CA1242764A - Ion-sensitive electrode - Google Patents
Ion-sensitive electrodeInfo
- Publication number
- CA1242764A CA1242764A CA000489961A CA489961A CA1242764A CA 1242764 A CA1242764 A CA 1242764A CA 000489961 A CA000489961 A CA 000489961A CA 489961 A CA489961 A CA 489961A CA 1242764 A CA1242764 A CA 1242764A
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- CA
- Canada
- Prior art keywords
- bulb
- tube
- ion
- radiation
- sensitive
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/28—Electrolytic cell components
- G01N27/30—Electrodes, e.g. test electrodes; Half-cells
- G01N27/36—Glass electrodes
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- Chemical & Material Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Health & Medical Sciences (AREA)
- Biochemistry (AREA)
- General Physics & Mathematics (AREA)
- Electrochemistry (AREA)
- Physics & Mathematics (AREA)
- Analytical Chemistry (AREA)
- Molecular Biology (AREA)
- General Health & Medical Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Investigating Or Analysing Materials By Optical Means (AREA)
- Glass Compositions (AREA)
- Surface Treatment Of Glass (AREA)
- Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)
- Vessels And Coating Films For Discharge Lamps (AREA)
Abstract
Abstract of the Disclosure An improved ion-sensitive electrode is formed from an infrared-absorbent glass tube (12) and a preform (30) of an infrared-transparent ion-sensitive material. A bulbous head (32) of the preform (30) has a diameter substantially larger than that of the tube (12). With the bulbous head (32) resting on the lip of the tube (12), an infrared source (15) shines on the lip, fusing it and bonding the tube (12) to the head (32). When the fused assembly cools, the portion of the preform (30) tends to crack and fall away, leaving a completed electrode body.
Description
~2~64 Field of the Invention The invention relates to ion-sensitive electrodes and comprises a flat surface electrode formed from a portion of a bulb of ion-selec~ive membrane material fused to the end of a tube through the use of radiation.
It is particularly useful in forming low resistance electrodes from high resistivity material.
Background of the Invention Ion-sensitive electrodes measure the activity of ions in solution (both aqueous and non-aqueous)and are well known in the art of analytical chemistry. One example of such a measurement is pH, which is a measure of the activi~y of hydrogen ions in solution, and is an important parameter for many chemical processes.
Another example is the measurement of sodium ions in foods or biological fluids.
Ion-sensitive electrodes are commonly formed from a tubular shell having one end sealed with an ion-selective membrane. The membrane is selectivelypermeable to ions of one type, while excluding others present in the sample solution. Inside the tube there is a means for providing a fixed potential, either a solution of fixed composition or a solid conduc~or in contact with the membrane. The potential across the ~ 7~-~ D23-014 membrane, measured from the internal contact, through the sample to a second reference contact provides a measure of the sample ion activity.
Ion-selective membranes are most commonly formed with either a bulbous or a flat shape. For membranes formed in the glassy state, bulbous-shaped electrodes are more readily formed than flat-membrane electrodes, and are suitable for measurements of liquid samples where there is a significant quantity of liquid available for measurement. Flat-membrane electrodes, in contrast, are desirable, or even required, for measuring samples where there is a limited quantity of material available, and for measuring ~oist solids where the membrane must be pressed against the sample without immersion in it.
The membranes used for ion-sensitive electrodes typically present a high input impedence to the measuring instrument, e.g., up to 1000-20000 mego~ms. This impeoence limits the accuracy of measurements because of noise pickup in the electrode. In particular, the ion-selective membranes for pH-sensing electrodes are commonly formed from glass. In common pH-sensing glasses, high selectivity for a hydrogen ion is ~ypically also accompanied by high resi~tivity, and thus the improved sensitivity otherwise obtainable from the material is masked by the increased noise pickup caused by the higher resistivity. This can be particularly a ~ Z ~ ~ 7~ 4 D23-014 problem with flat surface membranes in which conventional manufacturing techniques place stringent limits on the extent to which ~he membrane thickness (and thus, it resistance for a material of given resistivity) may be controlled.
