JPH10208691A - Icp mass spectrograph - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize plasma flame by automatically compensating for the detuning between a power supply and an output coil for plasma excitation caused by a fluctuation in a load as seen from a high-frequency generator when a sampling cone as the sample inlet of a mass spectrograph M approaches the plasma flame in the mass spectrograph using inductively coupled plasma(ICP) as an ion source. SOLUTION: Capacitors constituting a matching circuit 2 for use in tuning between a high-frequency generator 1 and an output coil 3 are previously provided with capacity capable of tuning when a sampling cone 6 is kept away from plasma flame and capacity capable of tuning when the sample cone 6 is brought near the plasma flame. The capacity of each capacitor is adjusted to the corresponding value, respectively by a combination of the approach and withdrawal of the sampling cone.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mass spectrometer using high frequency inductively coupled plasma (ICP) as an ion source.
In particular, the present invention relates to a matching circuit for establishing matching between the high-frequency power supply and the output coil.

[0002]

2. Description of the Related Art In an analyzer using an ICP, a matching circuit is provided between a high-frequency power supply and a high-frequency output coil for exciting the plasma in order to easily and reliably turn on the plasma and stably maintain the plasma. Before the plasma is turned on, the output coil can be regarded as a mere air-core coil and a transformer whose secondary side is open. However, after the plasma is turned on, the load is connected to the secondary side, and the output coil seen from the power source has a reduced inductance. . For this reason, usually two main and sub capacitors are prepared in the matching circuit, and the lighting of the plasma is detected by detecting the reflected wave between the power supply and the matching circuit, so that the sub capacitor is added to the circuit. Has become. This capacitor is semi-fixed and adjusted in advance so that the matching between the power supply and the output coil is established when the plasma is turned on.

[0003]

In the conventional ICP analyzer as described above, since mass spectrometry is performed using the ICP as an ion source, when the sampling cone is brought close to a plasma flame, this becomes a new load on the secondary side of the output coil. In addition, when viewed from the power supply, the inductance of the output coil is further reduced as compared with the plasma flame lighting state. Therefore, it is necessary to further add capacitance to the matching circuit in order to maintain the matching between the power supply and the output coil. Conventionally, in order to obtain this additional capacity, a semi-fixed capacitor to be put in the matching circuit at the time of plasma lighting has been manually adjusted. Since it takes relatively long time to manually bring the sampling cone close to the plasma flame, there is no difficulty in the manual adjustment of the condenser itself, but after the mass analysis is completed, the condenser is prepared for the next plasma lighting. It was necessary to return the capacity of the sample to its original state, which was cumbersome for the person performing the analysis. The present invention seeks to eliminate this operational complexity.

[0004]

The capacity of a capacitor constituting a matching circuit for matching a high frequency power supply and an output coil for exciting a plasma flame is changed by a sampling cone serving as a sample introduction port of a mass spectrometer. The distance between the high-frequency power supply and the output coil in a state away from the plasma flame is varied between a value at which the matching is established when the sampling cone is brought close to the plasma flame, and the sampling cone is varied. The capacitor is changed between the two values in conjunction with the operation of moving the capacitor in and out.

[0005] The means for changing the capacity of the capacitor between the two values may be performed by adding or removing another capacitor to the matching circuit, or by changing the capacity of one capacitor by driving the trimmer between two positions. Also, the means for interlocking with the contact and separation of the sampling cone is to mechanically interlock with the back and forth movement of the sampling cone to switch the switch or drive the trimmer, or to detect the reflected wave between the high frequency power supply and the matching circuit When the reflected wave level exceeds the set value,
The means for changing the capacitance of the capacitor may be operated.

[0006]

FIG. 1 shows one embodiment of the present invention. 1 is a high frequency generator, 2 is a matching circuit, and 3 is an output coil. A carrier gas containing a sample is blown out from a plasma torch (not shown), and is ionized by a high-frequency electromagnetic field formed by the output coil 3 to form a plasma flame F. M, which is opposite to the plasma flame, is a mass analyzer, 4 is its mass analyzer, and 5 is a sample introduction unit. The sample introduction part consists of a skimmer cone 7 and an ion lens 8 having the same shape as the sampling cone 6 protruding toward the plasma flame and having a small hole formed at the tip from the left in the figure. And the ion lens portion are connected to an exhaust system. The sampling cone 6 sucks a gas containing ions from the plasma flame through a small hole at the tip. The sucked gas is depressurized between the sampling cone and the skimmer cone, and a part of the gas passes through a small hole at the tip of the skimmer cone, and is made to enter the mass spectrometry unit 4 through the ion lens.

