JP5965743B2 - ICP device, spectroscopic analyzer, and mass spectrometer - Google Patents

Description

  The present invention relates to an inductively coupled plasma (hereinafter referred to as ICP) apparatus mainly used as an excitation source or an ion source, and more particularly to an ICP apparatus that greatly reduces the amount of plasma gas used.

  The ICP device is used as an excitation source for emission spectroscopic analysis or as an ion source for a mass spectrometer that targets ions generated in plasma. This ICP device has conventionally been provided with a plasma torch having a multiple tube structure made of quartz glass or ceramics.

  FIG. 7 shows an ICP emission spectroscopic analysis (ICP-OES) apparatus and shows an example of the use of a conventional ICP apparatus. The plasma torch 32 has a concentric triple tube structure, the center of which is a sample introduction tube 321 (introducing the sample into the plasma together with the carrier gas) and an auxiliary gas tube 322 (plasma as the auxiliary gas) provided on the outer periphery of the sample introduction tube. And a plasma gas pipe 323 provided on the outer periphery of the auxiliary gas pipe. The region surrounded by the plasma gas tube 323 at the top of the sample introduction tube 321 is a portion called a plasma chamber for generating plasma. A bonnet 30 is interposed between the induction coil 312 and the plasma gas pipe 323. The bonnet 30 is used to prevent discharge that occurs between the induction coil 312 and the plasma gas. Therefore, the normal bonnet is provided so that the induction coil 312 is interposed in a region where the plasma torch is wound.

  On the other hand, ICP devices generally use expensive argon or helium as the plasma gas. Conventionally, the consumption of plasma gas requires about 15 to 20 liters per minute in order to stably obtain a plasma flame. For this reason, studies have been made to suppress a large amount of plasma gas consumption, which is a factor of the running cost of the ICP device.

  For example, in a plasma torch, the plasma gas ejection region is narrowed and the outer wall of the plasma gas tube is made longer than the carrier gas gas tube to form a shield from the atmosphere. A cooling gas cylinder is concentrically surrounded on the outside of the gas pipe, and the cooling gas is allowed to flow in a rotating manner so that the plasma gas cylinder is cooled so as not to melt, and a plasma flame is formed to be long. Thus, the sensitivity is increased (Patent Document 1). Also, in the ICP apparatus used for mass spectrometry, the plasma gas consumption is suppressed by forming the shield and narrowing the plasma gas ejection region to reduce the plasma gas flow rate. In this case, the flow rate is reduced to about half by halving the ejection width formed by the plasma gas tube and the auxiliary gas tube among the concentric triple tubes (Non-patent Document 1).

Japanese Patent Laid-Open No. 2003-194723 (FIG. 8)

Analytical Chemistry vol.52, No.8, pp.559-568, 2003, Analytical Society of Japan

  However, first, if the plasma gas tube is lengthened to provide a shielding effect and the plasma flame is not engulfed in the atmosphere, it becomes impossible to perform photometry due to deposition of deposits on the inner surface facing the plasma flame. In addition, when a part of the plasma gas pipe is cracked due to heat, it is necessary to replace each plasma torch, which is complicated and uneconomical due to the cost of the plasma torch. It was.

  Secondly, in order to solve the above problem, a cylindrical bonnet independent of the plasma torch having a length that surrounds the plasma flame is adopted, but there is a new problem that causes abnormal discharge when the plasma is turned on. occured.

  In order to solve the above first and second problems at the same time, an ICP apparatus of the present invention includes a sample introduction part for introducing a sample, an inner tube for carrier gas, a middle tube for auxiliary gas, and a plasma gas A plasma torch that has a concentric triple tube structure consisting of an outer tube and has an open end with these gas inlets at one end is separated from the plasma torch, and the generated plasma flame The cylindrical bonnet has a height that sufficiently surrounds the tip of the plasma torch, and the bonnet surrounds the plasma generation region adjacent to the plasma torch opening end where the plasma flame is generated. Inductively placed induction coil, gas control unit for controlling carrier gas, auxiliary gas and plasma gas, inner surface of bonnet and outer A modified gas introduction mechanism for introducing a modified gas for flow path modification of the plasma gas in the gap portion formed by the outer surface of the tube, characterized in that it comprises.