Flat-membrance surface ion-sensitive electrodes are commonly constructed by a dipping process in which a tubular section of glass is immersed in a molten bath of membrane material. A bead of molten ma~erial typically adheres to the end of the tub~lar section, and is fabricated into a flat membrane on cooliny. The molten glass must have a coefficient of expansion closely matching that of the tube. If the coefficients of expansion of the tube and the molten glass differ greatly, either the tube or the membrane material will frequently crack upon cooling, due to differing rates of contraction. Further, the seal between.~he tube and the membrane glass is often irregularly formed and prone to failure. In addition, dipping processes are difficult to control for uniformity and repeatability of membrane thickness. Sample to sample thickness variations may lead to large variations in strength or electrical resistance.
Once the dipped tube has cooled, the pH glass may be ~round to a desired thickness for the flat membrane required. Grinding is a time consuming process and z~
results in a high percentage of defective electrode bodies due to accidental breaking of the thinned membrane material. Further the grinding process introduces micro-grooves and stresses into the membrane. Impurities from the grinding material may also embed themselves into the areas that are ground and thereby distort membrane properties. Finally, there is a physical limit to the thickness to which one can grind a material, without breaking that material. The limitation is due to the impact nature of the grind-ing process and the brittle nature of membrane material. This limitation has prevented the use, in flat or substantially flat membranes, of low-sodium interference high-resistivity glass.
A need therefore exists for a new method of manufacturing electrode bodies which will allow for the development of improved electrodes utilizing improved materials and having none of the drawbacks of conventional electrodes.
- Surnmary of the Invention According to one aspect of the invention there is pro-vided Eor manufacturing an ion-sensitive-electrode body having a portion formed of an ion-selective membrane material, a method comprising the steps of:
A. inserting an end of a tube, which tube consists essen-tially of material that absorbs radiation of a predetermined wave-length, into a bulb consisting essentially of an ion-selective membrane material that is substantially transparent to radiation of the predetermined wavelength so that the end of said tube con-tacts an inner surface of said bulb; and .
6~
B. shining radiation of the predetermined wavelength throuyh said bulb onto the end of said tube in contact with said bulb to fuse said end of said tube to the inner surface of said bulb.
According to another aspect of the invention there is provided an ion-sensitive electrode comprising a tubular body bonded at oné end to a flat thin membrane of a material whose resistivity is greater than 105 ohm-centimeters and which is selectively permeable to an ion whose concentration is to be mea-sured.
According to a further aspect of the invention there is provided an ion-sensitive electrode of low electrical resistance comprising a body of an infrared absorbent material bonded by infrared radiation to an ion-selective membrane having a resis-tivity greater than 105 ohm-centimeters, having limited thickness, and comprising material transparent to infrared radiation.
According to yet anther aspect of the invention there is provided an ion-sensitive electrode formed according to a method comprising the steps of:
a. forming a bulb of ion-sensitive membrane material which is transparent to radiation;
b. resting said bulb upon a tube of radiation absorbtive material; and c. irradiating said bulb and said tube in order to form a bond therebetween.
Brief Description of the Drawings The foregoing and other features and ad~antages of the ~2~2~76~
invention will be apparent from the following more particular description of the preferred embodiment of the invention, as illus-trated in the accompanying drawings, in which like reference characters refer to the same parts throughout the different views.
The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.
, .
~Z~2~6~
Figure 1 is an expanded cross sectional view of a portion of an electrode formed by a dipping process. It depicts the prior art.
Figure 2 is a partial cross-section view of an ion-sensitive electrode.
Figure 3 is a view of the electrode body prior to membrane bonding in which an infrared light source is shown schematically.
Figure 3A is an enlarged view of a portion of Figure 3A.
- Figure 4 is an expanded cross-section of the operational end of the ion-sensitive electrode of Figures
It is particularly useful in forming low resistance electrodes from high resistivity material.
Background of the Invention Ion-sensitive electrodes measure the activity of ions in solution (both aqueous and non-aqueous)and are well known in the art of analytical chemistry. One example of such a measurement is pH, which is a measure of the activi~y of hydrogen ions in solution, and is an important parameter for many chemical processes.
