WO2001023102A1

WO2001023102A1 - Sample introduction device and sample analysis method using thereof

Info

Publication number: WO2001023102A1
Application number: PCT/KR2000/000047
Authority: WO
Inventors: Gae Ho Lee; Rae Seok Jung; Dong Keun Shin
Original assignee: Gae Ho Lee; Rae Seok Jung; Dong Keun Shin
Priority date: 1999-09-29
Filing date: 2000-01-22
Publication date: 2001-04-05
Also published as: AU2329100A

Abstract

The present invention is related to an injector of samples and a method for analysis of samples thereby, and more particularly to a new type of an injector of samples and a method for analysis by the device, which, by simultaneously heating and vaporizing a sample, far excels in efficiency the conventional methods which have first to nebulize the solution of a sample into minute droplets and next to heat it, the new device and method of the present invention also being available for a broader range of work than the conventional ones in disregard of the difference in kinds and degrees of viscidity of samples.

Description

SAMPLE INTRODUCTION DEVICE AND SAMPLE ANALYSIS METHOD USING THEREOF

TECHNICAL FIELD

The present invention relates to an injector of samples and a method for their analysis by the use of the said injector, which can be made good use of by connection with various implements analyzing the infinitesimal heavy metals and such like generally contained in water or environmental and frontier science materials.

BACK GROUND ART

In the inductively coupled plasma^'s atomic emission system (ICP- AES), which is a representative analyzer, a magnetic field is produced when an electric current of radio frequency is flowed through its quartz tube. Through the interaction of the thus produced magnetic field, the ions of argon produced from the argon gas, and electrons, a plasma of high temperature is formed. When a sample is injected into the plasma, the ground state electrons of the atoms of the sample receive energy from the plasma, get excited to a high level, and as they return to the stable ground state they emit a light peculiar to the atoms. The ICP-AES spectroscope is an implement to analyze this light to determine the constituents of the sample and their contents.

When a sample is injected into a plasma, the sample is turned into aerosol and injected together with argon gas. and the implement which injects the sample for analysis into such an analyzer as ICP-AES, ICP-MS. AAS, etc. is called "an injector of samples.^" Generally, an injector consists of a pump, a nebulizer, a cloud chamber, etc. At times a heater and a device for desolvation are added for improvement of the efficiency of nebulization. Of the constituents of an analyzer, the implement to turn the sample into aerosol is called "nebulizer." For precision analysis, the plasma is required to be stable, and the more even the aerosol is, the more stable the plasma gets. Accordingly, it is required to ensure that the sizes of the nebulized particles be even. If the nebulized particles are too large in size, they are removed at the cloud chamber and fail to be injected into the plasma. As the result, the nebulization efficiency is lowered. Thus, it is imperative that nebulization be performed not to yield aerosol particles too large in sizes. Accordingly, when the nebulized sample is reduced to small-sized aerosol particles, more sample is injected into the plasma causing the lower detection limit lowered.

For nebulization for the ICP-AES a concentric pneumatic nebulizer, a cross flow nebulizer, or a supersonic nebulizer is often used. Where the concentration of elements is on ppm level, a concentric pneumatic nebulizer and a cross flow nebulizer are used. However when the concentration of the element is on ppb level, either the sample is enriched because it is impossible directly to analyze it, or a supersonic nebulizer is resorted to. An ICP-MS can overcome that problem, but this latter is a device much expensive, compared with an ICP-AES spectroscope, in prices and in administration costs alike. Therefore, an ICP-AES equipped with a supersonic nebulizer is in general use.

The principle of a supersonic nebulizer's operation is to bring forth an vibration of high frequency by providing an electric energy of 1.4MHz to a piezocrystal. By supplying a liquid sample to the vibrating surface, the sample is turned into an aerosol of even and fine particles. Next the aerosol is heated for vaporization, and, after the solvent in the sample is removed by the use of a desolvation device, the sample is then injected into an ICP- AES spectroscope. However because a supersonic nebulizer atomizes the piezocrystal by vibrating it. and, after its vaporization by heating with an electric heater, removes the particles of the larger sizes from the aerosol, it greatly affects the nebulization efficiency and the sizes or evenness of the aerosol particles according to the kind and the viscidity of the sample. In other words, in the case of a sample of high viscidity, when the quantity of the sample first fed to the nebulizer is compared with that of the sample finally injected into the sample injector, subtracting that of the sample failing to be nebulized and falling out, the actual nebulization efficiency comes to only about 30% when calculated in percentage.