  In the ICP device of the present invention, the correction gas introduction mechanism includes a capillary that ejects the correction gas, and the ejection side end of the capillary is arranged to face the gap portion of the fixed side end of the bonnet. Alternatively, the correction gas introduction mechanism has a flow path for correction gas, and this flow path is disposed along part or all of the gap portion on the gas introduction portion side of the plasma torch, and the portion along the gap portion Some or all of them were open.

Further, the ICP device of the present invention has an end portion on the side where the correction gas is introduced so that the correction gas increases or decreases in association with the increase or decrease of the plasma gas in the capillary or the flow path. It was made to connect with the gas flow path branched from the middle of the gas flow path connected to.
Further, the bonnet is provided with one or a plurality of photometric slits or holes.
The ICP device of the present invention was used for a spectroscopic analyzer or a mass spectrometer.

  According to the present invention, the use of individual shields (bonnets) eliminates air entrainment in the plasma flame associated with the plasma light emitting device, and the use of a unique plasma gas correction mechanism also improves plasma lighting. The plasma gas consumption can be halved without loss of sensitivity and accuracy. Therefore, it is possible to provide a plasma light emitting device having high economic efficiency.

1 is an overall schematic diagram of an ICP device according to a first embodiment of the present invention. It is the schematic of the principal part of the ICP apparatus of 1st Example which concerns on this invention. It is the whole ICP device schematic diagram of the 2nd example concerning the present invention. (A) It is the schematic of the principal part of the ICP apparatus of 2nd Example which concerns on this invention. (B) It is a general-view figure of the correction gas introduction mechanism seen from the b direction of (a). (C) It is BB 'sectional drawing of (a). (A) It is the schematic of the bonnet of the ICP apparatus which concerns on this invention. (B) It is another schematic diagram of the bonnet of the ICP device according to the present invention. (A) It is a figure which shows the example of the gas path | route which concerns on this invention. (B) It is a figure which shows the separate gas path | route which concerns on this invention. It is a whole schematic diagram of an ICP spectral light emitting device using a conventional ICP device.

The plasma light emitting device according to the present invention will be described below with reference to the drawings.
1 and 3 are overall schematic views of an ICP device according to a first embodiment of the present invention.
The ICP apparatus of this embodiment is roughly composed of a plasma generation unit 11, a sample introduction unit 13, a plasma torch 12, a bonnet 10A, a plasma torch support member 14, and a correction gas introduction unit 15A. JIS K 0116 (light emission) It is based on the ICP device specified in the spectroscopic analysis general rules).

The plasma generation unit 11 causes the sample 134, which is atomized with the plasma gas P such as argon, to be carried on the carrier gas CA, flows to the plasma torch 12, and applies a high frequency voltage to the induction coil 112 provided outside the bonnet 10A. Is generated.
The sample introduction unit 13 includes a nebulizer 132 for sucking a sample, a suction tube 133, and a spray chamber 131. The sample introduction unit 13 includes a carrier gas CA such as argon, and a plasma 134 that generates a sample 134 through the sample gas tube 121. Introduce.

  The plasma torch 12 has a concentric triple tube structure, and a sample introduction tube (inner tube) 121 for a sample 134 introduced together with a carrier gas CA such as argon (Ar) gas is located at the center thereof, and on the outside thereof. An auxiliary gas pipe (middle tube) 122 for controlling the vertical position of the plasma is surrounded by a plasma gas pipe (outer tube) 123 for flowing a plasma gas to the outside thereof.

