Pure water quality analysis method and pure water production system operating method

Abstract

To provide a pure water quality analysis method comprising measuring a trace amount of an analysis target component contained in pure water using gas chromatography-mass spectrometer.SOLUTION: A pure water quality analysis method disclosed herein comprises moving an agitator 61 for concentrating an analysis target component in a pure water sample to cause the analysis target component in the sample to be adsorbed and concentrated on the agitator 61, vaporizing the concentrated analysis target component, and analyzing the vaporized analysis target component using a gas chromatography-mass spectrometer 21 to identify ingredients of the analysis target component.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for analyzing the quality of pure water and a method for operating a pure water production system. [Background technology]

[0002] It has been pointed out that organic matter in pure water may contribute to the formation of residues on semiconductor wafers. Therefore, in order to reduce organic matter in pure water, it is necessary to identify the source of trace organic contamination. Currently, methods for analyzing organic matter in pure water using gas chromatography are being investigated. However, due to the low concentration of organic matter in pure water, analyzing organic matter using gas chromatography can be difficult. Patent Document 1 states that the concentration of gases in ultrapure water can reach extremely low levels, on the order of a few μg / L (ppb), and that direct measurement of this concentration using existing gas chromatographs is insufficient due to the sensitivity. This also applies to organic matter in pure water. The International Roadmap for Devices and Systems (IRDS) states that organic contamination in pure water is currently measured by measuring the concentration of total organic carbon (hereinafter referred to as TOC), without taking into account the types of organic matter that make up the TOC. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2023-58213 Summary of the Invention [Problem to be solved by the invention]

[0004] TOC concentrations in pure water can reach extremely low levels of a few μg / L (ppb). Direct measurement of organic matter at these concentrations using existing gas chromatograph mass spectrometers is difficult due to sensitivity limitations, making it difficult to identify the trace organic species present in pure water and to estimate the source of contamination. Similar challenges exist for trace amounts of non-organic impurities.

[0005] An object of the present invention is to provide a method for analyzing the quality of pure water, which comprises measuring trace amounts of target components contained in the pure water using a gas chromatograph mass spectrometer. [Means for solving the problem]

[0006] The method for analyzing the quality of pure water of the present invention comprises moving a stirrer that concentrates a target component for analysis in a sample of pure water, causing the target component contained in the sample to be adsorbed onto the stirrer and concentrated; vaporizing the concentrated target component for analysis; and analyzing the vaporized target component for analysis with a gas chromatograph mass spectrometer to identify the target component for analysis. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a method for analyzing the quality of pure water, which comprises measuring trace amounts of a target component to be analyzed contained in pure water using a gas chromatograph mass spectrometer. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic configuration diagram of an ultrapure water manufacturing system to which the present embodiment is applied. [Figure 2] FIG. 1 is a conceptual diagram showing the apparatus and procedure used in the analysis of the quality of pure water. [Figure 3] FIG. [Figure 4] 1 is a chromatogram in Example 1. [Figure 5] 1 is a chromatogram in Example 2. [Figure 6] 1 is a chromatogram in Example 3. [Figure 7] 1 is a chromatogram in Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0009] An embodiment of the present invention will be described with reference to the drawings. In this embodiment, a method for analyzing the quality of ultrapure water and a method for operating an ultrapure water production system will be described, but the present invention can be widely applied to methods for analyzing the quality of pure water and methods for operating a pure water production system. Pure water refers to water with an electrical resistivity of 0.1 MΩ·cm or more, and pure water with an electrical resistivity of 1.5 MΩ·cm or more (the maximum value is 18.24 MΩ·cm for theoretically pure water) is called ultrapure water. In the following description, when there is no need to distinguish between pure water and ultrapure water, the term "pure water" may be used. In this embodiment, organic matter contained in pure water is used as the target component for analysis. However, in the present invention, the target component for analysis is not limited as long as it can be concentrated using a stirrer. For example, impurities other than organic matter are also included as the target component for analysis.

