Spraying method

Abstract

The present invention provides a spraying method for mist containing peroxynitrite which can be used for wide applications such as finger disinfection and indoor spraying, wherein the spraying method can change a half-life for attenuation of concentration and a peak value of concentration of peroxynitrite contained in mist according to the application. In the spraying method, peroxynitrite is continuously generated by a spraying device with a plasma activated mist having a pH in the range of 2 to 5, the mist being generated from an aqueous solution containing nitrite having a concentration ranging from 10 micromolar to 10 millimolar.

Description

Spraying method

[0001] The present invention relates to a method for spraying a mist containing peroxynitrite.

[0002] Peroxynitrite is known to have bactericidal properties. For example, Patent Document 1 discloses a method for spraying a mist containing peroxynitrite. However, in the method disclosed in Patent Document 1, the half-life of the generated peroxynitrite is approximately one second (see paragraphs

[0047] and

[0053] of Patent Document 1). In the above-described spraying method, peroxynitrite is generated only in the plasma activation section of the spraying device. Therefore, the method disclosed in Patent Document 1 cannot be used for a wide range of purposes, such as hand disinfection and indoor spraying. To date, no method has been developed for spraying a mist containing peroxynitrite that can be used for a wide range of purposes, such as hand disinfection and indoor spraying.

[0003] Therefore, there is a need for a method for spraying a mist containing peroxynitrite that can be used for a wide range of purposes, such as for hand disinfection, indoor spraying, etc. It is also desirable to be able to change the peak concentration of peroxynitrite contained in the mist and the half-life time of the concentration decay depending on the purpose.

[0004] Special table 016-519596 (WO2014 / 145570)

[0005] The object of the present invention is to provide a method for spraying a mist containing peroxynitrite that can be used for a wide range of applications, such as for hand disinfection and indoor spraying, and that can change the peak concentration value of peroxynitrite contained in the mist and the half-life time for the concentration to decay depending on the application.

[0006] The spraying method of the present invention continuously generates peroxynitrite using a plasma-activated mist with a pH ranging from 2 to 5, which is generated by a spraying device from an aqueous solution containing nitrite at a concentration ranging from 10 micromolar to 10 millimolar.

[0007] In the spraying method of the present invention, the peak concentration of peroxynitrite contained in the mist and the half-life time of the concentration decay can be changed by changing the concentration of nitrite in the aqueous solution used to generate the mist to be sprayed and the pH of the plasma-activated mist.

[0008] In the spraying method of the first embodiment of the present invention, a pH adjuster which is an acid, a base, or a combination of an acid or a base and a pH buffer is added to the aqueous solution.

[0009] In the spraying method of the second embodiment of the present invention, a sufficient amount of pH buffer is added to the aqueous solution so that the pH of the plasma activated mist is the same as the pH of the aqueous solution.

[0010] If the aqueous solution does not contain a pH buffer, the pH changes significantly due to plasma activation. On the other hand, if the amount of pH buffer in the aqueous solution is sufficient, the pH change due to plasma activation is almost negligible, and the pH of the plasma-activated mist is the same as the pH of the aqueous solution. Therefore, the pH of the plasma-activated mist can be determined by the pH of the aqueous solution.

[0011] In the spraying method of the third embodiment of the present invention, the pH of the aqueous solution is adjusted by adding an acid or a base, and a sufficient amount of a pH buffer is further added so that the pH of the plasma-activated mist is the same as the pH of the aqueous solution.

[0012] According to this embodiment, the pH of the plasma-activated mist can be determined by adjusting the pH of the aqueous solution by adding an acid or a base.

[0013] In the spraying method of the fourth embodiment of the present invention, the transition of the concentration of peroxynitrite in the mist generated is estimated by a numerical calculation simulation based on the measured values ​​of the concentration of active species and pH of the mist generated.

