JP2012013541A - Atomizer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve high efficiency of an atomizer.SOLUTION: An atomizer has a rod-shaped electrode 10 and a sample electrode 11 arranged a fixed distance apart from the tip of the rod-shaped electrode 10. The tip of the rod-shaped electrode 10 is housed in a ceramic tube 14 in such a manner that the axial direction is made coincident therewith. A gap is arranged between the inside wall of the ceramic tube 14 and the rod-shaped electrode 10 and an electric discharge is passed between the gap in the tip side axial direction of the rod-shaped electrode 10. The sample electrode 11 is covered with a ceramic tube 15 and has a mortar-shaped recess 16 because the outside diameter of the tip of the ceramic tube 15 is expanded. The sample electrode 11 is exposed to the bottom surface of the recess 16. A sample is held in the recess. The rod-shaped electrode 10 and the sample electrode 11 are connected to a high pressure pulse power source 18. As shown in FIG.2, the high pressure pulse power source 18 outputs a rectangular pulse voltage that alternates between positive and negative.

Description

  The present invention relates to an atomizer that atomizes a target element in a sample using atmospheric pressure plasma, and is characterized by a power source for generating atmospheric pressure plasma.

  In atomic absorption analysis and atomic emission analysis, an apparatus for atomizing a sample (atomizer) is required. Conventionally, as an atomizer, a graphite furnace has been widely used for atomic absorption analysis, and an ICP apparatus has been widely used for atomic emission analysis. Further, as in Patent Document 1, an atomizer using atmospheric pressure plasma is also known.

  Patent Document 1 describes the following luminescence analysis method. First, the sample containing the target element is irradiated with atmospheric pressure plasma using an atomizer to atomize the sample, and the metal element vapor in the atomized sample is mixed into the atmospheric pressure plasma, and high-energy electrons in the plasma are mixed. Excited to emit light. This luminescence is measured through a spectroscope to measure the density of the target element in the sample.

  In order to generate atmospheric pressure plasma of the atomizer, it is described that the voltage of a commercial AC power source is boosted and applied to an electrode.

JP2008-241293

  However, when a commercial AC power supply is used, the voltage rises gently, so that a time delay occurs until the discharge start voltage is reached, and the atomization efficiency is poor. For this reason, depending on the type of the target element, the emission intensity is reduced, making measurement difficult.

  Accordingly, an object of the present invention is to increase the efficiency of atomization in an atomizer using atmospheric pressure plasma.

  A first invention is an atomizer that generates atmospheric pressure plasma by applying a voltage using a power source, and irradiates the sample with atmospheric pressure plasma to atomize the sample, and the power source alternately inverts positive and negative. An atomizer that outputs a rectangular pulse voltage.

  According to a second invention, in the first invention, a rod-shaped first electrode and a tubular shape are provided so that the first electrode is separated from the inner wall of the tube around the axis of the first electrode. An insulating tube that holds the tip of one electrode, and in which a discharge gas flows in the axial direction on the tip of the first electrode in a gap between the inner wall of the tube and the first electrode, is spaced a certain distance from the tip of the first electrode. And a sample holding portion made of an insulating material having a concave portion for holding the sample and exposing the second electrode on the bottom surface of the concave portion, and the power source includes the first electrode and the first electrode An atomizer characterized by applying a voltage between two electrodes.

  Ar, He, nitrogen, oxygen, air, or the like can be used as the discharge gas.

  As materials for the first electrode and the second electrode, SUS, copper, tungsten, or the like can be used. However, it is necessary not to use a material containing an element to be analyzed, or to coat the second electrode with a material that does not contain an element to be analyzed. This is to prevent the second electrode from being atomized and affecting the analysis.

  According to the present invention, since the rising and falling edges of the rectangular wave can be instantaneously applied up to the discharge start voltage, and the state of high emission intensity is maintained for a certain period, the efficiency of atomization of the sample is increased. Can be achieved. As a result, the emission intensity is improved and the analysis accuracy can be improved. Further, the voltage is pulsed to suppress an increase in the plasma temperature, and the dispersion of the atomized sample can be suppressed. As a result, the density of the atomized sample is improved, the density of the atomized sample contained in the atmospheric pressure plasma is also improved, and the emission intensity is improved. Further, since the positive rectangular pulse and the negative rectangular pulse are alternately applied, the atmospheric pressure plasma can be generated stably.

FIG. 3 is a diagram illustrating a configuration of an atomizer of Embodiment 1. The graph which showed the voltage waveform of the pulse high voltage power supply, and the light emission waveform of plasma. The graph which showed the voltage waveform of the commercial AC power supply, and the light emission waveform of plasma. The graph which showed the time dependence of emitted light intensity. The graph which showed the relationship between pulse width and the temperature of atmospheric pressure plasma. The graph which showed the relationship between pulse width and the electron density of atmospheric pressure plasma. The graph which showed the relationship between pulse width and emitted light intensity.