The present invention relates to a means of heating, more particularly to a sample injector leading to successful analysis even with a small amount of sample by the use of microwave and a method for analysis thereby. To begin with, heaters in prior arts making use of microwave are looked into, and they are as follows.

USP 5,389.335 reveals a device, which uses microwave to heat an object to a high temperature in a short time and also a method for heating materials sensitive to heat.

USP 5,683,381 reveals a device which uses microwave continuously to warm blood or solutions for intravenous injection to an even temperature and a device to calculate the temperature of the blood or solutions.

These references are on patents on heating of materials by the use of microwave, and these prior arts are different from the present invention in that the structures and uses of their heaters have nothing to do with the heating device in the present invention.

Also, a nebulizer which produces minute droplets or aerosol by nebulizing a liquid sample heating the aerosol by irradiation with microwave for its vaporization has been revealed in USP 5.534,998. This patent, too, makes use of microwave, but its nebulization efficiency is 45% which is not so high.

Furthermore, both the concentric pneumatic nebuilizer and the supersonic variety have their bodies and the cloud chambers all made of glass. Therefore, they have problems in that fluoric acid cannot be used directly in the general process of analysis of samples.

DISCLOSURE OF INVENTION

The present invention is intended to overcome the above-mentioned shortcomings of the conventional sample injectors and sample analyzers, and to provide a sample injector and a sample analyzer which both can attain their purposes with only a very small amount of a sample.

Another objective of the present invention is to provide a sample injector and a sample analyzer which can be used in disregard of the difference in kinds and quantities of a sample available.

Further, the present invention is to provide a sample injector which is not affected even if fluoric acid and such other acids are used at the preliminary treatment process.

To attain the above-mentioned objectives, in the present invention, the sample solution is immediately heated, without nebulization first, and is vaporized, and then the solvent is cooled for desolvation. to be injected as sample for analysis into an analyzer.

The microwave nebulizer of the present invention nebulizes a sample by taking advantage of its vaporization. In other words, microwave is passed through a tube which the sample passes, and in this way the present invention uses a method of a fast, instantaneous vaporizing of a sample, making use of microwave energy passing through. Thus, an aerosol of even and small particles, free of much influence of the kind or viscidity of a particular sample, is produced, therefore, characteristically a highly efficient nebulization is assured of.

A nebulizer is a device for turning a sample into aerosol for injection into an analyzer and, generally being connected with a cloud chamber, it removes from the aerosol particles of the larger sizes. Accordingly, by providing aerosol of even and smaller sized particles, it is possible to increase the amount of the aerosol finally entering into the analyzer, and thus, by stabilizing the conditions of the analyzer and decreasing the possible errors in analysis, to decrease the lower limit of detection.

The present inventor, while seeking a means for raising the efficiency in nebulization, has was able in developing a device, and a method thereby, for analysis even with a very small amount of sample through nebulizing (or releasing) simultaneously with its vaporization, instead of the conventional methods of first nebulizing and next vaporizing.

An embodiment example of the present invention comprises a pump, a sample tube, a microwave neulizer, and a condenser. Of these constituents, the microwave nebulizer is different in its concept from the conventional nebulizer. That is, the constituent of the conventional sample injector, nebulizer, nebulizes a liquid sample into aerosol and, then it is heated for its vaporization by a heating-means. While in the present invention, in contrast, the stage of vaporizing a sample is performed simultaneously with that of nebulization. Strictly speaking, the microwave nebulizer, of the sample injector of the present invention, is dissimilar to the conventional ones which spray liquid sample in aerosol by physical pressure, where in the present invention the sample issues from the nebulizer by over 95% in the form of steam.

