Fluorescence test solution

Abstract

This fluorescence test solution contains: water as a solvent; and a flavin derivative as a blue fluorescent dye that emits blue fluorescence. The flavin derivative has a flavin skeleton and uses riboflavin as a starting material.

Description

Fluorescent inspection liquid

[0001] The present invention relates to a fluorescent inspection liquid used in leak inspection.

[0002] Leak inspections are conducted for equipment that requires airtightness and for piping systems in factories, etc. One type of leak inspection is a fluorescent leak inspection method that uses an inspection liquid containing a fluorescent dye (fluorescent inspection liquid). Japanese Patent Application Laid-Open No. 10-221196 describes the use of a food additive as the fluorescent agent in the fluorescent inspection liquid.

[0003] However, there is a problem in that there are almost no fluorescent test solutions that emit blue fluorescence (wavelength 360 to 500 nm) that are highly safe for the human body and can emit fluorescence with sufficient brightness.

[0004] Coumarin derivatives are an example of a blue fluorescent agent. However, coumarin derivatives are toxic to the human body and are therefore avoided for use in, for example, food equipment. Quinine is another example of a substance that emits blue fluorescence. Quinine is used as a bittering agent in soft drinks (tonic water) and is a substance that is safe for the human body. However, quinine has low water solubility at room temperature, so there is a problem in that sufficient fluorescent brightness cannot be obtained when used as a fluorescent test solution in aqueous solution.

[0005] Therefore, the inventors of the present invention have considered the need for a fluorescent test liquid that is safe for the human body, has high fluorescent brightness, and emits blue light.

[0006] An object of the present invention is to solve the above-mentioned problems.

[0007] One aspect of the following disclosure is a fluorescent test solution that includes water and a flavin derivative as a blue fluorescent dye that emits blue fluorescence, the flavin derivative having a flavin skeleton and derived from riboflavin as a starting material.

[0008] The fluorescent inspection liquid of the above aspect is highly safe for the human body and emits blue fluorescence with high fluorescent brightness, and therefore can be suitably used for leak inspection in various fields.

[0009] FIG. 1 is a diagram illustrating a method for producing a flavin derivative using riboflavin as a raw material. FIG. 2A is a photograph of the fluorescent test solution (first fluorescent test solution) according to Experimental Example 1, taken indoors under fluorescent lighting. FIG. 2B is a photograph of the first fluorescent test solution under ultraviolet light irradiation in a darkroom. FIG. 3A is a photograph of a metal piece coated with ultrapure water (Comparative Example 1) and dried, taken indoors under ultraviolet light irradiation, according to Experimental Example 2. FIG. 3B is a photograph of a metal piece coated with the first fluorescent test solution (Experimental Example 1) and dried, taken indoors under ultraviolet light irradiation, according to Experimental Example 2. FIG. 4 is a photograph of a simulated test subject irradiated with ultraviolet light after being supplied with the first fluorescent test solution, taken in Experimental Example 3. FIG. 5 is a table showing the COD and BOD evaluation results for the first and second fluorescent test solutions, as well as the aqueous solutions according to the Reference Example.

[0010] (Embodiment) The fluorescent test solution contains water as a solvent and a fluorescent agent (blue fluorescent dye) that emits blue fluorescence. The blue fluorescent dye includes one or more types of flavin derivatives. The flavin derivative may include, for example, multiple flavin derivatives produced by photolysis of riboflavin. In one embodiment, the flavin derivative may include, as a main component, at least one of formylmethylflavin and lumichrome, which are obtained by photolysis of riboflavin. For example, lumichrome (7,8-dimethylalloxazine) has a fluorescence emission peak at 450 to 480 nm and emits blue fluorescence by absorbing ultraviolet light.

