Water-soluble dye titration reagent with good stability and preparation method thereof

Abstract

The application discloses a water-soluble dye titration reagent with good stability and a preparation method thereof. The mass percentage composition of the water-soluble dye titration reagent comprises 0.1-2 wt% of ionic liquid, 1-10 wt% of a surfactant, 0.1-1 wt% of an ultraviolet absorber, 0.1-1 wt% of a free radical capturing agent, 0.1-1 wt% of an organic pigment dye, 0.1-10 wt% of a reaction titrant, 1-10 wt% of an amphiphilic small molecule solvent, and the balance of water. The ionic liquid and the ultraviolet absorber both contain an aromatic ring skeleton structure. The ionic liquid has a pi-pi stacking non-covalent bond modification effect on the ultraviolet absorber, and the surfactant has an emulsifying effect on the ultraviolet absorber, thereby significantly improving the solubility of the ultraviolet absorber in a water-soluble system, ensuring that the water-soluble dye titration reagent has excellent resistance to photo-oxidative degradation, and realizing the purpose of long-term quality stability without being prepared and used immediately.

Description

Technical Field

[0001] This invention relates to the field of titration analytical chemistry, specifically to a water-soluble dye titration reagent with good stability and its preparation method. Background Technology

[0002] Natural light is composed of electromagnetic waves with different wavelengths, with the visible wavelengths between 380 and 780 nm being the most visible to the human eye. The reason why traditional organic dye indicator solutions deteriorate upon exposure to the environment is partly due to the absorption of specific wavelengths of light by electrons in the specific chemical bonds of the substance's structure, leading to energy level transitions. According to quantum theory, the energy of a photon is directly proportional to its frequency, i.e., inversely proportional to the wavelength of light. A photon, also known as a light quantum, is denoted as v, representing a gauge particle that mediates electromagnetic interactions. The energy of a photon is the product of Planck's constant and the frequency of the electromagnetic radiation. Let be the expression for photon energy, where h is Planck's constant, v is the photon frequency, and λ is the photon wavelength. Natural light contains a portion of short-wavelength, high-energy ultraviolet light. Under ultraviolet light excitation, the chemical bonds in the core of organic dye indicators partially break, rendering them unable to exhibit their original colorimetric properties; that is, the organic dye indicator becomes ineffective.

[0003] Due to differences in chemical structure and luminescence principle, different organic molecules exhibit significant variations in their absorption performance for different wavelengths of light and the ease of photo-induced oxidative degradation. For example, azo dyes such as Acid Chrome Blue K contain conjugated unsaturated bonds and electron-depleted substituents, thus exhibiting significant ultraviolet absorption performance in short-wavelength light below 400 nm. However, their azo chemical bonds may also break due to electron excitation to antibonding orbitals, resulting in the loss of color development performance. Ultraviolet absorbers, such as 2-(3,5-di-tert-butyl-2-hydroxyphenyl)-5-chlorobenzotriazole (abbreviated as UV-327, CAS No. 3864-99-1), can strongly absorb the ultraviolet portion of sunlight and fluorescent light sources without undergoing any changes themselves. They then dissipate the absorbed energy as heat or harmless low-energy radiation through energy conversion.

[0004] Currently, a large number of UV absorbers are designed for use in plastics, synthetic fibers, paints, and petroleum products. They are particularly suitable for light-colored and transparent products, such as paints and various plastic products. They are especially effective in protecting polyvinyl chloride, polyester, acrylic, resin, polystyrene, and light-colored and transparent furniture. They are also good cosmetic additives to protect the above-mentioned products from photo-oxidative degradation caused by ultraviolet radiation, thus greatly extending the product's service life.

[0005] However, since the chemical structure of most UV absorbers is based on salicylates, benzophenones, benzotriazoles, substituted acrylonitriles, triazines, etc., which contain lipophilic hydrophobic groups such as long aliphatic chains or aromatic rings, and contain very little hydrophilic polar groups such as -OH, -SO3H, and -COOH, UV absorbers designed as additives for polymer products, although they have strong UV absorption performance and are inexpensive, have poor solubility and dispersibility in polar aqueous solutions, making it difficult to directly apply them to aqueous systems to achieve UV protection for organic dyes.

[0006] Indicators are a class of reagents in analytical chemistry, often used in titration operations. They utilize the highly sensitive and selective reaction of indicators with inorganic ions, and their rapid color change upon completion of the reaction, to indicate the endpoint of the titration reaction. Based on the type of titration reaction, indicators can be classified into three categories: acid-base indicators, redox indicators, and complexation indicators. Organic pigment dye molecules are typically used as indicators.

[0007] In traditional chemical analysis laboratories, samples are often taken intermittently for testing, and indicator solutions are prepared and used immediately to prevent deterioration. With the development of automated water quality monitoring sensing technology, there is a need to develop highly stable chemical reagents based on flow colorimetry for continuous monitoring of water quality indicators in outdoor environments. Therefore, research on titration reagents with long shelf lives, especially water quality titration reagents coupled with colorimetric continuous flow analyzers, has become a research focus.