  Hereinafter, specific examples of the present invention will be described with reference to the drawings. However, the present invention is not limited to the examples.

  FIG. 1 is a diagram illustrating a configuration of an atomizer according to the first embodiment. The atomizer of Example 1 has a rod-shaped electrode 10 (first electrode of the present invention) and a sample electrode 11 (second electrode of the present invention). The rod-like electrode 10 is a Cu rod having a diameter of 1.2 mm, and the sample electrode 11 is a stainless steel tube having an outer diameter of 2 m and an inner diameter of 1 mm.

  For the rod-shaped electrode 10, stainless steel, molybdenum, tungsten, or the like can be used in addition to Cu. In addition to stainless steel, Cu, molybdenum, tungsten, or the like can be used for the sample electrode 11. However, considering that the sample electrode 11 itself is atomized and affects analysis, the sample electrode 11 is made of a material that does not contain the target element, or is coated or plated with a material that does not contain the target element. Etc. need to be applied.

  The tip of the rod-shaped electrode 10 is housed in the ceramic tube 12 so that the axial directions thereof coincide with each other. In the ceramic tube 12, the tip end side of the sample electrode 11 is narrowed by one step, and the rod electrode 10 extends into the narrowed tube. A gap is provided between the rod-shaped electrode 10 and the inner wall of the ceramic tube 12. A space around the axis of the rod-shaped electrode 10 becomes a flow path of Ar gas.

  The ceramic tube 12 is connected to the insulating tube 13. The insulating tube 13 has a branch 13 a in a direction perpendicular to the axial direction, and the rod-like electrode 10 extending from the ceramic tube 12 into the insulating tube 13 is bent and inserted into the branch 13 a of the insulating tube 13. Is exposed to the outside. An insulating material such as a fluororesin can be used for the insulating tube 13.

  Further, a short ceramic tube 14 whose outer diameter substantially matches the inner diameter of the ceramic tube 12 is fitted on the tip end side of the sample electrode 11 of the ceramic tube 12.

  The insulating tube 13 is connected to a gas cylinder (not shown) filled with Ar as a discharge gas via a pressure reduction / flow rate controller or the like. Ar gas supplied from the gas cylinder is supplied in the axial direction from the inside of the insulating tube 13 to the inside of the ceramic tube 12, and between the rod-shaped electrode 10 and the inner wall of the ceramic tube 12 in the axial direction on the tip side of the rod-shaped electrode 10. The Ar gas is discharged from the tip of the ceramic tube 14.

  As the discharge gas, He, Ne, N, air, etc. can be used in addition to Ar.

  The sample electrode 11 is covered with a ceramic tube 15 having an inner diameter of 2 mm and an outer diameter of 3 mm. The tip of the ceramic tube 15 has an expanded outer diameter and has a mortar-shaped recess 16. The sample electrode 11 is exposed on the bottom surface of the recess 16. A sample to be atomized is held by the recess 16. Further, since the sample electrode 11 is tubular, a liquid sample can be supplied to the recess 16 at the tip of the ceramic tube 15 through the tube. The ceramic tube 15 is further covered with a fluororesin material 17. In addition, when holding a fixed amount of sample in a recessed part, the sample electrode 11 does not need to be tubular, and it is good also as a rod shape.

  The rod-shaped electrode 10 and the sample electrode 11 are connected to a high-voltage pulse power supply 18 and a rectangular pulse voltage in which positive and negative are alternately reversed is applied. By applying a voltage to the rod-like electrode 10 and the sample electrode 11 while flowing Ar gas between the rod-like electrode 10 and the inner wall of the ceramic tube 12 in the axial direction, the tip of the rod-like electrode 10 is applied. Atmospheric pressure plasma is generated, and the atmospheric pressure plasma extends to the sample electrode 11. Then, the atmospheric pressure plasma is irradiated onto the sample held in the recess 16 and the sample is atomized. Part of the atomized sample emits light when mixed in atmospheric pressure plasma, and this light emission is received by a light receiving device, and the emission spectrum is analyzed to perform quantitative analysis of the target element in the sample. it can. Further, it is possible to perform an absorption analysis by using a light source that emits a resonance line spectrum of the target element and irradiating the atomized sample with light from the light source.

  FIG. 2 is a graph showing the correspondence between the output voltage waveform of the high-voltage pulse power supply 18 and the emission waveform of atmospheric pressure plasma by the atomizer of the first embodiment. FIG. 3 is a graph showing a voltage waveform of a conventional commercial AC power supply and an emission waveform of atmospheric pressure plasma by an atomizer of a comparative example. Here, the atomizer of the comparative example is an atomizer in which the voltage of the commercial AC power supply is boosted and used instead of the pulse high voltage power supply in the atomizer of the first embodiment.

