JP2002257698A - Method of cocentrating liquid sample - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of concentrating a solute in a solution sample by means of a microwave heating, capable of performing the concentration of the same in of a high concentrating ratio a short time. SOLUTION: When the solution sample 2 held inside a vessel 3 with an open mouth is evapolated by a microwave heating 10 to have its solvent removed, a dielectric substance such as water having a high permittivity is brought into contact with at least a part of the external surface of the vessel to be also heated with the microwave.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for concentrating a liquid sample and an apparatus used for the method. More specifically, for example, the present invention relates to a concentration method using microwave heating which is useful as a pre-concentration when performing micro-analysis on a liquid sample, and a microwave heating apparatus suitably used for the concentration method.

[0002]

2. Description of the Related Art In recent years, in the field of semiconductor materials and the like, there is a high demand for purity of raw materials and products, and it is important to analyze impurities contained in a very small amount with high accuracy. For this purpose, for example, for a solution sample, the purpose is to remove matrix substances that may interfere with quantification, to make the analysis target component fall within the quantification limit of instrumental analysis, and to increase measurement accuracy. Then, an operation of concentrating the measurement sample (preconcentration) is performed.

As one means of preconcentration of a liquid sample, there is a method of removing a solvent or a dispersion medium by evaporating the solvent or the dispersion medium. When the solvent or the dispersion medium of the liquid sample is a dielectric having a high relative dielectric constant such as water, a simple method is to remove the solvent or the dispersion medium by evaporating the solvent or the dispersion medium using microwave heating, and to concentrate the solution. There is a known way to do this. This method utilizes the fact that a substance having a large relative dielectric constant, such as water, easily generates heat by a high-frequency electric field generated by microwave irradiation, and is characterized in that a concentration operation can be easily performed. In addition, in general, in the method, when a sample is heated, a dangerous gas such as a flammable gas or an acid is often generated. Therefore, in order to discharge these gases safely, heating is performed in a container. In general, the generated gas is isolated and discharged so as not to diffuse into the atmosphere.

For example, Japanese Patent Application Laid-Open No. Hei 6-82349 discloses that a solution sample in a sealable processing vessel having an inert gas supply pipe and an exhaust pipe is irradiated with microwaves to evaporate a solvent. A heat treatment apparatus for performing concentration or incineration processing by discharging vaporized solvent vapor with an inert gas to the outside of the system from an exhaust pipe has been disclosed. It is possible to carry out treatment while discharging safely and preventing contamination from outside. In addition, when using the device, the liquid sample is placed in a graduated test tube, and inserted and arranged in the processing container to perform concentration or incineration treatment.
It is also possible to perform a dilution operation after the treatment using the test tube.

[0005]

However, in the method of concentrating in a container using microwave heating, the concentration of the sample decreases with the concentration, and the rate of concentration decreases drastically. When concentrated, a phenomenon occurs in which the liquid volume does not decrease to 3 ml or less even with time. Anal. Chem., 72 , (13), 2908-2913 (200)
0)｝.

Accordingly, an object of the present invention is to provide a method capable of concentrating a liquid sample at a high magnification in a short time by utilizing microwave heating.

[0007]

The inventor of the present invention concludes that the concentration stops in the conventional method because the solvent or dispersion medium once vaporized is condensed before being discharged out of the system, and propagates along the container wall. I think that it may be due to returning (reflux),
Using an apparatus capable of introducing an inert gas as described in the above-mentioned publication, an attempt was made to directly blow the inert gas onto the liquid surface to promote evaporation. However, in this case, although the above-mentioned reflux did not occur, the liquid volume was reduced and the concentration rate was drastically reduced, so that the intended purpose could not be achieved.

It is considered that the cause of the reduction in the concentration rate is that a sufficient amount of heat cannot be obtained because the amount of the solvent or the dispersing medium as the heating element decreases, and it is necessary to further perform heating from the outside of the container to promote evaporation. I thought there was. As a result of various studies on a method of effectively heating the sample,
In the case where the container has a double structure, and the refluxed solvent or the like is allowed to collect outside the sample without returning to the sample, it has been found that the liquid sample can be dried in a short time, and the present invention is completed. Reached.

That is, a first aspect of the present invention is a liquid sample held in an open container, which is concentrated in a solvent or dispersion medium made of a dielectric having a higher relative dielectric constant than the constituent material of the open container. In the method of concentrating the concentrated target by microwave heating a solution sample in which a solute as a target substance is dissolved and evaporating and removing a solvent or a dispersion medium of the liquid sample, the liquid sample is heated by microwave. Contacting at least a part of the outer surface of the open container with a dielectric having a higher relative dielectric constant than the constituent material of the open container, and simultaneously microwave-heating the dielectric, thereby concentrating the liquid sample. Is the way.

