pH INDICATOR AND pH INDICATOR SYSTEM

Abstract

The present disclosure provides a pH indicator and pH indicator system for identifying a pH of an aqueous sample. The pH indicator may include a first pH-sensitive compound, a second pH-sensitive compound, and a third pH-sensitive compound. When the pH indicator is in contact with an aqueous sample, the pH indicator is configured to develop one of a plurality of colors. Each of the plurality of colors corresponds to one of a plurality of whole number pH values within a range of at least three consecutive whole number pH values and is defined by a Munsell Hue Value (MHV) in the Munsell Color System. Each of the plurality of colors corresponds to each of the plurality of whole number pH values differs from a preceding or following color corresponding to a preceding or following whole number pH value by a MHV difference of about 5 or greater.

Description

AttyDktNo .99544PCT-C63806- 10670 WO (01385) pH Indicator and pH Indicator SystemField of the Disclosure

[0001] The present disclosure relates to a pH indicator and a pH indicator system for identifying the pH of an aqueous sample. The pH indicator and pH indicator system may particularly include an additive for cat litter.Background

[0002] A pH level determines the acidity or alkalinity of a sample. The pH scale ranges from 0 to 14. A pH of 7 is neutral, whereas a pH below 7 is acidic and a pH above 7 is alkaline. A sample tested for pH may be an aqueous sample or solution, including bodily fluids. A pH indicator or pH indicator system may be used to test the pH of an aqueous sample. The pH of a bodily fluid such as urine, saliva, or blood can be used to detect illness in mammals such as human or animals. For instance, urine has a wide range of pH compared to other fluids. Testing the pH of urine in a typical urinalysis test can determine whether the person or animal has a kidney infection, acidosis, dehydration, or other ailment.

[0003] Testing pH of bodily fluid samples is a common analytical method in the medical field and in veterinary medicine. Many over the counter pH testing devices are likewise known, and pH indicators have also been included in products not typically considered as a medical device or health monitoring article. For example, feline litter products are known to include pH indicators and have been received favorably by consumers. Nevertheless, monitoring pH over a range of values with a single indicator can be difficult achieve without suffering from ambiguous readability. Accordingly, there remains a need in the art for pH indicators that are capable of use in a broad array of settings and capable of being incorporated into a variety of products.Summary of the Disclosure

[0004] In one or more embodiments, the present disclosure can relate to a pH indicator for identify ing a pH of an aqueous sample. The pH indicator may be configured as cither a liquid or a solid. The pH indicator may include a mixture of compounds that are pH-sensitive. The mixture of compounds may include at least a first pH-sensitive compound, a second pH-sensitive compound, and a third pH-sensitive compound. The pH sensitive compounds may be present in the mixture in a relative molar ratio range so that when the pH indicator is in contact with an aqueous sample, the pH indicator may develop one of a plurality of colors. Each of the plurality of colors may correspond to one of a plurality of whole number pH values. The pH indicator may cause color shifts within a range of consecutive whole number pH values in order to cover the range of typical pH values for a given sample. The range may be at least three consecutive whole number pH values, such as at least four, at least five, or even more consecutive whole number pH values. The range of consecutive whole number pH values can encompass at least one basic pH value and at least one acidic pH value. Each of the plurality of colors can be defined using a standard that provides for known determinations of color differences in a quantifiable manner. Any color determination system may be used. In one or more embodiments, the plurality of colors can be defined by a Munsell Hue Value (MHV) in the Munsell Color System (MCS). TheAttyDktNo .99544PCT-C63806- 10670 WO (01385) pH indicator can be configured so that each of the plurality of colors corresponding to each of the plurality of whole number pH values differs from a preceding or following color corresponding to a preceding or following whole number pH value by a quantifiable color difference that is sufficient to provide a clear visual distinction to a user with normal or average color perception. For example, when using the MCS as the standard, the MHV difference between colors can be about 5 or greater.

[0005] In the mixture, at least one of the first pH-sensitive compound, the second pH-sensitive compound, and the third pH-sensitive compound may be configured to be substantially colorless below a pH that encompasses a highest whole number pH value in the range of consecutive whole number pH values that a given test is configured to identify. The first pH-sensitive compound may include an azo dye selected from the group consisting of methyl red, Alizarin red S, methyl orange, cresol red, cresolphthalein (meta) and cresol purple. The second pH-sensitive compound may include phthalein dye selected from the group consisting of bromothymol blue, bromocresol green, bromocresol purple, and thymol blue. The third pH-sensitive compound may include a phthalein dye selected from the group consisting of a-naphtholphthalein. phenolphthalein, cresolphthalein, and thymolphthalein.

[0006] A relative molar ratio range of the first pH-sensitive compound to the second pH-sensitive compound to the third pH-sensitive compound may range from 1:0.5:25 to 1 :0.5:50. A relative molar ratio range of the first pH-sensitive compound to the second pH-sensitive compound to the third pH-sensitive compound may include 1 :0.5:30. The relative molar ratio range of the first pH-sensitive compormd to the second pH-sensitive compormd may range from 0.5:0.25 to 1.5:0.75. The relative molar ratio range of the first pH-sensitive compormd to the third pH-sensitive compound may range from 0.5:25 to 1.5:45. The relative molar ratio range of the second pH-sensitive compound to the third pH-sensitive compound may range from 0.25:25 to 0.75:45.

[0007] In some embodiments, the mixture of the pH-sensitive compounds may include at least one water soluble polymer. The at least one water-soluble polymer may include at least one of polyvinylpyrrolidone, N- methylpyrrolidone, N-vinylpyrrolidone, or N-ethylpyrrolidone.

[0008] Each of the plurality of colors corresponding to each of the plurality of whole number pH values may differ from a preceding or following color corresponding to a preceding or following whole number pH value by a MHV difference of about 7 or greater. The plurality of whole number pH values may be within a range of at least 5 consecutive whole number pH values. At least one of the plurality of colors can be a red hue and at least one of the plurality of colors may be a blue hue.

[0009] In some embodiments, the present disclosure may provide a pH indicator system including at least one carrier and the pH indicator. The carrier may be present in various forms such as in a particulate, a sheet, or a stick form. The carrier may include one or more of a cellulosic material, a clay material, and a silica material. The pH indicator or pH indicator system may be an animal litter additive. The animal litter additive may be applied to a pre-existing litter product.

[0010] In some embodiments, the present disclosure may provide a pH indicator that may include a first pH- sensitive compound, a second pH-sensitive compound, a third pH-sensitive compound. A mole ratio of theAttyDktNo .99544PCT-C63806- 10670 WO (01385) first pH-sensitive compound to the second pH-sensitive compound to the third pH-sensitive compound may range from 1:0.5:25 to 1:0.5:45. The pH indicator may be configured either as a liquid or as a solid.

[0011] When in contact with an aqueous sample, the pH indicator may be configured to develop one of a plurality of colors. Each of the plurality of colors may correspond to one of a plurality of whole number pH values within a range of at least three consecutive whole number pH values.