However, "nebulizer^" is the word in general use for that constituent of a sample injector, and the step of discharging the elements in the sample which have not been turned into steam and a part of the liquid may still fairly be called "nebulization.' wherefore, the words 'nebulizer,' "nebulizing,^" and 'nebulization^" are indiscriminately used in the following, also. Only it is to be noted that the nebulization in the present invention is different and distinct from the nebulization in the ordinary sense, for in the present invention the nebulization is not done by spraying a sample by physical pressure into aerosol. So it is that, in the present invention, nebulization is often used in the same meaning as just discharging or emitting.

The wording 'nebulization efficiency' in the present Specification, drawings, and patent claims is defined, likewise, as the actual percentage of the sample getting injected into an analyzer, discounting the amount of the sample which fails to get nebulized but falls out from the total which is fed.

In the microwave nebulizer, a sample tube is placed in the microwave cavity, and it is irradiated with microwave. Then the molecular motion takes place by the microwave in the sample through the revolution of dipoles and the movement of ions. The energy by the molecular movement comes to heat the sample, causing its vaporization. Whereupon the difference in kind and viscidity of the sample can have no big influence, and hence a high nebulization efficiency results.

Searches of methods for further, better nebulization efficiency have led to attainment of much greater efficiency enabled by intensive, than the ordinary way of, irradiation with microwave. That is, by intensive concentrating irradiation with microwave of the sample tube which the sample passes through, it has been possible to raise the efficiency of heating the sample by microwave, bringing forth higher efficiency in heating than by the ordinary way of microwave irradiation.

When a microwave absorbent, which absorbs microwave and generates heat, is used, the sample does not merely get heated by the molecular movement through the revolution of the dipoles and the movement of ions but by the heat generated by the absorption of the microwave while the microwave passes the sample tube, whereupon its vaporization gets further stimulated. Whereby more efficient vaporization can be performed. As such an absorbent, generally ferrite is used, ferrite being a compound of iron oxide in the main having magnetism, or such magnetic ceramic material generally added to with ions of ferric oxide, divalent metals, and others to substitute for part of ferrous ions or bonded and then condensed and sintered at high temperature. Ferrite generates heat when it absorbs microwave. For another absorbent, carbon, made by condensing and sintering graphite, is used. Such absorbents absorb microwave and generate heat. Apart from ferrite or carbon rods, other microwave absorbents can also be used.

Accordingly, the ferrite is entwined with a sample tube, as is with a coil, and when a sample is made to pass it and irradiated with microwave, it is heated to a high temperature by the microwave, and it is also heated by the heat emitted from the ferrite which has absorbed the microwave, the vaporization getting greatly stimulated. In other words, such a microwave absorbent as ferrite simultaneously performs the role of microwave absorbent and of generator of heat, thus promoting the vaporization of the sample as well.

Wherefore, even when the viscidity of a sample is great, the possible yield of uneven and large sized particles from a supersonic nebulizer can be partly avoided through the vaporization of the sample. Wherefore, again, by increase of the sample finally reaching the analyzer a sample can be efficiently analyzed with an exceedingly small quantity of it without bothering a separate process of concentration.

An embodiment example of the present invention has used a geared pump. Because the sample is pumped into the nebulizer by a geared pump and also because all the processes of vaporization and desolvation are performed by the use of Teflon tubes and containers, any kind of acid whatsoever, including fluoric acid, can safely be used. Besides, because a geared pump is used there is an advantage in that the speed of injecting the sample can be adjusted to 0.1 - 3.0 ml/min at will. In fact, at the time of analysis of samples it is usual to treat them with such acids as nitric, sulfuric. hydrochloric, and fluoric acids. But in the case of fluoric acid, there was a problem, because this acid corroded glass. Now in the present invention all the constituent parts of the injector are made of Teflon material, and as a consequence there is no risk or problem of corrosion of the sample tube or of contamination of the sample itself.

In the injector of samples in the present invention, a variety of coolers can be used for desolvation of the nebulized or emitted sample, but most preferably a cooling by TEC (thermoelectric cooling) is adopted. TEC, being a method for electronic cooling with thermoelements, otherwise called thermoelectric material, as basic material, is a technique for cooling materials, making use of the Peltier effects. The Peltier effects mean the phenomena of cooling or heating that take place when an electric current flows to the point of contact between different kinds of metal: that is, if an electric current flows through thermoelectric elements an electric current is generated within the elements, and when the electrons move from a metal of lower energy to that of higher energy they absorb the energy from the surroundings, thus causing a cooling, and, the other way around, when the electrons move from a metal of higher to that of lower energy, heat is generated. To cool the condenser TEC, instead of water, is used, and so the construction is rendered simpler.

