JPS5916706B2 - Ion detection device of mass spectrometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ion detection device used in a mass spectrometer, and particularly to a detection device that can detect positive ions and negative ions by switching them with a simple operation.

Conventional mass spectrometers analyze only positive ions, but recently the effectiveness of mass spectrometry of negative ions has been advocated, and mass spectrometers that can analyze both positive and negative ions with a single device have been developed. .

In such a device, both positive ion and negative ion detection devices must be provided as ion detection devices. In magnetic field mass spectrometers equipped with an analysis magnetic field, the ion accelerating voltage is usually as high as several volts, so even if the conventional detection device for positive ions is used as is, negative ions cannot be taken into the detection device and detected. Yes, it is extremely advantageous.

However, when a detection device for positive ions is used as is for negative ions, an electric current is applied to the ion multiplier (which converts incident ions into electrons and multiplies them) inside the detection device to adjust the gain. When the voltage is changed, a phenomenon occurs in which the multiplication factor of the ion multiplier decreases as shown by a in FIG. 1 when the voltage is equal to the ion accelerating voltage, for example around 3V. 5 This is considered to be because the negative ions are decelerated by the negative voltage applied to the ion multiplier, and the velocity becomes close to zero, so that the probability of the negative ions entering the ion multiplier becomes low.

Since the voltage applied to the ion multiplier is variable for gain adjustment, it is desirable that the multiplication factor varies linearly in accordance with the voltage, and such a phenomenon is undesirable. The present invention has been made in view of the above points.V) By adding a simple configuration to the conventional positive ion detection device, it is possible to detect negative ions without reducing the multiplication factor. The purpose is to provide a detection device.

The present invention will be explained in detail below using the drawings. FIG. 2 is a perspective view showing an embodiment of the present invention.

θ In the figure, 1 is an ion multiplier having a first dynode D1 to an n-th dynode Pn, and 2 is a slit disposed close to the first dynode D. In front of the slit 2, two ground electrodes 3 and 4 are arranged in i5 order so that the ion passage ports coincide with each other, and the ion beam I selected by a magnetic field type mass spectrometry system (not shown) passes through the passage ports. , and enters the first dynode D1. Reference numerals 5 and 6 denote a conversion electrode and a counter electrode arranged between the electrodes 3 and 4 with the ion 7 path in between. A positive high potential of 1 to several KV or a ground potential is selectively applied from a DC power source 8.

With the above-mentioned configuration, when positive ions are detected, the switch 7 is turned to side a and the conversion electrode 5 is given a ground potential, so no electric field is generated between the ground electrodes 3 and 4, and the positive ions I are As shown in FIG. 3, which is a vertical cross-sectional view of FIG. 1, the light beam continues straight, enters the first dynode D to which a negative high voltage is applied, and is detected. Next, when negative ions are detected, the switch 7 is turned to the b side and a high positive potential is applied to the conversion electrode 5 by the power source 8, so that there is a gap between the conversion electrode 5 and the counter electrode 6 in the direction across the ion path. A deflection electric field is generated.

Therefore, as shown by the broken line in FIG. 3, the negative ions approach the conversion electrode 5 in a parabola due to the deflected electric itching.
Finally, it collides with the electrode 5. On the other hand, if allowed, ions become electrode 5.
The strength of the deflection electric field and the length of the electrode 5 are set so that the deflection electric field collides with the electrode 5. The surface of the electrode 5 is formed of a material that is easily ejected as positive ions upon collision with negative ions, and the electrode 5 is given a sufficient potential of several KV. Therefore, a number of positive ions corresponding to the number of collided negative ions are generated from the negative ion collision point of the electrode 5. The positive ions are accelerated by being attracted by the negative high voltage applied to the first dynode D1, enter the dynode, and are detected.

According to the present invention, the entire amount of negative ions is irradiated to the conversion electrode, and the negative ions do not directly enter the ion multiplier, so even if the voltage applied to the ion multiplier is changed, the multiplication rate is There is no decrease in the voltage, and a linear characteristic as shown by b in FIG. 1 is achieved. The rate at which positive ions generated from the circumferential conversion electrode 5 are incident on the ion multiplier 1 varies greatly depending on the position where they are generated.