Furthermore, the bonnet 10 </ b> A is provided by fitting it outside the plasma gas pipe 122. When the plasma is ignited on the upper part of the sample gas pipe 121, it has the purpose of preventing instability of the plasma flame due to entrainment of the atmosphere from the outside and reduction in measurement sensitivity due to light emission derived from the atmosphere. For this, a cylindrical quartz glass tube can be used, and a predetermined gap d is formed with respect to the plasma gas tube 123.
The plasma torch support member 14 includes a base portion 141 and a fastening portion 142. The fastening part 142 opens and fixes the plasma torch in a form separated from or connected to the base part 141.

  The correction gas introduction portion 15A is used to prevent the plasma gas from staying in the gap d between the bonnet 10A and the opening end of the plasma gas tube 123, which causes abnormal discharge during plasma lighting, particularly when the flow rate of the plasma gas P is small. It is provided in order to generate a jet air flow in the same direction as the flow direction of the plasma gas P. Thereby, the plasma can be turned on with a small plasma gas P.

Example 1
Hereinafter, the ICP device of FIG. 1 will be described in detail.
The plasma torch 12 is made of quartz glass, and a sample introduction tube (inner tube) 121, an auxiliary gas tube (middle tube) 122, and a plasma gas tube (outer tube) 123 each have an outer diameter of 7 mm, It is a 17 mm and 20 mm concentric triple tube structure. The wall thickness of each part is about 1.0 mm, and the opening diameter of the sample introduction tube is limited to 2 mmφ or less. Moreover, the position of the open end of each gas pipe is shifted on the stairs so that the outside becomes higher when standing.

  The plasma torch 12 is fixed by being sandwiched between the base portion 141 of the plasma torch support member 14 and the attaching / detaching fastener 142. In this case, the fastener 142 may be pressed and fixed to the base portion 14 along the outer circular shape of the plasma torch 12, and one of the left and right sides thereof may be hinged to open and close with a single opening. . Then, the plasma gas P is introduced inside the plasma gas pipe 123 so as to form a spiral flow from its lower part and flow out from the opening end.

  Furthermore, the plasma gas P reduces the flow rate in order to suppress consumption, thereby reducing the ejection speed from the opening end. Therefore, the width of the gap end portion corresponding to the outlet of the passage of the plasma gas P formed by the inner surface of the plasma gas tube 123 and the outer surface of the auxiliary gas tube 122 may be adjusted to be narrow. By doing in this way, even if it is a case where the flow volume of plasma gas is suppressed, it can adjust so that a flow rate may not reduce, and the plasma flame of predetermined | prescribed height can be obtained stably. Note that argon gas was used as the plasma gas P in this example.

  Next, the bonnet used for the ICP device of the present invention will be described. The bonnet 10 </ b> A is cylindrical quartz glass (inner diameter 21 mm, wall thickness 1.3 mm) that is externally fitted to the plasma torch 12. Accordingly, the gap d is determined in relation to the size of the plasma torch 12 and is about 0.5 mm.

The bonnet 10A is characterized in that it is independent from a simple cylindrical plasma torch and protrudes to the upper part of the region related to the induction coil 112, as compared with the conventional bonnet 30 shown in FIG. Usually, the opening end of the outer tube, which is a plasma gas pipe, and the end of the induction coil are arranged so as to cover the region of the plasma generation unit 11, and therefore, about a dozen mm above these ends. Was surrounded by a bonnet. The length of the enclosure is set to a range in which the plasma flame is stabilized without involving the atmosphere, and is about 20 mm in this embodiment. Further, making it independent from the plasma torch has the effect of allowing only the bonnet to be replaced with easy detachability, as will be described later.

  The bonnet 10A is fixed to an extension formed at one end portion of a capillary support member 151a included in the correction gas introduction mechanism 15A, which will be described later, provided along the circular shape outside the plasma torch. A portion was provided, and fitted and fixed to a guide on the portion. In this case, a slit 101 may be provided on the fixed end side circumference of the bonnet 10A so as to be aligned with the convex portion 154a provided on the capillary support member 151a. By doing in this way, alignment of the circumferential position of bonnet 10A can be made easy.