[0012] Aspects and advantages of these exemplary' embodiments and other embodiments, are discussed in detail herein. Moreover, it is to be understood that both the foregoing information and the following detailed description provide merely illustrative examples of various aspects and embodiments and are intended to provide an overview or framework for understanding the nature and character of the claimed aspects and embodiments. Accordingly, these and other objects, along with advantages and features of the present disclosure, will become apparent through reference to the following description and the accompanying drawings. Furthermore, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and may exist in various combinations and permutations.Brief Description of the Drawings

[0013] The accompanying drawings, which are included to provide a further understanding of the embodiments of the present disclosure, are incorporated in and constitute a part of this specification, illustrate embodiments of the present disclosure, and together with the detailed description, serve to explain principles of the embodiments discussed herein. No attempt is made to show structural details of this disclosure in more detail than may be necessary for a fundamental understanding of the embodiments discussed herein and the various ways in which they may be practiced. According to common practice, the various features of the drawings discussed below are not necessarily drawn to scale. Dimensions of various features and elements in the drawings may be expanded or reduced to more clearly illustrate embodiments of the disclosure.

[0014] FIG. 1 is an image illustrating a comparison of a pH test for Example 1, Comparative Example 1, and Comparative Example 2.

[0015] FIG. 2 is an image illustrating a comparison of a pH test for Comparative Example 3.

[0016] FIG. 3 is an image illustrating a comparison of a pH test for Comparative Example 4.

[0017] FIG. 4 is an image illustrating a comparison of a pH test for Comparative Example 5.

[0018] FIG. 5 is an image illustrating a comparison of a pH test for Comparative Example 6.

[0019] FIG. 6 is an image illustrating a comparison of a pH test for Comparative Example 7.

[0020] FIG. 7 is a graph showing a difference in Munsell Hue Values between Example 1 and Comparative Examples 1-7.

[0021] FIG. 8 is a graph showing a difference in Munsell Hue Values between Example 2, Example 3. and Comparative Examples 8-11.Detailed Description of the Disclosure

[0022] The invention now will be described more fully herein after through reference to various embodiments. These embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Indeed, the invention may be embodiedAttyDktNo .99544PCT-C63806- 10670 WO (01385) ill many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. As used in the specification, and in the appended claims, the singular forms "a", "an", "the", include plural referents unless the context clearly dictates otherwise.

[0023] The description may use the phrases “in certain embodiments,” “in various embodiments,” “in an embodiment,” or “in embodiments,” which may each refer to one or more of the same or different embodiments. Furthermore, the tenns “comprising,” “including,” “having,” and the like, as used with respect to embodiments of the present disclosure, are synonymous. The term “about” or “approximately” are defined as being close to as understood by one of ordinary skill in the art. In one non-limiting embodiment, the terms are defined to be within 10%, preferably within 5%, more preferably within 1%. and most preferably within 0.5%. The terms “removing.” “removed.” “reducing,” "reduced,” or any variation thereof, when used in the claims and / or the specification includes any measurable decrease of one or more components in a mixture to achieve a desired result. The use of the words “a” or “an” when used in conjunction with any of the terms “comprising,” “including,” “containing,” or “having,” in the claims or the specification may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one,” and “one or more than one.” The term “plurality” as used herein refers to tw o or more items or components. The terms “wt.%”, “vol.%”. or “mol.%” refers to a weight, volume, or molar percentage of a component, respectively, based on the total weight, the total volume of material, or total moles, that includes the component. In a non-limiting example, 10 grams of component in 100 grams of the material is 10 wt.% of component.

[0024] The present disclosure relates to pH indicators and pH indicator systems that may include a mixture of pH-sensitive compounds that is configured to yield quantifiable color differences that allow easy identification of pH value associated with a specific color when the pH indicator or pH indicator system is used to test the pH of an aqueous sample. The quantifiable color differences can be configured for visual identification by a user with normal, average color perception, and the color differences can be clearly and easily identified using one or more standards of evaluation. Thus, when the pH indicator is used, for example, in testing a bodily fluid of a human or animal, an observer can identify pH of the fluid sample based on a color shift caused by contact with the fluid sample and be able to determine physiological indications associated with the identified pH value of the fluid sample.

[0025] The measurement of the hydrogen ion concentration (pH) of a solution yields information about the solution in a chemical, biological, and physical context. pH is defined as the negative logarithm of the concentration of hydrogen ions and is measured on a scale of 0-14. pH values less than 7 indicate an acid, while pH values greater than 7 indicate a base. For example, strong acids such as hydrochloric acid or sulfuric acid have pH values less than 1, while strong bases such as sodium hydroxide have pH values greater than 13. The pH value of pure water is 7, which is considered a neutral pH.

[0026] The pH value of a solution may be measured in a laboratory setting using an instrument such as a pH sensor, colorimeter, or spectrophotometer. The pH value may also be measured using commercially available products including a solution or material treated with a pH indicator compound or dye. or a mixture ofAttyDktNo .99544PCT-C63806- 10670 WO (01385) compounds or dyes, and this can comprise observing a color change or color shift of the solution or material and comparing the observed color change with a pH value chart that is standardized for the specific indicator.

[0027] In one or more embodiments, the present disclosure provides pH indicators that are suitable for use in identifying a pH value of a liquid sample and are configured to experience defined color changes in response to contact with the liquid samples, the color changes being quantifiably correlated with different possible pH values of the liquid samples. The present pH indicators address a previous inability to achieve clearly and easily identifiable color changes across a wide range of pH values using only a single composition. While known pH indicators may use different pH indicators to identify different, corresponding pH values, it can be particularly difficult to achieve a single composition that can shift between colors that correspond to different pH values across a range of pH values. According to the present disclosure, however, it is possible to provide a single composition comprising a mixture of a plurality of different pH-sensitive compounds, the single composition being configured to shift between a plurality of different colors that correspond to different pH values across a range of pH values. Accordingly, when a pH indicator according to the present disclosure is in contact with an aqueous sample, the pH indicator can be configured to develop one of a plurality of colors, each of the plurality of colors corresponding to one of a plurality of whole number pH values within a range of whole number pH values.

[0028] An aqueous sample suitable for pH measurement using a pH indicator according to the present disclosure can be any aqueous liquid for which knowledge of the pH thereof is desirable. For example, bodily fluids, either of human or animal origin, may be tested to identify data relative to a health status of the human or animal. Such bodily fluids may include any of blood, saliva, mine, and mucosal secretions. Similarly, pH of a water source can provide different types of information about the water source. Likewise, pH can be an important data point for various uses in the food and beverage industry . Accordingly, the present pH indicators can be configured for use in any setting or product regardless of industry .

[0029] In pH measurement, ease of color identification is the benchmark for usability’ of the pH indicator. Many pH-scnsitivc materials can exhibit a color shift depending upon the pH of a sample to which they arc exposed. If the color shift is subtle or minor, it can be difficult to observe the change, and accurate pH identification is unobtainable. In one or more embodiments, the presently disclosed pH indicators utilize a mixture of pH-sensitive materials that are combined in a maimer that achieves distinct color changes across a range of pH values. The distinctness of the color changes is quantifiable by utilizing a known, color standard. The present pH indicators are configmed so that, by using the known standard, a measured pH can be accurately identified due to the quantifiably distinct colors corresponding to different possible pH values in the range to be measmed.

[0030] In the present disclosure, each of the plurality of colors that correspond to a measurable pH value can be defined by a Munsell Hue Value (MHV) in the Munsell Color System (MCS). As used herein, the "Munsell Color System” refers to a color notation system created by Albert H. Munsell and then revised by the Optical Society of America. According to the MCS, each color is expressed by three attributes: hue. value, and chroma. The “hue” means the attribute of color which can be found in the spectrum of light. In the MCSAttyDktNo .99544PCT-C63806- 10670 WO (01385) red (R), yellow (Y), green (G), blue (B), and purple (P) are selected as five principal hues and are placed at equal intervals around a circle or wheel. Yellow-red (YR), green-yellow (GY), blue-green (BG), purple-blue (PB), and red-purple (RP) are arranged between the five principal hues as five intermediate hues. In these ten hues, the degree of each hue is expressed in equally spaced relation around the circle such that the maximum degree of each hue is 10. The “value" indicates the lightness of a color. In the MCS, the value is expressed in equally spaced relation such that black, which completely absorbs light, has a value of 0, and white, which completely reflects light, has a value of 10. In the MCS. “chroma" means sharpness of color. In other words, it is the departure degree of a color from the neutral color of the same value. For example, colors of “low chroma" are described as "weak," while those of "high chroma" are described as "highly saturated." “strong,” or “vivid.”