[0010] 1 shows a schematic configuration of an ultrapure water production system 1 to which this embodiment is applied. The ultrapure water production system 1 has a primary pure water system 2 that produces pure water from raw water, and a secondary pure water system (hereinafter referred to as subsystem 3) that further removes impurities from the pure water produced in the primary pure water system 2 to produce ultrapure water of the quality required at a point of use 4. The primary pure water system 2 includes a raw water tank, a heat exchanger, a turbidity membrane device, an activated carbon tower, a decarbonation membrane device, a reverse osmosis membrane device, an ultraviolet irradiation device, a degassing membrane device, etc. (not shown).

[0011] Subsystem 3 includes a pure water tank 31, a pure water supply pump 32, a heat exchanger 33, an ultraviolet oxidation device 34, a membrane degassing device 35, an ion exchange device 36, and an ultrafiltration membrane device 37, which are arranged in the above order on a main pipe L1 along the direction D of pure water flow. Main pipe L1 is connected to a point of use 4, and ultrapure water produced in subsystem 3 is supplied to the point of use 4. Ultrapure water not used at the point of use 4 is returned to the pure water tank 31 through a return pipe L2 connected to main pipe L1. The configuration of subsystem 3 is not limited to the above configuration; for example, the membrane degassing device 35 can be omitted, and the order of the above devices 32 to 37 can be changed as appropriate. Because the ultraviolet oxidation device 34, the membrane degassing device 35, the ion exchange device 36, and the ultrafiltration membrane device 37 change the quality of pure water, they are sometimes referred to as a water treatment device 5. The membrane degassing device 35, ion exchange device 36, and ultrafiltration membrane device 37 each have two systems A and B installed in parallel, and while one system is operating, the other system is on standby. Although not shown, the pure water supply pump 32, heat exchanger 33, and ultraviolet oxidation device 34 can also have two systems installed in parallel. The number of systems is not limited to two, and may be three or more. Note that only one system of the above devices 32 to 37 may be provided.

[0012] The pure water tank 31 stores pure water produced in the primary pure water system 2. The pure water supply pump 32 supplies the pure water stored in the pure water tank 31 to the heat exchanger 33. The ultraviolet oxidation device 34 irradiates the pure water whose temperature has been adjusted in the heat exchanger 33 with ultraviolet light to decompose organic matter contained in the pure water. The membrane degassing device 35 degasses the pure water, i.e., removes dissolved oxygen and carbon dioxide contained in the pure water. The ion exchange device 36 removes ionic components from the pure water. The ion exchange device 36 is a non-regenerative cartridge polisher packed with a mixed bed of cation exchange resin and anion exchange resin. The ion exchange device 36 may be packed with a monolithic or fibrous ion exchanger. The ultrafiltration membrane device 37 finally removes fine particles contained in the pure water.

[0013] FIG. 2 shows the equipment and procedures used for analyzing the quality of pure water. Pure water samples are collected from at least one location, preferably multiple locations, on the main pipe L1 of the subsystem 3. For this purpose, as shown in FIG. 1, at least one (multiple in this embodiment) sampling pipe L3 is provided branching off from the main pipe L1. While the location from which the sample is collected is not particularly limited, it is preferable to collect the sample from the outlet water of a water treatment device 5 (referred to as a specific water treatment device 6) that includes a liquid-contact portion with organic matter (i.e., a liquid-contact portion containing the target component for analysis) among the multiple water treatment devices 5 constituting the subsystem 3. The outlet water is the water discharged from the water treatment device 5 and flowing through the main pipe L1. If another water treatment device 5 is located downstream of the main pipe L1 in the water flow direction D, the outlet water is the water flowing upstream of all downstream water treatment devices 5. If no water treatment device 5 is located downstream of the main pipe L1 in the water flow direction D, the outlet water is the water flowing anywhere between the water treatment device 5 and the point of use 4. In this embodiment, samples are collected from the end P1 of the primary pure water system 2, position P2 between the membrane degassing device 35 and the ion exchange device 36, position P3 between the ion exchange device 36 and the ultrafiltration membrane device 37, and position P4 between the ultrafiltration membrane device 37 and the point of use 4.

