JP2002039944A - Icp light source apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ICP light source apparatus capable of cooling a plasma chamber, even without having to particularly prepare a device for cooling to cool the chamber. SOLUTION: In the ICP light source apparatus, a coolant gas introduction pipe 6 for supplying a coolant gas to a plasma torch 2 is buried in a cooling block 10 mounted in the plasma chamber 1, so as to wind an outer periphery of the chamber 1. As a means for adiabatically expanding the coolant gas, an electromagnetic mass flow unit (constant differential pressure regulating valve) 12a for deciding its pressure is arranged near the chamber 1, that is, at the introduction pipe 6 immediately before starting the winding, and the chamber 1 is cooled by utilizing the temperature drop when the gas undergoes adiabatic expansion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ICP (high frequency inductively coupled plasma) emission spectroscopy or ICP mass spectrometer (ICP-MS) for performing qualitative or quantitative measurement of sample elements.
The present invention relates to an ICP light source device used for plasma emission or ionization of a solution sample.

[0002]

2. Description of the Related Art In ICP emission spectroscopy, a liquid sample is atomized by a nebulizer to form a sample aerosol, which is guided together with argon gas into a discharge tube called a plasma torch.
An induction coil is placed on the outer periphery of the plasma torch, and a high-frequency current is supplied from a power supply to generate an electric field by electromagnetic induction at the center of the plasma torch, thereby generating an argon plasma flame. When the aforementioned sample aerosol passes through the argon plasma flame, the atoms and molecules of the sample are heated and excited to emit light. An ICP emission spectrometer is used to perform qualitative / quantitative measurement of the elements in the sample by spectral analysis of this emission using a spectroscope. At the same time, many elements are ionized in the plasma flame, An ICP mass spectrometer is a device that discriminates ions having different mass numbers with a mass analyzer, detects ions with an ion detector, and analyzes the components of an organic compound as a sample. What is used as a light source or an ion source in such an analysis is an ICP light source device.

Conventionally, this ICP light source device has
The configuration shown in FIG. 2 is employed. That is,
Reference numeral 2 denotes a plasma torch having a coaxial triple tube structure made of quartz, in which a carrier gas pipe 7 is formed at the center, a plasma gas pipe 9 is formed outside the carrier gas pipe 7, and a coolant gas pipe 5 is formed at the outermost side. A high frequency induction coil 4 in which a copper tube through which cooling water passes is wound in a coil shape is attached to an upper portion of the plasma torch 2. The plasma chamber 1 has a nebulizer 1 at one end.
1 is inserted, and is commonly used as the nebulizer 11 is a quartz coaxial double tube structure, in which the center is a tube into which a solution sample is sucked, and the outside is a tube through which a carrier gas flows. A sample aerosol introduction tube 8 is connected to the plasma torch 2 at an upper portion of the other end of the plasma chamber 1, and a drain for discharging waste liquid is provided at a lower portion.

An argon gas is generally used as the carrier gas, the plasma gas, and the coolant gas, and is supplied from the gas supply unit 16. The argon gas is piped from an argon gas cylinder 13 through electromagnetic mass flows (constant differential pressure regulating valves) 12a, 12b, and 12c. The electromagnetic mass flow 12a, 1
2b and 12c are D / A converters 14a and 1
The flow rate of the argon gas is adjusted according to the control voltage signals supplied from 4b and 14c. The control unit 15 is composed of a microcomputer, and each D / A converter 14
a, 14b, and 14c are provided with flow rate instruction signals composed of digital signals.

The conventional ICP light source device is as described above. Excitation and emission and ionization of atoms and molecules of a solution sample are performed as follows. A carrier gas is introduced into the plasma chamber 1 from the outer peripheral tube of the nebulizer 11.
At the tip of the nebulizer 11, the sample solution is sucked and atomized at the same time by the negative pressure action of the carrier gas, and only mist having a small particle diameter is selected in the plasma chamber 1 and reaches the plasma torch 2 through the sample aerosol introduction pipe 8. In general, most of the solution does not become fine mist, but settles out under its own weight as large droplets and is discarded through the drain. When a high-frequency current (several MHz to several tens of MHz) is applied to the high-frequency induction coil 4 placed on the outer periphery of the upper part of the plasma torch 2, a high-frequency magnetic field is formed in the plasma torch 2 around the high-frequency induction coil 4. This high-frequency magnetic field generates an electric field in the center of the plasma torch 2 by electromagnetic induction. The electric field generates a plasma flame 3 by the argon gas introduced into the plasma torch 2. At this time, the shape of the plasma flame 3 becomes a donut shape, and the sample aerosol introduced into the center through the carrier gas pipe 7 is heated to about 6000 ° K while passing through the plasma flame 3, whereby the sample atoms and molecules are excited and emit light. , Also ionized. The plasma gas pipe 9 of the plasma torch 2 is for flowing the plasma gas to slightly float the plasma flame 3 from the tip of the carrier gas pipe 7.
Is for cooling the quartz tube outside the plasma torch 2 by flowing a coolant gas, and also serves to shield the center of the plasma flame 3 from air.