[0014] According to this embodiment, the peak concentration of peroxynitrite contained in the mist and the half-life time of the concentration decay can be estimated by numerical simulation based on the measured values ​​of the concentration of active species and pH of the generated mist.

[0015] In the spraying method of the fifth embodiment of the present invention, the concentration of the nitrite in the aqueous solution is in the range of 100 micromolar to 1600 micromolar, and the pH of the aqueous solution is in the range of 2.5 to 3.

[0016] In the spraying method according to the sixth embodiment of the present invention, the spraying device is provided with a plasma active part having a surface DBD structure.

[0017] 1 is a graph showing the concentrations of hydrogen peroxide, nitrous acid, nitrate ions, and nitrite ions in a mist generated by a plasma active unit with a surface DBD structure when an aqueous solution of sodium nitrite is used.

[0023] FIG. 1 is a graph showing the pH of a mist generated by a plasma active unit with a surface DBD structure when an aqueous solution of sodium nitrite is used.

[0024] FIG. 1 is a graph showing the relationship between the concentration of sodium nitrite in an aqueous solution and the rate of production of peroxynitrite, calculated by substituting the data shown in FIGS. 1 and 2 into equation (2).

[0025] FIG. 1 is a graph showing the change over time in the concentration of active species calculated by numerical simulation when the concentration of sodium nitrite in an aqueous solution is 1200 micromolar.

[0026] FIG. 2 is a graph showing the change over time in the concentration of peroxynitrite when the concentration of sodium nitrite in an aqueous solution is 2000 micromolar.

[0027] FIG. 2 is a graph showing the change over time in the concentration of peroxynitrite when the concentration of sodium nitrite in an aqueous solution is 1200 micromolar.

[0028] FIG. 3 is a graph showing the change over time in the concentration of peroxynitrite when the concentration of sodium nitrite in an aqueous solution is 2000 micromolar. 9A is a diagram showing the relationship between the concentration of sodium nitrite in an aqueous solution and the rate of production of peroxynitrite when the pH of the plasma-activated mist is set to 3. FIG. 9B is a diagram showing the change in the concentration of peroxynitrite in the mist over time when the pH of the plasma-activated mist is changed with the sodium nitrite concentration in the aqueous solution set to 2000 micromolar. FIG. 9B is an enlarged view of the range of peroxynitrite concentrations from 0 to 2 micromolar in FIG. 9A. FIG. 9C is a flow chart explaining how to determine the concentration of nitrite in an aqueous solution and the pH of the plasma-activated mist. FIG. 9D is a diagram showing an example of a spraying device. FIG. 9E is a diagram showing an example of the structure of a plasma activation unit of a spraying device.

[0018] FIG. 11 shows an example of a spraying device used in the spraying method of the present invention. The spraying device, which is a plasma mist generator, includes a mist generating unit 100 and a plasma activating unit 200. The mist generating unit 100 may be a device that converts a water-based liquid stored in a tank into mist using an ultrasonic vibrator. The ultrasonic vibrator may be, for example, an ultrasonic humidification unit NB-80E-01-H manufactured by TDK Corporation. The diameter of the mist droplets is 0.5 to 30 micrometers. The plasma activating unit 200 is tubular and includes a tubular external electrode 220 installed outside the tube 210, a tubular internal electrode 230 installed inside the tube 210, and a high-frequency power source 240. The tubular internal electrode 230 protrudes from the upper end of the tube 210. The tube 210 is made of a dielectric material. The high-frequency power source 240 is connected to apply a high-frequency voltage between the external electrode 220 and the internal electrode 230. The terminal of the high-frequency power source 240 connected to the internal electrode 230 is grounded. Typically, the frequency of the RF power supply 240 ranges from 1 kHz to 100 kHz, preferably from 5 kHz to 30 kHz, and the peak-to-peak voltage of the RF power supply 240 ranges from 1 kilovolt to 30 kilovolts.

