Microparticle analysis methods

Abstract

To provide a particle concentration method capable of concentrating particles at a high concentration ratio using an electroosmotic flow, and a particle analysis method using this particle concentration method.SOLUTION: There are provided: a particle concentration method in which sample water is made to pass through a particle concentrator having electrodes arranged with gaps, and AC voltage is applied between the electrodes to concentrate the sample, in which the AC voltage with a frequency of 50 to 100 kHz at 20 to 100 Vpp is applied; and a particle analysis method in which a particle concentration in the sample water is analyzed by concentrating the sample water using this particle concentration method and then analyzing the concentrated water.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for concentrating fine particles in water, and particularly to a fine particle concentration method using electroosmotic flow. The present invention also relates to a fine particle analysis method using this fine particle concentration method. BACKGROUND ART

[0002] Conventional fine particle analysis techniques include online fine particle monitors and filter filtration-SEM method. However, the former has a problem that it is difficult to detect fine particles in the case of a liquid with few fine particles such as ultrapure water. Although the latter can detect even a small amount of fine particles in liquid, it has a problem that capturing fine particles takes time. Furthermore, improvements in the sensitivity of online fine particle monitors and improvements in the filtration period in filter filtration have been desired.

[0003] As prior art of a fine particle concentration and extraction device using electroosmotic flow, the one described in Patent Document 1 can be mentioned.

[0004] The particle concentration device of Patent Document 1 includes at least one pair of electrodes arranged along a flow path for a fine particle-containing liquid, and an alternating current power supply that applies an alternating voltage to the electrodes, and is configured to increase the concentration of fine particles flowing in the flow path by alternating current electroosmotic flow in the vicinity of the electrodes.

[0005] In this particle concentration device, in the particle concentration section, an alternating voltage is applied to at least a pair of electrodes to generate an alternating current electroosmotic flow by an alternating electric field in the gap space between the electrodes. By using this alternating current electroosmotic flow, particles in the liquid can be accumulated. The accumulated particles are conveyed by the liquid flow toward the particle take-out section. PRIOR ART DOCUMENTS PATENT DOCUMENTS

[0006] Patent Document 1 International Publication No. 2012 / 032802 [Overview of the project] [Problems that the invention aims to solve]

[0007] Conventional online particulate monitors have had difficulty detecting the small number of particulates in ultrapure water. For example, if the sensitivity of a particulate monitor is 1 particle / mL, it is impossible to count the number of particulates in ultrapure water with a particle count of 0.5 particles / mL.

[0008] Conventional filter filtration-SEM The method required a long time to capture fine particles. For example, to analyze 10 nm fine particles with an accuracy of 1 particle / mL, the required filtration volume was 1000 L, and the filtration period was 2 weeks.

[0009] In the particulate matter concentration and extraction apparatus described in Patent Document 1, the concentration ratio was low, and a sufficient concentration ratio could not be obtained when the processing flow rate was set to a practical amount. Specifically, the processing flow rate was 10 -4 At a flow rate of mL / min, the concentration ratio was approximately 5 times, but at a processing flow rate of 1 mL / min, the concentration ratio was approximately 1.5 times. Furthermore, Patent Document 1 states that the frequency of the AC voltage applied between the electrodes is preferably in the range of 0.1 to 10 kHz, and particularly preferably in the range of 1 to 5 kHz, and that the AC voltage is preferably 5V or less, and particularly preferably in the range of 1 to 5V. This corresponds to approximately 9Vpp or less, preferably approximately 2.8 to 9Vpp.

[0010] The object of this invention is to provide a method for concentrating fine particles at a high concentration ratio using electroosmotic flow, and a method for analyzing fine particles using this fine particle concentration method. [Means for solving the problem]

[0011] The gist of this invention is as follows:

[0012] [1] A method for concentrating fine particles, comprising passing sample water through a sample water channel of a fine particle concentrator having electrodes arranged with a gap between them, and concentrating by applying an AC voltage between the electrodes, characterized in that an AC voltage with a frequency of 50 to 100 kHz is applied at 20 to 100 Vpp.

[0013] [2] A method for concentrating fine particles according to [1], wherein the gap extends in the direction from the inlet of the sample water to the outlet of the concentrated water, the gap spacing is 5 to 50 μm, and the gap length is 5 to 30 mm.

[0014] [3] A method for analyzing the concentration of fine particles in a sample water by concentrating the sample water using the fine particle concentration method of [1] or [2], and then analyzing the concentrated water obtained.