The main effect of the bonnet 10A is that the atmosphere around the opening caused by the decrease in the flow velocity of the plasma gas P at the opening end of the plasma torch 12 generated when the flow rate of the plasma gas P is reduced (for example, 10 L or less per minute). It is to prevent the entrainment. Therefore, it becomes more effective by surrounding the area corresponding to the height of the plasma flame with the bonnet 10A, the consumption of the plasma gas P can be reduced, and economical measurement is realized. Further, as described above, the bonnet 10A and the plasma torch 12 are independent from each other, and thus can be individually replaced. In particular, on the inner surface of the bonnet facing the plasma flame, white turbidity due to precipitates or cracking due to heat or the like may occur. However, even in such a case, it is possible to deal with it only by replacing an inexpensive bonnet.
In addition, the induction coil 112 was placed on the bonnet 10A so as to be aligned with the opening end of the outer tube so as to cover the region of the plasma generation unit 11 as described above.

Next, the correction gas introduction mechanism 15A provided in the ICP device according to the present invention will be described.
The correction gas C prevents a part of the plasma gas P from being caught and staying in the gap d between the opening ends of the bonnet 10 </ b> A and the plasma torch 12 when the plasma is turned on, and the staying gas is removed from the plasma gas. It plays a role of returning and correcting the original flow path. This stagnation of the plasma gas causes an abnormal discharge when the plasma is turned on, and hinders obtaining a stable plasma flame. Moreover, the situation was not solved only by adjusting the flow rate of the plasma gas P. The inventors have intensively studied in order to obtain a stable plasma flame in the configuration using the bonnet 10A, and have come to adopt the modified gas introduction mechanism 15A. The correction gas C is introduced with a gap d formed between the inner surface of the bonnet 10A and the outer surface of the plasma torch 12 from the fixed end (lower) side to the other end (upper) side.

As shown in FIG. 1, this mechanism includes a capillary support member 151a fixed to the upper portion of the base portion 14, a capillary 152a for introducing the correction gas C, and a fastener 153a for pressing the capillary. In FIG. 2, the perspective view regarding arrangement | positioning of the bonnet 10A and the correction gas introduction mechanism 15A is shown. A capillary with an inner diameter of 0.75 mm was used. Further, the capillary was fixed so that the tip thereof was directed to the slit 101 by using the slit 101 provided on the circumference on the fixed end side of the bonnet 101A. This direction only needs to be a direction in which the correction gas enters the gap d from the slit 101. By adjusting the flow rate, a problem in the direction can be tolerated to some extent. In order to introduce the correction gas efficiently, it is better to follow the flow direction of the plasma gas. Further, the direction of the capillary tip may be adjusted along the gap d so as to form a spiral flow. Also, capillary handling flexible ones rather by capital case, such as PTFE (polytetrafluoroethylene) can be utilized. In FIG. 1, the capillaries are arranged so as to face upward at 45 degrees with respect to the plane direction of the base portion 14.

  The gases used in the ICP device of the present invention are carrier gas CA, auxiliary gas A, plasma gas P and correction gas C related to plasma torch 12. Argon gas was used for those gases. Further, the correction gas C only needs to correct the gas retention at the opening end of the gap d, and may be increased or decreased in the same manner as the plasma gas P increases or decreases. Therefore, as shown in FIG. 6 (a), the gas introduction path is such that the carrier gas CA, the auxiliary gas A, and the plasma gas P are introduced by a single gas control system as before, and the correction gas C is introduced into the plasma gas P. The structure introduced as a branch pipe was adopted. In this way, the correction gas C can be linked to the increase or decrease of the plasma gas P. The flow rate of the correction gas C can be adjusted in advance with the inner diameter of the branch pipe or a simple manual flow meter.

Further, it is not necessary to individually control the flow rate of the correction gas C, and no additional equipment such as a controller or a valve is required on the apparatus. Therefore, an efficient apparatus configuration can be provided simply and inexpensively.
In addition, you may control the correction gas C by another system as shown in FIG.6 (b). In this case, although the effects described above are not provided, it is significant in that an inexpensive gas other than expensive argon can be used as the correction gas C. For example, air may be blown by an air pump.
Further, although not shown, when the plasma is turned on, a chamber gas path for replacing the inside of the system with a gas once used may be introduced in addition to the above gas path.