Another example is the measurement of sodium ions in foods or biological fluids.
Ion-sensitive electrodes are commonly formed from a tubular shell having one end sealed with an ion-selective membrane. The membrane is selectivelypermeable to ions of one type, while excluding others present in the sample solution. Inside the tube there is a means for providing a fixed potential, either a solution of fixed composition or a solid conduc~or in contact with the membrane. The potential across the ~ 7~-~ D23-014 membrane, measured from the internal contact, through the sample to a second reference contact provides a measure of the sample ion activity.
Ion-selective membranes are most commonly formed with either a bulbous or a flat shape. For membranes formed in the glassy state, bulbous-shaped electrodes are more readily formed than flat-membrane electrodes, and are suitable for measurements of liquid samples where there is a significant quantity of liquid available for measurement. Flat-membrane electrodes, in contrast, are desirable, or even required, for measuring samples where there is a limited quantity of material available, and for measuring ~oist solids where the membrane must be pressed against the sample without immersion in it.
The membranes used for ion-sensitive electrodes typically present a high input impedence to the measuring instrument, e.g., up to 1000-20000 mego~ms. This impeoence limits the accuracy of measurements because of noise pickup in the electrode. In particular, the ion-selective membranes for pH-sensing electrodes are commonly formed from glass. In common pH-sensing glasses, high selectivity for a hydrogen ion is ~ypically also accompanied by high resi~tivity, and thus the improved sensitivity otherwise obtainable from the material is masked by the increased noise pickup caused by the higher resistivity. This can be particularly a ~ Z ~ ~ 7~ 4 D23-014 problem with flat surface membranes in which conventional manufacturing techniques place stringent limits on the extent to which ~he membrane thickness (and thus, it resistance for a material of given resistivity) may be controlled.
Flat-membrance surface ion-sensitive electrodes are commonly constructed by a dipping process in which a tubular section of glass is immersed in a molten bath of membrane material. A bead of molten ma~erial typically adheres to the end of the tub~lar section, and is fabricated into a flat membrane on cooliny. The molten glass must have a coefficient of expansion closely matching that of the tube. If the coefficients of expansion of the tube and the molten glass differ greatly, either the tube or the membrane material will frequently crack upon cooling, due to differing rates of contraction. Further, the seal between.~he tube and the membrane glass is often irregularly formed and prone to failure. In addition, dipping processes are difficult to control for uniformity and repeatability of membrane thickness. Sample to sample thickness variations may lead to large variations in strength or electrical resistance.
Once the dipped tube has cooled, the pH glass may be ~round to a desired thickness for the flat membrane required. Grinding is a time consuming process and z~
results in a high percentage of defective electrode bodies due to accidental breaking of the thinned membrane material. Further the grinding process introduces micro-grooves and stresses into the membrane. Impurities from the grinding material may also embed themselves into the areas that are ground and thereby distort membrane properties. Finally, there is a physical limit to the thickness to which one can grind a material, without breaking that material. The limitation is due to the impact nature of the grind-ing process and the brittle nature of membrane material. This limitation has prevented the use, in flat or substantially flat membranes, of low-sodium interference high-resistivity glass.
A need therefore exists for a new method of manufacturing electrode bodies which will allow for the development of improved electrodes utilizing improved materials and having none of the drawbacks of conventional electrodes.
- Surnmary of the Invention According to one aspect of the invention there is pro-vided Eor manufacturing an ion-sensitive-electrode body having a portion formed of an ion-selective membrane material, a method comprising the steps of:
A. inserting an end of a tube, which tube consists essen-tially of material that absorbs radiation of a predetermined wave-length, into a bulb consisting essentially of an ion-selective membrane material that is substantially transparent to radiation of the predetermined wavelength so that the end of said tube con-tacts an inner surface of said bulb; and .
6~
B. shining radiation of the predetermined wavelength throuyh said bulb onto the end of said tube in contact with said bulb to fuse said end of said tube to the inner surface of said bulb.
