Abstract:
The present invention pertains to a means of combining and configuring specific hydrophilic and dielectric materials in such a way as to allow an antimony/reference electrode pH sensor to be packaged and stored dry yet become fully hydrated to an activated state after exposure to aqueous liquids. The sensor is packaged and stored dry to maintain component stability and minimize component degradation. When the user removes the sensor from the package and the sensor tip is submerged in a hydration (ion conduction) media or solution, the hydrophilic coating along with the impregnated reference wick, absorb the fluid to create an electrolytic gel inside the reference wick, which activates the pH sensor.

Description:
FIELD OF THE INVENTION 
       [0001]    The art to which this invention relates is in the field of monitoring pH or other constituents. More specifically, an invention which utilizes a means of combining and configuring materials within a pH sensor that allows dry packaging and rapid hydration to attain an activated state. 
       BACKGROUND OF THE INVENTION 
       [0002]    Since the inception of the modern pH scale, a variety of devices have been developed to monitor and interpret changes in the negative log of the concentration of hydrogen protons in a solution, “pH”. 
         [0003]    For general or industrial applications, pH papers or liquid indicators that change color as the pH level of a solution varies are used. These indicators are convenient to use, but have limitations on their accuracy, and can be difficult to interpret correctly in some conditions. 
         [0004]    For laboratory applications, a more accurate tool is employed that relies on electronic pH measurement means. This equipment typically consists of three parts: a pH measuring electrode, a reference electrode, and a high input impedance meter. The pH measuring electrode and reference electrode can be thought of as a battery, with a voltage that varies with pH of the measured solution. The system can be made up of a large glass bulb with a hydrogen ion sensitive coating. This coating creates a millivolt output that varies with changes in relative hydrogen ion concentration inside and outside of the bulb. The reference electrode can consist of a combination of metals, chemicals, and liquid commonly known as electrolytic fluid or gel, that create a millivolt output that does not vary with changes in hydrogen ion concentration. 
         [0005]    In medical applications where the environmental pH of the esophagus or pharyngeal regions need to be measured, a smaller, more compact sensor system is utilized. The pH sensing element usually consists of an exposed antimony metal segment, that changes voltage with the change in pH, and a silver/silver chloride reference electrode, that does not change voltage with the change in pH. The reference electrode of these pH sensors is usually protected from outside contaminants by nesting the element within the body of the pH sensor and surrounding it with ion conducting electrolytic gel. The reference wick, typically a strand of fibrous material, is used as a conduit between the ion conducting gel and the environment which is to be measured. 
         [0006]    As moisture is necessary to maintain the ion conducting properties of the electrolytic gel, these esophageal or pharyngeal pH sensors must be packaged in a way as to retain sufficient moisture for ion conduction. Manufacturing a pH sensor that has a fluid element, as well as packaging to retain that moisture during shipping and storage, poses a number of challenges such as moisture retention, fluid migration, and component deterioration. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention pertains to a means of combining and configuring specific hydrophilic and dielectric materials in such a way as to allow an antimony/reference electrode pH sensor to be packaged and stored dry yet become fully hydrated to an activated state after exposure to aqueous liquids. 
         [0008]    The following drawings and specification details the construction of the present invention. The distal section of the pH sensor shows an antimony metal segment that is encased in a dielectric material to maintain isolation from the reference electrode. Adjacent to the antimony is the reference wick, impregnated with a dry matrix of hygroscopic materials such as hydroxyethylcellulose and sodium chloride, which when hydrated, forms an electrolytic gel. The reference wick is sheathed with a polymer tube, which acts as a capillary tube, facilitating the liquid flow. An expansion plug at the proximal end of the tube regulates the amount of liquid absorbed and controlling the electrolyte concentration. To initiate hydration and increase the wet ability of the reference wick, a hydrophilic and/or hydroscopic coating is applied to the sensor tip. 
         [0009]    The sensor is packaged and stored dry to maintain component stability and minimize component degradation. When the user removes the sensor from the package and the sensor tip is submerged in a hydration solution, the hydrophilic coating along with the impregnated reference wick, absorb the solution to create an electrolytic gel inside the reference wick, which activates the pH sensor. When the hydration solution contacts the reference element, the pH sensor is activated. 
         [0010]    These and other features, aspects and advantages of the present invention will become better understood with reference to the following descriptions and claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a partially sectional side view of the sensor apparatus kit demonstrating in detail the orientation and components of the pH sensing means. 