[0010] In the enrichment method of the present invention, an open container holding a liquid sample is disposed inside a closed container having a gas inlet and a gas outlet, and a space between the inner surface of the closed container and the outer surface of the open container is provided. In the space, a dielectric having a higher relative dielectric constant than the constituent material of the open container is interposed so as to be in close contact with at least a part of the outer surface of the open container, and the dielectric is microwave-heated simultaneously with the liquid sample. Thereby, the concentration operation can be performed safely while preventing contamination from the outside. Further, the gas in the closed container is discharged by sucking from the gas discharge hole or introducing gas from the gas introduction hole during microwave heating, and the solvent or the dispersion medium evaporated by the microwave heating is removed. At least a portion is condensed, and when obtained, the condensate is interposed in a space between the inner surface of the closed container and the outer surface of the open container so as to be in close contact with at least a part of the outer surface of the open container, so that the concentration can be performed in a shorter time. It is possible to do. Further, in this case, there is no need to separately prepare a dielectric having a higher relative dielectric constant than the constituent material of the open container.

In the enrichment method of the present invention, since the open container holding the liquid sample is in contact with the dielectric having a high relative dielectric constant, which easily generates heat by microwave heating, the solvent or the dispersion medium is reduced to reduce the liquid. Even if the calorific value of the sample itself decreases, the heat necessary for continuing the concentration continues to be supplied by heat conduction, and it is considered that the concentration efficiency does not decrease.

[0012] The present invention also relates to a closed container for disposing an open container holding a liquid sample therein, the container having a gas inlet and a gas outlet, and a solvent or dispersion generated from the liquid sample. A steam condensing section for condensing the vapor of the medium, and a closed container having a condensed liquid holding section for collecting the condensed liquid condensed in the steam condensing section and holding the condensed liquid in contact with the outer surface of the open container; An apparatus body having a container holding chamber for holding the covered container, a liquid sample in the covered container arranged in the container holding chamber, and a condensate present between the inner surface of the covered container and the outer surface of the open container. A microwave generating device for performing microwave heating.

By using the apparatus of the present invention, the concentration method of the present invention can be carried out simply and efficiently.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The concentration method of the present invention utilizes a microwave heating method. Here, the microwave heating method is
A type of electromagnetic wave heating, in which a high-frequency electric field rotates an electric dipole generated inside a dielectric by high frequency, causing friction between molecules, and heating using the heat generated by the friction. This is a heating method using radio waves as a method for creating an electric field. In microwave heating, usually, a magnetron is mainly used and 2450 MHz, 91
Heating is performed using a frequency of 5 MHz and a waveguide and oven are used. In addition, a stirring fan may be used in order to uniformly irradiate the radio waves.

In the concentration method of the present invention, the liquid sample held in the open container is concentrated using the microwave heating as described above. Holding a liquid sample in an open container
This is for diffusing and removing the solvent or the dispersion medium that has been heated and vaporized. The material of the open container is not particularly limited as long as it is an insulator. However, from the viewpoint of preventing the material itself from being heated to a high temperature or being deformed, the relative permittivity is small, particularly the relative permittivity ( epsilon _r) is 15 or less, it is preferable that further consists of 10 or less of the dielectric. In addition, borosilicate glass (ε _r = 4.5 to 5.0) and alumina porcelain (ε _r = 9.3) can also be used. However, from the viewpoint that impurities are hardly eluted from a container into a solution, quartz glass (ε _r = 9.3) is used. ε _r = 3.5 to 4.5) or polytetrafluoroethylene (ε _r = 2.1), polyvinylidene fluoride (ε _r = 8.4)
It is particularly preferable to use a fluororesin.

The closed container and the open container need not always be separate from each other, and a double-structured closed container in which the open container and the open container are integrated may be used.