[0031] Using the MCS, relationships between colors can be defined by whole number spacings. On the MCS color wheel, two adjacent color hues would be defined as having a MHV difference of 1. Two color hues separated by a single other color hue would be defined as having a MHV difference of 2. Thus. MHV can define a degree of separation between color hues. Color hues that are very near one another can be difficult to clearly distinguish from each other visually. While spectroscopy may be used for very accurate quantification of color hues and thus can accurately distinguish betw een color hues that are closely spaced in terms of MHV, color perception by the human eye. or visual color determination, can be more limited. As such, the present disclosure provides pH indicators that enable quantifiable differences in color result as can be clearly and accurately identified visually by a human with normal, average color perception. With the present pH indicators, each of a plurality of colors that correspond to a specific pH to be measured in an aqueous sample can be defined by an MHV. Moreover, the plurality of colors corresponding to a plurality of different pH values can have a degree of separation that enables such clear and accurate identification. The degree of separation of two color hues means the spacing difference on the MCS w heel betw een the two color hues. In other w ords, it is the number of spacings of a color hue from a preceding or following color hue. To enable clear and accurate identification of different colors corresponding to different pH values of a liquid sample, the degree of separation of color / pH pairs can be about 5 or greater. In further embodiments, the degree separation can be about 6 or greater, about 7 or greater, about 8 or greater, or about 9 or greater. As such, a pH indicator according to the present disclosure can be configured to match specific colors to specific, measured pH values (so-called “color / pH pairs"), and the pH indicator can be configured to exhibit a plurality of different colors, each corresponding to a different pH value. More particularly, each of the plurality of colors corresponding to each of the plurality of pH values can differ from a preceding or following color corresponding to a preceding or following pH value by a MHV difference of about 5 or greater, about 6 or greater, about 7 or greater, about 8 or greater, or about 9 or greater.

[0032] The present pH indicators are configured to identify a plurality of different pH values, and each pH value can be a whole number pH value. A “whole number” pH value can be any of a pH value of 1, 2. 3. 4, 5, 6. 7, 8, 9, 10, 11, 12, 13, and 14. The pH indicators can be configured to identify whole number pH values across a range consecutive whole number pH values. The range of whole number pH values can be atAttyDktNo .99544PCT-C63806- 10670 WO (01385) least three consecutive whole number pH values, at least four consecutive whole number pH values, or at least five whole number pH values. The sensitivity of the pH indicators can be particularly suited for identifying a pH of about the specified pH according to the color generated and is not intended to indicate a pH to a one hundredth pH value or even a one tenth pH value. Thus, generation of a color may indicate the associated whole number pH value ±0.4, ±0.3, ±0.2, or ±0.1.

[0033] The range of consecutive whole numbers comprising the pH range identifiable by the pH indicator can be configured to encompasses at least one basic pH value and at least one acidic pH value. This would necessitate a range with a lower end of 6 or less and a higher end of 8 or greater. It can be particularly difficult to provide accurate pH indication with a single composition in both the acidic and basic pH ranges. The present pH indicators can be configured to provide pH indication across a whole number pH range of 6 to 8. 5 to 8, 4 to 8, 3 to 8. 6 to 9, 5 to 9, 4 to 9. 3 to 9, 6 to 10. 5 to 10. 4 to 10, or 3 to 10.

[0034] The MVH for a color achieved with the present pH indicators can be confirmed by using any suitable measuring device, such as a spectrometer. In one or more embodiments, color can be measured using a Mach5±™ spectrophotometer, which is a camera-based multispectral color measurement instrument that yields L*a*b* values, XYZ-values. and percentage reflection from 400 to 700 nm for a specifically imaged area. Data from the spectrophotometer can be evaluated using appropriate processing, such as the BabelColor® software program, which is particularly suited to convert the measured values into the MHV.

[0035] In one or more embodiments, the present pH indicators can comprise a plurality of pH-sensitive compounds, which can be referenced as pH indicator compounds. Combining a plurality of pH indicator compounds can be useful to achieve a single composition effective for identifying pH across a range of pH values. The pH indicator compounds thus can be selected to achieve a desired pH-related color change. For example, the pH indicator compound methyl red is a dye that exhibits a red color in acidic solutions and exhibits a shift from red to orange to yellow as pH value increases. Methyl red can exhibit such shift in a pH range of about 4.4 to about 6.2. Similarly , the pH indicator compound bromothymol blue (also known as bromothy mol sulfone phthalein or BTB) has a yellow to green to blue color shift in the pH range of about 6.0 to about 7.6. Providing distinctive color shifts across a wide range of pH values using a single composition is not as simple as merely mixing two known compounds with two known pH indicating ranges.

[0036] When multiple pH indicators are used together, the chosen compounds cannot undergo color transitions that mutually interfere with one another. As an example, a combination of methyl red and bromothymol blue would be expected to provide a color shift from red to blue when changing from acidic to basic conditions. At about a neutral pH, the composition will exhibit a yellow color hue. When in contact with an acidic sample, the color of the methyl red compound will change from yellow to a red color hue. When in contact with a basic sample, the color of the bromothymol blue will change from yellow to a blue color hue or a purple color hue. In each case, the original, yellow color hue of the unchanged pH indicator compound remains in the composition and competes with the color change. In the acid sample, the yellow color hue of the bromothymol blue compound has only a minimal effect on the red color hue achieved by the methyl red compound. In the basic sample, however, the yellow color hue of the methyl red compound altersAttyDktNo .99544PCT-C63806- 10670 WO (01385) the blue color hue or purple color hue of the bromothymol blue compound, and this results in a green color hue or violet color hue. In other words, each of the pH indicator compounds utilized in the pH indicator composition should undergo a distinctly different color transition at different pH ranges without interfering with one another.

[0037] In one or more embodiments, the pH indicator composition of the present disclosure may comprise a plurality of different pH indicators, or pH-sensitive compounds. The composition may comprise at least two, at least three, or at least four pH-sensitive compounds. For example, the composition may comprise at least a first pH-sensitive compound, at least a second pH-sensitive compound, and at least a third pH-sensitive compound. Each of the pH-sensitive compounds may be different from one another. Each of the pH-sensitive compounds can have the same color or a different color at substantially neutral pH. Each of the pH-sensitive compounds can exhibit different color shifts at different pH ranges. The pH color shift ranges for two of the pH-sensitive compounds or all three of the pH-sensitive compounds may be non-overlapping. The types of pH-sensitive compounds that can be used in the present disclosure are discussed following. Although the types of compounds are related to the first, second, and third pH-sensitive compounds, it is understood this is merely for ease of discussion, and orders of the classes may be rearranged.