According to another aspect of the invention there is provided an ion-sensitive electrode comprising a tubular body bonded at oné end to a flat thin membrane of a material whose resistivity is greater than 105 ohm-centimeters and which is selectively permeable to an ion whose concentration is to be mea-sured.
According to a further aspect of the invention there is provided an ion-sensitive electrode of low electrical resistance comprising a body of an infrared absorbent material bonded by infrared radiation to an ion-selective membrane having a resis-tivity greater than 105 ohm-centimeters, having limited thickness, and comprising material transparent to infrared radiation.
According to yet anther aspect of the invention there is provided an ion-sensitive electrode formed according to a method comprising the steps of:
a. forming a bulb of ion-sensitive membrane material which is transparent to radiation;
b. resting said bulb upon a tube of radiation absorbtive material; and c. irradiating said bulb and said tube in order to form a bond therebetween.
Brief Description of the Drawings The foregoing and other features and ad~antages of the ~2~2~76~
invention will be apparent from the following more particular description of the preferred embodiment of the invention, as illus-trated in the accompanying drawings, in which like reference characters refer to the same parts throughout the different views.
The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.
, .
~Z~2~6~
Figure 1 is an expanded cross sectional view of a portion of an electrode formed by a dipping process. It depicts the prior art.
Figure 2 is a partial cross-section view of an ion-sensitive electrode.
Figure 3 is a view of the electrode body prior to membrane bonding in which an infrared light source is shown schematically.
Figure 3A is an enlarged view of a portion of Figure 3A.
- Figure 4 is an expanded cross-section of the operational end of the ion-sensitive electrode of Figures
2 and 3.
Detailed Description of the Invention ' In figure 1, a typical flat membrane electrode formed by the usual dipping process characteristic of the prior art is shown. The membrane material 5 which is bonded to the tube 8 during the dipping process has an irregular contour on its inner surface 6. This irregular contour cannot be corrected by grinding and as a result, varies with each electrode manufactured. This results in a membrane of variable and high resistance and thus of adverse noise pickup characteristics.
An improved ion sensitive electrode 10 is shown in Figure 2. The electrode 10 has an electrode body 12 of , 7~i~
generally tubular shape having one end thereof sealed by a substantially flat membrane 14. The electrode body is formed from an energy absorbent (preferably infrared-absorbent) glass tube and a bulbous membrane preform as detailed below. ~se of the bulbous preform for theelectroae body permits the manufacture of flat surface electrodes with high resistivity membrane materials. As is common in ion sensitive electrodes, an internal filling solution 16 provides an electrically conductive path between the membrane and an electrode element 18 which measures a potential difference caused by a change in the ion concentration in the sample filling solution.
The membrane 1~ is preferably formed from a pH or other ion selective glass. Such glasses are typically a mixture of several oxides incl~ding Li2o, Cs2O, La2O3, ; CaO, and Na2o. A variety of other similar consti~uents have also been used. Further, the membrane 14 is formed of a thin, substantially flat material, preferably less than 0.025 inches thick, and as thin as .005 inches.
This is a f~ar thinner membrane section than previously could be used on flat membrane ion exchange electrodes, ana therefore can be formea of low-interference materials such ac low-sodium interference glasses having resistivities greater than 105 ohm-centimeter~. Although such materials have high resistivities, preferably about 2.5 X 10~ ohm-centimeters, the reduced membrane thickness offsets the increased resistivity, and results in a membrane with overall moderate resistance. Accordingly, electrical noise pick up is significantly reduced and a more accurate measurement of an increased pH range is obtained. For example, ~lat-membrane electrodes capable of measuring pH over the range of 0 to 14 can produced by the present process.
In order to protect the glass electrode body 12 from accidental breakage during use, an outer protective tube 20 is placea around it. This outer tube is preferably constructed of resilient plastic and is attached to the membrane end of the inner tube 12 by means of a shock absorbing rubber gasket 22. A cap 24 and lead wires 26 are attached at the remote end of the electrode boay to complete the structure.