In the enrichment method of the present invention, since the above-described microwave heating is used, the solvent or dispersion medium of the liquid sample to be used has a higher relative dielectric constant than that of the material constituting the open container holding the liquid sample, preferably. Needs to have a relative dielectric constant of 20 or more. The solvent or dispersion medium of the applicable liquid sample is not particularly limited as long as the above conditions are satisfied,
Water or a known organic solvent may be used. As an example of a solvent or dispersion medium that can be suitably used in the present invention, water (ε _r = 8
1); ketones such as acetone (ε _r = 20.7), methanol (ε _r = 32.6), ethanol (ε _r = 24.
And alcohols such as 3). These may be used alone or as a mixture of a plurality of types. Among these, water has a high boiling point and is difficult to evaporate by other methods, but easily becomes steam by microwave heating.Therefore, the method of the present invention uses water or a mixture of water and a water-soluble organic solvent as a solvent. Or, it is most effective to apply to a sample to be used as a dispersion medium.

The solute or suspension to be concentrated in the liquid sample is not particularly limited, and is appropriately determined according to the purpose. When the liquid sample is an aqueous solution, it is often a salt and is often dissolved in the form of ions. From the viewpoint of concentration efficiency, the solute or suspension that is the concentration target is preferably less volatile than the solvent or the dispersion medium, but also has a high boiling point using a collector even when it has volatility. By forming a complex, concentration becomes possible. For example, after a required amount of mannitol is added to concentrate boron to form a boron-mannitol complex, concentration can be performed.

The liquid sample may contain other substances such as various acids, alkalis and salts in addition to the substance to be concentrated.

In the concentration method of the present invention, when the liquid sample held in the open container is microwave-heated, a dielectric having a higher relative dielectric constant than the constituent material of the open container (hereinafter referred to as an external heating dielectric). The feature of the present invention is that the dielectric material is brought into contact with at least a part of the outer surface of the open container, and the dielectric material is simultaneously microwave-heated.
The external heating dielectric is brought into contact with the open container, and the microwave is heated together to transfer the heat generated from the external heating dielectric to the liquid sample. Can be continuously evaporated.

The dielectric for external heating is not particularly limited as long as its dielectric constant is higher than that of the constituent material of the open container. From the viewpoint of its heating effect, the dielectric having a dielectric constant of 20 or more is used. It is preferred that Specific examples of the external heating dielectric that can be preferably used are the same as those exemplified as the suitable solvent or dispersion medium for the liquid sample, titanium oxide (ε _r = 80), and barium titanate (ε). _r = 1700).

In the concentration method of the present invention, the solvent or dispersion medium once evaporated from the liquid sample can be condensed, and the obtained condensate can be used as a dielectric for external heating. To use the condensate as an external heating dielectric,
For example, an open container holding a liquid sample is placed inside a covered container, the vapor of a solvent or a dispersion medium generated by microwave heating is condensed on the upper inner wall surface of the covered container, and the condensate is passed through the wall surface to a lower portion of the closed container. Then, the condensed liquid may be guided to the space between the open container and the outer surface of the open container.

In the above-mentioned closed container, the lid is detachable so that the open container holding the liquid sample can be taken in and out, and a gas is generated by heating or a pressurized state by expansion of the gas inside. It is preferable to provide an exhaust hole for sucking and exhausting the internal gas in order to keep the pressure equal to the outside and to keep the pressure equal to the outside or to promote the evaporation of the solvent or the dispersion medium. In addition, in the case of suction and exhaust, a gas introduction hole for introducing a gas such as an inert gas supplied from the atmosphere or the outside into the closed container is provided to prevent the inside from being excessively decompressed. Preferably, it is provided. When both the gas introduction hole and the exhaust hole are provided, even if an inert gas or the like is forcibly introduced from the outside through the gas introduction hole and the gas in the covered container is exhausted from the exhaust hole, the same as the above-described suction exhaust. The effect of can be obtained.

The material of the closed container is not particularly limited, but is preferably the same as that of the open container for the same reason as described above. The size of the lid is not particularly limited, but the shape of the lid is such that condensed liquid formed on the inner surface of the lid does not return to the inside of the open container, but wraps around the side of the lid to cover the bottom of the closed container, that is, the outside of the open container. It is desirable that the shape is, for example, a dome shape in order to collect the water. Further, in order to enhance the external heating effect, the space volume between the inner surface of the closed container and the outer surface of the open container, which is formed when the open container is placed on the inner bottom thereof, is particularly 20 to 30% of the volume of the closed container. The height of the open container is preferably such that the condensate remaining in this space does not flow into the open container.

The concentration method of the present invention can be suitably performed using the above-described microwave heating device of the present invention.
Hereinafter, the concentration operation using the microwave heating device of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic diagram of a typical microwave heating device 1 of the present invention. The microwave heating device 1 includes:
A container 4 for placing the open container 3 holding the liquid sample 2 therein, an apparatus body (oven) 6 having a container holding chamber 5 for holding the container, and a container holding chamber 5 Microwave heating of the liquid sample 2 in the placed covered container 4 and the condensate 8 existing in the space between the inner surface of the covered container and the outer surface of the open container (hereinafter, also referred to as the external heating dielectric holding space). And a microwave generating means 7 for performing the operation.