[0008] In recent years, flow injection analysis (FIA) has emerged as a highly efficient and automated method for continuous sampling and analysis of water samples, enabling the mixing of samples and reagents in a specific order and ratio using a peristaltic pump. This ensures highly reproducible and quantifiable mixing and reaction times. Consequently, there is a need to develop liquid titration reagents that can be coupled with the peristaltic pump of such continuous flow analyzers and are stable in environmental conditions. Clearly, the stability of readily prepared indicator solutions in laboratories is insufficient to meet the long-term stability requirements of continuous flow analyzers for sampling in field environments for weeks or months. Summary of the Invention

[0009] The purpose of this invention is to overcome the defects in the existing technology and provide a water-soluble dye titration reagent with good stability and its preparation method. The ionic liquid and surfactant play a solubilizing role for the lipid-soluble ultraviolet absorber. Specifically, the ionic liquid modifies the π-π stacked non-covalent bonds of the ultraviolet absorber, and the surfactant emulsifies the ultraviolet absorber. The synergistic effect of the two significantly improves the solubility of the ultraviolet absorber in the water-soluble system. The relatively high concentration of ultraviolet absorber can effectively absorb ultraviolet light in the transmitted light from the outside, thereby improving the long-term stability of organic pigment dyes and ensuring that the water-soluble dye titration reagent has excellent resistance to photo-induced oxidative degradation. It does not require fresh preparation and can be used immediately, thus achieving the goal of long-term quality and stability.

[0010] To achieve the above objectives, one of the technical solutions of the present invention is to design a water-soluble dye titration reagent with good stability, the composition of which is as follows by mass percentage: 0.1-2 wt% ionic liquid, 1-10 wt% surfactant, 0.1-1 wt% ultraviolet absorber, 0.1-1 wt% free radical scavenger, 0.1-1 wt% organic pigment dye, 0.1-10 wt% reaction titrant, 1-10 wt% amphiphilic small molecule solvent, and the balance being water. The ionic liquid and ultraviolet absorber both contain aromatic ring skeleton structures.

[0011] The preferred technical solution is that the ionic liquid is composed of aromatic cations and anions, the surfactant is a nonionic surfactant, the ultraviolet absorber is a benzotriazole ultraviolet absorber, and the reaction titrant is one of acid, alkali, oxidant, reducing agent, and chelating agent.

[0012] A further preferred technical solution is that the aromatic cation is one or more of imidazolium cations, pyridinium cations, and isoquinolineium cations, the structures of which are shown in Table 1. 1 ~R 5 It is one of hydrogen atoms, alkyl groups, and heteroalkyl groups;

[0013] Table 1 General structural formulas of aromatic cations

[0014]

[0015] The anion is one or more of the following: halide ions, aryl sulfonate ions, alkyl sulfate ions, tetrafluoroborate ions, hexafluorophosphate ions, trifluoromethanesulfonate ions, and carboxylate ions.

[0016] A further preferred technical solution is that, in the aromatic cation, R 1 ~R 5 It is one of methyl, ethyl, n-propyl, isopropyl, n-butyl, and tert-butyl.

[0017] Another preferred technical solution is that the surfactant is one or more of fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, and polysorbate.

[0018] A further preferred technical solution is that the surfactant is one or more of lauryl alcohol, cetyl alcohol, oleyl alcohol, polyethylene glycol nonylphenyl ether, polyethylene glycol octylphenyl ether (also known as Triton X-100), Tween-20, and Tween-80.

[0019] A preferred technical solution is that the ultraviolet absorber is one of 2-benzotriazole-2-yl-4,6-bis-tert-pentylphenol (also known as UV-320), 2-(2'-hydroxy-3',5'-di-tert-butylphenyl)-5-chlorobenzotriazole (also known as UV-327), 2-(3,5-di-tert-pentyl-2-hydroxyphenyl)benzotriazole (also known as UV-328), and 2-(2'-hydroxy-3'-isobutyl-5'-tert-butylphenyl)benzotriazole (also known as UV-350).

[0020] In a preferred embodiment, the free radical scavenger is one or more of potassium sorbate, 2-tert-butylphenol, 3-tert-butylphenol, 2-tert-butyl-4-methylphenol, and 2,6-di-tert-butyl-4-methylphenol; the organic pigment dye is one or more of Acid Chrome Blue K, Naphthol Green B, Methyl Orange, Bromocresol Green, Methylene Blue, and Bromothymol Blue; and the amphiphilic small molecule solvent is one or more of ethanol, isopropanol, ethylene glycol, glycerol, acetone, and methyl acetate.

[0021] The second technical solution of the present invention is to propose a method for preparing the above-mentioned stable water-soluble dye titration reagent. The components are mixed and stirred to dissolve according to the above-mentioned mass percentages, and then subjected to ultrasonic treatment or mechanical shearing treatment for 10 to 30 minutes to obtain a stable water-soluble dye titration reagent.

[0022] Preferred technical solutions include setting the following parameters during ultrasonic treatment: power of 100–1800W, amplitude of 5–20μm, frequency of 20–100kHz, and ultrasonic time of 10–30min; and performing mechanical shearing treatment in a homogenizing emulsifier.

[0023] Compared to traditional methods of chemical covalent modification to introduce hydrophilic polar groups such as -OH, -SO3H, and -COOH into molecules to improve their solubility in aqueous solutions, non-covalent modification of UV absorbers offers more diverse advantages. This is because non-covalent modification does not involve additional chemical steps and does not disrupt conjugated sp2 bonds. 2The large π bonds in the region avoid affecting the molecular orbital energy levels. This invention provides a water-soluble dye titration reagent with good stability. The non-covalent modification of the ultraviolet absorber involves possible π-π stacking, cation-π interactions, and surfactant emulsification, ultimately enabling the lipid-soluble ultraviolet absorber to dissolve at a high concentration in an aqueous medium while simultaneously ensuring that light transmission is not impaired, resulting in a complex solution that remains clear and transparent. The ultraviolet absorber effectively prevents photo-induced oxidative degradation of organic pigment dye molecules under heat and photon irradiation, ensuring the long-term stability of the water-soluble dye titration reagent as an indicator under ambient light.

