JPH0748372B2 - Ion source for mass spectrometer - Google Patents

Description

TECHNICAL FIELD The present invention relates to an ion source for a mass spectrometer, in which a sample is irradiated with a primary beam and the sample is ionized by the impact of the sample.
In particular, the present invention provides a suitable ion source to be used when the sample liquid from the liquid chromatograph is directly introduced online into the ionization chamber for ionization.

[Prior Art] As an ion source of a type in which a sample liquid separated by a liquid chromatograph is directly introduced into a mass spectrometer, there is an ion source having a structure as shown in FIG.

In FIG. 5, 1 is a mass analysis system of a mass spectrometer, 2 is an ion source, 3 is an ionization chamber, 4 is an electrode group for accelerating and focusing the ions generated in the ionization chamber, 5 is a primary beam generator, Reference numeral 6 is a liquid chromatograph, and 7 is an introduction tube for introducing the sample liquid separated by the liquid chromatograph 6 into the ionization chamber 3. A fused silica tube, for example, is used as the introduction tube. Further, as shown in an enlarged cross-sectional view of FIG. 6, the tip portion of the introduction tube 7 inserted into the ionization chamber is covered with a stainless tube 8 and, further, a glass tube (a metal tube such as stainless steel is also provided on the outside thereof). Good) 9 is covered. Then, the porous member 10 is attached so as to close the opening of the introduction tube. As this porous member, for example, a filter (frit) made by sintering stainless powder is used. An appropriate voltage is applied to the stainless pipe 8 from a repeller power supply 11.

In such a configuration, the sample liquid separated by the liquid chromatograph 6 is sequentially introduced into the ionization chamber 3 through the introduction pipe 7, and exudes to the surface through the porous member 10 attached to the tip of the introduction pipe. To do. The sample liquid that has exuded to the surface is impacted by the primary beam B from the primary beam generator 5 and is ionized, and the generated ions are introduced into the mass spectrometric section 1 for mass analysis.

[Problems to be Solved by the Invention] Meanwhile, in exuding the sample liquid separated by the liquid chromatograph 6 onto the surface of the porous member 10, the conventional sixth method is used.
As shown in the figure, the sample solution is introduced from the back side of the porous member and exudes to the front side (primary beam irradiation surface). Since the solvent component in the sample liquid evaporates while passing through the porous member, the concentration of the sample component is high at the time of reaching the primary beam irradiation surface. In order to increase the concentration action to increase the amount of produced ions and improve the sensitivity, it is necessary to lengthen the distance (thickness) t from the sample liquid introducing tube of the porous member to the exuding surface.

However, when the thickness t of the porous member is increased in this way, the flow rate of the sample liquid slows down, and the sample liquid moves while diffusing into a spherical shape centered on the sample injection portion within the porous member. Therefore, as shown in FIG. 7, when the sample solution F is introduced into the porous member 10 through the introduction tube 7, the straight portion F1 first reaches the central portion of the primary beam irradiation surface A of the porous member. Then, the portion F2 that has exuded and diffused and moved reaches the primary beam irradiation surface A with a certain time delay and exudes to the periphery thereof.

As described above, the phenomenon that the simultaneously injected sample components exude to different positions of the primary beam irradiation surface A at different times is due to the fact that when the sample liquid separated by the liquid chromatograph is introduced, And the sample component of (3) simultaneously exude to the primary beam irradiation surface A and are ionized, which causes a memory phenomenon.

In order to prevent this, a cap with a primary beam passage hole formed in front of the primary beam irradiation surface may be placed to irradiate only the central portion of the porous member with the primary beam. There are disadvantages that the sample liquid irradiation area is small, the amount of generated ions is small, and the sensitivity is low. In this case, the primary beam amount may be increased in order to increase the ion amount, but there is a risk that the porous member will be damaged or the sample will be destroyed.

Therefore, the present invention has been made in view of such inconvenience, and an object thereof is to provide an ion source capable of improving the sensitivity while preventing the occurrence of a memory phenomenon with a simple configuration.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides an ionization chamber, an introduction pipe for introducing a sample solution into the ionization chamber from the outside, and a distal end of the introduction pipe. Apparatus provided with a porous member into which the sample liquid is injected from the introduction tube, and a primary beam generating means for irradiating the sample liquid that has passed through the porous member and exuded to its surface with a primary beam for ionization In, while injecting the sample liquid from the introduction tube into the porous member so that the sample liquid flows along the primary beam irradiation surface in the porous member, a primary irradiation region limiting member for limiting the primary beam irradiation region is provided. It is characterized in that it is arranged between the beam generating means and the porous member.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[Examples] FIG. 1 is an enlarged sectional view of an essential part showing an example of an ion source for a mass spectrometer according to the present invention, FIG. 2 is a left side view of FIG.
3 and 4 are diagrams for explaining the operation of the present invention, and the same reference numerals as those in FIGS. 5 and 6 denote the same components.

