JP2890730B2 - Method for measuring the number of fine particles in the test solution - Google Patents

Description

The present invention relates to a method for measuring the number of fine particles in a test solution. The test solution whose number of microparticles is known by this measurement method is used to calibrate the microparticle counter.

[Conventional technology]

The particle counter measures the number of particles in a liquid, such as water used in an integrated circuit manufacturing process, an organic solvent, water used in a pharmaceutical manufacturing process, physiological saline,
It is a measuring instrument used to control the number of fine particles contained in a buffer solution or the like, or lubricating oil, hydraulic oil, engine oil or the like used in various machines.

However, in the past, there is no calibration solution containing fine particles at a known density necessary to calibrate the measurement value of such a particle counter, and thus the measurement value of the particle counter is not absolute. It was a relative thing. Therefore, if the number of the microparticles can be accurately measured for a known amount of the test solution containing the microparticles, the microparticle counter can be strictly calibrated using the test solution, and the measured value of the microparticle counter can be further measured. Can be made absolute.

Under such circumstances, a method for measuring the number of fine particles in a test solution has been proposed as Japanese Patent Application No. 63-193003. This measurement method is a method in which a test solution containing a plurality of fine particles is dropped in a known amount onto a hydrophilic substrate, and after the test solution is dried, the number of fine particles remaining on the substrate is counted. . In this measuring method, in order to accurately count the number of fine particles so as not to omit counting, it is actually necessary to take a micrograph and count the number of fine particles on the photograph.

[Problems to be solved by the invention]

However, in the above-described measurement method, the fine particles are left over the entire area occupied by the test liquid droplets formed on the substrate first. Therefore, when the particle diameter of the fine particles in the test liquid is small, The number of fields required for observing all of the fine particles with a microscope or the number of photographs required for taking a microscopic photograph of all of the fine particles is considerably large.

This is because the smaller the particle size of the fine particles in the test solution,
Although it is necessary to increase the magnification of the microscope to enlarge the microparticle image to such an extent that it can be recognized as a single particle by the naked eye, if the magnification of the microscope is increased, the area of one field of view is naturally reduced as a result. In addition, when the amount of the test solution collected is very small, the amount of the test solution cannot be accurately controlled or weighed, so that the droplet formed by reducing the amount of the test solution dropped on the substrate is Is to cause a large error.

As described above, the measurement area in which the number of microparticles remains after the test solution is dried is large, and the number of fields of view or the number of photographs required for counting all of the microparticles is increased. However, there is a problem that the obtained measurement values vary greatly.

The present invention has been made in order to solve the above problems, and even when the particle diameter of the fine particles in the test solution is small, it is possible to accurately measure the number of the fine particles by a microscope. The aim is to provide a method that can.

[Means for solving the problem]

In the method for measuring the number of fine particles in a test solution of the present invention, a test solution containing a plurality of fine particles is dropped on a grounded substrate, and the droplets of the test solution on the substrate are evaporated to reduce the droplets. And drying, and then counting the number of fine particles remaining on the substrate.

According to such a measurement method, the diameter of the droplet is reduced as the dispersion medium liquid evaporates from the droplet of the test liquid formed on the grounded substrate, but the fine particles are less mobile. It is in a state where it is sufficiently high and moves so that it always exists in the droplet, and as a result, the fine particles concentrate as the diameter of the droplet decreases, and finally the fine particles concentrate in a small area Will remain. Therefore, by counting the number of fine particles with a microscope, for example, using this area as a measurement area, the number of fine particles can be accurately measured for the test solution.

 Hereinafter, the present invention will be described specifically.

The test solution to which the measurement method of the present invention is applied is a dispersion of fine particles whose number is to be measured, for example, 1 × 10 ³ to
Fine particles are dispersed in a liquid dispersion medium at a density of 1 × 10 ⁸ particles / ml.

The fine particles in the assay solution are not particularly limited,
Spherical fine particles are preferred. Specific examples of the fine particles include polymer particles made of a polymer such as a styrene resin such as polystyrene, an acrylic resin such as polymethyl methacrylate, polyethylene, nylon, phenol resin, and polybenzguanamine; and gold and silver. And metal particles made of metals such as copper and nickel; and inorganic particles made of other inorganic materials such as silica, titania and zirconia. The fine particles of the assay liquid are preferably polymer particles made of a polystyrene-based resin having a particularly high particle size uniformity and a specified particle size.

The particle diameter of the fine particles to which the method of the present invention is applied is not particularly limited as long as the fine particles move so as to stay in the droplet when the diameter of the droplet is reduced on the substrate. However, the measurement method of the present invention is advantageously applied to fine particles having a particle size in the range of 0.05 to 20 μm. In particular, the measurement method of the present invention has a particle size of 0.5 μm or less, which is difficult to measure accurately according to the conventional measurement method because of large variations in the measured values, and especially fine particles having a particle size of 0.35 μm or less. This is useful in that the number can be measured.