[0038] The first pH-sensitive compound can be a compound exhibiting a shift from a first color hue at substantially neutral pH to a second color hue at an acidic pH. The second color hue at the acidic pH can be a red color hue. The first color hue can be a yellow color hue or an orange color hue. Example embodiments of suitable pH-sensitive compounds having such properties may include at least one an azo dye. For instance, the azo dye may be selected from the group consisting of methyl red, Alizarin Red S, methyl orange, cresol red. cresolphthalein (meta) and cresol purple. Methyl red, for example, has a color shift from red to orange to yellow in the pH range of 4.4 to 6.2. The first pH-sensitive compound thus can be effective to provide color transition indicative of an acidic pH.

[0039] The second pH-sensitive compound can be a compound exhibiting a shift from a first color hue at substantially neutral pH to a second color hue at a basic pH. The second color hue at the basic pH can be a green color hue or a blue color hue. The first color hue can be a yellow color hue or a green color hue. Example embodiments of suitable pH-sensitive compounds having such properties may include at least one phthalein dye. For instance, the phthalein dye may be selected from the group consisting of bromothymol blue, bromocresol green, bromocresol purple, and thymol blue. Bromothymol blue, for example, has a yellow to green to blue color shift in the pH range of 6.0 to 7.6. The second pH-sensitive compound thus can be effective to provide a color transition indicative of a basic pH.

[0040] In one or more embodiments, at least three pH-sensitive compounds may be utilized in order to account for color interference, as discussed above. For example, the pH indicator composition may include a single pH-sensitive compounds that changes color under acidic conditions and include at least two pH- sensitive compounds that change color under basic conditions. As another example, the pH indicator composition may include a single pH-sensitive compound that changes color under basic conditions and includes at least two pH-sensitive compounds that change color under acidic conditions. Where two pH-AttyDktNo .99544PCT-C63806- 10670 WO (01385) sensitive compounds that change color under the same acidity conditions are used, at least one of the pH- sensitive compounds can be configured to be substantially colorless under a substantially neutral conditions or under conditions opposite the color changing conditions. For example, at least one pH-sensitive compound configured to change color under basic conditions can be configured to be substantially colorless at substantially neutral pH or can be configured to be substantially colorless at substantially acidic conditions. Likewise, at least one pH-sensitive compound configured to change color under acidic conditions can be configured to be substantially colorless at substantially neutral pH or can be configured to be substantially colorless at substantially basic conditions. Alternatively, if the pH indicator is configured for use only for indicating acidic pH values or only for indicating basic pH values, the choice of colorless pH-sensitive compounds may be connected to the lowest or the greatest pH value that is measured. For example, at least one pH-sensitive compound can be configured to be substantially colorless below a pH that encompasses a highest whole number pH value in the range of consecutive whole number pH values across which the pH indicator composition is configured to measure. Alternatively, at least one pH-sensitive compound can be configured to be substantially colorless above a pH that encompasses a lowest whole number pH value in the range of consecutive whole number pH values across which the pH indicator composition is configured to measure.

[0041] A colorless pH-sensitive compound may be used as the third pH-sensitive compound. The third pH-sensitive compound may be a phthalein dye that is substantially colorless at a substantially neutral pH but shifts to a blue color hue at a basic pH. The third pH-sensitive compound may include a phthalein dye selected from the group consisting of a-naphtholphthalein, phenolphthalein, cresolphthalein, and thymolphthalein. For example, a-naphtholphthalein is colorless below its transition point, which is in the range of pH 7.3 to 8, and shifts to a blue color hue above the transition point.

[0042] In one or more embodiments, each of the three pH-sensitive compounds may have a pKa value. The first pH-sensitive compound may have a pKa value below a pKa value of the second pH-sensitive compound, where the pKa value of the first pH-scnsitivc compound may range from 6.5 or below. The second pH- sensitive compound may have a pKa value between a pKa value of the first pH-sensitive compound and a pKa value of the third pH-sensitive compound, where the pKa value of the second pH-sensitive compound may range from above 6.5 to below 9. The third pH-sensitive compound may have a pKa value greater than a pKa value of tire first pH-sensitive compound and a pKa value of the second pH-sensitive compound, where the pKa value of the third pH-sensitive compound may range from 9 or above.

[0043] In example embodiments, a pH indicator may include the pH-sensitive compounds methyl red. bromothymol blue, and a-naphtholphthalein in order to provide a red color hue at the lowest, acidic pH and provide a blue color hue at the highest, basic pH while providing other color hues at intermediate pH values (i.e., any value between the highest and lowest pH values included for detection by the pH-indicator). If only methyl red and bromothymol blue are present in the pH indicator mixture, it is not possible to achieve a distinctive, blue color hue at a higher pH, such a pH 8 or pH 9. Rather, a green color hue will occur due to a mixing of the yellow color hue from the unshifted methyl red and the blue color hue from the shiftedAttyDktNo .99544PCT-C63806- 10670 WO (01385) bromothymol blue. By including the a-naphtholphthalein in combination with the methyl red and the bromothymol blue, the added blue color hue contributed by the a-naphtholphthalein achieves a distinct blue color hue that is visibly discernable to the human eye. Since the a-naphtholphthalein remains colorless below its transition pH, the addition to the pH indicator composition does not adversely affect the color shift in the acidic pH range.

[0044] The amounts of each of the pH-sensitive compounds present in the mixture may be varied. Specific molar ratios may be provided and can be in a context related to the transition pH of the pH-sensitive compounds. The following molar ratios can relate particularly in the context wherein the first pH-sensitive compound is one that exhibits a color shift at an acidic pH range, the second pH-sensitive compound is one that exhibits a color shift at a basic pH range, and the third pH-sensitive compound is one that also exhibits a color shift at a basic pH range and is colorless below its transition pH (i.e., the pH at which it changes from colorless to exhibiting a visibly identifiable color hue). The relative molar ratio range of the first pH-sensitive compound to the second pH sensitive compound to the third pH-sensitive compound may range from 1:0.5:25 to 1:0.5:45, from 1:0.5:27 to 1:0.5:43, from 1:0.5:29 to 1:0.5:41, from 1:0.5:31 to 1:0.5:39, or from 1:0.5:33 to 1:0.5:37. A relative molar ratio range of the first pH-sensitive compound to the second pH sensitive compound to the third pH-sensitive compound may specifically include a molar ratio of 1:0.5:30. In one or more embodiments, the relative molar ratio range of the first pH-sensitive compound to the second pH sensitive compound may range from 0.5:0.25 to 1.5:0.75, from 0.6:0.30 to 1.4:0.70, from 0.7:0.35 to 1.3:0.65, from 0.8:0.40 to 1.2:0.60, or from 0.9:0.45 to 1.1:0.55. In one or more embodiments, the relative molar ratio range of the first pH-sensitive compound to the third pH-sensitive compoimd may range from 0.5:25 to 1.5:45, from 0.6:27 to 1.4:43, from 0.7:29 to 1.3:41, from 0.8:31 to 1.2:39, or from 0.9:33 to 1.1:37. In one or more embodiments, the relative molar ratio range of the second pH-sensitive compound to the third pH sensitive compoimd may range from 0.25:25 to 0.75:45, from 0.3:27 to 0.7:43. from 0.35:29 to 0.65:41, from 0.4:31 to 0.6:39, or from 0.45:33 to 0.55:37.

