THEREFORE

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Application Serial No. 62/568,093 (SNX 0004 M3), filed October 4, 2017.

BACKGROUND

[0002] The present disclosure relates to pH sensors for measuring the hydrogen-ion activity in various test samples, and more particularly to pH sensors with a pH sensing chamber fabricated from a composition that results in both desirable DC conductivity and corrosion resistance.

BRIEF SUMMARY

[0003] There are visual, photometric, and potentiometric methods for determining pH. Visual and photometric methods rely on color changes while potentiometric methods measure the potential difference between an electrode that is sensitive to hydrogen ions and a reference electrode. Potentiometric determination of pH can be used in almost any application, as potentiometric sensors are very sensitive and selective to the hydrogen ion. A pH sensor is an example of an ion selective electrode (ISE), or measuring electrode, used during potentiometric determination of pH. The pH sensor may comprise the measuring electrode reacting on a special ion type, such as a hydrogen ion, and a reference electrode that are jointly immersed in a test sample.

[0004] Determination of a pH measurement with a pH sensor relies on the measurement of a voltage. In order to measure the voltage, two points with different electrical potential values (i.e., electrical signals) are required. The reference electrode is designed to maintain a constant electrical potential that is independent of the test sample composition and temperature. In contrast, the measuring electrode of the pH sensor provides an electrical potential that is dependent upon the activity of the hydrogen ions in the test sample. The difference between these potentials, the voltage, determines the pH value based on the Nernst equation.

[0005] With a pH sensor, a pH sensing chamber is connected to a distal end of a pH fluid chamber. A sensing membrane portion of the pH sensing chamber is filled with a pH fluid of known pH, which is typically a pH of 7. The pH sensing chamber design creates an environment with constant binding of hydrogen ions to the measuring electrode inside of the pH sensing chamber, while the outside of the pH sensing chamber is exposed to the test sample in which a variable amount of hydrogen ions exist. The difference in hydrogen ion activity creates a potential that is read against the potential of the reference electrode.

[0006] The shape of the pH sensing chamber may vary so as to ensure optimal moistening of the pH sensing chamber. Bulb-shaped and coned-shaped pH sensing chambers may be used for most applications. Some applications may require a spear-tipped pH sensing chamber, such as applications that require the penetration of a semi-solid test sample. Other applications may require a flat pH sensing chamber, such as applications that require the measurement of a solid surface, such as skin.

[0007] The reference electrode and the measuring electrode may be present in separate chambers or they may be combined in a single pH sensor. The pH sensor may be immersed in the test sample such that the reference fluid is connected to the test sample through the fluidic reference junction, as the fluidic reference junction serves to close the electrical circuit in the pH sensor.

[0008] Current state-of-the-art pH sensors have either desired DC conductivity or desired corrosion resistance. That is, state-of-the-art pH sensors may provide desired DC conductivity and thus desired pH sensor response times, but suffer from less than desirable corrosion resistance while immersed into solutions for which the pH is being measured. In the alternative, current state-of-the-art pH sensors may provide desired corrosion resistance within solutions for which the pH is being measured, but have less than desired DC conductivity (i.e., high DC resistance) and thus slow sensor response times.

[0009] To overcome these problems, the inventor has discovered that a novel glass composition having a desired range or combination of a redox buffer component and a corrosion resistance component provide the glass composition with both high DC conductivity (i.e., fast sensor response times) and excellent corrosion resistance [0010] According to the subject matter of the present disclosure, a pH sensor and methods for measuring the hydrogen-ion activity in various solutions with the pH sensor are provided.

[0011] In accordance with one embodiment of the present disclosure, a pH sensor is illustrated comprising a pH sensing element, a reference sensing element, and a fluidic reference junction. The pH sensing element comprises a measuring electrode, a pH fluid chamber, and a pH sensing chamber. The reference sensing element comprises a reference electrode, a reference fluid chamber, and a reference fluid partition. The reference fluid partition is configured to define a fluid flow barrier between an interior of the reference fluid chamber and a test sample that is characterized by an indeterminate pH. The fluidic reference junction forms a reference fluid diffusion path across the reference fluid partition, wherein the measuring electrode resides in the pH sensing chamber. The pH sensing chamber is fluidly coupled to the pH fluid chamber. The reference electrode resides in the reference fluid chamber. A sensing membrane portion of the pH sensing chamber is fabricated from a glass composition comprising from about 59.0 mol% to about 72.0 mol% Si0 ₂ , from about 20.0 mol% to about 32.0 mol% Li ₂ 0, from about 0.3 mol% to about 4.0 mol% La ₂ 0 _3i from about 0.3 mol% to about 5.0 mol% Ta ₂ 0 _5, an amount A of a corrosion resistance component comprising Ti0 ₂ , where A is from about 0.3 mol% to about 5.0 mol%, an amount B of Cs ₂ 0, where B > 0.0 mol%, and an amount C of a redox buffer component comprising Ce0 ₂ , where C > 0.0% and A>B>C.

[0012] In accordance with another embodiment of the present disclosure, a pH sensor is illustrated comprising a pH sensing element, a reference sensing element, and a fluidic reference junction. The pH sensing element comprises a measuring electrode, a pH fluid chamber, and a pH sensing chamber. The reference sensing element comprises a reference electrode, a reference fluid chamber, and a reference fluid partition. The reference fluid partition is configured to define a fluid flow barrier between an interior of the reference fluid chamber and a test sample that is characterized by an indeterminate pH. The fluidic reference junction forms a reference fluid diffusion path across the reference fluid partition, wherein the measuring electrode resides in the pH sensing chamber. The pH sensing chamber is fluidly coupled to the pH fluid chamber. The reference electrode resides in the reference fluid chamber. A sensing membrane portion of the pH sensing chamber is fabricated from a glass composition comprising from about 59.0 mol% to about 72.0 mol% Si0 ₂ , from about 20.0 mol% to about 32.0 mol% Li ₂ 0, from about 0.3 mol% to about 4.0 mol% La ₂ 0 _3i from about 0.3 mol% to about 5.0 mol% Ta ₂ Os _i an amount A of a corrosion resistance component comprising Ti0 ₂ , where A is from about 0.3 mol% to about 5.0 mol%, an amount B of Cs ₂ 0, where B > 0.0 mol%, and an amount C of a redox buffer component.