[0024] The ionic liquids used in this invention are typically liquid at room temperature and at standard pressure within the range of 300°C (the boiling point of water is 100°C under standard atmospheric pressure), and compared to water and hydrophilic solvents, ionic liquids can dissolve a large number of organic molecules to a suitable extent. It has been shown that groups in aromatic systems readily undergo π-π stacking interactions, and cation-π interactions can be achieved using either metal or organic cations. In summary, organic cations containing aromatic groups can generally effectively solubilize UV ​​absorbers containing aromatic conjugated groups. These organic cations are typically preferred to be imidazolium, pyridinium, or isoquinolineium cations, preferred due to the planar structure and aromatic group structure of the cations.

[0025] To characterize the interaction degree and binding sites between the ionic liquid and the ultraviolet absorber, saturation transfer difference nuclear magnetic resonance spectroscopy (STD-NMR) can be used to describe the binding epitopes and interaction degree between the ionic liquid and the ultraviolet absorber. STD-NMR selectively saturates the acceptor macromolecule and interacts with it intramolecularly. 1 H- 1 H-cross relaxation measurements combined with saturation transfer of ligands reveal site-specific interactions of ligand molecules.

[0026] Here, the spatial proximity of the ionic liquid cations relative to the UV absorber was determined, and the interaction sites of 1-butyl-3-methylimidazolium acetate ([bmim][OAc]), 1-butyl-3-methylimidazolium chloride ([bmim]Cl), and 1-butyl-1-methylpyrrolidine trifluoromethanesulfonate ([bmpyrr][OTf]) were visualized as an epitope map. The aim was to confirm that any structural changes were indeed the result of ionic liquid interactions.

[0027] From the attached figure Figure 1The saturation transfer difference nuclear magnetic resonance (STD-NMR) epitope maps show that all ionic liquids produce STD signals, indicating a direct interaction between the ionic liquids and the UV absorber surface. When considering the cation-related STD signals, the strongest interaction sites for imidazole cations [bmim] are the terminal -CH3 group of the alkyl chain and the C-2 position of the [bmim] ring. The STD signals of imidazole cations in 1-butyl-3-methylimidazole chloride ([bmim]Cl) and 1-butyl-3-methylimidazole acetate ([bmim][OAc]) show very little difference (see Appendix). Figure 1 a and append Figure 1 (d) This indicates that the binding mode of the UV absorber to the ionic liquid depends primarily on the cation binding mode, and is independent of the anion pairing. The -CH3 group in the acetate anion was used to study the spatial proximity of 1-butyl-3-methylimidazolium acetate ([bmim][OAc]) with the UV absorber. When considering the NMR signals of both the anion and cation, the strongest interaction site was the -CH3 group of the acetate anion (see Appendix). Figure 1 (c).

[0028] For pyrrole cations [bmpyrr], in responses similar to those observed with imidazole cations [bmim], the alkyl-terminal -CH3 group gives the strongest STD response of saturation transfer difference (see Appendix). Figure 1 (b) Unlike imidazole cations [bmim], the protons around the charge center of the pyrrolidine ring produce a relatively low saturation transfer difference (STD) response, indicating that aromatic substituents play a key role in the interaction between the ionic liquid and the UV absorber. This is related to the affinity between the π-π stacking of the aromatic rings of the ionic liquid and the UV absorber and the cation-π interaction.

[0029] A wide variety of commercially available surfactants are widely used in homogenization and solubilization. Typically, the hydrophobic end of a surfactant has an affinity for lipophilic components, while the hydrophilic end is exposed in polar environments such as aqueous solutions. If a surfactant's hydrophobic end possesses π-π interactions and solubilization capabilities with the lipophilic component, the adsorption of the hydrophobic end to the lipophilic component is enhanced. Therefore, the use of surfactants promotes the stability of the prepared multiphase emulsion, especially its stability under dilution and changes in solution conditions. In summary, highly functionalized ionic liquids and surfactants are needed as additives to wet, disperse, and stabilize ultraviolet absorbers used in liquid formulations.

[0030] Because sunlight contains a large amount of harmful ultraviolet (UV) light with wavelengths of approximately 290-460 nm, this high-energy UV light causes photo-oxidative degradation, ultimately leading to the decomposition and fading of organic dye molecules. To enhance or slow down the photo-oxidation process, light stabilizers are added. Based on their stabilization mechanisms, light stabilizers can be classified as UV absorbers, light shielding agents, UV quenchers, and free radical scavengers. UV absorbers are light stabilizers that absorb the UV portion of sunlight radiation (especially wavelengths of 290-400 nm) without undergoing any change themselves. They are typically used as additives to slow down the photo-oxidative degradation process in material systems exposed to UV radiation. UV absorbers are the most widely used type of light stabilizer. Based on their structure, they can be classified as salicylates, benzophenones, benzotriazoles, substituted acrylonitriles, triazines, etc., with benzophenones and benzotriazoles being the most commonly used in industry. However, since ultraviolet absorbers designed for applications such as polymer materials are usually insoluble or poorly soluble in water, such ultraviolet absorbers have almost never been used in aqueous solution systems in previous application studies.

[0031] Appendix Figure 2 The UV-vis absorption spectra of UV-327, an ultraviolet absorber, under different solvent conditions are shown below. Figure 2 As can be seen, when 10 mg of the lipid-soluble ultraviolet absorber UV-327 is added to 10 mL of deionized water, UV-327 is completely insoluble in the water. Subsequently, 100 mg of the surfactant Triton is added and thoroughly ultrasonicated. The resulting solution is tested, and the UV-vis absorption spectrum is denoted as A. Although the ultraviolet absorber is partially dispersed in the water under the action of the surfactant, the UV-vis absorption spectrum shows a signal with approximately equal intensity in the 250-850 nm range, indicating that at this point, 0.1 wt% of the lipid-soluble ultraviolet absorber UV-327... 27. Under the action of 1wt% surfactant Triton, it appears as aggregated suspended solid particles. When 10mg of ionic liquid 1-ethyl-3-methylimidazolium hexafluorophosphate is further added, the resulting solution's UV-Vis absorption spectrum is denoted as B. The UV-Vis absorption spectrum shows a significant absorption peak near 350nm, indicating that the lipid-soluble UV absorber UV-327 exhibits molecular-level dissolution and dispersion under the action of 0.1wt% ionic liquid. This effectively protects other components in the solution from oxidation by UV irradiation at wavelengths below 400nm. In summary, the lipid-soluble UV absorber UV-327 can be dispersed in aqueous solution under suitable additives and solvent conditions, showing a maximum absorption wavelength near 350nm and possessing good UV absorption performance. However, in unfavorable solvent conditions, the lipid-soluble UV absorber UV-327 shows no UV absorption, exhibiting a scattering baseline and lacking UV protection capability.