[0045] The pH indicator compositions may include one or more further components in addition to the plurality of pH-sensitive compounds. In one or more embodiments, the pH indicator may also include a water- soluble polymer. The water-soluble polymer may include polyvinylpyrrolidone (PVP). The water-soluble polymer may act as a stabilizer and binds the pH indicator compounds to a surface of a carrier or substrate material. The water-soluble polymer also maintains the stability of the pH color shift from pH 5 to 9 due to the presence of the nitrogen-containing functional group. Other PVP derivatives that are water-soluble and function well as the binding polymer for binding one or more water-soluble dyes to the surface of a carrier or substrate and may include N-methylpyrrolidone (NMP). N-ethylpyrrolidone (NEP), and N-vinylpyrrolidone.

[0046] The water soluble polymer may be present in the mixture of the pH indicator in an amount ranging from about 0.01% to about 5% dissolved in solute, from about 0.1% to about 4.9%, from about 0.2% to about 4.8%, from about 0.3% to about 4.7%, from about 0.4% to about 4.6%. from about 0.5% to about 4.5%, from about 0.6% to about 4.4%. from about 0.7% to about 4.3%, from about 0.8% to about 4.2%. from about 0.9% to about 4.1%, from about 1.0% to about 4.0%, from about 1.1% to about 3.9%, from about 1.2% to aboutAttyDktNo .99544PCT-C63806- 10670 WO (01385)3.8%, from about 1.3% to about 3.7%, from about 1.4% to about 3.6%, from about 1.5% to about 3.5%, from about 1.6% to about 3.4%, from about 1.7% to about 3.3%, from about 1.8% to about 3.2%, from about 1.9% to about 3.1%, or from about 2.0% to about 3.0%.

[0047] The pH indicator composition, in some embodiments, may particularly be configured to define three different pH values by matching to three different colors, define four different pH values by matching to four different colors, define five different pH values by matching to five different colors, or define six different pH values by matching to six different colors. The colors can be selected from the following color hues: red. orange, yellow, green, blue, and violet. The colors can be identified relative to the MCS standard as already described. In an example embodiment, a pH indicator can be configured to exhibit the following pH and color hue combinations: red / pH5, orange / pH6, yellow / pH7. green / pH8, and blue / pH9.

[0048] The pH indicator composition can be provided in a variety of formats. In one or more embodiments, the pH indicator can be configured as a liquid. The liquid may be applied to various materials to be provide in a wide variety of formats so that the pH indicator can be configured as a solid. In some embodiments, the pH indicator may be applied to various materials or surfaces to provide the ability of the material to indicate pH of a liquid sample that is contacted to the material. The pH indicator may be formed as a liquid that can be applied to at least one surface of a material that acts as a carrier or substrate. The pH indicator may be sprayed, coated, embedded, impregnated, adsorbed, absorbed, blended, mixed, or added into or onto a substrate or carrier. In addition, the pH indicator may be formed as a solid without any substrate or carrier. The pH indicator may be dried as a film, pellet, or tablet, etc. The solid form of the pH indicator may be applied to test the pH of a liquid sample by, for example, dropping the film, pellet, or tablet into a liquid sample to result in a color shift to indicate pH. Alternatively, the pH indicator may be combined with other materials, such as polymers, which may be solidified to encapsulate the pH indicator.

[0049] In one or more embodiments, the present disclosure can provide a pH indicator system. Such system may include at least one carrier that includes a pH indicator composition as described herein. The carrier, which may also be referenced as a substrate, may have a variety of forms. For example, the carrier may be in a particulate form, may be in a sheet form, may be in a stick form, may be in a strip form, or may be in another form suitable for a particular use. The carrier likewise may be formed of any material that does not otherwise interfere with operability of the pH indicator to change color for indicating a pH of a liquid sample when contacted by the liquid sample. Non-limiting examples of suitable materials include cellulosics. lignins, clays, silicas, polyethylene terephthalate (PET), polypropylene (PP), polyethylene (PE), polyvinylchloride (PVC), polyvinyl acetate (PVA), wood, nut shells, plant fibers, and paper.

[0050] The pH indicator system can be useful as a stand-alone item. As such, the pH indicator system can be configured as units for sale. As a non-limiting example, the pH indicator may be configured as a pH test strip. In other embodiments, the pH indicator system may be configured as a material that is combinable with other materials for use.

[0051] In an example embodiment, the pH indicator system may be configured as a material that is combinable with a pet litter composition. Urine pH can be an indicator of a number of possible health issuesAttyDktNo .99544PCT-C63806- 10670 WO (01385) ill pets, particularly in cats. As cats are notorious for hiding their diseases, an option for monitoring cat health can include providing pH indicators in combination with a cat litter product. Cat mine has a normal pH range of 6 to 7. If the pH of the urine is above 8, it may indicate a urinary tract infection and / or kidney stones (Struvite stones). If the pH of the mine is less than 6, it may indicate kidney acidosis and / or kidney stones (calcium oxalate stones). Furthermore, changes in the pH level of urine are an accurate way to indicate illnesses. Rapid, repeated changes over a short period of time could indicate abnormalities that would require veterinary' intervention. Often, cat owners notice diseases in their pets only once they have advanced to a latestage. The presently disclosed pH indicator systems can be particularly suitable for use as an animal litter additive, such as for addition to a pet litter box, and particularly a cat litter box. The present pH indicators are particularly useful due to their ability' to provide clear, visually distinguishable colors corresponding to different pH values of a contacted liquid, including in the range of pH 5 to pH 9, which can be a useful range for identifying certain health problems in pets. A pet litter additive may be configured as granules, flakes, tablets, discs, or other formats that can be sprinkled in a litter box so that, when contacted with pet urine, the pH indicator composition included in or on the pet litter additive will provide a color indication corresponding to a pH of the urine. In such instances, it may be useful for the pet litter additive to have a size that is large enough to be noticeable to an individual inspecting the pet litter or scooping the pet litter but small enough to not discourage use of the litter pan by the animal. This may be defined in relation to an average diameter or an average length and width. For example, the average length and the average width can be in the range of about 1 mm to about 20 mm, about 1.5 mm to about 15 mm, about 2 mm to about 10 mm, or about 2.5 mm to about 7.5 mm. An average diameter may' also be within the same ranges. In addition, the color indication may last for a time of one to three horns.

[0052] Although the pH indicator system may be provided as a litter additive, it may also be incorporated directly into an animal litter product. For example, the pH indicator may be coated or otherwise applied to at least a portion of the particles forming the pet litter. Pet litters may include an amount of non-absorbent particles in combination with absorbent particles. The pH indicator composition may be applied to one or both of the non-absorbent particles and the absorbent particles. The pH indicator may alternatively be provided as an additive, as discussed above, but directly mixed with the pet litter instead of being provided separately to a consumer for use as needed. When provided as part of a pet litter, the pH indicator system material may comprise about 10% or less by weight, about 5% or less by weight, about 3% or less by weight, about 2% or less by weight, or about 1% or less by weight of the pet litter, based on the total weight of the pet litter. For example, the pH indicator system material may comprise about 0.1% to about 10% by weight, about 0.2% to about 8% by weight, about 0.3% to about 5% by weight, about 0.4% to about 3% by weight, or about 0.5% to about 2% by weight of the pet litter based on the total weight of the pet litter.

[0053] In some embodiments, the present disclosure may be directed to a method for indicating the pH of a sample. The method may include contacting a sample to a pH indicator or a pH indicator system as described herein. The method also may include observing a color change of the pH indicator or the pH indicator system by visual inspection.AttyDktNo .99544PCT-C63806- 10670 WO (01385)Examples

[0054] The present disclosure is more fully illustrated by the following examples, which are set forth to illustrate certain embodiments of the present disclosure and are not to be construed as limiting thereof.