[0013] In accordance with yet another embodiment of the present disclosure, a pH sensing element is illustrated comprising a measuring electrode, a pH fluid chamber, and a pH sensing chamber. The measuring electrode resides in the pH sensing chamber. The pH sensing chamber is fluidly coupled to the pH fluid chamber, and a sensing membrane portion of the pH sensing chamber is fabricated from a glass composition comprising from about 59.0 mol% to about 72.0 mol% Si0 ₂ , from about 20.0 mol% to about 32.0 mol% Li ₂ 0, from about 0.3 mol% to about 4.0 mol% La ₂ 0 ₃ , from about 0.3 mol% to about 5.0 mol% Ta ₂ Os, an amount A of a corrosion resistance component comprising Ti0 ₂ , where A is from about 0.3 mol% to about 5.0 mol%, an amount B of Cs ₂ 0, where B > 0.0 mol%, and an amount C of a redox buffer component.

[0014] Although the concepts of the present disclosure are described herein with primary reference to a pH sensor fabricated from a glass composition that results in both desirable DC conductivity and corrosion resistance, it is contemplated that the concepts will enjoy applicability to any system where it would be beneficial to measure the pH of a test sample.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0015] The following detailed description of specific embodiments of the present disclosure can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which:

[0016] Fig. 1 is a diagram of a pH sensor, according to one or more embodiments presently described.

[0017] Fig. 2 is a diagram of the pH sensing chamber of the pH sensor, according to one or more embodiments presently described.

[0018] Fig. 3 is a graph showing the DC resistance of comparative pH sensors and pH sensors according to one or more embodiments presently described.

[0019] Fig. 4 is a graph showing the asymmetry potential of comparative pH sensors and pH sensors according to one or more embodiments presently described.

DETAILED DESCRIPTION [0020] Referring to Fig. 1, a pH sensor 10 is illustrated comprising a pH sensing element 20, a reference sensing element 30, and a fluidic reference junction 40. The pH sensing element 20 comprises a measuring electrode 22, a pH fluid chamber 24, and a pH sensing chamber 26. The reference sensing element 30 comprises a reference electrode 32, a reference fluid chamber 34, and a reference fluid partition 36. The reference fluid partition 36 is configured to define a fluid flow barrier between an interior of the reference fluid chamber 34 and a test sample that is characterized by an indeterminate pH.

[0021] The fluidic reference junction 40 forms a reference fluid diffusion path across the reference fluid partition, wherein the measuring electrode 22 resides in the pH sensing chamber 26. The pH sensing chamber 26 is fluidly coupled to the pH fluid chamber 24. The reference electrode 32 resides in the reference fluid chamber 34. A sensing membrane portion 28 of the pH sensing chamber 26 is fabricated from a glass composition comprising from about 59.0 mol% to about 72.0 mol% Si0 ₂ , from about 20.0 mol% to about 32.0 mol% Li ₂ 0, from about 0.3 mol% to about 4.0 mol% La ₂ 0 _3i from about 0.3 mol% to about 5.0 mol% Ta ₂ Os _i an amount A of a corrosion resistance component comprising Ti0 ₂ , where A is from about 0.3 mol% to about 5.0 mol%, an amount B of Cs ₂ 0, where B > 0.0 mol%, and an amount C of a redox buffer component comprising Ce0 ₂ , where C > 0.0% and A>B>C.

[0022] Referring now to the glass composition, in certain embodiments, the glass composition comprises from about 60.0 mol% to about 65.0 mol% Si0 ₂ , from about 25.0 mol% to about 30.0 mol% Li ₂ 0, from about 2.3 mol% to about 2.8 mol% La ₂ 0 ₃ , from about 1.5 mol% to about 1.9 mol% Ta ₂ Os, an amount A of a corrosion resistance component comprising Ti0 ₂ , where A is from about 3.4 mol% to about 3.8 mol%, an amount B of Cs ₂ 0, where B is from about 1.6 mol% to about 2.0 mol%, and an amount C of a redox buffer component comprising Ce0 ₂ , where C is from about 0.7 mol% to about 1.1 mol%.

[0023] In further embodiments, the glass composition comprises about 62.0 mol% Si0 ₂ , about 27.4 mol% Li ₂ 0, about 2.6 mol% La ₂ 0 ₃ , about 1.7 mol% Ta ₂ Os, an amount A of a corrosion resistance component comprising Ti0 ₂ , where A is about 3.6 mol%, an amount B of Cs ₂ 0, where B is about 1.8 mol%, and an amount C of a redox buffer component comprising Ce0 ₂ , where C is about 0.9 mol%.

[0024] Referring to the glass composition, the glass composition may comprise (in mol%) greater than about 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8 or 4.9 and less than about 5.0, 4.9, 4.8, 4.7, 4.6, 4.5, 4.4, 4.3, 4.2, 4.1,

4.0, 3.9, 3.8, 3.7, 3.6, 3.5, 3.4, 3.3, 3.2, 3.1, 3.0, 2.9, 2.8, 2.7, 2.6, 2.5, 2.4, 2.3, 2.2, 2.1, 2.0, 1.9,

1.8, 1.7, 1.6, 1.5, 1.4, 1.3, 1.2, 1.1, 0.9, 0.8, 0.7, 0.6, 0.5 or 0.4 of an amount A of the corrosion resistance component.

