JPH0323653Y2 - - Google Patents

Description

[Detailed explanation of the invention] [Industrial application field] The invention uses atmospheric pressure plasma as an ion source.
The present invention relates to an ion attraction device used in mass spectrometry.

[Summary of the idea]

In a mass spectrometer that uses atmospheric pressure plasma as an ion source, there is a sampling cone with a circular orifice at the tip to extract ions from the atmospheric pressure plasma, and a circular orifice at the tip to guide the ions extracted from the sampling cone to a quadrupole mass spectrometer. A skimmer with a circular orifice is installed with the center axes of each circular orifice offset by a distance greater than the sum of the radii of both orifices, and the skimmer blocks the light generated at the orifice of the sampling cone so that it does not enter the quadrupole mass spectrometer. An ion attraction device is provided that reduces background signals due to light in a quadrupole mass spectrometer.

[Conventional effect]

A conventional configuration is shown in FIG. atmospheric pressure plasma 5
The sample passes through a conical sampling cone 1 having an orifice (diameter 0.3 to 1.5 mm) at its tip, and is drawn from an exhaust pipe 6 into a chamber at a pressure of about 1 Torr, which is evacuated by a vacuum pump (not shown). The plasma drawn into the chamber is transferred to a second chamber which is depressurized by a vacuum pump (not shown) connected to the exhaust pipe 7, and is transferred to a conical chamber with an orifice at the tip located on the same axis as the sampling cone. skimmer 2. In the plasma that has entered the second chamber, only positive ions are focused by the ion lens 3, guided to the quadrupole mass spectrometer 4, and subjected to mass analysis. A light shielding plate 8 made of a metal plate with a diameter of about 3 mm functions to block light generated at the orifice of the sampling cone 1 and reduce background signals caused by light from the quadrupole mass spectrometer.

[Problem that the invention attempts to solve]

In the prior art, a light shielding plate (Fig. 2, 8) was placed inside the ion lens (Fig. 2, 3) in order to block the light generated at the orifice of the sampling cone. However, since the light shielding plate blocks light and ions at the same time, the amount of ions entering the quadrupole mass spectrometer (Figure 2, 4) also decreases.
This has the problem of reduced sensitivity.

[Means for solving problems]

In order to solve the above problem, it is necessary to remove the light shielding plate in the ion lens and to prevent light from entering the quadrupole mass system. Therefore, this idea is
The axes of the sampling cone and skimmer are spaced apart by at least the sum of the radii of their respective orifices, and this arrangement prevents light generated by the sampling cone orifice from entering the quadrupole mass spectrometer. Furthermore, since a light shielding plate inside the ion lens is not required, there is no reduction in sensitivity.

[Effect]

According to the present invention, the light generated at the orifice of the sampling cone can be blocked without using a light shielding plate, so that ions do not decrease in the ion lens. Therefore, the background is low and there is no decrease in sensitivity, so it is 3 times faster than conventional devices.
~10 times more sensitivity can be obtained.

〔Example〕

Hereinafter, the present invention will be explained in detail based on the drawings.
FIG. 1 shows an atmospheric pressure plasma mass spectrometer according to an embodiment of the present invention, in which atmospheric pressure plasma 5 is generated by a combustible gas flame, arc discharge, high frequency electrodeless discharge, etc. The atmospheric pressure plasma is composed of ions, electrons, and neutral particles, and is passed through a sampling cone 1 having an orifice (diameter 0.3 to 1.5 mm) at the tip, and is reduced in pressure (0.1 mm) by a pump (not shown) connected to an exhaust pipe 6. ~10Torr) 1st
is pulled into the club room. The plasma drawn into the chamber is passed through an orifice (diameter 0.5 to 2 mm) at the tip.
It passes through the skimmer 2 with a holder and is drawn into a second chamber whose pressure is reduced by a vacuum pump (not shown) connected to an exhaust pipe 7. The skimmer 2 is
The center of the circular orifice of the skimmer is set apart from the center of the circular orifice of the sampling cone 1 by at least the sum of the radii of both orifices.
The plasma that has passed through the sampling cone 1 expands in the first chamber, and the plasma density is uniform within a radius of 10 mm around the orifice of the sampling cone 1. The amount of ions drawn into the chamber does not decrease. Only the ions of the plasma drawn into the second chamber are focused by a cylindrical ion lens 3 installed on the central axis of the skimmer 2, and are introduced into a quadrupole mass spectrometer 4. The mass is analyzed using a heavy pole mass spectrometer.

[Effect of idea]

According to the present invention, there is no need for a light shielding plate.
This has the effect of reducing the background signal due to light without reducing the amount of ions entering the heavy pole mass spectrometer, and can improve the sensitivity of the atmospheric pressure plasma mass spectrometer.

[Brief explanation of the drawing]

FIG. 1 shows a block diagram of an apparatus according to the present invention, and FIG. 2 shows a block diagram of a conventional apparatus. 1... Sampling cone, 2... Skimmer,
3...Ion lens, 4...Quadrupole mass spectrometer,
5... Atmospheric pressure plasma, 6... Exhaust pipes 1, 7...
Exhaust pipes 2, 8...shading plates.

Claims (1)

[Scope of utility model registration request] A sampling cone with a circular orifice at the tip that takes in plasma existing under atmospheric pressure,
a low-pressure chamber connected to the sampling cone, a skimmer having a circular orifice at its tip that draws in the plasma that has passed through the low-pressure chamber, a second low-pressure chamber connected to the skimmer, and installed within the second low-pressure chamber. In an atmospheric pressure plasma mass spectrometer comprising an ion lens that focuses ions of the plasma that has passed through the skimmer and a mass spectrometer that performs mass analysis of the focused ions, the central axis of the orifice of the sampling cone and the orifice of the skimmer An atmospheric pressure plasma mass spectrometer characterized in that a sampling cone and a skimmer are installed so that the central axis of the orifice is separated by at least the sum of the radii of both orifices.