[0015] [4] A method for analyzing fine particles, wherein the sample water is ultrapure water.[3] [Effects of the Invention]

[0016] According to the present invention's method for concentrating fine particles, in an electroosmotic flow fine particle concentrator in which electrodes are installed in a flow channel with a gap between them, a high-frequency (50-100 kHz) AC voltage (20-100 Vpp) is applied to the electrodes to concentrate the fine particles in the gap between the electrodes.

[0017] According to the present invention's method for concentrating fine particles, fine particles can be concentrated more efficiently than in Patent Document 1. For example, processing flow rate 10 -4 A concentration ratio of approximately 10 times can be achieved at a flow rate of mL / min, and a concentration ratio of approximately 5 times can be achieved at a processing flow rate of 1 mL / min.

[0018] According to the present invention's method for analyzing microparticles, for example, when measuring microparticles in ultrapure water with a sensitivity of 1 particle / mL and a particle count of 0.5 particles / mL using an online microparticle monitor, by installing a concentration device with a concentration ratio of 5 times before the microparticle meter, the number of microparticles in the ultrapure water can be counted with 5 times the sensitivity. Furthermore, by installing a concentration device with a concentration ratio of 5 times before the filter filtration device, the filtration period can be shortened to 1 / 5. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] [Figure 1] It is a configuration diagram of a concentration apparatus used in the fine particle concentration method according to the embodiment. [Figure 2] It is a sectional view along the line II-II in Fig. 1. [Figure 3] It is a sectional view along the line III-III in Fig. 1. [Figure 4] It is a sectional view along the line IV-IV in Fig. 1. [Figure 5] It is a sectional view along the line V-V in Fig. 1. [Figure 6] It is a sectional view along the line VI-VI in Fig. 1. [Figure 7] It is a sectional view along the line VII-VII in Fig. 1. [Figure 8] It is a sectional view along the line VIII-VIII in Fig. 1. [Figure 9] It is an electric field intensity distribution diagram between electrodes of the concentration apparatus in Example 1 and Comparative Example 1. DESCRIPTION OF EMBODIMENTS

[0020] Embodiments will be described below with reference to the drawings. Fig. 1(a) is a plan view of a concentration apparatus used in the fine particle concentration method according to the embodiment, and Fig. 1(b) is a sectional view along the line B-B in Fig. 1(a). Figs. 2 to 8 are sectional views along the lines II-II to VIII-VIII in Fig. 1, respectively.

[0021] This concentration apparatus 1 includes a flat plate-shaped substrate 2, a flow path forming body 3 provided to overlap the upper surface of the substrate 2, a flow path 4 formed between the substrate 2 and the flow path forming body 3, electrodes 5 and 6 disposed in the flow path 4, a sample water inlet 7, a concentrated water outlet 8, diluted water outlets 9 and 10, and the like provided in the flow path forming body 3.

[0022] In this embodiment, the substrate 2 is a glass substrate and the flow path forming body 3 is made of synthetic resin, but the constituent materials of the substrate 2 and the flow path forming body 3 are not limited to these.

[0023] In this embodiment, the substrate 2 has a rectangular shape in plan view. The upper surface of the substrate 2 is a smooth surface. A channel forming body 3 is provided near the center of the shorter width direction of the upper surface of the substrate 2, extending in the longitudinal direction of the substrate 2. The channel forming body 3 extends from one end 2a (near one short side) to the other end 2b (near the other short side) of the substrate 2. The channel forming body 3 also has a rectangular shape in plan view, but is not limited to this.

[0024] The channel-forming body 3 has its lower peripheral edge watertightly attached to the upper surface of the substrate 2 around its entire circumference. The lower surface of the channel-forming body 3, excluding the peripheral edge, is a recess that slopes upward, and this recess forms the channel 4. In other words, the channel 4 is the space between the top surface 4a of the recess and the upper surface of the substrate 2.

[0025] An inlet 7 for sample water is provided at one end of the channel forming body 3, penetrating the top surface 4a. At the other end of the channel forming body 3, an outlet 8 for concentrated water and outlets 9 and 10 for dilute water are provided, penetrating the top surface 4a.

[0026] The center point of the sample water inlet 7 is located midway between one long side 3a and the other long side 3b of the flow channel forming body 3. The center point of the concentrated water outlet 8 is located midway between one long side 3a and the other long side 3b of the flow channel forming body 3.

[0027] The dilute water outlets 9 and 10 are located upstream of the concentrated water outlet 8 (on one end 2a of the substrate 2). Dilute water outlet 9 is located near the long side 3a, and dilute water outlet 10 is located near the long side 3b.