           [0012]      FIG. 2  is a side view of a container filled with a hydration solution that is used to activate the sensor apparatus. 
           [0013]      FIG. 3  is a top view of the terminal end of one embodiment of the sensor apparatus demonstrating the orientation of the reference wick separated by an inner bridge from the antimony metal segment in a multi-luminal design. 
           [0014]      FIG. 4  is a top view of the terminal end of another embodiment of the sensor apparatus demonstrating the offset co-linear orientation of the antimony metal segment and the reference wick. 
           [0015]      FIG. 5  is a sectional side view of the terminal end of another embodiment sensor apparatus demonstrating the orientation of the antimony metal segment and wire assembly that is electrically isolated from the reference sensor and reference wick in a dry state. 
           [0016]      FIG. 6  is a sectional side view of the sensor apparatus demonstrating the orientation of the antimony metal segment and wire assembly which is electrically isolated from the reference sensor and reference wick whereby the sensor is activated by the controlled uptake of the hydration solution into the reference wick. 
           [0017]      FIG. 7  is the present invention sensor being used in an example liquid environment. 
           [0018]      FIG. 8  is the present invention sensor being used in an example humid gaseous environment. 
           [0019]      FIG. 9  is the present invention sensor being used in an example clinical application. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0020]    The present invention pertains to an apparatus that includes a controlled activation means in a sensor that can detect changes in pH levels of humidified gases and liquid samples. When electronically connected to a computerized or analog display means, sensitive quantitative measurements can be obtained. Given the construction of current pH devices available today, there is a need in the field for a novel, controlled activation pH probe that can be used in fluid or humidified gases. 
         [0021]      FIG. 1  illustrates the present invention consisting of a sensor apparatus  10  comprised of several components. As shown in this Figure, a typical partially sectional side view of the sensor apparatus demonstrates the orientation and components of the pH sensor apparatus  10 . 
         [0022]    As shown by the combination of  FIGS. 1 and 2 , it is contemplated by the Applicant that the present invention will be supplied as a kit  12  whereby a “dry state” sensor  10  will be packaged with a hydration solution  36  sealed in a hydration (activation) container  35 . The pH sensor apparatus  10  is packaged and stored “dry” to maintain component stability and minimize component degradation. When desired, the user removes the sensor from the package and submerges the sensor tip in a hydration solution whereby the hydrophilic coating and electrolyte loaded wick (for example, a dry matrix of hygroscopic materials such as hydroxyethylecellulose and sodium chloride) absorbs the solution, creating an electrolytic gel inside the wick and around the reference element  30 , which activates the pH sensor. 
         [0023]    A typical hydration solution  36  for sensor activation consists of an aqueous, another polar solution, or a conduction fluid which may contain sodium chloride, potassium chloride or other conductive ion formation materials. 
         [0024]    Now referring to  FIGS. 3-6 , the sensor apparatus  10  and  14  consists of an outer tubular member  15  that is usually fabricated by an extrusion or dip coating process using a variety of polymeric materials including polyimide, polyethylene, polypropylene, polyvinyl chloride, polystyrene, ABS, nylon, acetal, polyethylene terephthalate (PET), fluorinated ethylene-propylene (FEP) or polytetrafluoroethylene (PTFE). The outer tubular member  15  generally has an outside diameter in the range of 0.030″ to 0.070″, and preferably between 0.040″ and 0.060″. Its wall thickness is typical for its diameter and generally is in the range of 0.005″ to 0.020″ and preferably between 0.0010″ and 0.015″. The outer tubular member  15  may include a coating specific for certain applications, e.g. protection from acid environments, dielectric isolation, etc. 
         [0025]    Co-linearly, coaxially or multi-luminally aligned within the outer tubular member  15  is a first inner tubular member  17  and a second inner tubular member  37  that is also usually fabricated by an extrusion or dip coating process using a variety of polymeric materials including polyimide, polyethylene, polypropylene, polyvinyl chloride, polystyrene, ABS, nylon, acetal, polyethylene terephthalate (PET), fluorinated ethylene-propylene (FEP) or polytetrafluoroethylene (PTFE). 