[0011] The above-mentioned flavin derivatives are suitable for use as fluorescent test solutions because they can generate fluorescence with a brightness easily visible to the naked eye even at concentrations as low as 5 ppm. The concentration of the flavin derivative contained in the fluorescent test solution is not particularly limited, but can be 5 ppm to 20 ppm. A fluorescent test solution containing a flavin derivative at a concentration of 5 ppm or more is suitable because it exhibits sufficient fluorescence brightness. Furthermore, a fluorescent test solution containing a flavin derivative at a concentration of 20 ppm or less is suitable from the viewpoint of meeting the COD (Chemical Oxygen Demand) and BOD (Biochemical Oxygen Demand) standards (160 mg / L or less) established as sewage discharge standards in Japan. However, the concentration of the flavin derivative contained in the fluorescent test solution may be higher than 20 ppm depending on national and local environmental standards.

[0012] The flavin derivative has a flavin skeleton and is produced using riboflavin (vitamin B2) as a starting material. The flavin derivative of this embodiment may contain at least one of formylmethylflavin and lumichrome as a main component. As an example, as shown in FIG. 1, the flavin derivative is produced by oxidizing riboflavin with sodium periodate (NaIO). ４ Alternatively, all or a portion of the resulting formylmethylflavin may be reacted with acetic acid to produce lumichrome, which is yet another type of flavin derivative.

[0013] The flavin derivative may be obtained by irradiating riboflavin with light. Irradiating an aqueous solution of riboflavin with light decomposes the riboflavin to produce flavin derivatives such as formylmethylflavin, lumiflavin, carboxymethylflavin, and lumichrome. Irradiating a sufficient amount of light to an aqueous solution (neutral) of riboflavin that emits green fluorescence yields a blue fluorescent dye that emits strong blue fluorescence. Such a blue fluorescent dye may contain at least one of formylmethylflavin and lumichrome as a flavin derivative as a main component. The fluorescent test solution may contain lumiflavin, carboxymethylflavin, and undecomposed riboflavin in addition to lumichrome and formylmethylflavin.

[0014] The flavin derivatives derived from riboflavin are substances generated in vivo as metabolic products of riboflavin. If ingested in excess, these flavin derivatives are excreted from the body through the same metabolic mechanisms as riboflavin. Furthermore, flavin derivatives are also found in foods as photodecomposition products of riboflavin, and are ingested on a daily basis. Therefore, fluorescent test solutions containing flavin derivatives as fluorescent agents are considered to have relatively low toxicity to the human body and excellent safety.

[0015] The fluorescent inspection solution may further contain a preservative to prevent spoilage (decomposition) of the flavin derivative. Examples of preservatives include parabens such as butylparaben, isopropylparaben, propylparaben, and ethylparaben, and isothiazolinones such as methylisothiazoline. Methylparaben is a preservative used in cosmetics and pharmaceuticals, and is highly safe for humans. In one embodiment, the amount of preservative added may be, for example, 10 ppm. A preservative concentration of 10 ppm meets Japanese food hygiene standards and is suitable for use in, for example, food equipment inspections. Alternatively, the amount of preservative added may be, for example, 100 ppm or less. A preservative concentration of 100 ppm meets Japanese standards for pharmaceuticals and medical devices and is safe for use in applications where the product is not intended for human consumption.

[0016] Experimental Example 1 In Experimental Example 1, the color of a fluorescent test solution containing a 5 ppm flavin derivative (hereinafter referred to as the "first fluorescent test solution") was examined. The flavin derivative in Experimental Example 1 was obtained by photolysis of an aqueous solution of riboflavin. The fluorescent test solution containing a 5 ppm flavin derivative was obtained by photolysis of an aqueous solution of riboflavin with a 5 ppm concentration. In other words, the concentration of the raw material riboflavin was referred to as the concentration of the flavin derivative in the experimental example. As shown in Figure 2A, the first fluorescent test solution was colorless and transparent under room lighting. On the other hand, as shown in Figure 2B, when the first fluorescent test solution was irradiated with ultraviolet light in a dark room, it was confirmed that it emitted blue fluorescence with a brightness that was easily visible.