  In the ICP apparatus according to the present invention employing the gas path of FIG. 6A, high frequency energy is generated in the induction coil 112 under the conditions of a frequency of 27.12 MHz and an output of 1.2 kW, and argon gas is used at the start of the previous plasma lighting. After igniting for several tens of seconds under the conditions of the The plasma gas flow rate during steady operation was switched. In this case, the argon gas flow rate at the start of plasma lighting was 0.3 L or less per minute from the capillary 152a for the correction gas C which is this branch pipe, while the plasma gas P was set to 20 L per minute. Further, the flow rates of the plasma gas P and the correction gas C during steady operation were 8 L and 0.1 L or less per minute, respectively. As a result, plasma having a photometric height of several tens of millimeters was formed on the upper part of the sample introduction tube 121, and a stable plasma flame could be obtained consistently from the time of lighting to the time of measurement. The plasma gas flow rate at this time is the above-mentioned condition, and was able to be substantially halved while maintaining the sensitivity equal to or higher than the plasma gas flow rate of 15 to 20 L / min in the conventional ICP apparatus. Therefore, it was confirmed that it has high economic efficiency.

(Example 2)
Next, a modified gas introduction mechanism 15B different from the first embodiment will be described. Since Example 1 is common except for the correction gas introduction mechanism, the reference numerals are the same.

  FIG. 3 shows an ICP device according to the present invention, in which the introduction of the correction gas C is replaced with the capillary related to the correction gas introduction mechanism 15A of the first embodiment, and a gap is formed on the fixed end (lower) side of the bonnet 10B of the flow path member 151b. The one provided with the ejection 152b of the correction gas C provided along the circumference of d is shown. FIG. 4A is a perspective view showing the path of the ejection 152b. FIG.4 (b) shows the gas path | route at the time of seeing from the b direction (directly above) of (a). FIG. 4C shows the positional relationship between the gap d formed by the outer peripheral surface of the plasma gas tube 123 and the inner peripheral surface of the bonnet 10B in the B-B ′ cross section of FIG. Here, jets are provided in half of the circumference of the bonnet 10B, but a plurality of holes may be arranged so as to be provided on the entire circumference or intermittently along the circumference. In addition, the gas flow path may be formed with a through hole in the base portion 14 or may be used by remodeling the capillary as long as the ejection 152b can be formed. Further, in order to facilitate positioning of the bonnet 10B, a slit 101 may be provided on the fixed end side of the bonnet 10B as in the first embodiment.

With this structure, the gas at the opening end of the plasma torch 12 did not stay and the same result as in Example 1 could be obtained, and the same effect was shown.
The ICP apparatus of the present invention can be used for an ICP emission spectroscopic analysis (ICP-OES) apparatus or an ICP mass spectrometer (ICP-MS). In addition, the present invention can be used for other apparatuses using plasma emission.

Further, when photometry is performed from the lateral direction of the plasma, at least one of the slits 102-L and 102-R can be provided in the vicinity of the photometry unit in the bonnets 10A and 10B. By doing so, even if the inner surface of the bonnet is clouded, photometry is not hindered. The slit for photometry may be a hole or any shape as long as the influence of the atmosphere on the plasma flame can be prevented.
The plasma gas is not limited to argon, and nitrogen, helium, etc. can be used.

  Further, the ICP device of the present invention can be provided by incorporating the bonnet and the correction gas introduction mechanism according to the present invention, which are the main parts thereof, into the conventional ICP device. This eliminates the need to dispose of the existing apparatus and can enjoy the effects of the present invention, and this is also excellent in terms of economy.