[0014] Specifically, the specified water treatment device 6 comprises a membrane degassing device 35, an ion exchange device 36, and an ultrafiltration membrane device 37. That is, the specified water treatment device 6 includes at least one of an ion exchanger, a filtration membrane, and a degassing membrane. The pure water contains organic matter contained in the raw water and organic matter generated by ultraviolet irradiation, as well as organic matter eluted from the ion exchanger, filtration membrane, degassing membrane, etc. of the specified water treatment device 6. The organic matter eluted from the specified water treatment device 6 varies depending on the specified water treatment device 6, but examples include alcohols, ketones, carboxylic acids, phenols, ethers, esters, aldehydes, epoxides, aliphatic compounds, aromatic compounds, heterocyclic compounds, alicyclic compounds, and hydrocarbon halides.

[0015] First, a pure water sample collected through the sampling pipe L3 is placed in a container 51 (also called a vial) and sealed with a lid 52. A stirrer 61 is housed in the container 51. The stirrer 61 may be placed in the container 51 after collecting the pure water. Figure 3 shows a schematic perspective view of the stirrer 61. The stirrer 61 is a glass rod 63 with a built-in magnet 62, the surface of which is coated with polydimethylsiloxane (PDMS) as an adsorbent 64. An example is the Twister manufactured by Gestell Corporation. Liquid-liquid partitioning between the pure water and the PDMS adsorbs and concentrates some of the organic matter contained in the sample onto the adsorbent 64. Preferably, the stirrer 61 is driven by a magnetic stirrer 71. The magnetic stirrer 71 rotates its built-in magnet with a motor, creating a magnetic field that changes over time. The stirrer 61 moves through the sample due to the magnetic force of the magnet 62. This allows the organic matter contained in the sample to be efficiently adsorbed onto the adsorbent 64.

[0016] Next, the stirring bar 61 is removed from the container 51 and placed in the glass tube 81, and a lid 82 is attached. The glass tube 81 is then attached to a gas chromatograph mass spectrometer (hereinafter referred to as GC / MS 11). The GC / MS 11 includes a gas chromatograph 21, a mass analyzer 31, and a control unit 41. The gas chromatograph 21 includes a sample introduction unit 22 and a separation column 23. The sample introduction unit 22 has the function of heating and vaporizing the sample. A hole 83 through which the sample flows is formed at the tip of the glass tube 81, and the vaporized sample flows out from the hole 83 and is supplied to the separation column 23. The sample introduction unit 22 includes a carrier gas supply port 24, and a carrier gas such as helium is supplied to the sample introduction unit 22 through the supply port 24. The vaporized sample is carried by the carrier gas and passes through the separation column 23. In the separation column 23, organic substances contained in the sample are separated.

[0017] The mass analyzer 31 comprises an ionization unit 32, a mass analysis unit 33, and a detection unit 34. The ionization unit 32 ionizes the introduced sample. The mass analysis unit 33 separates the ionized sample according to the ratio (m / z) of the ion's mass (m) to its charge (z). The detection unit 34 detects the separated and ionized sample. The control unit 41 controls the gas chromatograph 21 and the mass analyzer 31, and also identifies the organic components and detects the concentration of each component. Specifically, the control unit 41 identifies the components by obtaining a mass spectrum from the output of the detection unit 34 and comparing it with a library stored in the control unit 41. When candidate organic components are known in advance, the components can also be identified by comparing the retention time of the peak in a standard sample with the retention time of the detected peak. The control unit 41 calculates the concentration of a specific mass spectral component from the area of ​​the component. The control unit 41 is equipped with a display for displaying the components and concentrations and a storage device (not shown) for storing detection results. In this manner, in this embodiment, the organic matter adsorbed and concentrated on the adsorbent material 64 of the stirring bar 61 is vaporized, and the vaporized organic matter is analyzed by GC / MS 11 to identify the components of the organic matter (qualitative analysis) and detect the concentration of each component (quantitative analysis).