[0055] To investigate the performance of the pH indicator and pH indicator system, examples and comparative examples were prepared according to the compositions in Tables 1, 3, 5, 7, 9, 11, and 13 shown below, a pH level test was carried out as shown in Figs. 1-6. and a color analysis of the pH level test was carried out as shown below in Tables 2, 4, 6, 8, 10, 12 and 14.

[0056] The color analysis was measured using a Mach5+™ spectrophotometer, which is a camera-based multispectral color measurement instrument. The L*a*b* values were measured for each of the examples and comparative examples. The L*a*b* values from the spectrophotometer were used as input for the BabelColor® software program, and converted to the Munsell Hue Values.

[0057] In order to test each indicator composition, each indicator in powder form was dissolved at specific ratios in ethanol. Next, PVP was added to the solution of the dissolved indicator(s) solution and mixed until dissolved. The solution was coated onto cellulose particles. The coated particles were dried in an oven for 10 minutes at 50°C. In order to assess the color shift of the pH indicator. ImL of pH-adjusted (pHs 5, 6, 7. 8 and 9) cat urine was dosed onto the particles after scattering the particles on sample cat litter. The color change was recorded after 1 minute of exposure to the cat urine. This process was repeated for three cellulose particles that are imaged, and the Mach5+™ spectrophotometer calculates the average L*a*b* values.

[0058] Example 1

[0059] In Example 1, tire relative molar ratio of the methyl red to the BTB to the a-naphtholphthalein (i.e., the first pH-sensitive compound to the second pH-sensitive compound to the third pH-sensitive compound) was 1 :0.5:30 as shown in the Table 1. The results of the color analysis, including a determination of the Munsell Hue Value and a calculation of the difference in Munsell Hue Value with the preceding pH, are shown in Table 2.

[0060] A comparison of the pH color shifts at a range of pH values of the coated particles for each of Example 1, Comparative Example 1, and Comparative Example 2 is shown in FIG. 1. As demonstrated in FIG. 1, Example 1 having a relative molar ratio of the methyl red to the BTB to the a-naphtholphthalein of 1:0.5:30 (middle row) achieved a clear and distinct blue color shift at a pH of 9 when compared to Comparative Example 1 and Comparative Example 2.

[0061] Table 1: pH indicator composition of Example 1AttyDktNo .99544PCT-C63806- 10670 WO (01385)

[0062] Table 2: Color Analysis for Example 1

[0063] Comparative Example 1

[0064] Comparative Example 1 was the same as Example 1, except that the amount of a-naphtholphthalein added to the indicator composition was higher than in Example 1 as shown in Table 3. The relative molar ratio of the methyl red to the BTB to the a-naphtholphthalein (z.e., first pH-sensitive compound to the second pH- sensitive compound to the third pH-sensitive compound) was 1 :0.5:100. The results of the color analysis, including a determination of the Munsell Hue Value and a calculation of the difference in Munsell Hue Value with the preceding pH. are shown in Table 4.

[0065] As demonstrated in FIG. 1, Comparative Example 1 having a relative molar ratio of the methyl red to the BTB to the a-naphtholphthalein of 1:0.5:100 (top row) had a green color shift at a pH of 9 when compared to Example 1, which had a clear and distinct blue color shift.

[0066] Table 3: pH indicator composition of Comparative Example 1AttyDktNo .99544PCT-C63806- 10670 WO (01385)

[0067] Table 4: Color Analysis for Comparative Example 1

[0068] Comparative Example 2

[0069] Comparative Example 2 was the same as Example 1, except that the amount of a-naphtholphthalein added to the indicator composition was lower than in Example 1 as shown in Table 5. The relative molar ratio of the methyl red to the BTB to the a-naphtholphthalein (i.e., first pH-sensitive compound to the second pH- sensitive compound to the third pH-sensitive compound) was 1:0.5:20. The results of the color analysis, including a determination of the Munsell Hue Value and a calculation of the difference in Munsell Hue Value with the preceding pH, are shown in Table 6.AttyDktNo .99544PCT-C63806- 10670 WO (01385)

[0070] As demonstrated in FIG. 1, Comparative Example 2 having a relative molar ratio of the methyl red to the BTB to the a-naphtholphthalein of 1:0.5:20 (bottom row) had a green color shift at a pH of 9 when compared to Example 1, which had a clear and distinct blue color shift.

[0071] Table 5: pH indicator composition of Comparative Example 2

[0072] Table 6: Color Analysis for Comparative Example 2

[0073] Comparative Example 3

[0074] Comparative Example 3 was the same as Example 1, except that only methyl red and bromothymol blue (BTB) were added to the indicator composition as shown in Table 7. Only methyl red and BTB wereAttyDktNo .99544PCT-C63806- 10670 WO (01385) present as the pH indicators. The results of the color analysis, including a determination of die Munsell Hue Value and a calculation of the difference in Munsell Hue Value with the preceding pH, are shown in Table 8.

[0075] A comparison of the pH color shifts at a range of pH values of the coated particles for Comparative Example 3 is shown in FIG. 2. As demonstrated in FIG. 2, Comparative Example 3 having only methyl red and BTB had a green color shift at a pH of 9 when compared to Example 1, which had a clear and distinct blue color shift.

[0076] Table 7: pH indicator composition of Comparative Example 3

[0077] Table 8: Color Analysis for Comparative Example 3

[0078] Comparative Example 4

[0079] Comparative Example 4 was the same as Example 1, except that only methyl red was added to the indicator composition as shown in Table 9. Only methyl red was present as the indicator. The results of theAttyDktNo .99544PCT-C63806- 10670 WO (01385) color analysis, including a determination of the Munsell Hue Value and a calculation of the difference in Munsell Hue Value with the preceding pH, are shown in Table 10.

[0080] A comparison of the pH color shifts at a range of pH values of the coated particles for Comparative Example 4 is shown in FIG. 3. As demonstrated in FIG. 3, Comparative Example 4 having only methyl red had a color shift of red at pH 5, orange at pH 6, and yellow at pHs 7-9 when compared to Example 1, which had a clear and distinct blue color shift at pH 9.

[0081] Table 9: pH indicator composition of Comparative Example 40082] Table 10: Color Analysis for Comparative Example 4

[0083] Comparative Example 5

[0084] Comparative Example 5 was the same as Example 1, except that only bromothymol blue (BTB) was added to the indicator composition as shown in Table 11. Only BTB was present as the indicator. The results of the color analysis, including a determination of the Munsell Hue Value and a calculation of the difference in Munsell Hue Value with the preceding pH. are shown in Table 12.AttyDktNo .99544PCT-C63806- 10670 WO (01385)

[0085] A comparison of the pH color shifts at a range of pH values of the coated particles for Comparative Example 5 is shown in FIG. 4. As demonstrated in FIG. 4, Comparative Example 5 having only BTB had a yellow color shift at a pHs 5 and 6, green at pH 7, and blue at pHs 8 and 9, when compared to Example 1. which had a clear and distinct blue color shift at pH 9 and a red color shift at pH 5.

[0086] Table 11 : pH indicator composition of Comparative Example 5

[0087] Table 12: Color Analysis for Comparative Example 5

[0088] Comparative Example 6

[0089] Comparative Example 6 was the same as Example 1, except that neither methyl red nor bromothymol blue (BTB) were added to the indicator composition as shown in Table 13. Only a-naphtholphthalein was present as the indicator. The results of the color analysis, including a determination of the Munsell Hue Value and a calculation of the difference in Munsell Hue Value with the preceding pH, are shown in Table 14.