The matching circuit 2 includes capacitors C ₁ and C ₂ for forming a resonance circuit together with the output coil 3. C ₂ is inserted into or removed from the matching circuit by a switch S. The switch S before plasma lighting is open. Capacity of C ₁ to resonate with the output frequency of the high frequency generator 1 in the capacitor C ₁ and the output coil 3 in this state are adjusted. When the plasma flame is turned on, the tuning of the matching circuit is broken, and the reflected wave is detected by the reflected wave detector 9 inserted between the high frequency generator 1 and the matching circuit 2. When this reflected wave exceeds a certain level, a signal is output, the switch S is closed, and the capacitor C ₂ is supplied to the matching circuit.
Is added. The capacitance of C ₂ is tuned to the input high frequency together with the capacitor C ₁ while the plasma flame is lit, and the capacitance tuned when the sampling cone 6 is brought close to the plasma flame is the two ends of the capacitance adjustment range. It is adjusted in advance so that When the sampling cone 6 is brought close to the plasma flame, a condenser C ₂ is connected to the rack connected to the mass spectrometer (or the output coil) and the pinion 10.
Adjusting shaft is driven, the capacitance of the capacitor C ₂ is switched to a value where the high-frequency power source and an output coil are aligned when the sampling cone is brought close to the plasma flame.

FIG. 2 shows a matching circuit according to another embodiment of the present invention. In this example, the capacitor C ₂ in FIG.
₂ and C ₂ ′. Switch S,
S 'is "open" before the plasma is turned on, S is first closed by the plasma flame lighting, and the switch S' is closed when the sampling cone is brought close to the plasma flame. The control means of the switches S 'and S' is optional, and S
S 'is performed by detecting the reflected wave in the same manner as in the example of FIG.
, Or both may be performed by the control circuit 11 controlled by the reflected wave detection signal. The control circuit 11 closes S with the first reflected wave detection signal, stores the fact, and operates to close S 'with the second reflected wave detection signal.

As means for linking the operation of bringing the sampling cone into and out of contact with the plasma flame and the operation of changing the capacitance of the capacitor of the matching circuit, in addition to the above-mentioned means, as shown in FIG. controls mechanism 13 for those who move the plasma torch from moving the high-frequency power source and the mass analyzer M drives the structurally easy) and volume adjustment knob of the capacitor C ₂ by the controller 14, manually control device it may be driven a volume adjustment knob of the capacitor C ₂ in parallel when to enter the instruction for the plasma torch proximate or backward and away the plasma flame to a sampling cone.

[0010]

According to the present invention, when the ICP is used as the ion source of the mass spectrometer, the misalignment between the high frequency power supply and the output coil which occurs when the sampling cone is moved toward and away from the plasma flame. The capacitance of the capacitor in the matching circuit for correction is automatically changed, and it is not necessary to return the device to its original state after analysis so that it does not interfere with the plasma flame lighting at the next use. For the person performing the analysis, the operation of the apparatus becomes easy, and the situation that the plasma flame is turned on next time due to forgetting the operation does not occur.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an example of an embodiment of the present invention.

FIG. 2 is a main part circuit diagram of another embodiment of the present invention.

FIG. 3 is a main part block diagram of still another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 High frequency power supply 2 Matching circuit 3 Output coil 4 Mass analysis part 5 Sample introduction part 6 Sampling cone 7 Skimmer cone 8 Ion lens 9 Reflected wave detector 10 Rack and pinion 11 Control circuit F Plasma flame M Mass spectrometer

Claims (1)

[Claims] 1. The capacitance of a capacitor constituting a matching circuit for matching a high-frequency power supply with an output coil for exciting a plasma flame is set such that a sampling cone serving as a sample inlet of a mass spectrometer is kept away from the plasma flame. In a state where the matching between the high-frequency power supply and the output coil is established, and the value at which the matching is established when the sampling cone is brought close to the plasma flame, and the sampling cone is moved toward and away from the plasma flame. An ICP mass spectrometer wherein the capacitor is changed between the two values in conjunction with an operation.