  As shown in FIG. 3, when a commercial AC power supply is used, the voltage gradually increases, so that there is a time delay until the discharge start voltage is reached, and the emission intensity of atmospheric pressure plasma gradually increases and decreases. It has become. That is, when a commercial AC power source is used, the efficiency of atomization of the sample is lowered.

  On the other hand, when a rectangular pulse voltage in which positive and negative are alternately reversed as shown in FIG. 2 is used, since the output voltage instantaneously rises to the discharge start voltage, the emission intensity of atmospheric pressure plasma also rises instantaneously, and the emission intensity is It is kept constant at a high emission intensity for a period substantially the same as the pulse width of the pulse high voltage power supply. Therefore, atomization of the sample can be performed with high efficiency. Further, since the voltage is a pulse, the rise in plasma temperature is suppressed, and the divergence of the atomized sample is suppressed. Therefore, the density of the atomized sample is improved, and the density of the atomized sample included in the atmospheric pressure plasma is also improved. As a result, the emission intensity of the target element in the sample can be improved. Further, since the positive and negative pulses are alternately reversed, atmospheric pressure plasma can be stably generated.

  FIG. 4 shows an emission analyzer using the atomizer and the light receiving device of Example 1, and using a water containing 1 ppm of Pb as a sample, the resonance line spectrum of Pb in the sample (wavelength: 283.3 nm) by the emission analyzer. It is the graph which measured the emitted light intensity of. As the high-voltage pulse power supply 18, a power supply having a duty ratio of 20% at 100 Hz and a power supply having a duty ratio of 30% at 150 Hz were used. In both cases, the pulse width is 2 ms, and the pulse interval is different. Moreover, it replaced with the atomizer of Example 1, and also measured the emitted light intensity of the resonance line spectrum of Pb at the time of using the atomizer of the comparative example using a commercial AC power supply.

  As shown in FIG. 4, when a commercial AC power supply is used, the emission intensity is very weak even at the peak. On the other hand, when the high-voltage pulse power supply 18 was used, the emission intensity at the peak was stronger than when the commercial AC power supply was used. In particular, the peak of the emission intensity at 150 Hz with a duty ratio of 30% was about 5 times stronger than that with a commercial AC power supply, and about 2.5 times stronger than at 100 Hz with a duty ratio of 20%.

  FIG. 5 is a graph showing the relationship between the pulse width of the output voltage of the high-voltage pulse power supply 18 and the temperature of the atmospheric pressure plasma. As the sample, water containing 1 ppm of Cu was used. As shown in FIG. 5, the plasma temperature rises slowly until the pulse width is around 2 ms, but when it exceeds 2 ms, the plasma temperature is almost constant.

  FIG. 6 is a graph showing the relationship between the pulse width of the output voltage of the high-voltage pulse power supply 18 and the electron density of the atmospheric pressure plasma. As can be seen from FIG. 6, the electron density does not depend much on the pulse width and is a substantially constant value.

  FIG. 7 is a graph showing the relationship between the pulse width of the output voltage of the high-voltage pulse power supply 18 and the light emission intensity. This is the emission intensity of the resonance line spectrum (wavelength 324 nm) of Cu in a sample using water containing 1 ppm of Cu as a sample. As shown in FIG. 7, the emission intensity depends on the pulse width, and it can be seen that a peak of the emission intensity exists when the pulse width is about 1 ms.

From the results of FIGS. 4 and 7, the emission intensity depends on the pulse width and pulse interval of the output voltage of the high-voltage pulse power supply 18, and the emission intensity (atomization efficiency of the sample) is controlled by controlling the pulse width and pulse interval. I found it possible.

  The atomizer of the present invention can be used in analyzers such as absorption spectrometry and luminescence analysis.

10: Rod electrode 11: Sample electrode 12, 14, 15: Ceramic tube 13: Insulating tube 16: Recess 18: Power supply

Claims (2)

An atomizer that atomizes the sample by applying a voltage using a power source to generate atmospheric pressure plasma, irradiating the sample with the atmospheric pressure plasma,
The power source outputs a rectangular pulse voltage in which positive and negative are alternately reversed.
An atomizer characterized by that. A rod-shaped first electrode;
A tip of the first electrode is held in the tube so that the first electrode is separated from the tube inner wall around the axis of the first electrode, and the tube inner wall and the first electrode are held in the tube. An insulating tube through which discharge gas flows in the axial direction on the tip end side of the first electrode,
A second electrode disposed at a certain distance from the tip of the first electrode;
A sample holding portion made of an insulating material having a concave portion for holding the sample, and the second electrode exposed on the bottom surface of the concave portion;
Have
The power source applies a voltage between the first electrode and the second electrode;
The atomizer according to claim 1.

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