[0006]

The conventional ICP light source device is as described above. However, when the solution sample is an organic solvent, it is gasified when sprayed from a nebulizer in a normal plasma chamber, and an effective mist is generated. Is not generated. To prevent this, it is necessary to cool the plasma chamber. The plasma chamber has a plasma flame of 6000.
Since it is arranged close to the plasma torch that reaches ゜ K, the plasma torch can be cooled by coolant gas,
Although the plasma torch chamber is exhausted to the outside by forced evacuation by a powerful air-cooling fan, the plasma chamber is constantly heated by the heat of the plasma torch, and the temperature of the plasma chamber rises. This means that the evaporation of the solvent in the plasma chamber gradually increases, the amount of the sample introduced into the plasma flame for a constant carrier gas flow rate gradually increases, and changes the state of the plasma, and the quantitative analysis value fluctuates. . Therefore, it is necessary to prevent the temperature of the plasma chamber from rising by cooling the plasma chamber, and to stabilize the temperature of the plasma chamber within a short time.

For these reasons, cooling of the plasma chamber has been conventionally performed. The main cooling method is to attach a water cooling jacket to the plasma chamber and circulate cold water to cool it.Also, using a Peltier element, the heat absorbing surface is fixed to the cooling block side, and the heat generating surface is fixed to the heat radiating plate side. The cooling block is placed in contact with the plasma chamber and cooled. However, in such a cooling method, it is necessary to prepare a cooling source in any case, and the size of the ICP light source device is increased, and an increase in cost is inevitable. The present invention has been made in view of such circumstances, and provides an ICP light source device that can cool a plasma chamber without preparing a special cooling device when cooling the plasma chamber. The purpose is to do.

[0008]

In order to achieve the above object, an ICP light source device according to the present invention winds a coolant gas supply tube supplied to a plasma torch around the plasma chamber and immediately before the winding. A means for adiabatically expanding the coolant gas is provided in the inlet pipe. The plasma chamber is cooled by the adiabatic expansion heat means. By this, ICP was originally
Coolant gas used for the light source device can be used as a cooling source.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a configuration diagram of an ICP light source device according to an embodiment of the present invention, and portions corresponding to the above-described conventional example are denoted by the same reference numerals. ICP of this embodiment
The light source device includes a plasma torch 2, a plasma chamber 1, and a gas supply unit 16. The plasma torch 2 has a quartz coaxial triple tube structure, in which a carrier gas pipe 7 is formed at the center, a plasma gas pipe 9 is formed outside the carrier gas pipe 7, and a coolant gas pipe 5 is formed at the outermost side. A high frequency induction coil 4 in which a copper tube through which cooling water passes is wound in a coil shape is attached to an upper portion of the plasma torch 2.

The plasma chamber 1 has a nebulizer 11 inserted at one end thereof. The nebulizer 11 generally has a coaxial double-tube structure made of quartz and has a center in which a solution sample is sucked and a carrier gas is supplied to the outside. It consists of a flowing tube. A sample aerosol introduction tube 8 is connected to the plasma torch 2 at an upper portion of the other end of the plasma chamber 1, and a drain for discharging waste liquid is provided at a lower portion. Then, there is a cooling block 10 in contact with the plasma chamber 1, and the plasma chamber 1 is placed in the cooling block 10.
The coolant gas introducing pipe 6 is buried so as to wind around the outer periphery of the coolant gas. The gas supply unit 16 includes an argon gas cylinder 13
Are connected to a coolant gas introduction pipe 6, a carrier gas introduction pipe 17, and a plasma gas introduction pipe 18, and electromagnetic mass flows (constant differential pressure regulating valves) 12a, 12b,
12c is connected. Each of these electromagnetic mass flows 1
2a, 12b, and 12c have signal lines from the control unit 15
It is wired through / A converters 14a, 14b, 14c. In particular, the electromagnetic mass flow 12a for the coolant gas is particularly close to the cooling block 10, ie,
The coolant gas introduction pipe 6 is attached at a position immediately before winding.