         [0026]    Located within the first inner tubular member  17  is a “dry state” reference wick  19  that is electrically isolated from the antimony metal segment  24  and wire assembly. The reference wick  19  is packaged in a dry, “non-activated” state which functions to maintain component stability and minimize component degradation. In one embodiment ( FIG. 3 ) the sensor apparatus utilizes a multi-lumen design to enclose the antimony metal segment  24  and the reference wick  19 , each of the lumens functioning to provide individual tubular members for the antimony metal segment  24  and reference wick  19 . In another embodiment ( FIG. 4 ), the reference wick  19  is enclosed within a tubular member that is co-linearly offset with the outer tubular member  15 . The reference wick  19 , enclosed within an appropriate tubular member, comprises a mesh or fibrous configuration which may incorporate one or more micro-channels (not shown). The dry “non-activated” reference wick  19  can be fabricated from a variety of polymeric based materials. Examples of such materials are polysaccharides, (cotton, regenerated cellulose) polyester, polyethylene, polypropylene, polyvinyl chloride (PVC), polystyrene, ABS, nylon, acetal, polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), collagen, Hytrel (thermoplastic polyester elastomer), a porous material selected from the group consisting of porous ceramic, metallic or polymeric material, or any material or combination of materials which exhibit a weave, felt or mesh design that facilitates wicking or ion conduction. One example of a preferable material for the reference wick  19  is a polyester fabric mesh. One or more micro-channels could be incorporated into the mesh to facilitate transport of the hydration solution  36 . The polymeric based materials of the wick  19  are impregnated with a matrix of hydrophilic and/or hydroscopic materials such as water soluble hydroxyethylcellulose and sodium chloride that when hydrated, becomes an electrolytic gel. One example of the wick  19  that can be used with the sensor  10  is a polysaccharide based gel, 1-10 percent, with a preferred range of 3-5 percent, which is incorporated with a solution of sodium chloride and water. Other materials that can function as the reference wick  19  with a hydration solution  36  include ion carrying gels, hydrogels, and excipients. These gels, hydrogels, and excipients aid in maintaining the stability of the reference element  30 . 
         [0027]    Located within the second inner tubular member  37  is an antimony metal segment  24  having a surface area  22  at the terminal end. The antimony metal segment  24  is generally 99% pure and free from significant contaminates. The Applicant contends that the antimony metal segment  24  could be replaced with other metallic substances like antimony that exhibit a change in electrical potential when immersed in different pH fluids. Furthermore, other potential materials such as specially formulated polymers, semiconductor technology, Ion Sensitive Field Effect Transistors (ISFETs), optical sensing, capacitive sensing, and nanotechnology could be employed. 
         [0028]    The antimony metal segment  24  is engaged at its proximal end to an electrical communication means  26 . Typically electrical wire  26  has an internal core comprised of an electrically conductive metallic material that is encased by a nonconductive jacket. The means of engagement typically employs standard soldering technology and can be supported by a variety of means to provide strain relief. The surface  22  of the antimony metal segment  24  defines the distal terminal boundary of the sensor and is the surface that is exposed to liquid or humid gaseous environments. 
         [0029]    Located proximally, from a range of 0.5-8.0 centimeters from the distal end of the reference wick  23  and preferably 0.1-3.0 centimeters, and engaging a portion of the reference wick, is a reference element  30 . Said reference element  30  is primarily composed of a silver core surrounded with a coating of silver chloride. Technology of dipping a silver core in a high temperature bath of silver chloride to produce the silver chloride coating is employed in the present invention. The resulting coating generally is 0.001″ to 0.010″ in thickness, and preferably 0.002″ to 0.005″. Reference element  30  is engaged to an electrical communication means  28 , e.g. typical wire that extends to the proximal end of the outer tubular member  15  and can terminate in a typical electrical connector (not shown). An expansion plug is optionally located at the proximal end of the tube and is made of a hydrophilic material. When dry, the plug is relatively loose allowing air to escape out the back of the tube during capillary liquid flow. When the liquid comes in contact with the plug, the plug expands and seals the proximal end of the tube preventing any further capillary action and liquid absorption, which can affect the electrolyte concentration. To initiate hydration and increase the wet ability of the reference wick, a hydrophilic and/or hydroscopic coating is applied to the sensor tip. When the hydration solution contacts the reference element, the pH sensor is activated. 