  As described above, the ICP device of the present invention eliminates the side effect (instability of the plasma flame due to the entrainment of the plasma atmosphere) by reducing the plasma gas consumption by the long cylindrical bonnet, and the bonnet. Side effects (abnormal discharge when the plasma is turned on due to stagnation of part of the plasma gas by the plasma torch and bonnet) are also eliminated, resulting in a significant reduction in plasma gas consumption during long-time operation. Made it possible to do.

Therefore, it is possible to provide an ICP device that is extremely economical as compared with the prior art.
Note that the embodiment of the present invention is not limited to the above description , and can be appropriately improved or changed without departing from the spirit of the present invention.

10A, 10B, 30 Bonnet 11, 31 Plasma generation unit 12, 32 Plasma torch 13, 33 Sample introduction unit 14 Plasma torch support member 15A, 15B Correction gas introduction unit

Claims (13)

In ICP equipment,
A sample introduction part for introducing a sample;
It is a concentric triple tube structure comprising an inner tube for carrier gas, a middle tube for auxiliary gas, and an outer tube for plasma gas, and an end portion including these gas introduction portions at one end portion is in an open state. With a plasma torch,
A cylindrical bonnet that is separated from the plasma torch, has a height that sufficiently surrounds the front end of the generated plasma flame, and is arranged so as to be externally fitted to the plasma torch by being separated by a predetermined distance ; ,
An induction coil that is externally fitted to the bonnet so as to surround a plasma generation region adjacent to the plasma torch opening end generated by the plasma flame;
A gas control unit for controlling the carrier gas, the auxiliary gas, and the plasma gas;
An ICP apparatus comprising: a correction gas introduction mechanism for introducing a correction gas for correcting a flow path of the plasma gas into a gap formed by an inner surface of the bonnet and an outer surface of the outer tube. The bonnet includes a slit that communicates the inside and outside of the cylinder in a part of the circumference of the opening end supported by the base portion that supports and fixes the bonnet,
2. The ICP device according to claim 1 , wherein the base portion includes a convex portion that can be fitted with the slit serving as a reference at the time of arrangement on a part of a line that is in contact with a cylindrical end portion on the fixed side of the bonnet. The correction gas introduction mechanism includes a capillary for ejecting the correction gas;
The ICP device according to claim 2 , wherein the ejection side end portion of the capillary is arranged so as to face the gap portion of the fixed side end portion of the bonnet.   The ICP device according to claim 3, wherein an end portion on the ejection side of the capillary is directed to the slit from an end side surface on the fixed side of the bonnet. The correction gas introduction mechanism includes a flow path for the correction gas;
The said flow path is arrange | positioned along a part or all of the said gap | interval part by the side of the gas introduction part of the said plasma torch, The part or all of the part along the said gap | interval part is opening. ICP device.   The capillary is connected to the outer tube of the gas control unit at the end on the side where the correction gas is introduced so that the correction gas increases or decreases in conjunction with the increase or decrease of the plasma gas. The ICP device according to claim 3, wherein the ICP device is connected to a gas flow path branched from the gas flow path.   The gas flow path connecting the end portion on the side where the correction gas is introduced to the outer tube of the gas control section so that the correction gas increases or decreases in conjunction with the increase or decrease of the plasma gas. The ICP device according to claim 5, wherein the ICP device is connected to a gas flow path branched from the middle.   The ICP device according to claim 3 or 4, wherein the capillary includes a gas control unit different from the plasma gas, and the correction gas is a gas different from the plasma gas.   The ICP device according to claim 5, wherein the flow path includes a gas control unit different from the plasma gas, and the correction gas is a gas different from the plasma gas. The hood, a slit or hole for photometry end or near the fixed side opposite to the base portion, but comprises one or more in any one of claims 2 to 4, 6 and 8 The ICP device as described.   The correction gas introduction mechanism includes a capillary for ejecting the correction gas;
  The ICP device according to claim 1, wherein the ejection side end portion of the capillary is arranged so as to face the gap portion of the fixed side end portion of the bonnet. Spectrometer equipped with an ICP apparatus according to any one of claims 1 to 11. Mass spectrometer equipped with an ICP apparatus according to any one of claims 1 to 11.