[0032] In addition to using ultraviolet absorbers as light stabilizers, free radical scavengers can also be used as additives to capture free radicals induced by residual ultraviolet irradiation of system components, thereby inhibiting the photo-oxidative degradation process caused by ultraviolet irradiation of the system by inhibiting the growth of free radical chains.

[0033] A solution is a homogeneous mixture of a single phase, in which the solute is homogeneously and stably distributed in another solvent in a molecular or ionic state. Most chemical reactions take place in liquid solutions. Although water is the most common and inexpensive liquid solvent in nature, and is the same medium used for the target water quality detection, the introduction of non-aqueous solvents can act as co-solvents to further promote the homogeneous dispersion of the solute components in the reagent. Without non-aqueous solvents, the composition sometimes fails to produce a well-dispersed, clear solution and phase separation occurs. Preferably, non-aqueous solvents with moderate polarity, such as ethanol, isopropanol, ethylene glycol, glycerol, acetone, and methyl acetate, are used as co-solvents. These short-chain alcohols or short-chain esters are representative of non-aqueous solvent molecules that are miscible with water in any proportion. Since surfactants reduce the surface tension of the target solution by oriented alignment on the adsorption layer surface, non-aqueous solvent molecules with smaller molecular lengths than surfactants can further reduce the interfacial tension at the solid-liquid interface of the UV absorber in aqueous solution by adjusting their configuration and orientation in aqueous solution, thereby improving the solubility of the UV absorber in aqueous solution.

[0034] After the above components are mixed and added, the ultraviolet absorber needs to be thoroughly mixed in the aqueous solution using methods such as ultrasound. The term "ultrasound" refers to mechanical waves in the frequency range greater than 20 kHz. Ultrasound utilizes mechanical effects to assist in promoting the kinetic dispersion of the solute, thereby achieving the solubilization and dispersion of the ultraviolet absorber. The dispersion mechanism is that ultrasound requires an energy carrier—a medium—to propagate. During transmission, there is an alternating period of positive and negative pressure. In the positive phase, it compresses the medium molecules to increase the medium density; in the negative phase, acoustic cavitation occurs between the solvent and the sample, creating cavitation and resulting in the instantaneous generation of bubbles filled with saturated vapor in the liquid. To maintain the interfacial tension between the solution and the ultraviolet absorber at approximately the same value as the interfacial tension of the solution (i.e., the interfacial tension between the solution and vapor in the bubbles), the energy of the liquid-vapor interface must be comparable to the energy required for the intermolecular forces of the ultraviolet absorber molecules to be dispersed. During ultrasonic treatment, ultraviolet absorbers are forced to separate instantaneously, creating cavities. If organic cations, surfactants, and non-aqueous solvents in the solution dynamically fill these cavities through π-π stacking, cation-π interactions, and surfactant emulsification, these organic cations, surfactants, and non-aqueous solvents will adhere to the surface of the ultraviolet absorbers through intermolecular forces during this stage, preventing the absorber molecules from re-aggregating. This achieves the solubilizing effect of such ultraviolet absorbers in aqueous solutions. Increasing the contact area between the sample and the solvent improves the dissolution rate of the target substance from the solid phase to the liquid phase. The secondary effects of ultrasound, such as mechanical vibration, emulsification, diffusion, and agitation, all contribute to thorough mixing of the raw materials in all directions, resulting in a more effective dispersion than typical unidirectional stirring.

[0035] The advantages and beneficial effects of this invention are as follows:

[0036] 1. This invention provides a water-soluble dye titration reagent with good stability. The ionic liquid and surfactant solubilize the lipid-soluble ultraviolet absorber. Specifically, the ionic liquid modifies the π-π stacked non-covalent bonds of the ultraviolet absorber, and the surfactant emulsifies the ultraviolet absorber. The synergistic effect of the two significantly improves the solubility of the ultraviolet absorber in the water-soluble system. The relatively high concentration of ultraviolet absorber can effectively absorb ultraviolet light from transmitted light, thereby improving the long-term stability of organic pigment dyes and ensuring that the water-soluble dye titration reagent has excellent resistance to photo-induced oxidative degradation. It does not require fresh preparation and achieves the goal of long-term quality and stability.

[0037] 2. This invention provides a water-soluble dye titration reagent with good stability. The amphiphilic small molecule solvent, as a moderately polar non-aqueous solvent, is miscible with aqueous solution in any proportion. Since the surfactant reduces the surface tension of the solution by oriented arrangement on the adsorption layer surface, the amphiphilic small molecule solvent with a smaller molecular length than the surfactant can further reduce the solid-liquid interfacial tension of the ultraviolet absorber in the aqueous solution by adjusting its configuration orientation in the aqueous solution, thereby further improving the solubility of the ultraviolet absorber in the aqueous solution system.

