JPH0450701B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an ion source for a mass spectrometer that ionizes a sample, and particularly to a mass spectrometer in which a sample introduced from a liquid chromatograph is ionized by glow discharge. The present invention relates to a discharge type ion source of the device.

[Prior art] For example, in 1985, ORGANIC MASS, published by Wiley Haydn, was used as a discharge-type ion source for a mass spectrometer that introduces and ionizes a liquid sample separated by a liquid chromatograph (LC).
This is described in a paper titled ``Chemical ionization mass spectrometry using a glow discharge ion source combined with a spray sampling device'' in SPECTROMETRY, VOL. 20, No. 3. This ionization device makes a hole in the side wall of the ionization chamber, and
A cathode is attached to this side wall via an insulator, and a voltage is applied between the two to generate a glow discharge, thereby ionizing the sample sprayed from a nozzle provided in the vacuum spray device.

[Problems to be Solved by the Invention] A discharge type ion source with such a configuration has a problem in that the structure is complicated because a hole must be made in the side wall of the ionization chamber and a cathode for glow discharge must be attached. It was hot.

The present invention has been made in view of the above-mentioned conventional problems, and aims to provide a discharge type ion source for a mass spectrometer that can achieve ionization of a sample without complicating the ionization chamber. purpose.

[Means for Solving the Problems] The discharge type ion source according to the present invention is housed in a low pressure chamber, and is connected to an interface from a liquid chromatograph.
a nozzle that sprays a sample introduced through a probe; a desolvation chamber that is connected to the low pressure chamber and that heats the sample sprayed by the nozzle with a heater; and a desolvation chamber that is connected to the low pressure chamber via the desolvation chamber. and an ionization chamber for ionizing the sample sprayed from the nozzle, and a voltage source connected to a voltage output terminal so as to apply a voltage higher than the acceleration voltage of the ionization chamber to the interface probe. It is prepared.

The voltage source includes a DC power source that supplies a constant current to the interface probe, and a DC power supply that supplies a constant current to the interface probe.
The control circuit may include a control circuit that controls the DC power source as a constant current source by comparing the voltage of the probe with a predetermined reference voltage.

Further, the voltage source may be connected between ground and the interface probe, and further may be connected in series between the accelerating voltage source of the ionization chamber and the interface probe.

[Function] In the present invention, a voltage higher than the accelerating voltage of the ion source block is applied to the interface probe to generate a glow discharge between the two, so positive ions are attracted to the nozzle and are This can prevent contamination and therefore stabilize the generation of ions due to discharge.

[Embodiment] FIG. 1 shows an embodiment of the present invention, and is a schematic configuration diagram of a discharge type ion source of a mass spectrometer.
In the figure, reference numeral 1 denotes a frame, which houses a nozzle 2 for injecting a sample and an interface probe 3 connected to the nozzle 2 to guide the sample from the liquid chromatograph on the left side of the figure. The frame 1 is connected to a vacuum pump (RP, not shown) via an exhaust pipe 1a provided on its side wall.
A low pressure chamber 1b is formed by exhausting the gas inside the chamber.

4 is a desolvation chamber communicating with the frame 1, around which a heater 5 for heating the solvent is wound. Reference numeral 6 denotes an ion source block, which includes an ionization chamber 7 that communicates with the frame 1 via a desolvation chamber 4.
is formed. The ionization chamber 7 is connected to a vacuum pump (RP) not shown on the right side of the figure.
This exhausts the gas inside.

8 is a constant voltage control circuit to which the reference voltage Vs and the voltage Vi from the interface probe 3 are applied. The output of the constant voltage control circuit 8 is a constant voltage source 9
The output voltage Vi is controlled to be a low voltage. Since the output end of the constant voltage source 9 is connected to the interface probe 3 via the resistor R having a high resistance value, the constant voltage source 9 constitutes a constant current source together with the constant voltage control circuit 8 and the resistor R. However, the voltage Vi is the ion acceleration voltage
It is equal to the value of Vac plus the constant α. This constant α
varies depending on the conductivity of the solvent used in liquid chromatography; for example, 0.05M
When a solvent containing a 1:1 mixture of CH ₃ COONH ₄ and CH ₃ CN is used, it is 0.8 to 1 kv. The reason why the voltage Vi is made higher than the accelerating voltage Vac of the ionization chamber 7 is that glow discharge is generated between the nozzle 1 and the desolvation chamber 4, and the nozzle 2 adsorbs the generated positive ions. This is to prevent contamination. That is, the voltage (Vac-
If α) is applied, the nozzle 2 will be contaminated, which is not preferable.

In such a configuration, a sample of a liquid chromatograph (not shown) is guided to the nozzle 2 via the interface probe 3, and thereby sprayed toward the desolvation chamber 4. The atomized sample is led to the ionization chamber 7 via the desolvation chamber 4, but the nozzle 2 is in a vacuum of around 1 Torr, and the interface probe 3 has a voltage Vi (>Vac).
is applied from the constant voltage source 9, so the nozzle 2
A glow discharge occurs between the nozzle 2 and the desolvation chamber 4, and the sample from the nozzle 2 is ionized in the ionization chamber 7.

In this case, the voltage Vi applied to the interface probe 3 is higher than the accelerating voltage Vac, and the glow discharge becomes stable.

In addition, as shown in Figure 2, the acceleration voltage Vac of the ionization chamber 7 is used, and the voltage necessary for discharge is added to this.
You may also add Via.

Furthermore, if a filament for implanting electrons is provided in the ionization chamber 7, both spectra of chemical ionization and the above-mentioned discharge ionization can be obtained.

[Effects of the Invention] As described above, according to the present invention, since a voltage higher than the acceleration voltage of the ionization chamber is applied to the interface probe, stable discharge and therefore stable ion generation can be obtained. Since there is no need to use a filament heater for sample ionization,
Even if an aqueous solvent is used, the discharge type ion source has the effect of being easy to maintain and having a long life.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram of a discharge type ion source showing one embodiment of the present invention, and FIG. 2 is a schematic block diagram of a discharge type ion source showing another embodiment of the present invention. 2: Nozzle, 3: Interface probe,
4: Desolvation chamber, 5: Heater, 6: Ion source block, 7: Ionization chamber, 8: Constant voltage control circuit, 9:
Constant voltage source.

Claims (1)

[Scope of Claims] 1. A nozzle that is housed in a low pressure chamber and that sprays a sample introduced from a liquid chromatograph via an interface probe;
An ion source comprising: a desolvation chamber that heats the sample sprayed by the nozzle with a heater; and an ionization chamber that is connected to the low pressure chamber via the desolvation chamber and ionizes the sample sprayed from the nozzle. , a voltage source is provided that connects a voltage output end to the interface probe to apply a voltage higher than the accelerating voltage of the ionization chamber, and generates a glow discharge between the ionization chamber and the nozzle. A discharge type ion source featuring: 2. The voltage source includes a DC power source that supplies a constant current to the interface probe, and a control circuit that controls the DC power source as a constant current source by comparing the voltage of the interface probe with a predetermined reference voltage. A discharge type ion source according to claim 1, characterized in that the discharge type ion source comprises: 3. The discharge type ion source according to claim 1, wherein the voltage source is connected between the ground and the interface probe. 4. The discharge type ion source according to claim 1, wherein the voltage source is connected in series between the accelerating voltage source of the ionization chamber and the interface probe.