Therefore, in actual use, the intensity of the deflection electric field is adjusted by adjusting the output of the DC power supply 8, and the negative ion collision position on the conversion electrode 5 is adjusted so that the positive ions generated from the collision position are most efficiently ion multiplied. Input to plier 1, exchange? If so, it is desirable to select the optimal location with the highest sensitivity. Incidentally, in a mass spectrometer, measurements are mainly performed by magnetic field sweep, but measurements are also performed by accelerating voltage sweep (continuous or stepwise).

If this acceleration voltage sweep is performed in conjunction with the measurement of negative ions, the collision position of the negative ions on the conversion electrode 5 will shift because the ion acceleration voltage changes (specifically, if the acceleration voltage is increased, the earth electrode 4 (in the direction of the ground electrode 3 when lowered), this results in a significant change in sensitivity. Figure 4 shows that by varying the deflection electric field strength in conjunction with the sweep of the negative ion accelerating voltage, the collision position of negative ions on the conversion electrode is prevented from moving, and the sensitivity fluctuations described above are prevented. FIG. 2 is a configuration diagram showing an example in which

Components in this figure that are the same as those in FIG. 2 are given the same numbers and symbols, and their explanations will be omitted. In FIG. 4, 9 is a mass spectrometry system equipped with a magnetic field 10 and an electric field 11, 12 is a positive and negative ion source, 13 is a grounded main slit, and 14 is for accelerating positive ions generated from the ion source 12. An accelerating power source for applying a negative potential to the ion source; 15 is the ion source 1;
2, an acceleration power source 14 for applying a positive potential to the ion source to accelerate the negative ions generated from the ion source;
This is a switch for selectively sending the output of 15 to the ion source 12. There is an interlocking relationship between the acceleration power supply 15 and the DC power supply 8 such that when the output voltages are Vl and V2, when V1 becomes large (when the acceleration voltage becomes low), V2 also becomes large. For example, a linear relationship as shown in FIG. 6 is given. Therefore, if the acceleration voltage is changed, for example, in the direction of increasing it when measuring negative ions with the switches 16 and 7 turned to the b side, the deflection electric field is also strengthened, so that the collision point of the negative ions on the conversion electrode is Earth electrode 4
Movement in the direction is prevented. When the accelerating voltage is changed to lower the accelerating voltage, the deflection electric field is weakened and the collision point is prevented from moving toward the earth electrode 3, so that the collision point of negative ions is eventually changed regardless of the change in the accelerating voltage. This means that the sensitivity can always be kept at the highest level. The counter electrode 6 in the embodiment described above is for adjusting the distribution of the deflection electric field, and even if omitted, negative ions are attracted to the V5 conversion electrode 5 by the deflection electric field formed around the conversion electrode. , it is not necessary as it will cause a collision.

In addition, the earth electrodes 3 and 4 are connected to the conversion electrode 5 due to electrical leakage from the surroundings.
This is to prevent an adverse effect on the deflection electric field formed by 9, and either or both can be omitted.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the relationship between the voltage applied to the ion multiplier and the multiplication factor, Fig. 2 is a perspective view showing the configuration of an embodiment of the present invention, Fig. 3 is a longitudinal sectional view thereof, and Fig. 4 5 is a diagram showing the configuration of another embodiment of the present invention, and FIG. 5 is a diagram showing the relationship between the acceleration voltage and the output of the DC power source. 1... Ion multiplier, 5... Conversion electrode, 6
. . . Counter electrode, 7, 16 . . . Switch, 8 . . . DC power supply, 15 . . . Accelerating power supply for negative ions.

Claims (1)

[Claims] 1. An ion multiplier for converting and multiplying ions selected by the mass spectrometry system into electrons, and a conversion electrode disposed in front of the multiplier along the traveling direction of the selected ions. a power source that generates a positive voltage applied to the conversion electrode to form a deflection electric field around the conversion electrode to attract the ions toward the conversion electrode and cause them to collide with the conversion electrode; and a positive ion detection device. An ion detection device for a mass spectrometer, comprising a switching means for switching the conversion electrode to ground when detecting negative ions and to connect the conversion electrode to the power source when detecting negative ions.