[0038] 3. This invention provides a water-soluble dye titration reagent with good stability. The ionic liquid and surfactant also have a solubilizing effect on organic pigment dyes containing aromatic ring skeletons. Specifically, the ionic liquid modifies the π-π stacked non-covalent bonds of the aromatic ring skeleton of organic pigment dyes, and the surfactant emulsifies the organic pigment dyes. The two work synergistically to improve the solubility of organic pigment dyes containing aromatic ring skeletons in water-soluble systems, thereby facilitating the flexible preparation of water-soluble dye titration reagents with appropriate concentrations of organic pigment dyes according to usage requirements.

[0039] 4. The present invention provides a water-soluble dye titration reagent with good stability. The solvent is water and amphiphilic small molecule solvent, which ensures that the system has low viscosity and is easy to use with the peristaltic pump of a continuous flow analyzer. Attached Figure Description

[0040] Figure 1 The STD-NMR epitopes of (a) [bmim]Cl, (b) [bmpyrr][OTf], and (c, d) [bmim][OAc] anions and cations with ultraviolet absorbers were obtained by saturation transfer difference NMR (STD-NMR).

[0041] Figure 2 These are the UV-vis absorption spectra of UV-327, an ultraviolet absorber, under different solvent conditions;

[0042] Figure 3 This is the UV-vis absorption spectrum of UV-327-solubilized Acid Chrome Blue K;

[0043] Figure 4 This is the UV-vis absorption spectrum of methylene blue MB in the dye titration reagent of Example 7 as a function of time;

[0044] Figure 5 The UV-vis absorption spectrum of methylene blue MB in the dye titration reagent of Comparative Example 4 as a function of time is shown.

[0045] Figure 6The absorbance of methylene blue MB in the dye titration reagent of Example 7 and Comparative Example 4 decreases over time. Detailed Implementation

[0046] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and examples. The following examples are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0047] Example 1

[0048] A water-soluble dye titration reagent with good stability is shown in Table 2. Bromothymol blue is used as an organic pigment dye indicator and 0.5 wt% sulfuric acid is used as a reaction titrant. This water-soluble dye titration reagent can be used as a reagent for determining the alkalinity of water samples with medium alkalinity (10-100 ppm).

[0049] Table 2. Mass percentage composition of the water-soluble dye titration reagent in Example 1

[0050] type reagents Weight (wt%) Ionic liquids 1-Ethyl-3-methylimidazolium hexafluorophosphate 0.1 surfactants Qulaton 1 UV absorber UV-327 0.1 Free radical scavengers 2-tert-butyl-4-methylphenol 0.1 Organic pigments and dyes Bromothymol Blue 0.1 Reaction titrant sulfuric acid 0.5 non-aqueous solvents ethanol 5 water Deionized water 93.1

[0051] The components were mixed and stirred to dissolve, and then subjected to ultrasonic treatment or mechanical shearing for 10–30 min to obtain a water-soluble dye titration reagent with good stability. The parameters for ultrasonic treatment were set as follows: power 100–1800 W, amplitude 5–20 μm, frequency 20–100 kHz, and ultrasonic time 10–30 min.

[0052] A 10 mL water sample was drawn into a colorimetric analysis cell using a continuous flow analyzer. The sample containing 0.1 mol / L H2 was then gradually added to the cell using a peristaltic pump. + Hydrogen ion water alkalinity determination reagent was added and thoroughly mixed using a magnetic stirrer. The mixed solution turned blue after adding the reagent. With each 50 μL drop of the reagent added using a peristaltic pump, a sample of the red solution was intermittently taken and placed in a quartz cuvette for UV-Vis spectrophotometry to measure its absorption spectrum. Initially, when the solution was blue, the maximum absorption peak wavelength was at 602 nm, a characteristic peak of the deprotonated form of bromothymol blue. Subsequently, the reagent was gradually added in multiple batches to a 10 mL water sample; the mixed solution remained blue. Samples were taken intermittently at every 50 μL addition, and the absorption spectrum was measured, showing a maximum absorption peak at 602 nm on the UV-Vis absorption spectrum. When the total amount of reagent added reached 323 μL, the mixed solution changed from blue to yellow, indicating a titration inflection point. This was reflected in the UV-Vis absorption spectrum as a sudden jump in the maximum absorption peak to 427 nm. Therefore, the alkalinity of the water sample was:

[0053]

[0054] Example 2 sample

[0055] A water-soluble dye titration reagent with good stability is shown in Table 3. Bromothymol blue is used as an organic pigment dye indicator and 0.1 wt% sulfuric acid is used as a reaction titrant. This water-soluble dye titration reagent can be used as a reagent for determining the alkalinity of water samples with low alkalinity (1-10 ppm). Its preparation method is the same as in Example 1.

[0056] Table 3. Mass percentage composition of the water-soluble dye titration reagent in Example 2

[0057]

[0058] Example 3

[0059] A water-soluble dye titration reagent with good stability is shown in Table 4. Bromothymol blue is used as an organic pigment dye indicator and 10 wt% sulfuric acid is used as a reaction titrant. This water-soluble dye titration reagent can be used as a reagent for determining water alkalinity for the determination of high alkalinity (100-1000 ppm) water samples. The preparation method is the same as in Example 1.

[0060] Table 4. Mass percentage composition of the water-soluble dye titration reagent in Example 3.

[0061]

[0062]

[0063] Example 4

[0064] A water-soluble dye titration reagent with good stability is shown in Table 5 for its mass percentage composition. Acid Chrome Blue K-Naphthol Green B is used as an organic pigment dye indicator and 0.372 wt% disodium ethylenediaminetetraacetate is used as a reaction titrant. This water-soluble dye titration reagent is suitable for the determination of water hardness in the medium hardness management range (10-100 ppm). Its preparation method is the same as in Example 1.

[0065] Table 5. Mass percentage composition of the water-soluble dye titration reagent in Example 4.