[0028] Electrodes 5 and 6 are positioned between the sample water inlet 7 and the concentrated water outlet 8. Electrodes 5 and 6 are foil-like and formed on the upper surface of the substrate 2. In this embodiment, electrodes 5 and 6 are made of ITO, but the electrode constituent material is not limited to ITO.

[0029] Electrodes 5 and 6 are positioned within the flow channel 4, except for their terminal portions 5a and 6a. The terminal portions 5a and 6a of electrodes 5 and 6 extend outside the flow channel forming body 3 through the mating surface between the substrate 2 and the flow channel forming body 3. An AC voltage is applied to electrodes 5 and 6 via these terminal portions 5a and 6a.

[0030] Electrodes 5 and 6, excluding the terminal portions 5a and 6a, have a rectangular shape in plan view. Electrode 5 is located on the longer side 3a of the midpoint line of the flow channel 4 (a line passing through the center in the short-width direction of the flow channel 4 and extending in the longitudinal direction of the flow channel 4), and electrode 6 is located on the longer side 3b of the midpoint line of the flow channel 4. The sides of electrodes 5 and 6 along the midpoint line are parallel to the midpoint line, thereby forming a gap G of a certain width between electrodes 5 and 6 (Figures 4-6).

[0031] To perform the concentration treatment of sample water (water containing fine particles) using the concentration apparatus 1 configured in this way, the sample water is supplied into the flow path 4 from the inlet 7, and water is discharged from the concentrated water outlet 8 and the dilute water outlets 9 and 10, respectively, while an AC voltage with a frequency of 50 to 100 kHz and a Vpp (peak-to-peak voltage) of 20 to 100 V is applied to electrodes 5 and 6.

[0032] As a result, electroosmotic flow is generated near electrodes 5 and 6. In Figures 4-6, this electroosmotic flow is directed downwards in the gap G, away from gap G along electrodes 5 and 6, and towards gap G along the top surface 4a.

[0033] Therefore, within channel 4, a clockwise circulating flow is formed on the left half of Figures 4-6, and a counterclockwise circulating flow is formed on the right half. The fine particles in the sample water within channel 4 are carried along by this circulating flow and accumulate near gap G, which is the midpoint between the opposing circulating flows and corresponds to a stagnant point.

[0034] As the sample water flows continuously from inlet 7 towards outlets 8-10, the fine particles that accumulate near gap G flow to the right in Figure 1 and are extracted from concentrated water outlet 8 as concentrated water with a high concentration of fine particles.

[0035] On the other hand, the particulate matter concentration is lower on the longer sides 3a and 3b within the flow path 4. This dilute water with a low particulate matter concentration also flows to the right in Figure 1 and is extracted from the dilute water outlets 9 and 10.

[0036] In this type of AC electroosmotic concentration, if the frequency of the AC voltage applied between electrodes 5 and 6 is less than 50 kHz, the concentration efficiency in the gap portion is insufficient, and a high concentration ratio cannot be obtained. On the other hand, if the frequency of the AC voltage exceeds 200 kHz, the concentration efficiency becomes low. For this reason, in the present invention, an AC voltage with a frequency of 50 to 200 kHz, preferably 50 to 100 kHz, is applied. If the AC voltage applied between electrodes 5 and 6 is less than 20 Vpp, the concentration efficiency is insufficient, and a high concentration ratio cannot be obtained. On the other hand, if the AC voltage exceeds 100 Vpp, a high concentration ratio can be obtained, but electrode damage may occur. For this reason, in the present invention, an AC voltage of 20 to 100 Vpp, preferably 50 to 100 Vpp, is applied.

[0037] The concentrated water extracted from the concentrated water outlet 8 has its particulate matter concentration measured, for example, by a particulate matter concentration analyzer. Alternatively, the concentrated water may be further concentrated using the same type or another concentrating device (for example, a centrifugal concentrator).

[0038] In this invention, multiple of the above-mentioned concentration devices may be installed in parallel, sample water may be distributed and supplied to each concentration device, and the concentrated water from each device may be combined and extracted.

[0039] While the present invention is not particularly limited, considering the balance between ease of manufacture of the concentration device and the AC electroosmotic effect, the gap G, i.e., the distance between electrodes 5 and 6, is preferably 5 to 100 μm, and particularly preferably 5 to 50 μm. The length of the gap G, i.e., the longitudinal length of electrodes 5 and 6, is preferably 1 mm or more, and particularly preferably 5 to 30 mm.