[0090] A comparison of the pH color shifts at a range of pH values of the coated particles for ComparativeExample 6 is shown in FIG. 5. As demonstrated in FIG. 5, Comparative Example 6 having only a-AttyDktNo .99544PCT-C63806- 10670 WO (01385) naphtholphthalein had essentially no color shift at pHs 5-8, and a blue color shift at pH 9 when compared to Example 1, which had a clear and distinct red color shift at pH 5 and blue color shift at pH 9.

[0091] Table 13: pH indicator composition of Comparative Example 6

[0092] Table 14: Color Analysis for Comparative Example 6

[0093] Comparative Example 7

[0094] Comparative Example 7 was the same as Example 1. except that no water-soluble polymer, PVP, was added to the indicator composition as shown in Table 15. The results of the color analysis, including a determination of the Munscll Hue Value and a calculation of the difference in Munscll Hue Value with the preceding pH, are shown in Table 16.

[0095] A comparison of the pH color shifts at a range of pH values of the coated particles for ComparativeExample 7 is shown in FIG. 6. As demonstrated in FIG. 5, Comparative Example 6 having no PVP had essentially no color shift at pHs 5-9, maintaining only a red color when compared to Example 1. which had a clear and distinct red color shift at pH 5 and blue color shift at pH 9.AttyDktNo .99544PCT-C63806- 10670 WO (01385)

[0096] Table 15: pH indicator composition of Comparative Example 7

[0097] Table 16: Color Analysis for Comparative Example 7

[0098] Comparison of the Munsell Hue Value for each of Example 1 and Comparative Examples 1-7

[0099] As shown in Fig. 7, the only pH indicator composition that exhibited a difference in the Munsell Hue Value of 5 or more was the pH indicator having die relative molar ratio of methyl red to bromothymol blue to a-naphtholphthalein of 1:0.5:30. In Example 1, each of the Munsell Hue Values of a pH and a preceding pH (by 1 pH whole number) is different by a value of at least 5 Munsell Hue Value units.

[0100] Example 2

[0101] In Example 2. the relative molar ratio of the methyl red to the BTB to the a-naphtholphthalein (i.e.. the first pH-sensitive compound to the second pH-sensitive compound to the third pH-sensitive compound) was 1:0.5:30 as shown in the Table 17, but the concentration of the a-naphtholphthalein is 0.50% as noted inAttyDktNo .99544PCT-C63806- 10670 WO (01385)Table 17. The results of the color analysis, including a determination of the Munsell Hue Value and a calculation of the difference in Munsell Hue Value with the preceding pH, are shown in Table 18.

[0102] Table 17: pH indicator composition of Example 2

[0103] Table 18: Color Analysis for Example 2

[0104] Example 3

[0105] Example 3 was the same as Example 2, except that the amount of BTB added to the indicator composition was higher than in Example 2 as shown in Table 18. The relative molar ratio of the methyl red to the BTB to the a-naphtholphthalein (i.e.. first pH-sensitive compound to the second pH-sensitive compound to the third pH-sensitive compound) was 1 : 0.75:30. The results of the color analysis, including a detennination of the Munsell Hue Value and a calculation of the difference in Munsell Hue Value with the preceding pH. are shown in Table 20.

[0106] Table 19: pH indicator composition of Example 3AttyDktNo .99544PCT-C63806- 10670 WO (01385)

[0107] Table 20: Color Analysis for Example 3

[0108] Comparative Example 8

[0109] Comparative Example 8 was the same as Example 2, except that the amount of BTB added to the indicator composition was higher than in Example 2 as shown in Table 19. The relative molar ratio of the methyl red to the BTB to the a-naphtholphthalein ( / . e.. first pH-sensitive compound to the second pH-sensitive compound to the third pH-sensitive compound) was 1:1:30. The results of the color analysis, including a determination of the Munsell Hue Value and a calculation of the difference in Munsell Hue Value with the preceding pH, are shown in Table 22.

[0110] Table 21: pH indicator composition of Comparative Example 8AttyDktNo .99544PCT-C63806- 10670 WO (01385)

[0111] Table 22: Color Analysis for Comparative Example 8

[0112] Comparative Example 9

[0113] Comparative Example 9 was the same as Example 2, except that the amount of a-naphtholphthalein added to the indicator composition was higher than in Example 2 as shown in Table 20. The relative molar ratio of the methyl red to the BTB to the a-naphtholphthalein (i.e., first pH-sensitive compound to the second pH-sensitive compound to the third pH-sensitive compound) was 1:0.5:50. The results of the color analysis, including a determination of the Munsell Hue Value and a calculation of the difference in Munsell Hue Value with the preceding pH, are shown in Table 24.

[0114] Table 23: pH indicator composition of Comparative Example 9AttyDktNo .99544PCT-C63806- 10670 WO (01385)

[0115] Table 24: Color Analysis for Comparative Example 9

[0116] Comparative Example 10

[0117] Comparative Example 10 was the same as Example 2, except that the amount of a-naphtholphthalein added to the indicator composition was higher than in Example 2 as shown in Table 21. The relative molar ratio of the methyl red to the BTB to the a-naphtholphthalein (i.e., first pH-sensitive compound to the second pH-sensitive compound to the third pH-sensitive compound) was 1:0.5:70. The results of the color analysis, including a determination of the Munsell Hue Value and a calculation of the difference in Munsell Hue Value with the preceding pH, are shown in Table 26.

[0118] Table 25: pH indicator composition of Comparative Example 10AttyDktNo .99544PCT-C63806- 10670 WO (01385)

[0119] Table 26: Color Analysis for Comparative Example 10

[0120] Comparative Example 11

[0121] Comparative Example 11 was the same as Example 2, except that the amount of a-naphtholphthalein added to the indicator composition was higher than in Example 2 as shown in Table 22. The relative molar ratio of the methyl red to the BTB to the a-naphtholphthalein (i.e., first pH-sensitive compound to the second pH-sensitive compound to the third pH-sensitive compound) was 1:0.5:90. The results of the color analysis, including a determination of the Munsell Hue Value and a calculation of the difference in Munsell Hue Value with the preceding pH, are shown in Table 28.

[0122] Table 27: pH indicator composition of Comparative Example 11AttyDktNo .99544PCT-C63806- 10670 WO (01385)

[0123] Table 28: Color Analysis for Comparative Example 11

[0124] Comparison of the Munsell Hue Value for each of Example 2, Example 3 and Comparative Examples 8-11

[0125] As shown in Figs. 7 and 8, the pH indicator compositions having a molar ratio of methyl red to bromothymol blue to a-naphtholphthalein of 1:0.5:30 tol:0.5:50 exhibited a difference in the Munsell Hue Value of 5 or more. In addition, a relative molar ratio of 1:1:30 also achieved a Munsell Hue Value of 5 or more in each pH from the preceding pH.

[0126] Other objects, features and advantages of the disclosure will become apparent from the foregoing figures, detailed description, and examples. It should be understood, however, that the figures, detailedAttyDktNo .99544PCT-C63806- 10670 WO (01385) description, and examples, while indicating specific embodiments of the disclosure, are given by way of illustration only and are not meant to be limiting. Additionally, it is contemplated that changes and modifications within the spirit and scope of the disclosure will become apparent to those skilled in the art from the detailed description. In further embodiments, features from specific embodiments may be combined with features from other embodiments. For example, features from one embodiment may be combined with features from any of the other embodiments. In further embodiments, additional features may be added to the specific embodiments described herein.

