.

When performing mass fragment graphing using a magnetic field mass spectrometer, set the magnetic field strength so that the peak of an ion with a certain mass is at the center of the detector slit, and then switch the ion acceleration voltage to detect it. Stepwise mass scanning is performed so that some fragment ions reach the detector slit. In such a case, the present invention provides a device that digitally controls the magnetic field strength and sets the magnetic field strength so that the peak of ions of a specific mass is located at the detector slit position.

To set the magnetic field strength so that the ion peak of a specific mass is located at the detector slit position, introduce a standard sample of known mass into the mass spectrometer while changing the magnetic field strength, and then Fix the magnetic field strength at the detected location (Maslock)
do. At this time, if the magnetic field strength is controlled digitally, the magnetic field strength changes stepwise, so it is rare for the center of the ion peak to coincide with the center of the detector slit. There is a shift in the magnetic field strength equivalent to one bit, and the ion peak of the standard sample also shifts from its correct position. If there is such a shift with respect to the ion peak of the standard sample, the peak position of the fragment ion of the sample to be analyzed will also be shifted, causing an error in the measurement of ion intensity.

The present invention seeks to provide a device for correcting deviations in the magnetic field settings that occur in the above-mentioned mass lock when the magnetic field strength is digitally controlled. The present invention will be explained below with reference to Examples.

The figure shows an embodiment of the invention. 1 is a gas chromatograph, and 2 is an interface for connecting the gas chromatograph and a mass spectrometer, specifically a molecular separator for removing carrier gas from the gas flowing out of the gas chromatograph and concentrating sample components. . 3 is the ion source of the mass spectrometer, which consists of a sample ionization chamber, an ion accelerating electrode, etc. 4 is a magnet that generates a magnetic field for mass spectrometry;
5 is an ion detector. Reference numeral 6 denotes an excitation current supply power source for the magnet 4, and the output current is controlled by a controller 7. 8 is a control computer;
A magnetic field control signal is output from the same computer, and the D/
The signal is converted into an analog signal by the A converter D/A2 and inputted to the controller 7, and the magnetic field strength formed by the magnet 4 is controlled to a value specified by the computer 8. Reference numeral 9 denotes a magnetic field detection sensor which outputs a signal corresponding to the strength of the magnetic field formed by the magnet 4. This signal passes through an amplifier A1, is digitized by an A/D converter A/D1, and is input to a computer 8. . The computer 8 squares this digital signal and converts it into a mass number signal. A squaring means for converting the output of the sensor 9 into a signal corresponding to the mass number may be interposed between the amplifier A1 and the computer 8. Regardless of which method is used, the mass number converted from the output of the sensor 9 is displayed on the display device 10. A latch circuit 11 reads and holds the output of the A/D 1 when a latch signal is issued from the computer 8.

The circuit configuration shown in FIG. 1 will be explained below along with an explanation of the operation of the mass lock. When the apparatus is started, a reference ion accelerating voltage signal is output from the computer 8 and sent to the ion accelerating high voltage power supply control circuit 12 via the D/A converter D/A3. The ion accelerating high voltage power supply 13 is controlled to apply a reference ion accelerating voltage to the ion source 3. When the mass of the standard sample is instructed to the computer 8, the computer 8 outputs a corresponding magnetic field control signal to the D/A 2, and the magnet 4 forms a magnetic field of the intensity specified by the magnetic field control signal. The magnetic field strength set by the magnetic field control signal output from the computer 8 is a stepwise jump value as shown in Figure 2, and the magnetic field strength is closest to the magnetic field Bo corresponding to the mass Mo of the standard sample. Becomes B′. Depending on how you write the program, you can always set B′<Bo or B′>Bo, or in a more advanced form, determine which of the two magnetic field strengths Bo is closer to, and select the magnetic field that is closer to it. It can also be set to high intensity. Next, a standard sample is introduced into the ion source 3. Ions of the standard sample are detected by the ion detector 5, and the detection output is displayed on the display 16 via the amplifier 14 and the A/D converter 15, and is also input to the computer 8.
The output of the sensor 9 that detects the magnetic field of the magnet 4 is input to the error amplifier C via the amplifier A1, and the output of C is negatively fed back to C via the A/D1, latch circuit 11, and D/A converter D/Ao. has been done. Therefore, before the latch signal is applied to the latch circuit 11, the error amplifier C functions simply as a buffer amplifier, and the output of the A/D 1 is the magnetic field strength of the magnet 4 converted into digital data. Therefore, when the manual controller 17 is operated to input an appropriate voltage of ± to the adder Ad1, the magnetic field strength of the magnet 4 changes continuously and the ion detection strength changes. Adjust. Since the magnetic field strength of the magnet 4 at this time corresponds to the mass of the standard sample, a latch signal is sent to the latch circuit 11 to hold the data of the magnetic field strength at that time. Next, switch S
When switch 1 is switched to contact b side, magnet 4, sensor 9, error amplifier C, buffer 18, switch S
1. The magnetic field strength is controlled by the latch circuit 1 due to the feedback circuit of the controller 7, power supply 6, and magnet 4.
It will be held at the value held at 1,
Maslock operation is completed.

In the above explanation, the configuration is manually adjusted so that the detection signal of the ions of the standard sample is maximized, but switch S2 is switched to contact b side, and computer 8 is adjusted to correspond to the difference between Bo and B' in Fig. 2. The magnetic field control signal amount may be calculated and this data may be sent to the adder Ad1 through the D/A converter D/A1.

According to the present invention, when the magnetic field strength is set stepwise by computer control, even if the magnetic field strength corresponding to the reference mass is in the middle of the stepwise set magnetic field strengths, the predetermined magnetic field strength can be set accurately. Since it can be easily configured, the analysis accuracy of mass fragment graphing is improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an apparatus according to an embodiment of the present invention.
FIG. 2 is a graph of the magnetic field strength set by the computer.

Claims (1)

[Claims] 1. Set the magnetic field strength for mass spectrometry in stages, detect the difference from the magnetic field strength corresponding to a predetermined mass, and apply correction control corresponding to the difference to the magnetic field control value signal that sets the magnetic field strength in stages. A magnetic field setting device for a mass spectrometer, characterized in that the magnetic field is set by a signal including a value signal.