[0040] The thickness of electrodes 5 and 6 is preferably 50 to 300 nm, and particularly preferably around 100 to 150 nm.

[0041] The longitudinal length of the channel 4 is preferably 1 mm or more, and particularly preferably 5 to 30 mm. The transverse width of the channel 4 (width in the left-right direction in Figures 4 to 6) is preferably 0.5 to 5 mm, and particularly preferably 1 to 2 mm. The height of the channel 4, that is, the distance between the top surface of the substrate 2 and the top surface 4a of the channel, is preferably 20 to 100 μm, and particularly preferably 20 to 50 μm.

[0042] Examples of sample water include ultrapure water, pure water, and other low-conductivity liquids. The particle size of the fine particles in the sample water (measured by microscopy and dynamic light scattering) is preferably 2000 nm or less, and particularly preferably 500 nm or less.

[0043] The linear velocity of the sample water in channel 4 (average flow velocity from left to right in Figure 1) is preferably 50 mm / sec or less, and particularly preferably 2 mm / sec or less. [Examples]

[0044] A test solution (particle concentration 0.02 wt%) containing 100 nm diameter fluorescent polystyrene (PsNP) particles dispersed in ultrapure water was concentrated using the concentration apparatus shown in Figure 1. The main conditions of the apparatus were as follows:

[0045] Substrate 2: 0.7mm thick glass substrate Flow channel shaping body 3: Made of polydimethylsiloxane (PDMS) Channel 4: Width 2 mm, Height 50 μm, Length 30 mm Electrodes 5, 6: 150 nm thick indium tin oxide (ITO) film Gap width: 40 μm Gap length: 20mm Diameter of inlet 7: 1 mm Diameter of outlet 8: 1mm Diameter of outlets 9 and 10: 0.3 mm

[0046] [Example 1] The above test solution was passed through at a rate of 0.01 mL / min, and a voltage was applied at an AC frequency of 70 kHz and a voltage (Vpp) of 20 V.

[0047] Based on the fluorescence intensity, the concentration ratio was estimated to be approximately 6 times.

[0048] [Comparative Example 1] The conditions were the same as in Example 1, except that the AC frequency was set to 0.8 kHz. As a result, the concentration ratio was approximately 2 times. The fine particles accumulated approximately 60 μm to 120 μm away from the gap towards the wall (long sides 3a and 3b).

[0049] Figure 9 shows the electric field intensity distribution in the VV line cross-section (Figure 5) of Figure 1 for Example 1 and Comparative Example 1, with the vertical axis representing the specific intensity. The horizontal axis, "electrode," schematically represents the electrodes, with a gap G of 40 μm between them. The solid line in Figure 9(a) represents Example 1, and the solid line in Figure 9(b) represents Comparative Example 1.

[0050] As shown in Figure 9, under the conditions of Example 1, the electric field strength near the gap is significantly higher compared to Comparative Example 1. Note that the dashed lines in Figures 9(a) and 9(b) represent the cases where the same procedure was followed in Example 1 and Comparative Example 1, except that the voltage (Vpp) was set to 10V. It can be seen that a sufficient electric field strength cannot be obtained at 10Vpp. [Explanation of Symbols]

[0051] 1 Concentrator 2 circuit boards 3. Channel-forming body 4 Flow channels 5,6 electrodes 5a,6a terminal section 7. Sample water inlet 8 Concentrated water outlet 9,10 Dilute water intake

Claims

[Claim 1] A method for analyzing the concentration of fine particles in a sample water by using a fine particle concentrator comprising a substrate, a channel forming body provided on the upper surface of the substrate, a channel formed between the substrate and the channel forming body, and a pair of electrodes disposed in the channel, wherein a gap is formed between the electrodes, and after passing sample water through the channel and concentrating the sample water by applying an alternating voltage between the electrodes, the obtained concentrated water is analyzed. The sample water is ultrapure water, The pair of electrodes are formed on the upper surface of the substrate, are positioned opposite each other across the center of the short-width direction of the flow path, and extend in the longitudinal direction of the flow path. The gap extends in the direction from the inlet of the sample water toward the outlet of the concentrated water. The height of the aforementioned channel is 20 to 100 μm. The gap spacing is 5 to 50 μm, and the gap length is 5 to 30 mm. A method for analyzing fine particles, characterized by applying an AC voltage with a frequency of 50 to 100 kHz at 20 to 100 Vpp.

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