[0025] In some embodiments, the corrosion resistance component is Ti0 ₂ and the glass composition may comprise between about 0.3 mol% and about 5.0 mol%, about 0.4 mol% and about 4.8 mol%, about 0.6 mol% and about 4.8 mol%, about 0.8 mol% and about 4.8 mol%, about 1.0 mol% and about 4.8 mol%, about 1.2 mol% and about 4.8 mol%, about 2.9 mol% and about 4.3 mol%, about 3.0 mol% and about 4.9 mol%, about 3.1 mol% and about 4.1 mol%, about 3.2 mol% and about 4.0 mol%, about 3.3 mol% and about 3.9 mol%, about 3.4 mol% and about 3.8 mol%, or about 3.5 mol% and about 3.7 mol% of an amount A of the corrosion resistance component.

[0026] Referring still the glass composition, the glass composition may comprise (in mol%) greater than about 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0,

2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0 and less than about 4.0, 3.9, 3.8, 3.7, 3.6, 3.5, 3.4, 3.3, 3.2, 3.1, 3.0, 2.9, 2.8, 2.7, 2.6, 2.5, 2.4, 2.3, 2.2,

2.1, 2.0, 1.9, 1.8, 1.7, 1.6, 1.5, 1.4, 1.3, 1.2, 1.1, 0.9, 0.8, 0.7, 0.6, 0.5 or 0.4 of an amount B of Cs ₂ 0.

[0027] In some embodiments, the glass may comprise between about 0.3 mol% and about 4.0 mol%, about 0.4 mol% and about 3.8 mol%, about 0.6 mol% and about 3.6 mol%, about 0.8 mol% and about 3.4 mol%, about 1.0 mol% and about 3.2 mol%, about 1.2 mol% and about 3.0 mol%, about 1.4 mol% and about 2.8 mol%, about 1.6 mol% and about 2.6 mol%, about 1.6 mol% and about 2.4 mol%, about 1.6 mol% and about 2.2 mol%, about 1.6 mol% and about 2.0 mol%, about 1.7 mol% and about 2.0 mol%, or about 1.7 mol% and about 1.9 mol% of an amount B of Cs ₂ 0.

[0028] Referring still to the glass composition, the glass composition may comprise (in mol%) greater than about 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8,

1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8 or 3.9 and less than about 4.0, 3.9, 3.8, 3.7, 3.6, 3.5, 3.4, 3.3, 3.2, 3.1, 3.0, 2.9, 2.8, 2.7, 2.6, 2.5, 2.4, 2.3,

2.2, 2.1, 2.0, 1.9, 1.8, 1.7, 1.6, 1.5, 1.4, 1.3, 1.2, 1.1, 0.9, 0.8, 0.7, 0.6, 0.5, or 0.4 of an amount C of the redox buffer component. In certain embodiments, the redox buffer component may be Ce0 ₂ , V ₂ O ₅ , Ru0 ₂ , CoO, Pr ₂ 0 ₃ , or combinations thereof so long as the total concentration of the amount C of the redox buffer component comprising the glass composition is between about 0.3 mol% and about 4.0 mol%.

[0029] In some embodiments, the glass composition may comprise between about 0.3 mol% and about 4.0 mol%, about 0.4 mol% and about 3.0 mol%, about 0.5 mol% and about 2.0 mol%, about 0.5 mol% and about 1.8 mol%, about 0.5 mol% and about 1.6 mol%, about 0.5 mol% and about 1.4 mol%, about 0.5 mol% and about 1.3 mol%, about 0.5 mol% and about 1.2 mol%, about 0.5 mol% and about 1.1 mol%, about 0.5 mol% and about 1.0 mol%, or about 0.5 mol% and about 0.9 mol% of an amount C of the redox buffer component.

[0030] In embodiments, the redox buffer component is Ce0 ₂ and the glass composition may comprise between about 0.3 mol% and about 3.0 mol%, about 0.4 mol% and about 2.0 mol%, about 0.5 mol% and about 1.5 mol%, about 0.6 mol% and about 1.3 mol%, about 0.7 mol% and about 1.2 mol%, about 0.8 mol% and about 1.1 mol%, about 0.8 mol% and about 1.0 mol%, about 1.3 mol% and about 2.7 mol%, about 1.4 mol% and about 2.6 mol%, about 1.5 mol% and about 2.5 mol%, about 1.6 mol% and about 2.4 mol%, about 1.7 mol% and about 2.3 mol%, about 1.8 mol% and about 2.2 mol%, about 1.9 mol% and about 2.1 mol%, about 2.1 mol% and about 3.5 mol%, about 2.2 mol% and about 3.4 mol%, about 2.3 mol% and about 3.3 mol%, about 2.4 mol% and about 3.2 mol%, about 2.5 mol% and about 3.1 mol%, about 2.6 mol% and about 3.0 mol%, or about 2.7 mol% and about 2.9 mol% of an amount C of the redox buffer component.

[0031] Referring still to the glass composition, the glass composition may comprise a molar ratio of an amount A of the corrosion resistance component to an amount B of Cs ₂ 0 to an amount C of the redox buffer component. In some embodiments, the ratio of A to B to C may be between about 3:2: 1 to about 5:2: 1, about 3.5:2: 1 to about 5:2: 1, about 4:2: 1 to about 5:2: 1, about 4.5:2: 1 to about 5:2: 1, about 3:2: 1 to about 4.5:2: 1, about 3:2: 1 to about 4:2: 1, or about 3:2: 1 to about 3.5:2: 1. In certain embodiments, the ratio of A to B to C is about 4:2: 1.

[0032] In embodiments, the glass composition is substantially free from a functional amount of alkaline earth metals. It is noted that the term "alkaline earth metals," as used herein, encompasses elemental alkaline earth metals or any compounds comprising an amount of alkaline earth metals. Such materials are undesirable during the manufacturing process of the glass composition due to their high toxicity. Moreover, alkaline earth metals may also result in the need for increased temperatures during the manufacturing process of the glass composition.

