Abstract:
This invention discloses a voltage-type gas concentration sensor and sensing method thereof. An ionic sensing electrode, a solid electrolyte membrane and a gas-permeable membrane are provided. The ionic sensing electrode comprises a sensing window. The solid electrolyte membrane is disposed on the sensing window. The gas-permeable membrane is disposed on the solid electrolyte membrane. By detecting the change of a reaction voltage as a result of reaction between the ionic sensing electrode and a solution to be measured, the invention is able to determine the pH of the solution to be measured.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention generally relates to gas concentration sensors and sensing method thereof, especially a voltage-type gas concentration sensor and sensing method thereof. 
         [0003]    2. Description of the Prior Art 
         [0004]    Blood analyzers help patients monitor their own health conditions in a more cost-effective and convenient way before seeking a doctor for further diagnosis and treatment. Not only can patients monitor their health conditions by checking the densities of eight major parameters whenever they wish, but the information can also be provided to the doctors to facilitate diagnosis. When measuring the concentration of carbon dioxide, sensors that can provide stable and continuous measurements are needed. These sensors should be able quickly and accurately measure relevant data. Current methodologies for carbon dioxide analysis can be generally classified into three types: optical, current-type and voltage-type. Among these three types, voltage-type structures are usually simpler than the other two types of sensing structures. A voltage-type gas concentration sensor detects carbon dioxide concentration based on pH variation in its internal buffer solution. 
         [0005]    Conventional pH ionic sensing electrodes for voltage-type gas concentration sensors are usually made of traditional pH glass electrodes, thus they have shortcomings, for example, they are large in volume, not easy to preserve and costly. Moreover, a bicarbonate solution needs regular replacement to avoid deterioration. In addition, a gas-permeable membrane at the outermost layer of the electrode is also consumable. Therefore, there is a need for an invention that is simple and cheap while eliminating the need for regular replacement of the internal buffer solution. 
       SUMMARY OF THE INVENTION 
       [0006]    In view of the prior art and the needs of the related industries, the present invention provides a voltage-type gas concentration sensor and sensing method that solves the abovementioned shortcomings of the conventional voltage-type gas concentration sensors and sensing methods. 
         [0007]    One objective of the present invention is to provide a voltage-type gas concentration sensor that determines pH of solution to be measured by detecting the variation in reaction voltage of an ionic sensing electrode after reacting with the solution to be measured. 
         [0008]    Another objective of the present invention is to provide a voltage-type gas concentration sensing method by providing an ionic sensing electrode having a sensing window, so as to allow gaseous ions in a solution to be measured to pass through a gas-permeable membrane and react with a solid electrolyte membrane disposed on the sensing window, causing ions to deionize, and detecting variation in reaction voltage as a result of deionized ions. 
         [0009]    According to the above and other objectives, the present invention discloses a voltage-type gas concentration sensor, including an ionic sensing electrode including a sensing window, a solid electrolyte membrane and a gas-permeable membrane. The solid electrolyte membrane is disposed on the sensing window and the gas-permeable membrane disposed on the solid electrolyte membrane. The pH value of a solution to be measured can be determined by detecting variation in reaction voltage of the ionic sensing electrode after reacting with the solution to be measured. 
         [0010]    According to the above and other objectives, the present invention discloses a voltage-type gas concentration sensing method by providing an ionic sensing electrode having a sensing window, so as to allow gaseous ions in a solution to be measured to pass through a gas-permeable membrane and react with a solid electrolyte membrane disposed on the sensing window, causing ions to deionize, and detecting variation in reaction voltage as a result of deionized ions. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention, and together with the description serve to explain the principles of the disclosure. In the drawings: 
           [0012]      FIG. 1  is a schematic diagram illustrating the structure of a voltage-type gas concentration sensor according to one embodiment of the present invention; and 
           [0013]      FIG. 2  is a flow chart illustrating a voltage-type gas concentration sensing method according to one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0014]    The present invention is directed to a voltage-type gas concentration sensor and sensing method thereof. Detailed steps and constituents are given below to assist in the understanding the present invention. Obviously, the implementations of the present invention are not limited to the specific details known by those skilled in the art of voltage-type gas concentration sensor and sensing method thereof. On the other hand, well-known steps or constituents of digital watermarking are not described in details in order not to unnecessarily limit the present invention. Detailed embodiments of the present invention will be provided as follow. However, apart from these detailed descriptions, the present invention may be generally applied to other embodiments, and the scope of the present invention is thus limited only by the appended claims. 
         [0015]    A first embodiment of the present invention is a voltage-type gas concentration sensor, including a ionic sensing electrode, a solid electrolyte membrane and a gas-permeable membrane. The ionic sensing electrode has a sensing window. The solid electrolyte membrane can be disposed on the sensing window, while the gas-permeable membrane can be disposed on the solid electrolyte membrane. 
         [0016]    In this embodiment, the ionic sensing electrode can be preferably composed of the following materials, from outside to inside: zinc dioxide, carbon gel and poly vinyl chloride. In this embodiment, the solid electrolyte membrane can be preferably composed of one or a combination of the following materials: NaHCO 3 , NaCl, deionized water (D.I. water), poly vinyl alcohol (PVA), and carbonic anhydrase. In this embodiment, the gas-permeable membrane can be preferably composed of one or a combination of the following materials: dioctyl sebacate (DOS), valinomycin, silicon rubber and tetrahydrofuran (THF) solution. 