[0066]

[0067] Example 5

[0068] A water-soluble dye titration reagent with good stability is shown in Table 6 for its mass percentage composition. Acid Chrome Blue K-Naphthol Green B is used as an organic pigment dye indicator and 0.372 wt% disodium ethylenediaminetetraacetate is used as a reaction titrant. This water-soluble dye titration reagent is suitable for the determination of water hardness in the medium hardness management range (10-100 ppm). Its preparation method is the same as in Example 1.

[0069] Table 6. Mass percentage composition of the water-soluble dye titration reagent in Example 5.

[0070]

[0071]

[0072] Example 6

[0073] A water-soluble dye titration reagent with good stability is shown in Table 7. Acid Chrome Blue K-Naphthol Green B is used as an organic pigment dye indicator and 3.72 wt% disodium ethylenediaminetetraacetate is used as a reaction titrant. This water-soluble dye titration reagent is suitable for the determination of water hardness in the high hardness management range (100-1000 ppm). Its preparation method is the same as in Example 1.

[0074] Table 7. Mass percentage composition of the water-soluble dye titration reagent in Example 6

[0075]

[0076] Example 7

[0077] A water-soluble dye titration reagent with good stability is shown in Table 8. Methylene blue is used as an organic pigment dye indicator and 0.1 wt% sulfuric acid is used as a reaction titrant. This water-soluble dye titration reagent can be used as a reagent for determining the alkalinity of water samples with low alkalinity (1-10 ppm). Its preparation method is the same as in Example 1.

[0078] Table 8. Mass percentage composition of the water-soluble dye titration reagent in Example 7

[0079]

[0080]

[0081] Comparative Example 1

[0082] A water-soluble dye titration reagent differs from the stable water-soluble dye titration reagent in Example 4 in that it does not contain ionic liquids, and the proportion of water has been adjusted. Its mass percentage composition is shown in Table 9. Acid Chrome Blue K-Naphthol Green B is used as an organic pigment dye indicator, and 0.372 wt% disodium ethylenediaminetetraacetate is used as a reaction titrant. This water-soluble dye titration reagent is suitable for hardness determination of water samples in the medium hardness management range (10-100 ppm), and its preparation method is the same as in Example 1.

[0083] Table 9. Mass percentage composition of the water-soluble dye titration reagent in Comparative Example 1

[0084]

[0085] During the preparation process, it was found that when the UV absorber was added to the above component system, obvious solid-liquid separation occurred. This indicates that when the system contains only surfactant (Tween-80) and no ionic liquid, the lipid-soluble UV absorber UV-328 cannot be effectively dissolved in the system to resist UV radiation degradation.

[0086] Comparative Example 2

[0087] A water-soluble dye titration reagent differs from the stable water-soluble dye titration reagent in Example 4 in that it does not contain surfactants, and the proportion of water has been adjusted. Its mass percentage composition is shown in Table 10. Acid Chrome Blue K-Naphthol Green B is used as an organic pigment dye indicator, and 0.372wt% disodium ethylenediaminetetraacetate is used as a reaction titrant. This water-soluble dye titration reagent is suitable for hardness determination of water samples in the medium hardness management range (10-100ppm), and its preparation method is the same as in Example 1.

[0088] Table 10 shows the mass percentage composition of the water-soluble dye titration reagent in Comparative Example 2.

[0089]

[0090] During the preparation process, it was found that when the UV absorber was added to the above component system, a slight solid-liquid separation phenomenon occurred. This indicates that when the system contains only ionic liquid (1-ethyl-3-methylimidazolium tetrafluoroborate) and no surfactant, the lipid-soluble UV absorber UV-328 cannot be effectively dissolved in the system to resist UV radiation degradation.

[0091] Comparative Example 3

[0092] A water-soluble dye titration reagent differs from the stable water-soluble dye titration reagent in Example 4 in that it does not contain ionic liquids and surfactants, and the proportion of water has been adjusted. Its mass percentage composition is shown in Table 11. Acid Chrome Blue K-Naphthol Green B is used as an organic pigment dye indicator, and 0.372 wt% disodium ethylenediaminetetraacetate is used as a reaction titrant. This water-soluble dye titration reagent is suitable for hardness determination of water samples in the medium hardness management range (10-100 ppm), and its preparation method is the same as in Example 1.

[0093] Table 11 shows the mass percentage composition of the water-soluble dye titration reagent in Comparative Example 3.

[0094]

[0095] During the preparation process, it was found that when the UV absorber was added to the above component system, a severe solid-liquid separation phenomenon occurred, indicating that when the system does not contain ionic liquids and surfactants, the lipid-soluble UV absorber UV-328 cannot be effectively dissolved in the system to resist UV radiation degradation.

[0096] Comparative Example 4

[0097] A water-soluble dye titration reagent differs from the stable water-soluble dye titration reagent in Example 7 in that it does not contain a UV absorber, and the water ratio has been adjusted. Its mass percentage composition is shown in Table 12. Methylene blue is used as an organic pigment dye indicator, and 0.1 wt% sulfuric acid is used as a reaction titrant. This water-soluble dye titration reagent can be used as a water alkalinity determination reagent for the determination of low alkalinity (1-10 ppm) water samples. Its preparation method is the same as that in Example 1.

[0098] Table 12 shows the mass percentage composition of the water-soluble dye titration reagent in Comparative Example 4.

[0099] type reagents Weight (wt%) Ionic liquids 1-Butyl-3-methylimidazolium hexafluorophosphate 0.1 surfactants Qulaton 1 UV absorber - - Free radical scavengers 2-tert-butyl-4-methylphenol 0.1 Organic pigments and dyes Methylene blue 0.1 Reaction titrant sulfuric acid 0.1 non-aqueous solvents ethanol 5 water Deionized water 93.6

[0100] The water-soluble dye titrants in Examples 1-7 and Comparative Examples 1-4 were stored at room temperature (25±5℃) and protected from direct sunlight. The absorption spectra of the water-soluble dye titrants were periodically measured using a UV-Vis spectrophotometer to confirm their storage stability over time. As a relative measurement, it allows for a quantitative assessment of closely related formulation stability. The test results are shown in Table 13.