[0033] In further embodiments, the glass composition is substantially free from a functional amount of actinides. It is noted that the term "actinides," as used herein, encompasses elemental actinides or any compounds comprising an amount of actinides. Such materials are undesirable during the manufacturing process of the glass composition due to their high toxicity stemming from radioactivity. As such, actinides are an undesirable component of the glass composition.

[0034] In some embodiments the glass composition is substantially free from a functional amount Fe ₂ 0 ₃ . Fe ₂ 0 ₃ has typically been used as a redox buffer component in glass compositions. However, Fe ₂ 0 ₃ does not produce a desirable asymmetry stabilizing effect. As such Fe ₂ 0 ₃ is an undesirable component of the glass composition.

[0035] Without being bound by theory, the redox buffer component provides a redox couple active within the glass composition of the sensing membrane portion 28 and serves as a redox buffer to stabilize the asymmetry potential against polarization. In other words, when aging or corrosion of the sensing membrane portion 28 begins to polarize the membrane potential of the sensing membrane portion 28 to more cathodic or anodic potentials, the redox buffer component re-equilibrates and neutralizes the polarization.

[0036] For example, when an amount C of Ce0 ₂ is the redox buffer component, Ce ³⁺ exists in equilibrium with Ce ⁴⁺ within the sensing membrane portion 28 and the equilibrium ratio of Ce ³⁺ to Ce ⁴⁺ is determined by the glass composition of the sensing membrane portion 28 via a relationship known as "optical basicity." The local optical basicity can be affected by, for example, alkali leaching or glass etching, and thus the optical basicity can be affected by aging and corrosion of the sensing membrane portion 28.

[0037] Conventional pH-sensitive membranes tend to polarize through space charge effects caused by exposure to pH extremes or by irreversible alkali leaching. However, the Ce0 ₂ within the sensing membrane portion 28 serves as a redox buffer to stabilize the asymmetry potential against polarization. In addition, the corrosion resistance component, according to any of the described embodiments, can increase intrinsic alkali ion mobility (Li ⁺ ) in the sensing membrane portion 28. Accordingly, a synergistic effect is present between the redox buffer component and the corrosion resistance component to provide a corrosion resistant sensing membrane portion 28 with high DC conductivity. [0038] Referring again to Fig. 1, in certain embodiments, the pH sensing element 20 may be formed from a monolithic piece of glass comprising the glass composition according to any of the previously described embodiments. In other embodiments, the pH sensing element 20 may be formed from two or more connected pieces of glass, such as pieces of glass that have been fused together. When the pH sensing element 20 is formed from two or more connected pieces of glass, the sensing membrane portion 28 may comprise the glass composition according to any of the previously described embodiments while the rest of the pH sensing element 20 comprises a different composition. Suitable compositions of the pH sensing element 20 may include glass, plastic, or combinations thereof.

[0039] In certain embodiments, the pH sensing element 20 may comprise any suitable shape depending on the characteristics of a test sample to be measured. Suitable shapes of the pH sensing chamber 26 may include bulb-shaped, cone-shaped, cylindrical, spear-shaped, or flat. In preferred embodiments, the pH sensing chamber 26 is bulb-shaped.

[0040] In some embodiments, the measuring electrode 22 that resides in the pH sensing chamber 26 may comprise any suitable materials. Suitable materials of the measuring electrode 22 may include an Ag/AgCl composition, an Hg/Hg ₂ Cl ₂ composition, or an iodine/iodide composition.

[0041] In certain embodiments, the pH fluid chamber 24 may comprise any suitable shape. Without being bound by theory, the pH fluid chamber 24 may be cylindrical, cubical, or have a discontinuous shape.

[0042] In embodiments, the pH sensing chamber 26 has an outer diameter from between about 2.6 mm and about 9.5 mm, about 2.8 mm and about 9.3 mm, about 3.0 mm and about 9.1 mm, about 3.2 mm and about 9.0 mm, about 3.4 mm and about 8.8 mm, about 3.6 mm and about 8.6 mm, about 3.8 mm and about 8.5 mm, about 4.0 mm and about 8.5 mm, about 4.2 mm and about 8.4 mm, about 4.4 mm and about 8.3 mm, about 4.6 mm and about 8.2 mm, about 4.8 mm and about 8.1 mm, about 5.0 mm and about 8.0 mm, about 5.2 mm and about 7.9 mm, about 5.4 mm and about 7.8 mm, about 5.6 mm and about 7.7 mm, about 5.8 mm and about 7.6 mm, about 6.0 mm and about 7.5 mm, about 6.2 mm and about 7.4 mm, about 6.4 mm and about 7.3 mm, about 6.6 mm and about 7.2 mm, or about 6.8 mm and about 7.2 mm. In certain embodiments, the pH sensing chamber 26 has an outer diameter of about 7.0 mm. [0043] In further embodiments, the pH sensing chamber 26 has a surface area from between about 5 mm 2 to about 145 mm 2 , about 25 mm 2 to about 140 mm 2 , about 50 mm 2 to about 135 mm 2 , about 75 mm 2 to about 130 mm 2 , about 80 mm 2 to about 130 mm 2 , about 85 mm 2 to about

130 mm 2 , about 90 mm 2 to about 130 mm 2 , about 95 mm 2 to about 130 mm 2 , about 100 mm 2 to about 130 mm 2 , about 105 mm 2 to about 130 mm 2 , about 110 mm 2 to about 130 mm 2 , about 115 mm 2 to about 130 mm 2 , about 120 mm 2 to about 130 mm 2 , or about 125 mm 2 to about 130 mm 2. In certain embodiments, the pH sensing chamber 26 has a surface area of about 127 mm .