[0019] The mist generated by the mist generating unit 100 is sent to the plasma activation unit 200 from the lower end of a tube 210 shown in Figure 11. The mist flow rate is preferably in the range of 0.01 to 1000 microliters per second (μL / s). The mist is plasma-activated by applying a high-frequency voltage between the external electrode 220 and the internal electrode 230 using a high-frequency power supply 240, and is emitted as plasma-activated mist 300 from the tip of the tubular internal electrode 230 protruding from the upper end of the tube 210.

[0020] FIG. 12 shows an example of the structure of the plasma activation unit 200 of the spray device. The axial length of the tube 210 is 34 mm, the diameter is 3.9 mm, and the wall thickness is 0.7 mm. Generally, the diameter of the dielectric material tube is preferably in the range of 2 mm to 10 mm. The material of the tube 210 is quartz glass. In this example, the external electrode 220 installed on the outside of the tube 210 is a conductive copper foil adhesive tape covering the outer circumference of the tube 210. The width (axial length) of the conductive copper foil adhesive tape is 20 mm and the thickness is 0.7 mm. The upper end of the external electrode 220 is located 12 mm below the upper end of the tube 210. In this example, the tubular internal electrode 230 installed inside the tube 210 is a stainless steel tube. The axial length of the stainless steel tube is 20 mm, the outer diameter is 2.41 mm, and the wall thickness is 0.21 mm. The axial overlap length of the external electrode 220 and the internal electrode 230 is 3 millimeters. The internal electrode 230 protrudes from the upper end of the tube 210, and the axial length of the protruding portion is 5 millimeters. In this example, the plasma-activated mist 300 is generated along the inner surface of the tube 210, below the lower end of the internal electrode 230, in a region adjacent to the lower end where the external electrode 2210 is present on the outer surface of the tube 210.

[0021] Generally, the external electrode and the internal electrode are disposed at different positions in the axial direction of the tube. To facilitate the generation of a discharge between the two electrodes, it is preferable that the positions of the two electrodes partially overlap in the axial direction of the tube 210.

[0022] The structure of the plasma active section 200 shown in FIG. 12 is called a surface dielectric barrier discharge structure (surface DBD structure).

[0023] Peroxynitrite (HOONO) is known to have sterilizing properties. Conventionally, in the field of plasma engineering, it has been generally recognized that peroxynitrite is generated in a "plasma activation region" and then decreases with a half-life of approximately one second (see, for example, paragraphs

[0047] and

[0053] of Patent Document 1). The inventors of the present application focused on the possibility that peroxynitrite may be generated not only by the plasma activation region but also by active species in the plasma-activated mist, and analyzed the generation process. As a result, they found that nitrous acid, the raw material for peroxynitrite, tends to be depleted in the plasma-activated mist, and decided to use an aqueous solution of nitrite to generate the mist.

[0024] Figure 1 shows the concentrations of hydrogen peroxide, nitrous acid, nitrate ions, and nitrite ions in the mist generated by the plasma active part of the surface DBD structure when an aqueous solution of sodium nitrite is used. The horizontal axis of Figure 1 shows the concentration of sodium nitrite in the aqueous solution. The unit of concentration is micromolar. The vertical axis of Figure 1 shows the concentration of active species in the mist. The unit of concentration is millimolar. The peak-to-peak value of the voltage applied between the two electrodes is 16.3 kilovolts.

[0025] The concentration of active species was determined by collecting droplets from the mist using a glass plate or the like and measuring them by absorptiometry using an ultra-microcell.

[0026] Figure 2 shows the pH of the mist generated by the plasma-activated part of the surface DBD structure when an aqueous solution of sodium nitrite is used. The horizontal axis of Figure 2 shows the concentration of sodium nitrite in the aqueous solution. The unit of concentration is micromolar. The vertical axis of Figure 2 shows the pH of the mist.