[0101] The criteria for determining the failure of water-soluble dye titration reagents are as follows: Place the prepared reagent under ambient temperature and indoor lighting conditions, and monitor its absorbance at the characteristic maximum absorption wavelength in the non-ultraviolet band using UV-vis. If the absorbance at the characteristic maximum absorption wavelength in the non-ultraviolet band decreases to less than 50% of the initial value, it is considered to be ineffective; or if the degree of color change at the titration endpoint is insufficient to be recognized by the RGB sensor in the optical detection module of the continuous flow analyzer, it indicates that the reagent formulation has expired and failed.

[0102] Table 13. Stability test results of water-soluble dye titration reagents in Examples 1-7 and Comparative Examples 1-4

[0103]

[0104]

[0105] As can be seen from the experimental data in Table 13:

[0106] (I) The water-soluble dye titration reagents prepared in Examples 1-7 and Comparative Example 4 were initially clear and transparent solutions. However, the water-soluble dye titration reagent systems prepared in Comparative Examples 1-3 showed varying degrees of solid-liquid separation. The solid-liquid separation in the water-soluble dye titration reagent system prepared in Comparative Example 3 was the most severe. This indicates that ionic liquids and surfactants, when present alone, both have a certain degree of solubilizing effect on ultraviolet absorbers. The solubilizing effect on ultraviolet absorbers is optimal when ionic liquids and surfactants are present simultaneously. Ionic liquids and surfactants can synergistically improve the solubility of ultraviolet absorbers in aqueous solutions.

[0107] (II) The shelf life of the water-soluble dye titration reagents prepared in Examples 1-7 is more than one year under indoor conditions, while the shelf life of the water-soluble dye titration reagent systems prepared in Comparative Examples 1-4 is shorter, and the shelf life of Comparative Examples 1-3 is the shortest. This indicates that as the solubility of the ultraviolet absorber in water increases, the lifespan of the water-soluble dye titration reagent is longer. This confirms that the higher the concentration of the ultraviolet absorber dispersed at the molecular level in the aqueous solution, when external light passes through and irradiates the dye titration reagent, the ultraviolet absorber in the aqueous solution preferentially absorbs ultraviolet light and undergoes molecular thermal vibration, absorbing the photon energy in the high-energy ultraviolet light and converting it into heat energy for release. This protects the organic dyes in the aqueous solution from photo-induced oxidative degradation caused by high-energy ultraviolet radiation, thereby helping to improve the long-term stability of organic pigment dyes.

[0108] Appendix Figure 3 The UV-vis absorption spectrum of UV-327-solubilized Acid Chrome Blue K is shown below. Figure 3It can be seen that as the solubility ratio of UV-327 to Acid Chrome Blue K increases, the peak value of the absorption peak in the 300-400 nm range gradually increases; the solubilized UV-327 can effectively protect the stability of the corresponding groups in the ultraviolet absorption band of Acid Chrome Blue K, preventing it from being photo-oxidized and degraded by low-wavelength ultraviolet radiation. The specific experimental steps are as follows: 1 wt% Acid Chrome Blue K aqueous solution was prepared as solution C, and an aqueous solution of an ultraviolet absorber composed of 0.1 wt% lipid-soluble ultraviolet absorber UV-327, 1 wt% surfactant Triton, and 0.1 wt% ionic liquid 1-ethyl-3-methylimidazolium hexafluorophosphate was prepared as solution D. Then, solutions C and D were mixed sequentially at volume ratios of 1:1, 1:2, 1:3, and 1:4, and the UV-vis absorption spectra were measured. Figure 3 As can be seen, the absorption peak value gradually increases within the ultraviolet absorption band below 400nm. Under ambient temperature and indoor lighting conditions, the absorbance at its characteristic maximum absorption wavelength in the non-ultraviolet band is monitored using UV-Vis. Failure is defined as a decrease in absorbance at less than 50% of the characteristic maximum absorption wavelength in the non-ultraviolet band. Solutions C and D were mixed sequentially at volume ratios of 1:1, 1:2, 1:3, and 1:4, resulting in stability periods of 1 month, 3 months, 1 year, and over 2 years, respectively. This demonstrates that under the protection of the ultraviolet absorber aqueous solution D, the color development lifespan of Acid Chrome Blue K in solution C is effectively extended, achieving the goal of long-term quality and stability as an indicator.

[0109] The absorbance of methylene blue (MB) in the dye titration reagents of Example 7 and Comparative Example 4 was investigated over time. The specific experimental steps are as follows: The dye titration reagents prepared in Example 7 and Comparative Example 4 were placed in an indoor environment with natural light and a temperature of 20±10℃. The absorbance of the characteristic absorption peaks in the near-ultraviolet band of both reagents was monitored with UV-vis. The reagents were considered to be ineffective when the absorbance at the wavelength corresponding to the maximum characteristic absorption peak decreased to below 50%. A curve showing the change of the wavelength corresponding to the maximum characteristic absorption peak over time was plotted.