[0044] The pH sensing chamber 26, according to some embodiments, is comprised of the glass composition according to any of the previously described embodiments and has a thickness from between about 0.12 mm and about 0.36 mm, about 0.14 mm and about 0.34 mm, about 0.16 mm and about 0.32 mm, about 0.18 mm and about 0.30 mm, about 0.20 mm and about 0.28 mm, or about 0.22 mm and about 0.26 mm. In certain embodiments, the pH sensing chamber 26 has a thickness of about 0.24 mm.

[0045] Referring again to Fig. 1, in certain embodiments, the reference sensing element 30 may be formed from any suitable material. Suitable materials may comprise plastic, glass, or combinations thereof. In preferred embodiments, the reference sensing element 30 comprises polyetherimide.

[0046] In embodiments, the reference sensing element 30 has an outer diameter from between about 8.0 mm and about 16.0 mm, about 8.2 mm and about 15.8 mm, about 8.4 mm and about 15.6 mm, about 8.6 mm and about 15.4 mm, about 8.8 mm and about 15.2 mm, about 9.0 mm and about 15.0 mm, about 9.2 mm and about 14.8 mm, about 9.4 mm and about 14.6 mm, about 9.6 mm and about 14.4 mm, about 9.8 mm and about 14.2 mm, about 10.0 mm and about 14.0 mm, about 10.2 mm and about 13.8 mm, about 10.4 mm and about 13.6 mm, about 10.6 mm and about 13.4 mm, about 10.8 mm and about 13.2 mm, about 11.0 mm and about 13.0 mm, about 11.2 mm and about 12.8 mm, about 11.4 mm and about 12.6 mm, about 11.6 mm and about 12.4 mm, or about 11.8 mm and about 12.2 mm. In certain embodiments, the reference sensing element 30 has an outer diameter of about 12.0 mm.

[0047] In embodiments, the reference sensing element 30 has an inner diameter from between about 6.0 mm and about 12.0 mm, about 6.2 mm and about 11.8 mm, about 6.4 mm and about 11.6 mm, about 6.6 mm and about 11.4 mm, about 6.8 mm and about 11.2 mm, about 7.0 mm and about 11.0 mm, about 7.2 mm and about 10.8 mm, about 7.4 mm and about 10.6 mm, about 7.6 mm and about 10.4 mm, about 7.8 mm and about 10.2 mm, about 8.0 mm and about 10.0 mm, about 8.2 mm and about 9.8 mm, about 8.4 mm and about 9.6 mm, about 8.6 mm and about 9.4 mm, or about 8.8 mm and about 9.2 mm. In certain embodiments, the reference sensing element 30 has an outer diameter of about 8.9 mm.

[0048] In some embodiments, the reference electrode 32 that resides in the reference fluid chamber 34 may comprise any suitable materials. Suitable materials of the measuring electrode 22 may include an Ag/AgCl composition, an Hg/Hg ₂ Cl ₂ composition, or an iodine/iodide composition.

[0049] In certain embodiments, the reference fluid chamber 34 may comprise any suitable shape. Without being bound by theory, the reference fluid chamber 34 may be cylindrical, cubical, or have a discontinuous shape.

[0050] The reference fluid partition 36 is configured to define a fluid flow barrier between an interior of the reference fluid chamber 34 and a test sample that is characterized by an indeterminate pH. It should be noted that any reference herein to a test sample having an "indeterminate" pH refers to any sample where the pH of the sample is either unknown or needs to be measured, tested, or otherwise validated. For example, and not by way of limitation the test sample may be a solution, fluid, liquid, or any other fluid, fluidic solid, or solid that is compatible with the pH sensor described herein. In embodiments, the reference fluid partition 36 is a silicone bushing.

[0051] In embodiments, the pH sensor 20 may further comprise an intermediate reference fluid partition 38 defining a separate fluid flow barrier within the reference fluid chamber 34. The intermediate reference fluid partition 38 is configured to define a fluid flow barrier between an interior of the reference fluid chamber 34 and a test sample that is characterized by an indeterminate pH. In embodiments, the intermediate reference fluid partition 38 is a silicone bushing.

[0052] Referring again to Fig. 1, in certain embodiments, the fluidic reference junction 40 forms a reference fluid diffusion path across the reference fluid partition, wherein the measuring electrode 22 resides in the pH sensing chamber 26. In embodiments, the fluidic reference junction 40 is characterized by a reference fluid flow rate from between about 0 mL/day to about 2.0 mL/day, about 0.1 mL/day to about 1.9 mL/day, about 0.2 mL/day to about 1.8 mL/day, about 0.3 mL/day to about 1.7 mL/day, about 0.4 mL/day to about 1.4 mL/day, about 0.5 mL/day to about 1.5 mL/day, about 0.6 mL/day to about 1.4 mL/day, about 0.7 mL/day to about 1.3 mL/day, about 0.8 mL/day to about 1.2 mL/day, or about 0.9 mL/day to about 1.1 mL/day. In certain embodiments, the fluidic reference junction 40 is characterized by a reference fluid flow rate of about 1.0 mL/day.

[0053] In some embodiments, the reference fluid junction 40 comprises a fluid via formed in the reference fluid partition. The fluid via may comprise an annular gap, a cylindrical via, or any other opening suitable to form a reference fluid diffusion path across the reference fluid partition.

[0054] In other embodiments, the reference fluid junction 40 comprises a fluid permeable material extending across the reference fluid partition. The fluid permeable material may comprise a ceramic, a glass ceramic, a metal, or any of a variety of fibrous or non-fibrous fluid permeable materials. For example, and not by way of limitation, suitable materials include Pellon ®, ceramic, platinum, glass, ground glass, or plastic fibers.

[0055] The pH sensor 10, in certain embodiments, may further comprise an intermediate reference fluid junction 42. The intermediate reference fluid junction 42 may be described according to any of the preciously described embodiments of the reference fluid junction 40.