As is seen in Fig. 4, the courier gas, cooled in advance, is injected into the condenser in the tangential direction, whereby the vaporized sample is cooled, and it is let to enter scraping the basal wall, whereby diminishing the possible memory effect which the trace of other material previously analyzed may leave on the wall of the condenser to affect the present analysis. The functions of the cooled carrier gas in the present invention include the cooling of the solvent and diminishing of the memory effect also, aside from carrying of the sample, removed of solvent.

The microwave nebulizer, a constituent of the sample injector of the present invention, first vaporizes the sample and next nebulizes it, whereby, unlike when a supersonic nebulizer is used, it is assured of good vaporization regardless of the different kinds and different viscidity of the sample, and is enabled to produce an even and small-sized aerosol. Hence, a much better nebulization efficiency than ever results. Also, because in the present invention the sample is first vaporized and next nebulized, it does not require additional heating device as a supersonic nebulizer would require.

Further, the sample injector of the present invention is cheap in prices, and economical in maintenance costs, too. To elaborate, because the Magnetron (brand name), periodically to be replaced, is greatly cheaper in prices than the piezoelectric materials used for the supersonic nebulizer, both the prices and maintenance costs of the nebulizer in the present invention are no more than a fifth or even a tenth of those of the supersonic variety.

Moreover, because in the injector of the sample in the present invention a sample tube made of Teflon and the like, instead of glass, can be used, the problems faced by the conventional injector, that is. corrosion and contamination by such acids as hydrochloric, nitric, sulfuric. fluoric, etc., are all avoided. As a consequence, the injector of samples of the present invention can be made use of in analysis of samples of extreme purity in the semiconductor industries, also.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a conceptual sketch of an injector of samples according to an embodiment example of the present invention.

Fig. 2 is a sketch of a microwave nebulizer and a condenser according to an embodiment example of the present invention.

Fig. 3 is a sketch of the inside of a microwave nebulizer according to an embodiment example of the present invention.

Fig. 4 is a sketch of the scene from injecting the cooled carrier gas into the upper part of a condenser, seen from above. Numbers or symbols used in the drawings:

1. microwave absorption rod 2. microwave generator

3. sample tube 4. condenser 5, 5'. TEC 6. drain 7. carrier gas injection tube

BEST MODE FOR CARRYING OUT THE INVENTION

Below, the present invention is described in detail, making references to embodiment examples and comparative examples when necessary, provided that the embodiment examples given here should not limited or confined by the range of the present invention.

Embodiment Examples 1 through 4 and Comparative Example 1

In order to measure the nebulization efficiency of both the microwave nebulizer and the supersonic variety an experiment was performed by the use of distilled water.

In Examples 1 and 2, a tube of Teflon, which is non-absorbent of microwave, instead of microwave absorbent, was entwined by a sample tube, like coil, and in Example 1 the tube was not intensively irradiated with microwave while in Example 2 it was intensively irradiated. In Example 3 ferrite, the microwave absorbent, was entwined by a sample tube like coil, while in Example 4 a rod of carbon, made by concentrated sintering of graphite, was used as microwave absorbent. The supersonic nebulizer used in Example 1 was a US CETAC-made Model U-5000At+.

The nebulization efficiency was calculated in terms of the percentage of the quantity of the sample which actually entered the analyzer, out of the total which issued from the nebulizer. Table 1

According to Example 1 and Comparative Example 1 , of Table 1 above, which respectively indicate the efficiency in nebulization of distilled water of the conventional supersonic nebuilizer and the microwave nebulizer of the present invention, the efficiency of the microwave nebulizer of the present invention is by far the better than that of the conventional supersonic nebulizer. Thus, it has been demonstrated that nebulization after vaporization by heating excels nebulization by oscillation of piezoelectric materials in nebulization efficiency. It has also been learned that Example 2, the case of intensive irradiation with microwave, is better than Example 1, in which intensive irradiation with microwave was omitted. And according to Examples 2, 3, and 4 the microwave nebulizer using an absorbent showed better efficiency than did the others which used non-absorbent Teflon. These results prove that the absorbent, absorbing microwave and generating heat, leads to better vaporization. According to Examples 3 and 4 ferrite and graphite used as absorbent have similar efficiency in nebulization.