[0018] Referring to FIG. 1 , each sampling pipe L3 is provided with a TOC meter 38. The TOC meter 38 can measure the TOC concentration (total organic carbon concentration) of a sample collected at the same location as the sample analyzed by the GC / MS 11. In the ultrapure water production system 1, TOC is generally measured as a water quality control parameter. Since TOC is also measured in this embodiment, water quality control similar to that of conventional methods is possible. However, because TOC is a measure for determining the total amount of organic matter contained in water, it cannot identify organic components or detect the concentration of each component. While the GC / MS 11 can identify organic components and detect the concentration of each component, it is difficult to identify components and detect the concentration of each component in samples containing extremely small amounts of organic matter, such as pure water, especially ultrapure water (the concentration of organic matter in ultrapure water is generally on the order of a few μg / L). As described in the examples, in this embodiment, the organic matter contained in the sample is adsorbed and concentrated by the stirrer 61, making it possible to identify components and detect the concentration of each component.

[0019] In this embodiment, it may not be possible to identify all organic components contained in pure water. This is because the GC / MS 11 detects gases, and organic compounds with large molecular weights tend not to vaporize easily. In other words, the GC / MS 11 may only detect some of the organic components measured as TOC. Therefore, TOC can be used to verify the measurement results of the GC / MS 11. Specifically, TOC is calculated from the components identified by the GC / MS 11 and the concentrations of each component. The total TOC value T1 of all components should be equal to or smaller than the measured value T2 of the TOC meter 38. Therefore, if T1 > T2, it can be determined that the reliability of the measurement results of the GC / MS 11 is low.

[0020] The TOC of the sample is preferably 50 μg / L or less, and more preferably 10 μg / L or less. If the TOC exceeds 50 μg / L, the adsorbent 64 may become saturated, potentially making it difficult to obtain sufficient measurement accuracy. Generally, the TOC of ultrapure water is well below 50 μg / L, so the adsorbent 64 is unlikely to become saturated. However, if the TOC exceeds 50 μg / L or 10 μg / L, it is preferable to notify the operator by an alarm or other method. Furthermore, if the TOC exceeds 50 μg / L, it can be determined that the reliability of the GC / MS 11 measurement results is low.

[0021] This embodiment not only enables component identification and detection of the concentration of each component, but also enables operational management of the ultrapure water production system 1 and the pure water production system. As described above, the GC / MS 11 analyzes the outlet water of the specific water treatment device 6. Therefore, if the concentration of a component exceeds a preset reference value, it can be determined that the specific water treatment device 6, which discharges the outlet water from which the sample was collected, is degraded. For example, if the concentration of a component detected in the outlet water of the ion exchange device 36 is higher than the reference value, it can be determined that breakthrough of the ion exchange resin has occurred. If the above-described water quality analysis method determines that one of multiple systems is degraded, it can be switched to another system. For example, if a higher-than-normal concentration of a component is detected in the outlet water of the specific water treatment device 6 during operation of System A of the specific water treatment device 6, it can be switched to System B.

[0022] The reference values ​​for component concentrations may be the same for each component, or may be set for each component separately. In this case, it is preferable to determine in advance through experiments for each specific water treatment device 6 the components that leach when the specific water treatment device 6 deteriorates and the extent to which their concentrations increase. For example, the components that leach when the ion exchange resin breaks through and the concentrations of each component are determined in advance. This allows for determining the likelihood of breakthrough when the concentration of at least one component in the outlet water of the ion exchange device 36 exceeds the reference value for that component. Multiple reference values ​​may be set for each component. For example, if the concentration of a component varies depending on the deterioration state, a high and low reference value can be set. Operational management can be appropriately performed based on the concentration. For example, an alarm indicating the early stage of deterioration can be output when the concentration exceeds the low reference value, and an alarm urging operation to be switched off can be output when the concentration exceeds the high reference value.