[0027] According to the inventor's findings, peroxynitrite is produced from hydrogen peroxide and nitrous acid in the mist as raw materials according to the following formula: The rate of production of peroxynitrite can be expressed by the following formula (2). k is the reaction rate constant and the following values ​​were used: The rate of peroxynitrite production can be calculated by substituting the concentration of active species measured by the above method and the hydrogen ion concentration calculated from pH into equation (2). If the nitric acid concentration is higher than the nitrite concentration and no pH buffer is used, the hydrogen ion concentration can also be estimated from the nitrate ion concentration.

[0028] Figure 3 shows the relationship between the concentration of sodium nitrite in an aqueous solution and the rate of production of peroxynitrite, calculated by substituting the data shown in Figures 1 and 2 into equation (2). The horizontal axis of Figure 3 represents the concentration of sodium nitrite in an aqueous solution. The unit of concentration is micromolar. The vertical axis of Figure 3 represents the rate of production of peroxynitrite. The unit of production rate is micromolar per second (μM / s). It is presumed that the concentration and bactericidal activity of peroxynitrite are closely related to the rate of production of peroxynitrite.

[0029] The inventors then came up with the idea of ​​estimating the time-dependent changes in the concentrations of active species and peroxynitrite by numerical simulation. The numerical simulation used a zero-dimensional chemical reaction model that did not take spatial distribution into account, and determined the time-dependent changes in the concentrations of active species and peroxynitrite by implicitly solving ordinary differential equations for multiple non-equilibrium and equilibrium reaction equations related to the reactions. The non-equilibrium and equilibrium reaction equations used in the numerical simulation are shown in Table 1. The initial values ​​for the numerical simulation used the data shown in Figures 1 and 2.

[0030] Figure 4 shows the change in the concentration of active species over time obtained by numerical simulation when the concentration of sodium nitrite in the aqueous solution is 1200 micromolar. The horizontal axis of Figure 4 represents time, measured in seconds. The vertical axis of Figure 4 represents the concentration of active species, measured in micromolar. The data shown in Figure 1 was used for the initial concentration of active species in the mist, and the data shown in Figure 2 was used for the pH of the mist.

[0031] Figure 5 shows the change in concentration of active species over time obtained by numerical simulation when the concentration of sodium nitrite in the aqueous solution is 2000 micromolar. The horizontal axis of Figure 5 represents time, measured in seconds. The vertical axis of Figure 5 represents the concentration of active species, measured in micromolar. The data shown in Figure 1 was used for the initial concentration of active species in the mist, and the data shown in Figure 2 was used for the pH of the mist.

[0032] 6 is a graph showing the change in the concentration of peroxynitrite over time when the concentration of sodium nitrite in the aqueous solution is 1200 micromolar. The change in the concentration of peroxynitrite over time was determined by numerical simulation.

[0033] 7 shows the change in the concentration of peroxynitrite over time when the concentration of sodium nitrite in the aqueous solution is 2000 micromolar. The change in the concentration of peroxynitrite over time was determined by numerical simulation.

[0034] Here, we analyze the effect of the sodium nitrite concentration in the aqueous solution on the rate of peroxynitrite generation. Figure 1 shows that the total amount of nitrite ([NO2-] + [HNO2]) in the plasma-activated mist increases with the concentration of sodium nitrite in the aqueous solution. The ratio of nitrite to nitrite ions ([HNO2] / [NO2-]) decreases with the concentration of sodium nitrite in the aqueous solution. Figure 2 shows that the pH increases with the concentration of sodium nitrite. That is, the hydrogen ions (H+) decrease with the concentration of sodium nitrite. According to equation (2), the rate of peroxynitrite generation increases with an increase in the total amount of nitrite. On the other hand, the rate of peroxynitrite generation decreases with a decrease in the hydrogen ions and the ratio of nitrite to nitrite ions. Therefore, as shown in Figure 3, the rate of peroxynitrite generation increases with an increase in the concentration of sodium nitrite in the aqueous solution, reaching a maximum at approximately 1 millimolar, and then decreases with an increase in the concentration of sodium nitrite in the aqueous solution.