[0056] In embodiments, the pH sensor 10 further comprises a pH fluid residing in the pH fluid chamber 24. The pH fluid may comprise any fluid capable of creating a suitable diffusion potential. Examples of suitable pH fluids may include, but are not limited to, metal halide salts such as KC1. The pH fluid may have a pH from about 1 to about 13 and a concentration from about 0.001 M to about 10 M. In some embodiments, the pH fluid residing in the pH fluid chamber 24 has a viscosity from between 0.35 cP and 180 cP. In certain embodiments, the pH fluid is a KC1 gel having a pH of about 7.

[0057] Similar to the pH fluid chamber 24, the reference fluid chamber 34, in embodiments, further comprises a reference fluid residing in the reference fluid chamber 34. The reference fluid may comprise any fluid capable of creating a suitable diffusion potential. Examples of suitable reference fluids may include, but are not limited to, metal halide salts such as KC1. The reference fluid, in embodiments, may have a pH from about 6 to about 9 and a concentration from about 0.001 M to about 5 M. In certain embodiments, the reference fluid residing in the reference fluid chamber 34 has a viscosity from between 0.35 cP and 180 cP. The reference fluid, in embodiments, may be the same fluid that comprises the pH fluid.

[0058] Referring again to Fig. 1, the components of the pH sensing element 10 may be arranged coaxially, meaning that the pH sensing element 20 resides within the reference sensing element 30. In alternative embodiments, it is contemplated that the pH sensing element 20 and its components, and the reference sensing element 30 and its components are separated into multiple electrodes.

[0059] Referring now to Fig. 2, the reference sensing element 30 may further comprise a sensor extension portion surrounding at least a portion of the pH sensing chamber 26. The sensor extension portion and the pH sensing chamber 26 define a minimum displacement buffer gap between the sensor extension portion of the reference sensing element 30 and the pH sensing chamber 26. In certain embodiments, the minimum displacement buffer gap is between about 0.8 mm and about 2 mm. The minimum displacement buffer gap helps shield the pH sensing chamber 26 from any disturbances, such as shock from being dropped or jostled.

[0060] Referring again to Fig. 1, in additional embodiments, a pH sensor 10 is illustrated comprising a pH sensing element 20, a reference sensing element 30, and a fluidic reference junction 40. The pH sensing element 20 comprises a measuring electrode 22, a pH fluid chamber 24, and a pH sensing chamber 26. The reference sensing element 30 comprises a reference electrode 32, a reference fluid chamber 34, and a reference fluid partition 36. The reference fluid partition 36 is configured to define a fluid flow barrier between an interior of the reference fluid chamber 34 and a test sample that is characterized by an indeterminate pH.

[0061] The fluidic reference junction 40 forms a reference fluid diffusion path across the reference fluid partition, wherein the measuring electrode 22 resides in the pH sensing chamber 26. The pH sensing chamber 26 is fluidly coupled to the pH fluid chamber 24. The reference electrode 32 resides in the reference fluid chamber 34. A sensing membrane portion 28 of the pH sensing chamber 26 is fabricated from a glass composition comprising from about 59.0 mol% to about 72.0 mol% Si0 ₂ , from about 20.0 mol% to about 32.0 mol% Li ₂ 0, from about 0.3 mol% to about 4.0 mol% La ₂ 0 _3i from about 0.3 mol% to about 5.0 mol% Ta ₂ Os _, an amount A of a corrosion resistance component comprising Ti0 ₂ , where A is from about 0.3 mol% to about 5.0 mol%, an amount B of Cs ₂ 0, where B > 0.0 mol%, and an amount C of a redox buffer component. [0062] In further embodiments, a pH sensing element 20 is illustrated comprising a measuring electrode 22, a pH fluid chamber 24, and a pH sensing chamber 26. The measuring electrode 22 resides in the pH sensing chamber 26. The pH sensing chamber 26 is fluidly coupled to the pH fluid chamber 24, and a sensing membrane portion 28 of the pH sensing chamber is fabricated from a glass composition comprising from about 59.0 mol% to about 72.0 mol% Si0 ₂ , from about 20.0 mol% to about 32.0 mol% Li ₂ 0, from about 0.3 mol% to about 4.0 mol% La ₂ 0 ₃ , from about 0.3 mol% to about 5.0 mol% Ta ₂ Os, an amount A of a corrosion resistance component comprising Ti0 ₂ , where A is from about 0.3 mol% to about 5.0 mol%, an amount B of Cs ₂ 0, where B > 0.0 mol%, and an amount C of a redox buffer component.

EXAMPLES

[0063] The embodiments described herein will be further clarified by the following examples.

[0064] In Example 1, a pH sensor comprising a pH sensing chamber 26 fabricated from glass having a composition of 62.0 mol% Si0 ₂ , 27.4 mol% Li ₂ 0, 2.6 mol% La ₂ 0 ₃ , 1.8 mol% Cs ₂ 0, 0.9 mol% Ce0 ₂ , 1.7 mol% Ta ₂ Os, and 3.6 mol% Ti0 ₂ was tested for DC resistance and corrosion testing.

[0065] In Example 2, a pH sensor comprising a pH sensing chamber 26 fabricated from glass having a composition of 63.0 mol% Si0 ₂ , 27.8 mol% Li ₂ 0, 3.5 mol% La ₂ 0 ₃ , 2.9 mol% Cs ₂ 0, 1.6 mol% Ce0 ₂ , and 1.2 mol% Ta ₂ Os was tested for DC resistance and corrosion testing.

[0066] In Comparative Example 1, a current state-of-the-art pH sensor comprising a pH sensing chamber fabricated from glass having a composition of 65.0 mol% Si0 ₂ , 28.0 mol% Li ₂ 0, 4.0 mol% La ₂ 0 ₃ , and 3.0 mol% Cs ₂ 0 was subjected to the same DC resistance and corrosion testing as Examples 1 and 2 for comparison purposes.