[0023] Deterioration of a specific water treatment device 6 can also be determined based on multiple components and their concentrations. Materials eluted from ion exchange resins and various membranes typically vary from one specific water treatment device 6 to another, resulting in different combinations of components. For example, if the components A, B, and C primarily eluted from one membrane and the components A, B, and D primarily eluted from another membrane, the membrane cannot be identified by focusing on component A or B. However, membranes can be identified based on the combination of components A, B, and C or the combination of components A, B, and D. The reliability of membrane identification can be further improved by determining not only which components eluted (the combination of eluted components) but also the concentrations of multiple components in advance. For example, by setting a concentration standard for each component, it can be determined that the specific water treatment device 6 discharging the outlet water is deteriorated if the concentrations of multiple components exceed the corresponding standard values. In the above example, the reference values ​​a, b, c, and d for the concentrations of components A, B, C, and D are determined in advance, and if the concentrations of components A, B, and C exceed the reference values ​​a, b, and c, respectively, it can be determined that the membrane has deteriorated. In this case, when one of the multiple systems is determined to be deteriorated by the above-mentioned water quality analysis method, it is possible to switch to another system. For example, in the case of filtration membranes such as ultrafiltration membranes and microfiltration membranes, aromatic hydrocarbons, alcohols, aldehydes, etc. contained in the outlet water of a filtration membrane device equipped with the filtration membrane can be used as an indicator of filtration membrane deterioration. In the case of ion exchange resins, aromatic hydrocarbons, ketones, alcohols, aldehydes, etc. contained in the outlet water of an ion exchange resin tower filled with the ion exchange resin can be used as an indicator of ion exchange resin deterioration.

[0024] The reference values ​​for the concentration of components can also be set for each outlet water of the specified water treatment device 6. For example, because the ultrafiltration membrane device 37 is the most downstream specified water treatment device 6, a lower reference value can be applied to it than to the other specified water treatment devices 6. Alternatively, when measuring the outlet water of the same type of specified water treatment device 6 in the primary pure water system 2 and subsystem 3, a lower reference value can be applied to subsystem 3 than to the primary pure water system 2.

[0025] Example 1 100 μL of a 0.1 mg / L VOC standard sample was added to 8 mL of ultrapure water to create a sample with a toluene concentration of 1.25 μg / L. This sample was analyzed directly by GC / MS. The resulting chromatogram is shown in Figure 4(a). Next, a sample prepared in the same manner was adsorbed and concentrated onto the adsorbent material of the stirrer, and the concentrated organic matter was vaporized and analyzed by GC / MS. The resulting chromatogram is shown in Figure 4(b). In Figure 4(a), no peaks were observed, making it difficult to identify the components, but in Figure 4(b), a toluene peak was observed, making it possible to detect trace amounts of organic matter.

[0026] Example 2 Ultrapure water containing acetophenone was prepared as a sample and treated using a test apparatus similar to that shown in Figure 1 (except that all water treatment devices 5 were in a single series). Samples were collected at positions P1, P3, and P4 shown in Figure 1, and the organic matter was adsorbed and concentrated onto the adsorbent material 64 of the stirrer 61. The concentrated organic matter was vaporized and analyzed by GC / MS. The resulting chromatograms are shown in Figures 5(a) to 5(c). A peak for acetophenone appeared in each chromatogram, and it was confirmed that the acetophenone concentration decreased toward the later stages. This indicates that acetophenone was removed by the ion exchange device 36 and the ultrafiltration membrane device 37.