[0017] (Experimental Example 2) In Experimental Example 2, the presence or absence of luminescence from the first fluorescent inspection liquid after drying was investigated. In Experimental Example 2, two rectangular metal pieces were prepared. One was immersed in ultrapure water (Comparative Example 1) and the other was immersed in the first fluorescent inspection liquid (see Experimental Example 1). The two metal pieces were then dried. The surfaces of the dried metal pieces were then observed under room lighting and under UV light irradiation in a dark room. A photograph of the metal pieces immersed in ultrapure water is shown in Figure 3A. As shown, the metal pieces immersed in ultrapure water were colorless under room lighting. Furthermore, they did not exhibit any color due to fluorescence even under UV light irradiation in a dark room.

[0018] A photograph of a metal piece immersed in the first fluorescent test liquid is shown in Figure 3B. The metal piece immersed in the first fluorescent test liquid showed no fluorescence under room light. It was confirmed that the metal piece on which the first fluorescent test liquid had been dried emitted blue fluorescence under ultraviolet light. The fluorescence on the surface of this metal piece had a color and brightness that was clearly distinguishable from the blue-purple illumination light irradiated together with ultraviolet light from a black light, a source of ultraviolet light. These results confirmed that the first fluorescent test liquid maintains its fluorescent state even after drying, making it suitable for identifying leak locations. Furthermore, we checked whether the fluorescence disappeared when running water was poured over the metal piece to which the fluorescent agent of the first fluorescent test liquid had adhered. As a result, the fluorescence disappeared simply by running water, confirming that the fluorescent agent contained in the first fluorescent test liquid could be easily washed away with running water.

[0019] (Experimental Example 3) In Experimental Example 3, a leak test was performed by supplying the first fluorescent inspection liquid to an air cylinder as a simulated test object as shown in FIG. 4 . The simulated test object was an air cylinder with an air pipe connected to a port, and an intentional looseness (leakage point) was provided at the connection between the port and the air pipe. In Experimental Example 3, the first fluorescent inspection liquid was filled in a lubricator and supplied as a mist sprayed into compressed air. The mist of the first fluorescent inspection liquid was supplied into the inside of the simulated test object together with the compressed air.

[0020] As shown in the figure, leakage of the first fluorescent test liquid occurred at the leak location in the leak test of Experimental Example 3. The leakage of the first fluorescent test liquid was confirmed as blue fluorescence when irradiated with ultraviolet light. It was confirmed that the leak location could be easily identified from the location emitting the strongest fluorescence. It was also confirmed that the leakage flow rate at the leak location could be estimated from the distribution of the first fluorescent test liquid scattered around the leak location.

[0021] Experimental Example 4 In Experimental Example 4, the COD and BOD of the first and second fluorescent test solutions were evaluated. The second fluorescent test solution was the first fluorescent test solution to which 100 ppm of methyl parahydroxybenzoate was added as a preservative. The COD was calculated by converting the amount of oxidant consumed when oxidizing organic matter contained in the fluorescent test solution with potassium permanganate into the amount of oxygen. The BOD was calculated by measuring the amount of oxygen consumed by microorganisms in the water through respiration in the presence of dissolved oxygen over a five-day measurement period at 20°C.

[0022] As shown in Figure 5, the first fluorescent test solution in Experimental Example 1 had a COD of 17 mg / L and a BOD of 29 mg / L. The second fluorescent test solution had a COD of 16 mg / L and a BOD of 45 mg / L. These results confirm that both the first and second fluorescent test solutions were below the COD and BOD standards of 160 mg / L and 160 mg / L, respectively, which restrict their discharge into sewerage. Therefore, it was confirmed that there would be no problems with their discharge into sewerage. Note that Figure 5 also shows the COD and BOD of an aqueous solution containing the preservative methyl parahydroxybenzoate at a concentration of 100 ppm as a reference example. As shown in the reference example, the increase in COD and BOD due to the addition of the preservative was relatively small.