[0067] In Comparative Example 2, a current state-of-the-art pH sensor comprising a pH sensing chamber fabricated from glass having a composition of 64.49 mol% Si0 ₂ , 27.93 mol% Li ₂ 0, 3.69 mol% La ₂ 0 ₃ , 2.74 mol% Cs ₂ 0, 0.251 mol% P ₂ 0 ₅ , 0.63 mol% Ta ₂ 0 ₅ , 0.029 mol% CoO, and 0.24 mol% Pr ₂ 0 ₃ was subjected to the same DC resistance and corrosion testing as Examples 1 and 2 for comparison purposes.

[0068] According to one or more embodiments as described in Fig. 3, DC resistance for the pH sensors 10 of Examples 1 and 2, and Comparative Examples 1 and 2 were measured after hourly exposures to a corrosive solution of pressurized steam and condensed water vapor at a temperature of 125 °C and a pressure of 20 psig.

[0069] As shown in Fig. 3, the DC resistance of Comparative Examples 1 and 2 increased to about 800 megaohms (ΜΩ) after exposure to the corrosive solution. After 2 hours of exposure to the corrosive solution, the DC resistance of Comparative Example 2 increased to about 1200 ΜΩ and the DC resistance of Comparative Example 1 increased slightly to about 900 ΜΩ. For exposure times between 3 and 5 hours in the corrosive solution, the Comparative Examples 1 and 2 maintained a DC resistance between about 1000-1200 ΜΩ.

[0070] In contrast, the pH sensors 10 of Examples 1 and 2 maintained a low DC resistance even after 5 hours of exposure to the corrosive solution. Particularly, the glass probe pH sensor 10 of Example 1 increased only to about 400 ΜΩ after 5 hours of exposure to the corrosive solution, whereas the pH sensor 10 of Example 2 exhibited a slight increase of DC resistance and showed about 600 ΜΩ of resistance after 5 hours of exposure to the corrosive solution.

[0071] Accordingly, Fig. 3 demonstrates the pH sensors 10 of Examples 1 and 2 have superior DC conductivity (i.e., a reduced DC resistance) compared to current state of the art glass probes and the combination of the redox buffer component (here, 0.9 mol % Ce0 ₂ ) and the corrosion resistance component (here, 3.6 mol % Ti0 ₂ ) provides an increase in DC conductivity (i.e., a reduced DC resistance) compared to the addition of the redox buffer component alone.

[0072] According to one or more embodiments as described in Fig. 4, the asymmetry potential for the pH sensors 10 of Examples 1 and 2 and Comparative Examples 1 and 2 were measured after hourly exposures of the glass probes to the same corrosive solution used for the DC resistance testing discussed above. The asymmetry potential is a measure of a pH sensor's deviation from a pH of 7 when the pH sensor 10 is immersed and tested in a pH 7 buffer solution. In other words, the asymmetry potential represents an offset of the glass probe from a pH of 7 when immersed and tested in neutral pH solution.

[0073] As shown in Fig. 4, the pH sensors of Comparative Examples 1 and 2 exhibited a large asymmetry potential (i.e., a large offset from a pH of 7) with an offset from the pH of 7 from about 0.15 to about 0.3 pH units. In contrast, the pH sensors of Examples 1 and 2 showed a relatively small deviation of less than about 0.07 pH units from a pH of 7 even after 6 hours of exposure to the corrosive solution. Such a small deviation in pH accuracy, such as those derived from the sensors of Examples 1 and 2, results in the pH sensor maintaining fidelity to the calibration standard after exposure to corrosive conditions, including the combination of pressurized steam and condensed water vapor at a temperature of 125 °C and a pressure of 20 psig. As such, this level of pH sensor performance reliability indicates that the experimental pH sensors have applications in food and beverage industries, and also pharmaceutical manufacturing processes, such as industrial fermenting.

[0074] For the purposes of describing and defining the present invention, it is noted that reference herein to a characteristic of the subject matter of the present disclosure being a "function of a parameter, variable, or other characteristic is not intended to denote that the characteristic is exclusively a function of the listed parameter, variable, or characteristic. Rather, reference herein to a characteristic that is a "function" of a listed parameter, variable, etc., is intended to be open ended such that the characteristic may be a function of a single parameter, variable, etc., or a plurality of parameters, variables, etc.

[0075] It is also noted that recitations herein of "at least one" component, element, etc., should not be used to create an inference that the alternative use of the articles "a" or "an" should be limited to a single component, element, etc.

[0076] It is noted that the terms "typically" and "state-of-the-art" when utilized herein, are not utilized to limit the scope of the claimed invention or to imply that certain features are critical, essential, or even important to the structure or function of the claimed invention. Rather, these terms are merely intended to identify particular aspects of an embodiment of the present disclosure or to emphasize alternative or additional features that may or may not be utilized in a particular embodiment of the present disclosure.

[0077] For the purposes of describing and defining the present invention it is noted that the "about" is utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. The term "about" is also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue.

[0078] Having described the subject matter of the present disclosure in detail and by reference to specific embodiments thereof, it is noted that the various details disclosed herein should not be taken to imply that these details relate to elements that are essential components of the various embodiments described herein, even in cases where a particular element is illustrated in each of the drawings that accompany the present description. Further, it will be apparent that modifications and variations are possible without departing from the scope of the present disclosure, including, but not limited to, embodiments defined in the appended claims. More specifically, although some aspects of the present disclosure are identified herein as preferred or particularly advantageous, it is contemplated that the present disclosure is not necessarily limited to these aspects.

[0079] It is noted that one or more of the following claims utilize the term "wherein" as a transitional phrase. For the purposes of defining the present invention, it is noted that this term is introduced in the claims as an open-ended transitional phrase that is used to introduce a recitation of a series of characteristics of the structure and should be interpreted in like manner as the more commonly used open-ended preamble term "comprising."