In this embodiment, the sample solution S is formed by attaching the open end of the introduction tube 7 to the upper outer peripheral surface (end) of the disk-shaped porous member 10.
Is allowed to flow in the porous member along the primary beam irradiation surface A (hereinafter referred to as surface A) of the porous member. In the figure, reference numeral 12 is a support rod for supporting the porous member 10, which is removably attached to the side wall of the ion source 2. Reference numeral 13 denotes a bottomed cap which covers the tip end of the support rod 12 so as to surround the surface A, and an elliptical primary beam passage hole 14 is formed in the bottom portion.

In such a configuration, the sample solution S introduced from the introduction tube 7
Flows in the porous member 10 along the surface A, moves downward, and eventually leaves the porous member 10. During the transfer process, the solvent component in the sample liquid is vaporized, and the concentration of the sample component increases.

FIG. 3 (a) shows a change in concentration on the surface A when a sample solution having a constant concentration is continuously flowed by an equal concentration curve, and FIG. 3 (b) shows a line on the surface A. The change in concentration along l is shown. From these two figures, from the introduction pipe 7 to the porous member 10
It can be seen that the sample liquid injected inside spreads radially and was rapidly concentrated with it. Further, FIG. 7C shows the change of the flow velocity along the line l, and the concentration proceeds,
It can be seen that the viscosity increases as the concentration increases, and the moving speed decreases rapidly.

From this fact, as shown in FIG.
When the effluent from the liquid chromatograph represented by the chromatogram having the above is flown into the porous member 10 through the introduction pipe 7, the peak e reaches the central portion of the surface A as shown in FIG. At this point, the peaks a to d which have already passed are on the surface A
It can happen that it remains at the bottom of the.

Therefore, if the entire surface A is irradiated with the primary beam, the ions of the sample component existing in the respective peak portions are simultaneously generated, and the memory phenomenon cannot be avoided.

In order to avoid this, the surface A where the moving speed of the sample solution is high
It is sufficient to irradiate only the upper part of the primary beam with the primary beam, but the concentration near the uppermost part is not advanced and the amount of produced ions is small.

Therefore, considering the balance between the moving speed and the degree of concentration, for example, the primary beam passage hole 14 is set in the central portion surrounded by the broken line in FIG. 4 (b) so that only this portion is irradiated with the primary beam. By limiting the primary beam irradiation area, efficient ionization with a large amount of generated ions can be performed while preventing the memory phenomenon.

Further, since the opening 15 is provided at the lower end of the support rod 12, the sample liquid accumulated in the lower portion of the porous member 10 is promptly discharged into the cap 13, so that the sample accumulated below the porous member 10 The condition of the surface A on which the liquid is irradiated with the beam is not disturbed.

The above description is an example of the present invention, and various modifications can be considered in the implementation. For example, the mounting position of the introduction tube with respect to the porous member is not limited to the upper end portion as in the above-described embodiment, and the side surface (a surface parallel to the surface A) near the left and right end portions or the lower end portion or any one of the end portions. ) Is okay. However, in consideration of the action of gravity, it is more advantageous to arrange it above as in the above embodiment.

Further, the shape of the porous member is not limited to a disc shape, and may be a rectangular shape.

Further, if the vaporized gas from the surface A flowing out to the primary beam passage hole 14 side is reduced by exhausting the inside of the cap 13 with a vacuum pump, the ions taken out through the passage hole 14 are vaporized gas molecules. Since the probability of collision with and disappearance is reduced, the ions generated from the surface A can be efficiently guided to the mass analysis system, and the sensitivity can be improved.

[Effect] As described in detail above, according to the present invention, it is possible to obtain an ion source capable of improving the sensitivity while preventing the occurrence of the memory phenomenon.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of the present invention, and FIG.
Left side views of the drawings, FIGS. 3 and 4 are views for explaining the operation of the present invention, and FIGS. 5 to 7 are views for explaining a conventional example. 1: Mass spectrometric section, 2: Ion source 3: Ionization chamber, 4: Electrode group 5: Primary beam generator 6: Liquid chromatograph 7: Introduction tube, 10: Porous member 12: Support rod, 13: Cap 14: Primary beam passage hole 15: Aperture

Claims (1)

[Claims] 1. An ionization chamber, an introduction pipe for introducing a sample liquid into the ionization chamber from the outside, and a porous member arranged at the tip of the introduction pipe and injecting the sample liquid into the inside from the introduction pipe. In a device provided with a primary beam generating means for irradiating a sample solution exuding on the surface thereof through the porous member with a primary beam to ionize the sample solution, the sample solution is irradiated inside the porous member on its primary beam irradiation surface. The sample liquid is injected into the porous member from the introduction pipe so as to flow along the irradiation region, and an irradiation region limiting member for limiting the irradiation region of the primary beam is arranged between the primary beam generating means and the porous member. Ion source for mass spectrometer.