[0027] Example 3 Samples were collected from the water being treated flowing through the ultrapure water production system. As described above, the ultrapure water production system is configured with a primary pure water system and subsystems. Samples were collected from the middle of the primary pure water system, the end of the primary pure water system, and the end of the subsystem. Organic matter was adsorbed and concentrated onto the adsorbent material 64 of the stirrer 61. The concentrated organic matter was vaporized and analyzed by GC / MS. To determine the blank value, a new stirrer 61 that had not been subjected to adsorption and concentration of organic matter was also subjected to the same treatment and analyzed by GC / MS. The resulting chromatograms are shown in Figure 6. The vertical and horizontal axes of each chromatogram are on the same scale. The sample collected from the middle of the primary pure water system exhibited peaks for aliphatic compounds, aromatic hydrocarbons, and alcohols. Aliphatic compounds were almost completely removed at the end of the primary pure water system. Aromatic hydrocarbons were reduced to concentrations equivalent to the blank value at the end of the primary pure water system. Alcohol concentrations decreased downstream, but even at the end of the subsystem, concentrations higher than the blank value were detected. This showed that it was possible to obtain information such as changes in the concentration of various organic substances and which organic substances were being removed by which device.

[0028] Example 4 Ion exchange resin was placed in a container containing ultrapure water and shaken for a long period of time at a temperature higher than room temperature to create a sample containing organic matter eluted from the ion exchange resin. The organic matter in the undiluted sample and a diluted solution diluted to half the concentration was adsorbed and concentrated onto the adsorbent material 64 of the stirrer 61. The concentrated organic matter was then vaporized and analyzed by GC / MS. To obtain a blank value, a new stirrer 61 that had not been subjected to adsorption and concentration of organic matter was also subjected to the same procedure and analyzed by GC / MS. The resulting chromatograms are shown in Figure 7. The vertical and horizontal scales of each chromatogram are the same. The peak areas of aromatic hydrocarbons, ketones, alcohols, and aldehydes (shown by dashed frames in the figure) were larger in the undiluted solution than in the diluted solution. The peak areas of the diluted solution diluted to half the concentration of the undiluted solution were approximately half that of the undiluted solution, confirming a correlation between the organic matter concentration and peak area, confirming that these organic matter were eluted from the ion exchange resin. It was also found that useful information could be obtained to estimate the amount (concentration) of each organic substance eluted from the ion exchange resin. [Explanation of symbols]

[0029] 1. Ultrapure water production system 5. Water treatment equipment 6. Specific water treatment equipment 21 Gas chromatograph mass spectrometer (GC / MS) 35 Membrane degassing device 36 Ion exchange unit 37 Ultrafiltration Membrane Device 61 Stirrer 64 Adsorbed substances

Claims

1. moving a stirring bar for concentrating the target component in a pure water sample, and concentrating the target component by adsorbing it onto the stirring bar; vaporizing the concentrated target component for analysis; and analyzing the vaporized target component by a gas chromatograph mass spectrometer to identify the target component.

2. 10. The method of claim 1, further comprising measuring the total organic carbon concentration of the sample.

3. The water quality analysis method according to claim 2, wherein the total organic carbon concentration of the sample is 50 μg / L or less.

4. The water quality analysis method according to claim 1 , further comprising: analyzing the vaporized target component with the gas chromatograph mass spectrometer to detect the concentration of the target component.

5. 5. The water quality analysis method according to claim 4, wherein the sample is collected from the outlet water of at least one specific water treatment device having a liquid contact part containing the target component of analysis, among a plurality of water treatment devices constituting a pure water production system.

6. The water quality analysis method according to claim 5 , wherein the at least one specific water treatment device includes at least one of an ion exchanger, a filtration membrane, and a degassing membrane.

7. The water quality analysis method according to claim 5, wherein when the concentration of the component exceeds a reference value, it is determined that the specific water treatment device that discharges the outlet water from which the sample was collected is deteriorated.

8. The water quality analysis method described in claim 5, wherein a standard value for the concentration of the component is set for each component, and when the concentration of multiple components in the sample collected from any of the outlet water exceeds the standard value for that component, it is determined that the specific water treatment device discharging the outlet water is deteriorated.

9. A method for operating a pure water production system including the water quality analysis method according to claim 7 or 8, comprising: The at least one specific water treatment device has a plurality of lines installed in parallel, A method for operating a pure water production system, comprising, when the water quality analysis method determines that one of the plurality of lines is deteriorated, switching to another of the lines.

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