~ he electrode of Figure 2 is manufactured as follows: Referring to Figure 3, a preform 30 is formed in the shape of a cylindrical tube having a bulbous head 32 with a diameter substantially larger than that of the ena of body 12 on which the membrane is to be formed. As mentioned above, for pH electrodes, the preform 30 may advantageously be made from a low sodium-interference, high resistivity material which is transparent to infrared radiation. Further the bulb 32 is formed to a reduced wall thickness, e.g. on the order of 0.005 12~2'7~
inches. The wall thickness of the bulb is easily controlled by varying the bulb radius (R) for a given amount of glass.
The flatness of the bulb is controlled by selection of the ratio of bulb diameter to ~ube diameter. In particular, with reference to Figure 3A, the departure 'h' of the bulb membrane from perfect flatness (h=0) can readily be computed as h=~-~l-cos(sin~la)]/a, where r is the tube radius and a is the ratio, r/R, of tube radius to bulb raaius. For a ratio of a=0.5, h=0.268r, that is,the subtended portion of the membrane sealing, the tube departs from flatness by less than fourteen per cent of the tube diameter. For a=0.33, the departure is less than nine per cent.
Despite its limited thickness, the bulb is structurally quite strong and thus is relatively stable sh~pc and easy to handle. Further, the slightly arched ~
is beleved to contribute to the strengh, since glass is stronger in compression than tension. A flat plate of similar thickness would be extremely fragile and quite dif~icult to handle. Further, the bulb has a relatively constant wall thickness so that membrane thickness, and therefore resistance, may be closely controlled.
The preform 30 is placed over one end of the electrode body 12, with the bulb resting directly on the edge of the tubular body 12. As mentioned above, the '7~
body 12 preferably comprises an infrared absorbent glass.
Infrared absorbent glass is commonly called ~green glass"; examples include 'SRI' glass and 'STI' glass manufactured by the Nippon Electric Glass Co., Ltd., 1-1 KAKUDA-CHO, KITADU, Osaka, Japan, as well as certain glasses manufactura by the Schoot Company, e.y. Schott ~o. 4840E glass.
The next step in the ~anufacture of the electrode body is to focus a beam of radiation, such as from an infrarea source 15, slightly above the interface between the bulb 32 and the end 12a of body 12. Tne light passes through the infrared transparent bulb 32 with little absorption and thus little heating, and evenly heats the 'lip' of the infrared absorptive glass tube 12 at its area of contact with the membrane. The tube is rotated at this time in order to keep the heating uniform. The radiation is then brought to a focus at the interface so as to melt the lip of the tube to thereby enable fusing of the tube to the membrane. The infrared energy is then removed (e.9O/ the source is turned off).
It should be noted that the melting point of the glass of the tube is lower than that of the membranous b~lb. If this were not the case, the thin bulb might soften and collapse during the fusing process.
As the assembly begins to cool, it is useful to slightly pressurize the air space within the tubular 1 2 ~ Z7 6 4 D23-014 section 12 in oraer to promote formation of a uniform seal joint 34 (Figure 4) between the glass electrode body and the membrane 14. Ihis slight pressurization of the air space also eliminates internal stresses created by the fusing process in the membrane 14 and the joint 34.
As the fused assembly cools, the remainder of the membrane material tends to crack and fall away. The fusea assembly then need only be polished at any ragged edges about the periphery of the membrane 14 before it is ready for use. The main section of the membrane material, which is thin and unsupported, does not need to be polished or ground. The electrode body 12, with the fused membrane material 14 is then ready for final assembly and the electrode element 18 can be inserted into the boay and terminated at the opposite end of the housing.
The improved ion-sensitive electrode made by the above process is capable of superior operation when compared with previous flat surface, ion-sensitive pH
~o electrodes. The method of manufacture, as described above, permits virtually flat membrane wall thicknesses as low as .005 inches and therefore allows the use of much higher resistivity materials for flat membranes than those available previously. Thus, high performance materials, desirable for the reduced sodium interference effects which characterize them but hithereto 1 ~ ~ 2~ ~ ~ D23-014 contraindicated by their high resistivity which led to increased electerical noise pickup, can now advantageously be used to form pH electrodes operable ~ over a wide pH range.