[0035] Taking into consideration the above results obtained using measurements of the active species of the activated mist and numerical simulations, the inventors came up with the idea of ​​adjusting the rate of production of peroxynitrite by adjusting the pH of the plasma-activated mist.

[0036] Figure 8 shows the relationship between the concentration of sodium nitrite in an aqueous solution and the rate of peroxynitrite production when the pH of the plasma-activated mist is set to 3. The horizontal axis of Figure 8 represents the concentration of sodium nitrite in the aqueous solution. The unit of concentration is micromolar. The vertical axis of Figure 8 represents the rate of peroxynitrite production. The unit of production rate is micromolar per second (μM / s). The rate of peroxynitrite production was calculated using equation (2) using the data in Figure 1. Figure 8 shows that the rate of peroxynitrite production increases with the concentration of sodium nitrite in the aqueous solution. In this way, when a sufficient amount of pH buffer is added to the aqueous solution in advance and the pH of the plasma-activated mist is determined by the concentration of the aqueous solution, the rate of peroxynitrite production increases with the concentration of nitrite in the aqueous solution.

[0037] Figure 9A shows the change in the concentration of peroxynitrite in the mist as the pH of the plasma-activated mist is changed when the sodium nitrite concentration in the aqueous solution is set to 2000 micromolar. The horizontal axis of Figure 9A represents time, measured in seconds. The vertical axis of Figure 9A represents the concentration of peroxynitrite in the mist, measured in micromolar. The change in the concentration of peroxynitrite was determined by the numerical simulation described above using the data in Figure 1.

[0038] FIG. 9B is an expanded view of the peroxynitrite concentration range of 0 to 2 micromolar of FIG. 9A.

[0039] 9A and 9B, when the pH is changed from 2.5 to 4, the peak peroxynitrite concentration in the mist decreases from 15.8 micromolar to 0.28 micromolar, and the half-life of the peroxynitrite concentration in the mist increases from approximately 30 seconds to approximately 1600 seconds. Thus, when the nitrite concentration in the aqueous solution is held constant, the peak peroxynitrite concentration and the half-life of the concentration decay change according to the pH of the plasma-activated mist.

[0040] The inventors analyzed the relationship between the concentration of sodium nitrite in the plasma-activated mist and the rate of peroxynitrite generation (see Figure 8) and the change in the concentration of peroxynitrite in the mist over time when the pH of the plasma-activated mist is changed with a sodium nitrite concentration of 2000 micromolar in the aqueous solution (see Figure 9A). They came up with the idea of ​​adjusting the nitrite concentration in the aqueous solution and the pH of the plasma-activated mist to change the concentration of peroxynitrite in the mist over time. The peak and half-life of peroxynitrite concentration are important parameters in sterilization spraying. For example, a spraying method with a relatively high peak concentration and a relatively short half-life, as shown in Figure 6, is suitable for hand disinfection. On the other hand, a spraying method with a relatively low peak concentration and a relatively long half-life, as shown in Figure 7, is suitable for indoor spraying.

[0041] FIG. 10 is a flow chart illustrating how to determine the nitrite concentration of the aqueous solution and the pH of the plasma activated mist.

[0042] In step S1010 of FIG. 10, the target ranges for the peak concentration and half-life time of peroxynitrite are determined.

[0043] 10, the concentration of nitrite in the aqueous solution and the pH of the aqueous solution are tentatively determined. The concentration of nitrite in the aqueous solution ranges from 10 micromolar to 10 millimolar.

[0044] 10, an aqueous solution having the nitrite concentration and pH determined in step S1020 is sprayed using a spray device, and the resulting mist is collected and the concentrations of hydrogen peroxide, nitrate ions, nitrous acid, and nitrite ions and the pH are measured. The measurements are performed using an absorptiometric method using an ultra-microcell, with droplets collected from the mist on a glass plate or the like.