[0080] According to a first aspect of the present disclosure, a pH sensor may comprise a pH sensing element comprising a measuring electrode, a pH fluid chamber, and a pH sensing chamber; a reference sensing element comprising a reference electrode, a reference fluid chamber, and a reference fluid partition configured to define a fluid flow barrier between an interior of the reference fluid chamber and a test sample characterized by an indeterminate pH, and a fluidic reference junction forming a reference fluid diffusion path across the reference fluid partition, wherein the measuring electrode resides in the pH sensing chamber; the pH sensing chamber is fluidly coupled to the pH fluid chamber; the reference electrode resides in the reference fluid chamber; and a sensing membrane portion of the pH sensing chamber is fabricated from a glass composition comprising from about 59.0 mol% to about 72.0 mol% Si0 ₂ , from about 20.0 mol% to about 32.0 mol% Li ₂ 0, from about 0.3 mol% to about 4.0 mol% La ₂ 0 _3i from about 0.3 mol% to about 5.0 mol% Ta ₂ Os _, an amount A of a corrosion resistance component comprising Ti0 ₂ , where A is from about 0.3 mol% to about 5.0 mol%, an amount B of Cs ₂ 0, where B > 0.0 mol%, and an amount C of a redox buffer component comprising Ce0 ₂ , where C > 0.0% and A>B>C.

[0081] A second aspect of the present disclosure may include the first aspect, wherein the glass composition comprises a molar of A:B:C from about 3:2: 1 to about 5:2: 1.

[0082] A third aspect of the present disclosure may include the first or second aspects, wherein the glass composition is substantially free of a functional amount of alkaline earth metals, actinides, and Fe ₂ 0 ₃ . [0083] A fourth aspect of the present disclosure may include any of the first through third aspects, wherein the pH sensing chamber is bulb-shaped.

[0084] A fifth aspect of the present disclosure may include any of the first through fourth aspects, wherein the pH sensing element resides within the reference sensing element.

[0085] A sixth aspect of the present disclosure may include any of the first through fifth aspects, wherein the pH sensing chamber further comprises a sensor extension portion surrounding at least a portion of the pH sensing chamber; and the sensor extension portion and the pH sensing chamber define a minimum displacement buffer gap between the sensor extension portion and the pH sensing chamber.

[0086] A seventh aspect of the present disclosure may include any of the first through sixth aspects, wherein the minimum displacement buffer gap is between about 0.8 mm and about 2.0 mm.

[0087] An eighth aspect of the present disclosure may include any of the first through seventh aspects, wherein the outer diameter of the pH sensing chamber is between about 2.6 mm and about 9.5 mm.

[0088] A ninth aspect of the present disclosure may include any of the first through eighth aspects, wherein the fluidic reference junction is characterized by a reference fluid flow rate from between about 0 mL/day to about 2 mL/day.

[0089] A tenth aspect of the present disclosure may include any of the first through ninth aspects, wherein the pH sensor further comprises an intermediate reference fluid partition defining a fluid flow barrier within the reference fluid chamber; and an intermediate reference fluid junction.

[0090] An eleventh aspect of the present disclosure may include any of the first through tenth aspects, wherein the fluidic reference junction and the intermediate reference fluid junction are characterized by the same flow rate.

[0091] An twelfth aspect of the present disclosure may include any of the first through eleventh aspects, wherein the pH sensor further comprises a pH fluid residing in the pH fluid chamber. [0092] A thirteenth aspect of the present disclosure may include any of the first through twelfth aspects, wherein the pH sensor further comprises a reference fluid residing in the reference fluid chamber.

[0093] According to a fourteenth aspect of the present disclosure, a pH sensor may comprise a pH sensing element comprising a measuring electrode, a pH fluid chamber, and a pH sensing chamber; a reference sensing element comprising a reference electrode, a reference fluid chamber, and a reference fluid partition configured to define a fluid flow barrier between an interior of the reference fluid chamber and a test sample characterized by an indeterminate pH; and at least one fluidic reference junction forming a reference fluid diffusion path across the reference fluid partition, wherein the measuring electrode resides in the pH sensing chamber; the pH sensing chamber is fluidly coupled to the pH fluid chamber; the reference electrode resides in the reference fluid chamber; and a sensing membrane portion of the pH sensing chamber is fabricated from a glass composition comprising from about 59.0 mol% to about 72.0 mol% Si0 ₂ , from about 20.0 mol% to about 32.0 mol% Li ₂ 0, from about 0.3 mol% to about 4.0 mol% La ₂ 0 _3i from about 0.3 mol% to about 5.0 mol% Ta ₂ Os _, an amount A of a corrosion resistance component comprising Ti0 ₂ , where A is from about 0.3 mol% to about 5.0 mol%, an amount B of Cs ₂ 0, where B > 0.0 mol%, and an amount C of a redox buffer component.

[0094] According to a fifteenth aspect of the present disclosure, a pH sensing element may comprise a measuring electrode, a pH fluid chamber, and a pH sensing chamber, wherein the measuring electrode resides in the pH sensing chamber; the pH sensing chamber is fluidly coupled to the pH fluid chamber; and a sensing membrane portion of the pH sensing chamber is fabricated from a glass composition comprising from about 59.0 mol% to about 72.0 mol% Si0 ₂ , from about 20.0 mol% to about 32.0 mol% Li ₂ 0, from about 0.3 mol% to about 4.0 mol% La ₂ 0 _3i from about 0.3 mol% to about 5.0 mol% Ta ₂ Os _, an amount A of a corrosion resistance component comprising Ti0 ₂ , where A is from about 0.3 mol% to about 5.0 mol%, an amount B of Cs ₂ 0, where B > 0.0 mol%, and an amount C of a redox buffer component.