Claims

AttyDktNo .99544PCT-C63806- 10670 WO (01385)CLAIMS1. A pH indicator for identifying a pH of an aqueous sample, the pH indicator comprising: a mixture of a first pH-sensitive compound, a second pH-sensitive compound, and a third pH -sensitive compound in a relative molar ratio range so that when the pH indicator is in contact with an aqueous sample, the pH indicator is configured to develop one of a plurality of colors, each of the plurality of colors corresponding to one of a plurality of whole number pH values within a range of at least three consecutive whole number pH values; wherein each of the plurality of colors is defined by a Munsell Hue Value (MHV) in the Munsell Color System; and wherein each of the plurality of colors corresponding to each of the plurality of whole number pH values differs from a preceding or following color corresponding to a preceding or following whole number pH value by a MHV difference of about 5 or greater.

2. The pH indicator of claim 1, wherein the range of at least three consecutive whole number pH values encompasses at least one basic pH value and at least one acidic pH value.

3. The pH indicator of claim 1, wherein at least one of the first pH-sensitive compound, the second pH- sensitive compound, and the third pH-sensitive compound is configured to be substantially colorless below a pH that encompasses a highest whole number pH value in the range of at least three consecutive whole number pH values.

4. The pH indicator of claim 1, wherein the pH indicator is configured as a liquid.

5. The pH indicator of claim 1, wherein the pH indicator is configured as a solid.

6. The pH indicator of claim 1, wherein the first pH-sensitive compound comprises an azo dye having a pKa value below a pKa value of the second pH-sensitive compound ranging from 6.5 or below, and the azo dye is selected from the group consisting of methyl red, Alizarin red S, methyl orange, cresol red, cresolphthalein (meta) and cresol purple.

7. The pH indicator of claim 1. wherein the second pH-sensitive compound comprises phthalein dye having a pKa value between a pKa value of the first pH-sensitive compound and a pKa value of the third pH-sensitive compound ranging from above 6.5 to below 9, and the phthalein dye is selected from the group consisting of bromothymol blue, bromocresol green, bromocresol purple, and thymol blue.

8. The pH indicator of claim 1, wherein the third pH-sensitive compound comprises a phthalein dye having a pKa value greater than a pKa value of the first pH-sensitive compound and a pKa value of the second pH-AttyDktNo .99544PCT-C63806- 10670 WO (01385) sensitive compound ranging from 9 or above, and the phthalein dye is selected from the group consisting of a-naphtholphthalein, phenolphthalein, cresolphthalein, and thymolphthalein.

9. The pH indicator of claim 1, wherein the relative molar ratio range of the first pH-sensitive compound to the second pH-sensitive compound to the third pH-sensitive compound ranges from 1:0.5:25 to 1:0.5:45.

10. The pH indicator of claim 1, wherein the relative molar ratio range of the first pH-sensitive compound to the second pH-sensitive compound to the third pH-sensitive compound is 1:0.5:30.

11. The pH indicator of claim 1, wherein the relative molar ratio range of the first pH-sensitive compound to the second pH-sensitive compound ranges from 0.5:0.25 to 1.5:0.75.

12. The pH indicator of claim 1. wherein the relative molar ratio range of the first pH-sensitive compound to the third pH-sensitive compound ranges from 0.5:25 to 1.5:45.

13. The pH indicator of claim 1, wherein the relative molar ratio range of the second pH-sensitive compound to the third pH-sensitive compound ranges from 0.25:25 to 0.75:45.

14. The pH indicator of claim 1, wherein the mixture further comprises at least one water soluble polymer.

15. The pH indicator of claim 14, wherein tire at least one water-soluble polymer comprises polyvinylpyrrolidone, N-methylpyrrolidone, N -vinylpyrrolidone. orN-ethylpyrrolidone.

16. The pH indicator of claim 1, wherein each of the plurality of colors corresponding to each of the plurality of whole number pH values differs from a preceding or following color corresponding to a preceding or following whole number pH value by a MHV difference of about 7 or greater.

17. The pH indicator of claim 1, wherein the plurality of whole number pH values is within a range of at least 5 consecutive whole number pH values.

18. The pH indicator of claim 1, wherein at least one of the plurality of colors is a red hue and at least one of the plurality of colors is a blue hue.

19. A pH indicator system, comprising at least one carrier and a pH indicator according to any one of claims 1-18.

20. The pH indicator system of claim 19. wherein the carrier is in a particulate form.AttyDktNo .99544PCT-C63806- 10670 WO (01385)21. The pH indicator system of claim 19, wherein the carrier is in a sheet or stick form.

22. The pH indicator system of claim 19, wherein the carrier comprises one or more of a cellulosic material, a clay material, and a silica material.

23. The pH indicator system of claim 19, wherein the pH indicator system is configured as an animal litter additive.

24. An animal litter, comprising a pH indicator according to any one of claims 1-18.

25. A pH indicator, comprising: a first pH-sensitive compound; a second pH-sensitive compound; a third pH-sensitive compound; wherein a mole ratio of the first pH-sensitive compound to the second pH-sensitive compound to the third pH-sensitive compound ranges from 1:0.5:25 to 1:0.5:45.

26. The pH indicator of claim 25. wherein the pH indicator is configured as a liquid.

27. The pH indicator of claim 26, wherein the pH indicator is configured as a solid.

28. The pH indicator of claim 25, wherein the first pH-sensitive compound comprises an azo dye selected from the group consisting of methyl red, Alizarin red S, methyl orange, cresol red, cresolphthalein (meta) and cresol purple.

29. The pH indicator of claim 25, wherein the second pH-sensitive compound comprises phthalein dye selected from the group consisting of bromothymol blue, bromocresol green, bromocresol purple, and thymol blue.

30. The pH indicator of claim 25, wherein the third pH-sensitive compound comprises a phthalein dye selected from the group consisting of a-naphtholphthalein. phenolphthalein, cresolphthalein, and thymolphthalein.

31. The pH indicator of claim 25, wherein, when in contact with an aqueous sample, the pH indicator is configured to develop one of a plurality of colors, each of the plurality of colors corresponding to one of a plurality of whole number pH values within a range of at least three consecutive whole number pH values.AttyDktNo .99544PCT-C63806- 10670 WO (01385)32. The pH indicator of claim 31 , wherein at least one of tire first pH-sensitive compound, the second pH- sensitive compound, and the third pH-sensitive compound is configmed to be substantially colorless below a pH that encompasses a highest whole number pH value in the range of at least three consecutive whole number pH values.

33. The pH indicator of claim 25, wherein the relative molar ratio range of the first pH-sensitive compound to the second pH-sensitive compound to the third pH-sensitive compound is 1:0.5:30.

34. The pH indicator of claim 25, wherein the mixture further comprises at least one water soluble polymer.

35. The pH indicator of claim 34. wherein the at least one water-soluble polymer comprises polyvinylpyrrolidone. N-methylpyrrolidone, N -vinylpyrrolidone, or N-ethylpyrrolidone.

36. A pH indicator system, comprising at least one carrier and a pH indicator according to any one of claims 25 to 35.

37. The pH indicator system of claim 36, wherein the carrier is in a particulate form.

38. The pH indicator system of claim 36, wherein the carrier is in a sheet or stick form.

39. The pH indicator system of claim 36, wherein the carrier comprises one or more of a cellulosic material, a clay material, and a silica material.

40. The pH indicator system of claim 36, wherein the pH indicator system is configured as an animal litter additive.

41. An animal litter, comprising a pH indicator according to any one of claims 25 to 35.

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