Next, the operation of the ICP light source device shown in FIG. 1 will be described. Argon gas is generally used for the carrier gas, the plasma gas, and the coolant gas described above.
12b, 12c, and the electromagnetic mass flow 1
2a, 12b and 12c are D / A converters 14, respectively.
The gas flow rate is adjusted according to the control voltage signals provided from a, 14b, and 14c. The control unit 15 is composed of a microcomputer, and each D / A converter 14a,
A flow rate instruction signal composed of a digital signal is given to 14b and 14c.

The solution sample is sucked at the tip of the nebulizer 11 by the negative pressure of the carrier gas introduced from the carrier gas introduction pipe 17 also connected to the nebulizer 11, and at the same time, forms a mist in the form of a mist in the plasma chamber 1. Sprayed. Carrier gas pressure (flow rate)
The argon gas supplied from the argon gas cylinder 13 is determined by the electromagnetic mass flow 12b, which is performed by the D / A converter 14b sending a control voltage signal to the electromagnetic mass flow 12b based on a flow rate instruction signal output from the control unit 15. As for the atomized sample mist, only the mist having a small particle size is carried to the tip of the carrier gas pipe 7 by the carrier gas through the sample aerosol introduction pipe 8.
The mist that has not been introduced into the sample aerosol introduction tube 8 sinks by its own weight as large droplets and is discarded through the drain.

On the other hand, the coolant gas flowing from the argon gas cylinder 13 to the coolant gas pipe 5 of the plasma torch 2 by the coolant gas introduction pipe 6 is supplied to the cooling block 1.
The coolant gas, which is introduced around the outer circumference of the plasma chamber 1 during atmospheric pressure, becomes atmospheric pressure in the upper part of the plasma torch 2, and is supplied to the upstream side of the electromagnetic mass flow 12 a placed close to the cooling block 3.5 to 3.5 to 3.5. 4.5kg
/ Cm2 (about 20 l / min in flow rate) by issuing a flow rate instruction signal from the control unit 15 and controlling it through the D / A converter 14a.
The pressure drop of the insulated gas between the short distance between 2a and the top of the plasma torch 2 causes adiabatic expansion,
The coolant gas is cooled. Therefore, the cooling block 10
Is cooled, and the plasma chamber 1 in contact with the cooling block 10 is cooled.

When the sample solution is an organic solvent, when the plasma chamber 1 is cooled, gasification of the sample sprayed from the nebulizer 11 is limited, and effective mist is efficiently introduced into the carrier gas pipe 7. At the same time, the cooling of the plasma chamber 1 prevents heating due to the heat transfer from the plasma torch 2, which becomes high in temperature, and keeps the plasma chamber 1 at a constant temperature to obtain stable analysis values.

In the plasma torch 2, a plasma gas is also ejected from the argon gas cylinder 13 through the plasma gas introduction pipe 18 through the plasma gas pipe 9, and is formed in a donut shape by the high-frequency current supplied to the high-frequency induction coil 4 together with the above-mentioned coolant gas. Is generated. The sample mist introduced into the plasma flame 3 from the tip of the carrier gas pipe 7 is excited by the high-temperature heat of the plasma flame 3 to emit light and is ionized.

[0016]

According to the ICP light source device of the present invention, a coolant gas introducing tube for supplying a coolant gas to be supplied to a plasma torch is wound around the outer periphery of the plasma chamber, and the coolant gas is adiabatically expanded around the introducing tube immediately before the winding is started. An electromagnetic mass flow (constant differential pressure regulating valve) that determines the pressure of the coolant gas is used as a means to cool the plasma chamber without preparing a special cooling device. Smaller and lower manufacturing cost. The temperature drop when the gas undergoes adiabatic expansion is greater as the specific heat ratio is higher, and the argon used in the ICP light source device is a gas of monoatomic molecules, and has a higher specific heat ratio than other gases, so that the cooling effect is large. With. In addition, at the same time, the heating of the plasma chamber from the plasma torch is also prevented for general solution samples,
Analytical accuracy, reproducibility, and stable plasma chamber temperature
Stability and the like can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of an ICP light source device of the present invention.

FIG. 2 is a diagram showing a conventional ICP light source device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Plasma chamber 2 ... Plasma torch 3 ... Plasma flame 6 ... Coolant gas introduction pipe 10 ... Cooling block 11 ... Nebulizer 12a ... Electromagnetic mass flow 13 ... Argon gas cylinder 15 ... Control part 16 ... Gas supply part

Claims (1)

[Claims] 1. A light source device for an ICP which atomizes a solution sample in a plasma chamber and introduces the solution sample into a plasma torch and performs excitation light emission and the like by high-frequency inductively coupled discharge, and an introduction pipe for a coolant gas supplied to the plasma torch. And a means for adiabatically expanding the coolant gas in the inlet pipe immediately before the winding.