This process of manufacture also makes advantageous use of the highly uniform wall thicknesses that can be achieved in blowing glass bulbs. The bulb 32 of membrane material is blown to a uniform desired wall thickness; as a result the membrane formed on the tube 12 also possesses a uniform wall thickness. This avoids the unoesirable electroae resistance variations discussed in reference to figure 1.
The membrane is also structurally im~roved by the use of this process. The uniform joint between the tube boay 12 and membrane 14 is quite strong and less likely to separate than the joints formed by previous methods.
Further, microscratches and stresses which are induced by conventional grinding of a membrane surface to the proper thicknesses for flat membranes are completely eliminated by this process. The membraneoùs bulb needs no further processing after its fusing to the ~ubular body of the electrode probe. ~his results in an improved membrane surface with less likelihood of electrode cracking.
Finally, it should be noted that the process used in the manufacture of this improved ion sensitive electrode substantially reduces the cost of manufacture~ Since ~Z~27~
hand grinding and polishing is largely eliminated, the most time consuminy and delicate operation in the construction of flat sur-face ion sensitive electrodes has been eliminated. Further, waste caused by membrane breakage during grinding and polishing is also eliminated.
While the invention has been particularly shown and described with reference to the preferred embodiment thereof, it will be understood by those skilled in the art, that various changes in form and de-tail may be made therein without departing from the spirit and scope of the invention as defined by the append-ed claims. It is possible, for example, to utilize other electxo-magnetic energy sources such as ultraviolet light to fuse the material of the body to the membrane material. Further, the materials used to construct the probe need not be llmited to glass-es: ceramic and epoxy materials have also been used in ion sensitive electrode devices with good results. In appropriate cases, an intermediate meltable bonding material, compatible with both the tubular wall material and the membrane material, may be used to effectuate the desired bond in cases where the membrane material and the tubular wall material may not themselves be sufficiently compatible.
Detailed Description of the Invention ' In figure 1, a typical flat membrane electrode formed by the usual dipping process characteristic of the prior art is shown. The membrane material 5 which is bonded to the tube 8 during the dipping process has an irregular contour on its inner surface 6. This irregular contour cannot be corrected by grinding and as a result, varies with each electrode manufactured. This results in a membrane of variable and high resistance and thus of adverse noise pickup characteristics.
An improved ion sensitive electrode 10 is shown in Figure 2. The electrode 10 has an electrode body 12 of , 7~i~
generally tubular shape having one end thereof sealed by a substantially flat membrane 14. The electrode body is formed from an energy absorbent (preferably infrared-absorbent) glass tube and a bulbous membrane preform as detailed below. ~se of the bulbous preform for theelectroae body permits the manufacture of flat surface electrodes with high resistivity membrane materials. As is common in ion sensitive electrodes, an internal filling solution 16 provides an electrically conductive path between the membrane and an electrode element 18 which measures a potential difference caused by a change in the ion concentration in the sample filling solution.
The membrane 1~ is preferably formed from a pH or other ion selective glass. Such glasses are typically a mixture of several oxides incl~ding Li2o, Cs2O, La2O3, ; CaO, and Na2o. A variety of other similar consti~uents have also been used. Further, the membrane 14 is formed of a thin, substantially flat material, preferably less than 0.025 inches thick, and as thin as .005 inches.
This is a f~ar thinner membrane section than previously could be used on flat membrane ion exchange electrodes, ana therefore can be formea of low-interference materials such ac low-sodium interference glasses having resistivities greater than 105 ohm-centimeter~. Although such materials have high resistivities, preferably about 2.5 X 10~ ohm-centimeters, the reduced membrane thickness offsets the increased resistivity, and results in a membrane with overall moderate resistance. Accordingly, electrical noise pick up is significantly reduced and a more accurate measurement of an increased pH range is obtained. For example, ~lat-membrane electrodes capable of measuring pH over the range of 0 to 14 can produced by the present process.
