WO2025115170A1 - Fluorescence test solution - Google Patents

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 Fluid

The present invention relates to a fluorescent inspection liquid used for leak inspection.

Leak inspections are carried out on equipment that requires airtightness and on piping systems in factories, etc. One type of leak inspection is the fluorescent leak inspection method, which uses an inspection liquid containing a fluorescent dye (fluorescent inspection liquid). JP 10-221196 A describes the use of food additives as the fluorescent agent in the fluorescent inspection liquid.

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

One example of a blue fluorescent agent is a coumarin derivative. However, coumarin derivatives are toxic to the human body, so their use in food equipment, for example, is avoided. Another example of a substance that emits blue fluorescence is quinine. 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 that sufficient fluorescent brightness cannot be obtained when used as a fluorescent test solution in aqueous solution.

The inventors of this application therefore felt that a fluorescent test liquid that emits a blue color and has high fluorescent brightness, while being safe for the human body, was needed.

The present invention aims to solve the above problems.

One aspect of the disclosure below 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 being a derivative that uses riboflavin as a starting material.

The fluorescent inspection liquid described above is highly safe for the human body and emits blue fluorescence with high fluorescent brightness, making it suitable for use in leak inspections in a variety of fields.

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 according to Experimental Example 1 (first fluorescent test solution) under fluorescent lighting indoors, and FIG. 2B is a photograph of the first fluorescent test solution under ultraviolet light irradiation in a dark room. FIG. 3A is a photograph of a metal piece to which ultrapure water (Comparative Example 1) has been applied and dried, taken under indoor lighting and ultraviolet light irradiation, relating to Experimental Example 2. FIG. 3B is a photograph of a metal piece to which the first fluorescent inspection liquid (Experimental Example 1) has been applied and dried, taken under indoor lighting and ultraviolet light irradiation, relating to Experimental Example 2. FIG. 4 is a photograph showing the results of the test example 3 in which the first fluorescent test liquid was supplied to the mock test target and then the mock test target was irradiated with ultraviolet light. FIG. 5 is a table showing the evaluation results of COD and BOD for the first and second fluorescent inspection solutions, and the aqueous solution of the reference example.

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

The above flavin derivatives are suitable as fluorescent test solutions because they can generate fluorescence with a brightness that is easily visible to the naked eye even at low concentrations of, for example, about 5 ppm. The concentration of the flavin derivative contained in the fluorescent test solution is not particularly limited, but can be 5 ppm or more and 20 ppm or less. A fluorescent test solution containing a flavin derivative at a concentration of 5 ppm or more is suitable because it exhibits fluorescence emission of sufficient brightness. A fluorescent test solution containing a flavin derivative at a concentration of 20 ppm or less is suitable from the viewpoint of meeting the standard values (160 mg/L or less) of COD (Chemical Oxygen Demand) and BOD (Biochemical Oxygen Demand) 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.

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 may be obtained by reacting riboflavin with sodium periodate (NaIO ₄ ) to obtain formylmethylflavin. In addition, all or a part of the obtained formylmethylflavin may be reacted with acetic acid to obtain lumichrome, which is yet another type of flavin derivative.

Flavin derivatives may be obtained by irradiating riboflavin with light. By irradiating an aqueous solution of riboflavin with light, riboflavin is decomposed to generate flavin derivatives such as formylmethylflavin, lumiflavin, carboxymethylflavin, and lumichrome. By irradiating a sufficient amount of light to an aqueous solution (neutral) of riboflavin that emits green fluorescence, a blue fluorescent dye that emits strong blue fluorescence is obtained. Such a blue fluorescent dye may contain at least one of formylmethylflavin and lumichrome as a flavin derivative as a main component. In addition to lumichrome and formylmethylflavin, the fluorescent test solution may contain lumiflavin, carboxymethylflavin, and undecomposed riboflavin.

The above-mentioned flavin derivatives made from riboflavin are substances that are generated in the body as metabolic products of riboflavin. If such flavin derivatives are ingested in excess, they will be excreted from the body through the same metabolic mechanism as riboflavin. Flavin derivatives are also found in food as photodecomposition products of riboflavin, and are ingested on a daily basis. Therefore, fluorescent test solutions that contain flavin derivatives as fluorescent agents are considered to have relatively low toxicity to the human body and excellent safety.

The fluorescent inspection liquid may further contain a preservative to prevent spoilage (decomposition) of the flavin derivative. As the preservative, a paraben such as butylparaben, isopropylparaben, propylparaben, or ethylparaben, or an isothiazolinone preservative such as methylisothiazoline may be used. Methylparaben as a preservative is a substance used in cosmetics and medicines, and is highly safe for the human body. In one embodiment, the amount of preservative added may be, for example, 10 ppm. Addition of a preservative at a concentration of 10 ppm meets the food hygiene standards (Japan) and can be suitably used, for example, for inspection of food equipment. The amount of preservative added may also be, for example, 100 ppm or less. Addition of a preservative at a concentration of 100 ppm meets the standards for medicines and medical equipment (Japan) and can be used safely in applications where the product is not consumed by humans.