The covered container 4 comprises a container body 4a and a lid 4b.
The open container 3 can be installed inside the container body 4a by opening and closing the lid 4b. It is preferable that the container body has a fixing means such as a concave portion into which the open container 3 is fitted or a fall prevention wall in order to prevent the open container 3 from falling. Moreover, what was molded so that the covered container main body 4a and the open container 3 were integrated can also be used.

The lid 4b is provided with a gas introduction hole 4d and a gas discharge hole 4e. The gas introduction hole 4d may be provided with a filter for preventing contamination or connected to a clean inert gas source. The gas in the covered container 4 is evacuated to the outside of the apparatus via an exhaust pipe 9 connected to the gas discharge hole 4e (the exhaust pipe 9 extends through the apparatus main body 6 to the outside of the apparatus). The air is sucked and discharged by an exhaust means (not shown) such as a pump or an aspirator, and outside air or an inert gas is introduced into the closed container through the gas introduction hole 4d (gas replacement method A), or the gas is introduced into the gas introduction hole 4d. Outside air or an inert gas is supplied into the covered container 4 via a pipe (not shown) connected so as not to penetrate the introduction hole 4d, and the gas is supplied via an exhaust pipe 9 connected to the gas discharge hole 4e. By discharging the gas in the covered container to the outside of the apparatus (gas replacement method B), the gas in the covered container can be replaced. At this time, if the exhaust gas contains acid or alkali mist, etc., the exhaust gas is absorbed by water, etc.
What is necessary is just to neutralize.

When the gas replacement method B is adopted,
When gas is blown in the vicinity of the open container using a pipe penetrating the gas introduction hole 4d, vapor such as a solvent is discharged out of the system without being condensed, and the condensate is used as a dielectric for external heating. It should be noted that the enrichment method of the invention cannot be performed.

The apparatus main body 6 has a door (not shown), which can be opened and closed to set the covered container 4 in the container holding chamber 5.

FIG. 1 shows a mode in which the microwave generating means 7 is arranged on the ceiling of the container holding chamber 5 and the microwave 10 is irradiated from above, but the microwave is applied to the solution through a waveguide. Since the irradiation can be performed on a sample or the like, the position can be arbitrarily changed.

At the time of concentration, first, the open container 3 holding the liquid sample 2 is set in the covered container 4 and then set in the container holding chamber 5 of the apparatus main body 6 and, if necessary, the gas replacement is performed. The microwave generated by the microwave generating means 7 may be applied to the liquid sample 2 and the external heating dielectric holding space while performing the method A or B. The solution sample generates heat by microwave irradiation, the solvent is vaporized, and the vapor is led to the upper part. Since the covered container 4 itself does not easily generate heat and has a sufficient height, the upper part thereof becomes a vapor condensing part 4c for condensing the vapor of the solvent or the dispersion medium generated from the liquid sample, The condensate naturally travels along the wall and collects in the space between the lower opening container 3. The collected condensate 8 (that is, the external heating dielectric) is heated by microwaves and generates heat, and the generated heat is transmitted to the solution sample via the open container by heat conduction, and the concentration efficiency is not reduced. Can be concentrated to dryness.

[0033]

EXAMPLES The present invention will be described more specifically with reference to the following Examples and Comparative Examples, but the present invention is not limited to these Examples.

Example 1 An aqueous solution in which beryllium was dissolved at 1 ppb was concentrated using a microwave heating apparatus having the same structure as that shown in FIG. The concentration was performed by placing 10 ml of the sample solution in a Teflon (registered trademark) open container having an internal volume of 23 ml, placing the sample solution in a Teflon-covered container, setting it in a microwave heating apparatus, and then setting it at 2450 MHz (output 300 W). ) For 1 hour. During heating, suction was performed from the exhaust pipe using a vacuum pump with an exhaust speed of 10 l / min. At this time, a Teflon filter was connected to the gas vent so that the same amount of filtered air as that exhausted was introduced. Of course, it has been confirmed in advance that there is no beryllium from the atmosphere during operation.