         [0030]    The performance of the sensor may be enhanced in some environments by the inclusion of a coating or other surface modification on this distal surface. One example would be a hydrophilic and/or hygroscopic coating to enhance the absorption and retention of moisture on the sensor in humidified gases and aerosols. Materials such as hydrophilic and/or hygroscopic polyurethanes, polyacrylamides, poly(2-hydroxyethyl-methacrylate), other methacrylate copolymers, perfluorinated polymers, polysaccharides, polyvinyl chloride, polyvinyl alcohol and silicones could all be utilized. Examples of surface modifications could include plasma using H2O, Co2 and or N2, RF energy, or radiation either alone or in combination with other chemical depositions or reactions. A plasma treatment followed by grafting of hydrophilic monomers (acrylic acid and acrylamide) in the vapor phase could also be utilized. The coatings and surface modifications either alone, in combination, or with modifications could be utilized as surface enhancements to improve the wet ability and hence the absorption of moisture on the distal sensor tip in humidified gases and aerosol environments. 
         [0031]    Positioned proximal to the reference element  30  is a singular or plurality of sodium chloride rods  34  that are positioned in close proximity to the reference wick  19  which dissolves into the hydration solution to retain a stable electrolyte concentration. 
         [0032]    Proximal to the sodium chloride rods  34  is the expansion plug  32  generally located near the proximal end of the inner tubular member  17 . The expansion plug  32  allows venting of the inner tubular member  17  into the space of the outer tubular member  15 , encouraging capillary action and then seals against the inner tubular member  17  after it becomes hydrated. 
         [0033]    With the composition of hygroscopic and/or hydrophilic materials of the reference wick  19 , the hydroscopic and/or hydrophilic coating on the terminal end, and the proximal location of the expansion plug  32  and sodium chloride rods  34 , when the terminal end of the sensor is submerged into the hydration solution  36 , the solution  36  enters the terminal end of the reference wick  19  and is transported by capillary action through the reference wick  19  and towards the expansion plug  32 . 
         [0034]    Now referring specifically to  FIG. 6 , at the time activation of the sensor is desired, the tip of the sensor apparatus is submerged into a hydration solution  36 , whereby the hydrophilic and/or hygroscopic coating and the structure of the reference wick absorbs the fluid, creating an electrolytic gel  20  with and around the reference wick  19  inside inner tubular member  17 . The level of the absorbed fluid is influenced by the expansion plug  32  and sodium chloride rods  34  and is designed to at least reach the reference element  30 , thereby electrically activating the pH sensor  14 . The present invention sensor  10  will become activated within a typical period of approximately 1 to 10 minutes after immersion in the hydration solution  36  and will remain activated throughout its intended use. 
         [0035]      FIG. 7  is the present invention sensor  10  being used in an example liquid environment. Sensor apparatus  10  or  14  is shown immersed within a fluid  44  contained in a flask  42 . Extending from the sensor  10  or  14  are the antimony metal segment electrical communication means  26  and reference element  30  electrical communication means  28  which are connected to a display/processing means  40 . The sensor can provide an immediate reading of the pH level of the fluid  44  or the sensor could be used to monitor pH of the fluid continuously over time to detect changes in the pH. 
         [0036]      FIG. 8  is the present invention sensor apparatus  10  are being used in an example humid gaseous environment. Shown in  FIG. 8  is pump  46  forcing humid gas  48  through a passageway  47 . Sensor apparatus  10  is positioned within the passageway and exposed to the humid gas to provide a means for continuously monitoring the pH of the gas. 
         [0037]      FIG. 9  is the present invention sensor being used in an example clinical application. In  FIG. 9 , sensor apparatus  10  is shown attached to a nasal cannula or intranasal catheter (or a mask) that is positioned on the face of patient  50  so that it is exposed to the patient&#39;s exhaled breath either outside the body or in the patient&#39;s airway. In this example, the pH of the patient&#39;s breath can be continuously monitored. Extending from the sensor apparatus  10  are the antimony metal segment electrical communication means  26  and reference element electrical communication means  28 , which are connected to display/processing means  40 . The sensor can provide an immediate reading of the pH of the patient&#39;s breath or the sensor could be used to measure the pH of the patient&#39;s breath for a period of time to monitor and diagnose certain respiratory conditions. Another potential use of the sensor apparatus  10  in clinical applications is to detect the absence of breath, a condition known as sleep apnea. 
         [0038]    While the invention has been described in detail and with reference to specific embodiment thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.