Example 5 and Comparative Example 2

In order to measure the nebulization efficiency relative to different viscidity 3M sulfuric acid was used. In Example 5 ferrite was used as microwave absorbent, and the supersonic nebulizer used in Comparative Example 2 was US CETAC made Model U-5000T+. Table 2

In Example 2 and Comparative Example 2, of Table 2. indicating the efficiency in nebulization of 3M sulfuric acid with a rather high relative viscidity of 1.75 by the supersonic nebulizer and the microwave nubulizer of the present invention, show that the supersonic nebulizer, which makes use of the oscillation of piezoelectric material, yields an aerosol of the more uneven and the larger-sized particles, the greater quantity getting removed, as the larger the viscidity of the sample is, the resultant nebulization efficiency, therefore, the more inferior. In contrast, in the case of the microwave nebulizer of the present invention, first heating and vaporizing and next nebulizing, the efficiency remains high regardless of the viscidity of the sample.

The present inventor, thus inventing a microwave nebulizer which, free of the influence of the sample^"s different kinds and degrees of viscidity, has a far better nebulization efficiency than the supersonic nebulizer, has made it possible to increase the quantity of the sample that reaches the analyzer, that is, improved the nebulization efficiency, whereby lowering the analyzer^'s bottom limit of detection, while facilitating analyses without bothering separate complicated processes of concentrating the samples.

Claims

WHAT IS CLAIMED IS:

1. An injector of samples having the characteristic of nebulizing samples in liquid solution after it is first vaporized.

2. The injector of samples according to Claim 1, comprising a microwave nebulizer which vaporizes sample solution by a use of microwave.

3. The injector of samples according to Claim 2, comprising the microwave nebulizer which vaporizes sample solution by intensively irradiating it with microwave.

4. The injector of samples according to Claim 2 or Claim 3, comprising the microwave nebulizer which has a microwave absorbent stored in a microwave cavity.

5. The injector of samples according to Claim 4, comprising the microwave nebulizer in which the microwave absorbent is ferrite or a carbon rod.

6. The injector of samples according to Claim 4. comprising the microwave nebulizer in which a sample tube entwines a microwave absorbent like coil.

7. The injector of samples according to Claim 1 or Claim 2, comprising a condenser of thermoelectric cooling style.

8. The injector of samples according to Claim 1 or Claim 2, wherein gas cooled in advance is injected in the tangential direction so that it may simultaneously carry samples, cool solvents, and at the same time minimize memory effects by removing residues of the solvent sticking to the walls of the vessels.

9. A method for analyzing samples, comprising a step of vaporizing the sample, a step of nebulizing the sample solution to inject a vaporized sample solution into a condenser, a step of cooling the solvent contained in the sample solution nebulized into the said condenser down below its melting point, and a step of exhausting the cooled solvent and carrying the desolvated sample into a sample analyzing device.

10. The method for analyzing samples according to Claim 9, wherein the sample solution is vaporized by the use of microwave.

11. The method for analyzing samples according to Claim 10, wherein the sample solution is vaporized by intensive irradiation with microwave.

12. The method for analyzing samples according to Claim 10, wherein the sample solution is heated and vaporized by the use of a microwave absorbent.

13. The method for analyzing samples according to Claim 12, wherein the microwave absorbent is ferrite or a carbon rod.

14. The method for analyzing samples according to Claim 12, wherein the sample tube entwines the microwave absorbent like coil.

15. The method for analyzing samples according to Claim 9, wherein the step of cooling is performed in a style of thermoelectric cooling.

16. The method for analyzing samples according to Claim 9, wherein the gas cooled in advance is injected in the tangential direction so that it may carry desolvated sample, cool it, and minimize the memory effect of the residue of the solvent sticking to the walls of the vessels by removing it on the way.