When the inside of the covered container was observed after the heat treatment,
Water had accumulated between the open container. In addition, the solvent of the solution sample was completely lost and could not be aspirated with a pipette. Thereafter, the open container was taken out, and 0.5 ml of 1% nitric acid was added to the dried product to collect a solution. When this solution was analyzed by inductively coupled plasma mass spectrometry (ICP-MS), the beryllium concentration was 20 ppb, and the 1 ppb aqueous solution was changed from 10 ml to 0.5 ml.
There was no disappearance of beryllium during the double concentration operation, and it was confirmed that the solution was dried.

Comparative Example 1 In Example 1, instead of performing suction during heating, a gas introduction pipe was inserted through the gas introduction hole so that the tip was near the bottom of the covered container, and nitrogen gas was added at about 0.2 / Concentration was performed in the same manner as in Example 1 except that the mixture was introduced at a flow rate of min.

When the inside of the covered container was observed after the heat treatment,
The coagulation liquid did not accumulate between the open container. Also,
The solution sample remained in the open container, and the amount was confirmed by suction with a pipette.
It was found that the measurement with a large error had to be carried out in the operation of recovering with a ml solution.

Comparative Example 2 Heating was carried out in the same manner as in Comparative Example 1 except that the heating time was changed to 4 hours. After observing the inside of the covered container after the heat treatment,
About 0.25 ml of the solution sample remained in the open container.

COMPARATIVE EXAMPLE 3 An open container was not placed inside, and the upper lid was further removed with only a closed container, and concentration was performed by microwave. Heated for 4 hours,
About 0.5 ml of the solution sample remained.

[0040]

According to the concentrating method of the present invention, a liquid sample such as an aqueous solution or a suspension is easily and quickly evaporated and removed in a short time without being contaminated from the outside. Alternatively, the suspension can be concentrated. Moreover, in the conventional concentration method using microwave heating, the concentration efficiency decreases with the decrease in the amount of the solvent and the like, and it is difficult to perform high-magnification concentration.On the other hand, in the concentration method of the present invention, Such a decrease in concentration efficiency does not occur. Therefore, the concentration method of the present invention can be suitably used as a pre-concentration method when performing trace analysis.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a typical microwave heating device of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Microwave heating apparatus 2 ... Solution sample 3 ... Open container 4 ... Covered container 4a ... Container body 4b ... Cover 4c ... Steam condensing part 4d ... ..Gas introduction hole 4e ... gas discharge hole 5 ... container holding chamber 6 ... device body 7 ... microwave generation means 8 ... condensate 9 ... exhaust pipe 10 ... micro wave

Claims (4)

[The claims] 1. A liquid sample held in an open container, wherein a substance to be concentrated is dissolved in a solvent or dispersion medium made of a dielectric having a higher relative dielectric constant than the constituent material of the open container. Alternatively, in the method of concentrating the concentrated object by microwave heating a suspended liquid sample and removing the solvent or dispersion medium of the liquid sample by evaporating the liquid sample, when the liquid sample is heated by microwave, The method for concentrating a liquid sample according to claim 1, wherein a dielectric having a higher relative dielectric constant than a constituent material of the container is brought into contact with at least a part of the outer surface of the open container, and the dielectric is simultaneously microwave-heated. 2. An open container holding a liquid sample is disposed inside a covered container having a gas introduction hole and a gas discharge hole,
In the space between the inner surface of the open container and the outer surface of the open container, a dielectric having a higher relative dielectric constant than the constituent material of the open container is interposed so as to be in close contact with at least a part of the outer surface of the open container, The method according to claim 1, wherein the dielectric is heated by microwaves simultaneously with the liquid sample. 3. A method of sucking gas from the gas discharge hole or introducing gas from the gas introduction hole during microwave heating to discharge the gas in the closed container, and removing the solvent or the solvent evaporated by microwave heating. At least a portion of the dispersion medium is condensed, and the obtained condensate is interposed in a space between the inner surface of the closed container and the outer surface of the open container so as to be in close contact with at least a part of the outer surface of the open container. Item 3. The concentration method according to Item 2. 4. A closed container for arranging an open container holding a liquid sample therein, the gas container having a gas introduction hole and a gas discharge hole for condensing a vapor of a solvent or a dispersion medium generated from the liquid sample. A closed vessel having a steam condensing section, and a condensed liquid holding section for collecting the condensed liquid condensed in the steam condensing section and holding the condensed liquid in contact with the outer surface of the open container; and for holding the covered container. A device main body having a container holding chamber, and a microwave for microwave heating a liquid sample in a covered container disposed in the container holding chamber and a condensate existing between the inner surface of the covered container and the outer surface of the open container. A microwave heating device, comprising: a wave generation unit.