When the particle size of the fine particles is less than 0.05 μm,
For accurate counting, it is necessary to increase the magnification of the microscope considerably. On the other hand, when the particle size of the fine particles exceeds 20 μm, even if the fine particles are overlapped to some extent, they can be counted, so that the method of the present invention is not necessarily applied.

The liquid dispersion medium of the test solution is preferably water, but methanol, ethanol, isopropanol, acetone,
Organic solvents such as toluene, xylene, cellosolve, cellosolve acetate, and aqueous electrolytes may be used.

In relation to fine particles, the liquid dispersion medium must not dissolve or decompose the fine particles. For this reason, as the fine particles, generally insoluble and non-degradable crosslinked polymer particles or silica spherical particles may be used.

It is necessary that the liquid dispersion medium for the assay solution is one from which impurity particles (impurities in the assay solution) have been sufficiently removed. It is also preferable that the fine particles are sufficiently uniformly and stably dispersed in the assay solution. To improve the dispersion stability of the fine particles in the assay solution, an electrolyte, an emulsifier,
Additives such as dispersion stabilizers can be added to the assay solution. When the concentration of the additive is high, by drying the droplet,
Impurity particles may be formed, but even if such impure particles are formed, by the impure particles,
It suffices that the microscopic counting of the target fine particles is not impaired. From such a viewpoint, the above additives are generally used in an amount of 1% by weight or less, preferably about 1 ppm to 0.1% by weight or less of the assay solution.

Specific examples of the above electrolyte include salts such as sodium chloride, potassium chloride, sodium phosphate, potassium carbonate, and sodium borate; and acids such as hydrochloric acid, sulfuric acid, hydrofluoric acid, and acetic acid. Specific examples of the emulsifier include Sodium dodecylbenzenesulfonate, sodium laurate, polyoxyethylene-nonylphenyl ether,
Polyoxyethylene-polyoxypropylene block copolymer and the like, and specific examples of the dispersion stabilizer include polyvinyl alcohol, polyvinyl pyrrolidone,
Carboxymethyl cellulose, polyoxypropylene,
Polyvinyl acetate and the like can be mentioned, but in practice it is appropriately selected depending on the type of fine particles and dispersion medium used.

The measuring method according to the present invention is performed as follows. That is, first, a test solution is collected in an amount of 0.1 μl to 1 ml. The amount of this test solution must be accurately measured. For this reason, it is preferable to use a microsyringe or micropipette for collection, and it is preferable to test in advance the relationship between the actually used microsyringe and the scale of the micropipette, and the amount of liquid actually collected. . When using a microsyringe, a Teflon tube or the like can be attached to the needle in order to prevent deposition of particles on the needle.

On the other hand, as shown in FIG. 1, a flat conductive substrate 2 is held in a horizontal state on an electrically grounded ground plate 1, and As described above, a known amount of the test solution is dropped, thereby forming a test solution droplet D on the substrate 2.

Here, various substrates can be used without any particular limitation. In particular, those having low wettability of the liquid dispersion medium of the test liquid, that is, the contact angle of the liquid dispersion medium of the test liquid to be used is low. It is preferable to use a substrate having an angle of 90 degrees or more. By using such a substrate,
In the drying process, the droplets of the test liquid are surely and sufficiently reduced, the area where the fine particles remain is sufficiently small, and eventually the degree of concentration of the fine particles is sufficiently large, and the intended measurement is reliably performed. can do.

Specifically, for example, when the liquid dispersion medium of the test solution is water, a silicon wafer, a metal substrate, or the like can be used as the substrate, but a silicon wafer having a mirror surface is preferable. The surface of the substrate is preferably hydrophobic. The degree of hydrophobicity is such that the contact angle of water is 90
It is desirable that the temperature be equal to or higher. In order to impart sufficient hydrophobicity to the surface of the substrate, a means for oxidizing the surface, a means for removing an oxide film present on the surface by washing it with hydrofluoric acid or the like, a hydrophobic substance such as carbon may be used. Means for vapor deposition on the surface and other means can be used.

Further, the ground resistance of the substrate on which the test solution is dropped is desirably 15Ω or less, particularly preferably 8Ω or less. In order to realize this state, appropriate means can be used.

The substrate obtained in this way, on which the droplet D is present,
For example, the droplet D is kept horizontal in a desiccator where the humidity is constant and there is no influence of static electricity or ventilation, and the diameter of the droplet D is reduced by evaporating the liquid of the droplet D over a certain period of time. Allow to dry. This drying step
For example, the drying may be performed at a drying temperature of 10 to 70 ° C., a relative humidity of 0 to 60%, and a drying time of 5 minutes to 2 hours.

In the step of drying the droplets on the substrate described above, it is not always necessary to ground the substrate, but by grounding it, the effects of the present invention can be reliably obtained.