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

(Experimental Example 2)
In Experimental Example 2, the presence or absence of luminescence of the first fluorescent inspection liquid after drying under ultraviolet light was investigated. In Experimental Example 2, two rectangular metal pieces were prepared, one of which 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. Next, the surface of the dried metal pieces was observed under indoor lighting and under ultraviolet light irradiation in a dark room. A photograph of the metal pieces immersed in ultrapure water is shown in FIG. 3A. As shown in the figure, the metal pieces immersed in ultrapure water were colorless under indoor lighting. Also, they did not show any color due to fluorescence even under ultraviolet light irradiation in a dark room.

A photograph of the metal piece immersed in the first fluorescent inspection liquid is shown in Figure 3B. The metal piece immersed in the first fluorescent inspection liquid did not show any fluorescence under indoor lighting. It was confirmed that the metal piece on which the first fluorescent inspection liquid had been dried emitted blue fluorescence under ultraviolet light irradiation. 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, which is a source of ultraviolet light. From this result, it was confirmed that the first fluorescent inspection liquid maintains a fluorescent state even after drying, and is suitable for identifying the location of a leak. In addition, running water was poured over the metal piece on which the fluorescent agent of the first fluorescent inspection liquid was attached to confirm whether the fluorescence would disappear. As a result, it was confirmed that the fluorescence disappeared just by supplying running water, and that the fluorescent agent contained in the first fluorescent inspection liquid could be easily washed away with running water.

(Experimental Example 3)
In Experimental Example 3, a leak inspection was performed by supplying the first fluorescent inspection liquid to an air cylinder as a simulated inspection target as shown in Fig. 4. The simulated inspection target 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 in a state where it was sprayed in a mist with compressed air. The mist of the first fluorescent inspection liquid was supplied into the inside of the simulated inspection target together with the compressed air.

As shown in the figure, in the leak test of Experimental Example 3, leakage of the first fluorescent test liquid occurred at the leak location. The leakage of the first fluorescent test liquid could be confirmed as blue fluorescence by irradiating it 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.

(Experimental Example 4)
In Experimental Example 4, the first and second fluorescent test solutions were evaluated for COD and BOD. The second fluorescent test solution was prepared by adding 100 ppm of methyl paraoxybenzoate as a preservative to the first fluorescent test solution. The COD was calculated by converting the amount of oxidant consumed when the organic matter contained in the fluorescent test solution was oxidized 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 their respiration during proliferation over a measurement period of 5 days at 20°C in the presence of dissolved oxygen in the water.

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. From these results, it was confirmed that both the first and second fluorescent test solutions were below the COD 160 mg/L and BOD 160 mg/L standards that regulate discharge into sewage, and that there would be no problem with discharge into sewage. Note that Figure 5 also shows, as a reference example, the COD and BOD of an aqueous solution containing the preservative methyl paraoxybenzoate at a concentration of 100 ppm. As shown in the reference example, the increase in COD and BOD due to the addition of the preservative is relatively small.

Furthermore, after the leakage inspection, the equipment to be inspected is washed with water to wash away the fluorescent inspection liquid. In this washing, the fluorescent inspection liquid is usually diluted 200 times or more. Therefore, the COD and BOD values of the first or second fluorescent inspection liquid actually discharged through sewage, etc. will be 1/200th or less of the values shown in Figure 5. Therefore, when used under normal conditions, the first or second fluorescent inspection liquid meets the discharge standards for lakes, marshes, and oceans (for example, COD and BOD of 8 to 10 mg/L).

(Modification of the embodiment)
In this modified example, a multi-color fluorescent inspection liquid is obtained by adding a red fluorescent dye or a green fluorescent dye to the fluorescent inspection liquid.

In variant 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 that emitted blue-green fluorescence was obtained.

In variant 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 variant, a fluorescent test solution that emits purple fluorescence was obtained by mixing the flavin derivative of this embodiment with rhodamine B. It was also confirmed that by increasing the proportion of flavin derivative in the fluorescent test solution of this variant, the color changed from pinkish purple to more bluish, resulting in a fluorescent test solution that emits bluish purple fluorescence.

The above-mentioned modified examples 1 and 2 make it possible to produce fluorescent test liquid in multiple colors. This modified example increases the color options for fluorescent test liquid, making it possible to provide fluorescent test liquid with fluorescent colors that are highly visible depending on the installation environment of the test subject.

The present invention is not limited to the above disclosure, and various configurations may be adopted without departing from the gist of the present invention. The following notes are further disclosed in relation to the above disclosure.

(Appendix 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 being a derivative made 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, and therefore can be suitably used for leak tests in various fields.

(Appendix 2)
The fluorescent inspection solution according to Appendix 1 may contain the flavin derivative at a concentration of 5 ppm to 20 ppm. This fluorescent inspection solution is below the sewage discharge standard and has a low environmental impact.

(Appendix 3)
The fluorescent inspection liquid according to the appendix 1 or 2 may further contain a preservative, which can prevent spoilage (decomposition) of the flavin derivative as the fluorescent agent.

(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 safe and emits blue fluorescence with excellent visibility when irradiated with ultraviolet light, and therefore can be suitably used for leak inspection.

Claims (4)

A fluorescent test solution that contains water and a flavin derivative as a blue fluorescent dye that emits blue fluorescence, the flavin derivative having a flavin skeleton and being a derivative that uses riboflavin as a starting material. The fluorescent inspection solution according to claim 1, containing the flavin derivative at a concentration of 5 ppm or more and 20 ppm or less. The fluorescent inspection solution according to claim 1 or 2, further comprising a preservative. The fluorescent 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.

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