[0023] After the leak inspection, the equipment to be inspected is washed with water to wash away the fluorescent inspection liquid. In this washing process, the fluorescent inspection liquid is typically diluted 200 times or more. Therefore, the COD and BOD values ​​of the first or second fluorescent inspection liquid actually discharged into sewage or the like are 1 / 200 or less of the values ​​shown in FIG. 5 . Therefore, when used under normal conditions, the first or second fluorescent inspection liquid satisfies the discharge standards for lakes, marshes, and oceans (e.g., COD and BOD of 8 to 10 mg / L).

[0024] (Modification of the embodiment) In this modification, an example will be described in which a red fluorescent dye or a green fluorescent dye is added to the fluorescent test liquid to make the fluorescent test liquid multicolor.

[0025] In Modification 1, a fluorescent test solution was investigated in which riboflavin was added to the flavin derivative of this embodiment, which emits blue fluorescence. While riboflavin emits yellow-green fluorescence, a fluorescent test solution in which the flavin derivative of this embodiment was mixed with riboflavin emitted green fluorescence (wavelength 500 to 570 nm). Furthermore, by increasing the proportion of the flavin derivative of this embodiment, the blueness increased, and a fluorescent test solution emitting blue-green fluorescence was obtained.

[0026] In Modification 2, a fluorescent test solution was investigated in which rhodamine B was added to the flavin derivative of this embodiment. An aqueous solution of rhodamine B emits orange fluorescence. In this modification, a fluorescent test solution emitting purple fluorescence was obtained by mixing the flavin derivative of this embodiment with rhodamine B. It was also confirmed that increasing the proportion of the flavin derivative in the fluorescent test solution of this modification changed the color from pinkish purple to more bluish, resulting in a fluorescent test solution emitting bluish purple fluorescence.

[0027] The fluorescent test liquid can be produced in multiple colors by the above-described Modifications 1 and 2. These Modifications increase the color options for the fluorescent test liquid, and can provide a fluorescent test liquid with a fluorescent color that is highly visible depending on the installation environment of the test object.

[0028] The present invention is not limited to the above disclosure, and various configurations can be adopted without departing from the gist of the present invention.

[0029] (Supplementary Note 1) One aspect is a fluorescent test solution that includes water and a flavin derivative as a blue fluorescent dye that emits blue fluorescence, the flavin derivative having a flavin skeleton and derived from riboflavin as a starting material. This fluorescent test solution is highly safe for the human body and emits blue fluorescence with high fluorescent brightness, making it suitable for use in leak tests in a variety of fields.

[0030] (Supplementary Note 2) The fluorescent test solution according to Supplementary Note 1 may contain the flavin derivative at a concentration of 5 ppm to 20 ppm, which is lower than the sewage discharge standard and has a low environmental impact.

[0031] (Supplementary Note 3) The fluorescent test solution according to Supplementary Note 1 or 2 may further contain a preservative, which can prevent spoilage (decomposition) of the flavin derivative serving as the fluorescent agent.

[0032] (Appendix 4) In the fluorescent inspection solution according to any one of Appendices 1 to 3, the blue fluorescent dye may contain at least one of formylmethylflavin and lumichrome as a main component. This fluorescent inspection solution is highly safe and emits highly visible blue fluorescence when irradiated with ultraviolet light, making it suitable for use in leak inspections.

Claims

1. A fluorescence test solution comprising water and a flavin derivative as a blue fluorescent dye that emits blue fluorescence, wherein the flavin derivative has a flavin skeleton and is a derivative starting from riboflavin.

2. The fluorescence test solution according to claim 1, comprising the flavin derivative at a concentration of 5 ppm or more and 20 ppm or less.

3. The fluorescence test solution according to claim 1 or 2, further comprising a preservative.

4. The fluorescence test solution according to claim 1 or 2, wherein the blue fluorescent dye contains at least one of formylmethylflavin and lumichrome as a main component.