[0045] In step S1040 of FIG. 10, a numerical simulation is performed using the measurement value obtained in step S1030 as the initial value, and the transition of the concentration of peroxynitrite as shown in FIG. 9A is obtained.

[0046] In step S1050 of Fig. 10, it is determined whether the peak concentration value and half-life time of peroxynitrite are within their respective target value ranges. If they are within the target value ranges, the process ends. If they are not within the target value ranges, the process proceeds to step S1060.

[0047] In step S1060 of FIG. 10, the concentration of nitrite in the aqueous solution is increased or decreased depending on the peak value of the concentration of peroxynitrite.

[0048] In step S1070 of Figure 10, if the half-life of the peroxynitrite concentration is less than the target value, the pH of the plasma activated mist is increased, and if the half-life of the peroxynitrite concentration is greater than the target value, the pH of the plasma activated mist is decreased. The process then proceeds to step S1030. As described above, by adding a sufficient amount of pH buffer to the aqueous solution, the pH of the plasma activated mist can be determined by the pH of the aqueous solution.

[0049] As nitrite, sodium nitrite, which is inexpensive and suitable for use in humans and animals, and potassium nitrite, which is suitable for use in plants, are preferred, but the type of cation is not important as long as it is a nitrite. In addition, as a method for supplying nitrite, it is also possible to dissolve nitric oxide, nitrogen dioxide, dinitrogen trioxide, or dinitrogen tetroxide gas in advance.

[0050] A pH adjuster is used to adjust the pH of an aqueous solution. pH adjusters are acids, bases, or a combination of an acid or base with a pH buffer. Acids include nitric acid and hydrochloric acid. Bases include sodium hydroxide, potassium hydroxide, calcium hydroxide, and ammonia. pH buffers include citric acid, succinic acid, acetic acid, oxalic acid, phosphoric acid, and carbonic acid.

[0051] By using a pH adjuster, the concentration of nitrite in the aqueous solution and the pH of the plasma activated mist can be adjusted independently of each other.

[0052] When the concentration of active species in the mist is measured at a distance of, for example, 5 centimeters from the spray nozzle of the spray device a predetermined time after plasma activation, the results are nearly identical to the data from the numerical calculation simulation shown in Figures 4 and 5. This clearly shows that peroxynitrite is continuously produced by the spray method of the present invention. Even if similar measurements are performed using conventional spray methods such as those shown in Patent Document 1, measurement data of active species that achieve a sufficient production rate of peroxynitrite cannot be obtained. Thus, conventional spray methods do not result in the continuous production of peroxynitrite by the mist emitted from the plasma activation unit of the spray device.

Claims

1. A spraying method in which peroxynitrite is continuously produced by a plasma-activated mist having a pH in the range of 2 to 5, which is generated by a spray device from an aqueous solution containing nitrite at a concentration in the range of 10 micromolar to 10 millimolar.

2. The spraying method according to claim 1, wherein a pH adjuster which is an acid, a base or a combination of an acid or a base and a pH buffer is added to said aqueous solution.

3. The method of claim 1, further comprising adding a sufficient amount of a pH buffer to said aqueous solution to cause the pH of said plasma activated mist to be the same as the pH of said aqueous solution.

4. The method of claim 1, further comprising adding an acid or base to the aqueous solution to adjust the pH and further adding a sufficient amount of a pH buffer to cause the pH of the plasma activated mist to be the same as the pH of the aqueous solution.

5. A spray method as described in claim 1, in which the transition of the concentration of peroxynitrite in the mist generated is estimated by a numerical calculation simulation based on the measured values ​​of the concentration of active species and pH of the mist generated.

6. The spray method according to claim 1, wherein the concentration of the nitrite in said aqueous solution is in the range of 100 micromolar to 1600 micromolar, and the pH of said aqueous solution is in the range of 2.5 to 3.

7. The method of claim 1, wherein the spraying device comprises a plasma active portion having a surface DBD structure.

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