[0110] Figure 4 This is the UV-vis absorption spectrum of methylene blue (MB) in the dye titration reagent of Example 7, changing over time. Figure 4 As can be seen from the example, the dye titration reagent in Example 7 still has good absorbance after 270 days;

[0111] Figure 5 The image shows the UV-vis absorption spectrum of methylene blue (MB) in the dye titration reagent of Comparative Example 4 as a function of time. Figure 5 It can be seen from this that the dye titration reagent in Comparative Example 4 expires in about 200 days;

[0112] Figure 6These are the absorbance decay curves of methylene blue MB in the dye titration reagent of Example 7 and Comparative Example 4 over time. Figure 6 As can be seen from the example, the dye titration reagent used in Example 7, which is an organic pigment dye methylene blue solubilized by UV-327, has long-lasting stability, thus achieving the purpose of the invention.

[0113] According to Beer-Lambert law, the absorbance A of an organic dye is directly proportional to its concentration c, i.e., A = K * b * c, where A is the absorbance; K is the molar absorptivity, which is related to the molecular structure of the absorbing component and the wavelength λ of the incident light; c is the concentration of the absorbing substance; and b is the thickness of the absorbing layer. Therefore, the decrease in absorbance A at the maximum absorption wavelength is often proportional to the decrease in concentration c. The degradation process of organic pigments and dyes is accompanied by a decrease in absorbance at the maximum wavelength, and the retention rate of organic pigments and dyes can be expressed as α. t =C0-C t / C0*100%=A0-A t / A0*100%, where C0 is the initial concentration of the organic pigment dye, C t A represents the concentration of the organic pigment dye at the corresponding date; A0 represents the absorbance at the initial maximum characteristic absorption peak wavelength (668 nm). t The absorbance at the wavelength of the maximum characteristic absorption peak (668 nm) at the corresponding date can be used to determine the degradation and deterioration of methylene blue MB by monitoring the change of absorbance of the dye titration reagent over time in Example 7 and Comparative Example 4.

[0114] This invention provides a water-soluble dye titration reagent with good stability. The ionic liquid and surfactant solubilize the lipid-soluble ultraviolet absorber. Specifically, the ionic liquid modifies the π-π stacked non-covalent bonds of the ultraviolet absorber, and the surfactant emulsifies the ultraviolet absorber. The synergistic effect of the two significantly improves the solubility of the ultraviolet absorber in the water-soluble system. The relatively high concentration of ultraviolet absorber can effectively absorb ultraviolet light from transmitted light, thereby improving the long-term stability of organic pigment dyes and ensuring that the water-soluble dye titration reagent has excellent resistance to photo-induced oxidative degradation. It does not require fresh preparation and achieves the goal of long-term quality and stability.

[0115] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A water-soluble dye titration reagent with good stability, characterized in that, Its mass percentage composition is as follows: 0.1~2 wt% ionic liquid, 1~10 wt% surfactant, 0.1~1 wt% ultraviolet absorber, 0.1~1 wt% free radical scavenger, 0.1~1 wt% organic pigment dye, 0.1~10 wt% reaction titrant, 1~10 wt% amphiphilic small molecule solvent, and the balance is water. Both the ionic liquid and the ultraviolet absorber contain aromatic ring skeleton structures. The ionic liquid is composed of aromatic cations and anions. The aromatic cations are one or more of imidazolium cations, pyridinium cations, and isoquinolineium cations, and their structures are shown in Table 1. 1 ~R 5 It is one of hydrogen atoms, alkyl groups, and heteroalkyl groups; the anion is one or more of halide ions, aryl sulfonate ions, alkyl sulfate ions, tetrafluoroborate ions, hexafluorophosphate ions, trifluoromethanesulfonate ions, and carboxylate ions; The surfactant is one or more of fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, and polysorbate. The ultraviolet absorber is one of 2-benzotriazole-2-yl-4,6-bis-tert-amylphenol, 2-(2'-hydroxy-3',5'-di-tert-butylphenyl)-5-chlorobenzotriazole, 2-(3,5-di-tert-amyl-2-hydroxyphenyl)benzotriazole, and 2-(2'-hydroxy-3'-isobutyl-5'-tert-butylphenyl)benzotriazole; The amphiphilic small molecule solvent is one or more of ethanol, isopropanol, ethylene glycol, glycerol, acetone, and methyl acetate; Table 1 General structural formulas of aromatic cations 。 2. The water-soluble dye titration reagent with good stability as described in claim 1, characterized in that, The reaction titrant is one of the following: acid, base, oxidizing agent, reducing agent, and chelating agent.

3. The water-soluble dye titration reagent with good stability as described in claim 1, characterized in that, In the aromatic cation, R 1 ~R 5 It is one of methyl, ethyl, n-propyl, isopropyl, n-butyl, and tert-butyl.

4. The water-soluble dye titration reagent with good stability as described in claim 1, characterized in that, The surfactant is one or more of lauryl alcohol, cetyl alcohol, oleyl alcohol, polyethylene glycol nonylphenyl ether, polyethylene glycol octylphenyl ether, Tween-20, and Tween-80.

5. The water-soluble dye titration reagent with good stability as described in claim 1, characterized in that, The free radical scavenger is one or more of potassium sorbate, 2-tert-butylphenol, 3-tert-butylphenol, 2-tert-butyl-4-methylphenol, and 2,6-di-tert-butyl-4-methylphenol; the organic pigment dye is one or more of Acid Chrome Blue K, Naphthol Green B, Methyl Orange, Bromocresol Green, Methylene Blue, and Bromothymol Blue.

6. A method for preparing a water-soluble dye titration reagent with good stability as described in any one of claims 1 to 5, characterized in that, According to the mass percentage in claim 1, the components are mixed and stirred to dissolve, and then subjected to ultrasonic treatment or mechanical shearing for 10-30 minutes to obtain a water-soluble dye titration reagent with good stability. During the ultrasonic treatment, the parameters were set as follows: power 100~1800W, amplitude 5~20μm, frequency 20~100 kHz, and ultrasonic time 10~30 min; the mechanical shearing treatment was carried out in a homogenizing emulsifier.

Images