         [0017]    The voltage-type gas concentration sensor can include a reference electrode. The reference electrode outputs a constant reference voltage. The reference voltage serves as a reference for change in a reaction voltage measured by the voltage-type gas concentration sensor. The voltage-type gas concentration sensor can include a data processing device connected to the ionic sensing electrode and the reference electrode to detect the reaction voltage and the reference voltage thereof, respectively. The voltage-type gas concentration sensor can include a wireless transmission module electrically coupled to the ionic sensing electrode and the data processing device, such that the data processing device can wirelessly detect the variation in the reaction voltage of the ionic sensing electrode and the reference voltage of the reference electrode. 
         [0018]    Referring to  FIG. 1 , in a preferred example of this embodiment, the voltage-type gas concentration sensor  100  includes an ionic sensing electrode  102 , a solid electrolyte membrane  104 , a gas-permeable membrane  106 , a reference electrode  108  and a data processing device  110 . The ionic sensing electrode  102  has a sensing window  112 . The solid electrolyte membrane  104  can be disposed on the sensing window  112 , while the gas-permeable membrane  106  can be disposed on the solid electrolyte membrane  104 . The sensing window  112  on the ionic sensing electrode  102  can be placed inside a container  116  with a solution  114  to be measured, causing the ionic sensing electrode  102  to react with the solution  114  to create a reaction voltage. 
         [0019]    The reference electrode  108  outputs a constant reference voltage. The reference voltage serves as a reference for measuring change in the reaction voltage of the ionic sensing electrode  102 . The data processing device  110  can be connected to the ionic sensing electrode  102  and the reference electrode  108  to detect the reaction voltage and the reference voltage thereof, respectively. The voltage-type gas concentration sensor  100  can further include a wireless transmission module  118  electrically coupled to the ionic sensing electrode  102  and the data processing device  110 , such that the data processing device  110  can wirelessly detect the variation in the reaction voltage of the ionic sensing electrode  102  and the reference voltage of the reference electrode  108 . In this embodiment, the transmission protocol of wireless transmission module  118  can preferably be one or a combination of the following: WIFI, Bluetooth, ZigBee, WiMax, Wibree, UWB and infrared. 
         [0020]    Referring to  FIG. 2 , a second embodiment of the present invention is a voltage-type gas concentration sensing method  200 . First, as shown in step  202 , an ionic sensing electrode is provided, wherein the ionic sensing electrode includes a sensing window, a solid electrolyte membrane on the sensing window and a gas-permeable membrane on the solid electrolyte. Second, as shown in step  204 , placing the sensing window of the ionic sensing electrode in a container with a solution to be measured, causing the ionic sensing electrode to react with the solution to be measured to create a reaction voltage. 
         [0021]    In this embodiment, the ionic sensing electrode can be preferably composed of the following materials, from outside to inside: zinc dioxide, carbon gel and poly vinyl chloride. In this embodiment, the solid electrolyte membrane can be preferably composed of one or a combination of the following materials: NaHCO 3 , NaCl, deionized water (D.I. water), poly vinyl alcohol (PVA), and carbonic anhydrase. In this embodiment, the gas-permeable membrane can be preferably composed of one or a combination of the following materials: dioctyl sebacate (DOS), valinomycin, silicon rubber and tetrahydrofuran (THF) solution. 
         [0022]    The voltage-type gas concentration sensing method can include a step of outputting a reference voltage by a reference electrode, which serves as a reference for change in a reaction voltage measured by the voltage-type gas concentration sensor. The method can further include a step of placing the ionic sensing electrode in a buffer solution and using a reaction voltage created after reaction between the ionic sensing electrode and the buffer solution is stable as a reference voltage. 
         [0023]    The voltage-type gas concentration sensing method can include a data processing device connected to the ionic sensing electrode and the reference electrode to detect the reaction voltage and the reference voltage thereof, respectively. The voltage-type gas concentration sensing method can include a wireless transmission module electrically coupled to the ionic sensing electrode and the data processing device, such that the data processing device can wirelessly detect the variation in reaction voltage of the ionic sensing electrode and the reference voltage of the reference electrode. In this embodiment, the transmission protocol of wireless transmission module can preferably be one or a combination of the following: WIFI, Bluetooth, ZigBee, WiMax, Wibree, UWB and infrared. 
       EXAMPLE 1 
       [0024]    Preparation a voltage-type gas concentration sensor of the present invention requires the following steps of: 
         [0025]    (1) Mix and stir 5 mM/l of NaHCO 3  and 0.5 mM/l of NaCl into deionized water and extract a suitable amount of solution from the mixture. Add a 4 wt % poly vinyl alcohol (PVA. Then, add 10 mg/ml of carbonic anhydrase. Stir the solution of PVA and carbonic anhydrase. 
         [0026]    (2) Extract and dip 2.0 μl of the high-molecular solution in step (1) on the sensing window of the ionic sensing electrode. 
         [0027]    (3) Leave the element in room temperature for 30 to 60 minutes to complete the preparation of solid electrolyte membrane. 
         [0028]    (4) Dissolve 21.5 wt % dioctyl sebacate (DOS), 0.8 wt % valinomycin and 7.7 wt % silicon rubber in tetrahydrofuran (THF) solution (200 μl of THF is required for every 100 mg of silicon rubber). 
         [0029]    (5) Extract and dip 5.0 μl of the mixture in step (4) on the sensing window covered by the solid electrolyte membrane and leave the element under room temperature overnight. 
         [0030]    (6) Upon forming the gas-permeable membrane, the preparation of the voltage-type gas concentration sensor is completed. 
         [0031]    The foregoing description is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obvious modifications or variations are possible in light of the above teachings. In this regard, the embodiment or embodiments discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the inventions as determined by the appended claims when interpreted in accordance with the breath to which they are fairly and legally entitled. 
         [0032]    It is understood that several modifications, changes, and substitutions are intended in the foregoing disclosure and in some instances some features of the invention will be employed without a corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.