As described above, the diameter of the droplet is gradually reduced from the diameter at the time of dropping due to the evaporation of the liquid droplet. Accordingly, the fine particles in the droplet move due to the affinity with the liquid dispersion medium so as to remain in the reduced droplet. That is, as the outer surface of the droplet moves inward, the fine particles in this portion also move inward and concentrate. And, as a result, when all of the liquid dispersion medium is finally dried,
Fine particles remain in a state of being concentrated in a certain limited narrow area on the substrate.

The concentration of the fine particles in the droplet due to the reduction of the droplet is because the substrate on which the test solution is dropped is grounded and the electric charge on the substrate is removed. This is because the electric interaction is reduced and the mobility of the fine particles is increased. Moreover, according to the measuring method of the present invention, such a state that the fine particles have high mobility can be achieved by a very simple means of simply grounding the substrate.

As described above, the liquid dispersion medium of the droplets is dried and removed, and as a result, the fine particles remaining on the substrate are counted using a magnifying observation means such as a microscope. In order to eliminate the causes of errors such as omission of counting of fine particles and counting of foreign particles, it is desirable to take a microscopic photograph and count the fine particles photographed in this photograph. Here, as the microscope, it is preferable to use a scanning electron microscope having high resolution when the particle diameter of the fine particles is 1 μm or less.

Thus, in the method of the present invention, since the measurement region in which the fine particles remain as described above is much smaller than the region occupied by the initially formed droplet, the magnification of the microscope is increased. Even if the area covered by one field of view is small, the number of fields of view or the number of micrographs required to cover the entire measurement area does not increase, and the particle size of the fine particles decreases.
Even when it is 0.5 μm or less, the number of micrographs can be about 16 or less, and as a result, the number of fine particles can be accurately measured.

〔Example〕

Hereinafter, examples of the present invention will be described, but the present invention is not limited thereto.

Example 1 A test solution was prepared by dispersing spherical fine particles of a polystyrene resin having a particle size of 0.144 μm in ultrapure water so as to have a density of about 1 × 10 ⁶ particles / ml.

On the other hand, a substrate made of an FZ crystal silicon wafer having an oxide film (manufactured by Nippon Silicone Co., Ltd.) and having a hydrophobic surface with a water contact angle of about 100 degrees is placed on an earth plate as shown in FIG. The test solution was fixed horizontally, and 1 μl of the above-mentioned test solution was dropped on a top surface of the substrate using a micro syringe with a Teflon tube to form a droplet. The diameter of this droplet is about 1mm
Met.

This substrate was held horizontally in an anti-static desiccator for 10 minutes to reduce the diameter of the droplet, and finally dried.The area where the fine particles remained was contained in a circular area having a diameter of about 0.1 mm. Was.

Gold-palladium was vapor-deposited to a thickness of 300 ° on the substrate thus obtained, and then a micrograph was taken with a scanning electron microscope at a magnification of 3000 times in a measurement region where fine particles remained. The number of photographs required to capture the entire measurement area was 16 sheets.

The obtained photographs were arranged, and the number of microparticles present in 1 μl of the assay solution was determined by counting all the microparticles on the photograph.

As a result of repeating the above measurement operation a total of 10 times, the average number of fine particles obtained was 987 particles / μl, the standard deviation of the number of fine particles was 42 particles / μl, and the coefficient of variation (standard deviation / average value × 100).
Was 4.3%.

Comparative Example 1 1 μl of the same test solution was dropped in the same manner as in Example 1 except that the substrate was fixed horizontally on a sample base not grounded, to form droplets.

This substrate was held horizontally in an antistatic desiccator for 10 minutes to dry droplets in the same manner as in Example 1.
The region where the fine particles remained was a circular region having a diameter of about 0.5 mm.

When microphotographing of this substrate was performed with a scanning electron microscope at a magnification of 2000 in the same manner as in Example 1, the number of photographs required to photograph the entire measurement area was about 120. Thus, it was practically impossible to count the total number of particles.

From the above results, it is clear that the measurement method of the present invention achieves sufficiently reliable measurement.

〔The invention's effect〕

As described above, according to the method for measuring the number of microparticles in the test solution of the present invention, the measurement area where the microparticles remain is small, even when the particle size of the microparticles in the test solution is small.
With a microscope or the like, the number of all fine particles in the measurement area can be accurately measured with a small number of fields and a large magnification. Therefore, by using this assay solution, the fine particle counter can be strictly calibrated.

[Brief description of the drawings]

FIG. 1 is an explanatory perspective view showing a state in which a test solution is dropped on a substrate in one embodiment of the present invention. 1: ground plate, 2: substrate D: droplet

Claims (1)

(57) [Claims] 1. A test solution containing a plurality of fine particles is dropped on a grounded substrate, and the test solution droplets on the substrate are evaporated to evaporate the droplets to reduce and dry the droplets. A method for measuring the number of microparticles in a test solution, wherein the method comprises counting the number of microparticles generated.