In order to protect the glass electrode body 12 from accidental breakage during use, an outer protective tube 20 is placea around it. This outer tube is preferably constructed of resilient plastic and is attached to the membrane end of the inner tube 12 by means of a shock absorbing rubber gasket 22. A cap 24 and lead wires 26 are attached at the remote end of the electrode boay to complete the structure.
~ he electrode of Figure 2 is manufactured as follows: Referring to Figure 3, a preform 30 is formed in the shape of a cylindrical tube having a bulbous head 32 with a diameter substantially larger than that of the ena of body 12 on which the membrane is to be formed. As mentioned above, for pH electrodes, the preform 30 may advantageously be made from a low sodium-interference, high resistivity material which is transparent to infrared radiation. Further the bulb 32 is formed to a reduced wall thickness, e.g. on the order of 0.005 12~2'7~
inches. The wall thickness of the bulb is easily controlled by varying the bulb radius (R) for a given amount of glass.
The flatness of the bulb is controlled by selection of the ratio of bulb diameter to ~ube diameter. In particular, with reference to Figure 3A, the departure 'h' of the bulb membrane from perfect flatness (h=0) can readily be computed as h=~-~l-cos(sin~la)]/a, where r is the tube radius and a is the ratio, r/R, of tube radius to bulb raaius. For a ratio of a=0.5, h=0.268r, that is,the subtended portion of the membrane sealing, the tube departs from flatness by less than fourteen per cent of the tube diameter. For a=0.33, the departure is less than nine per cent.
Despite its limited thickness, the bulb is structurally quite strong and thus is relatively stable sh~pc and easy to handle. Further, the slightly arched ~
is beleved to contribute to the strengh, since glass is stronger in compression than tension. A flat plate of similar thickness would be extremely fragile and quite dif~icult to handle. Further, the bulb has a relatively constant wall thickness so that membrane thickness, and therefore resistance, may be closely controlled.
The preform 30 is placed over one end of the electrode body 12, with the bulb resting directly on the edge of the tubular body 12. As mentioned above, the '7~
body 12 preferably comprises an infrared absorbent glass.
Infrared absorbent glass is commonly called ~green glass"; examples include 'SRI' glass and 'STI' glass manufactured by the Nippon Electric Glass Co., Ltd., 1-1 KAKUDA-CHO, KITADU, Osaka, Japan, as well as certain glasses manufactura by the Schoot Company, e.y. Schott ~o. 4840E glass.
The next step in the ~anufacture of the electrode body is to focus a beam of radiation, such as from an infrarea source 15, slightly above the interface between the bulb 32 and the end 12a of body 12. Tne light passes through the infrared transparent bulb 32 with little absorption and thus little heating, and evenly heats the 'lip' of the infrared absorptive glass tube 12 at its area of contact with the membrane. The tube is rotated at this time in order to keep the heating uniform. The radiation is then brought to a focus at the interface so as to melt the lip of the tube to thereby enable fusing of the tube to the membrane. The infrared energy is then removed (e.9O/ the source is turned off).
It should be noted that the melting point of the glass of the tube is lower than that of the membranous b~lb. If this were not the case, the thin bulb might soften and collapse during the fusing process.
As the assembly begins to cool, it is useful to slightly pressurize the air space within the tubular 1 2 ~ Z7 6 4 D23-014 section 12 in oraer to promote formation of a uniform seal joint 34 (Figure 4) between the glass electrode body and the membrane 14. Ihis slight pressurization of the air space also eliminates internal stresses created by the fusing process in the membrane 14 and the joint 34.
As the fused assembly cools, the remainder of the membrane material tends to crack and fall away. The fusea assembly then need only be polished at any ragged edges about the periphery of the membrane 14 before it is ready for use. The main section of the membrane material, which is thin and unsupported, does not need to be polished or ground. The electrode body 12, with the fused membrane material 14 is then ready for final assembly and the electrode element 18 can be inserted into the boay and terminated at the opposite end of the housing.
The improved ion-sensitive electrode made by the above process is capable of superior operation when compared with previous flat surface, ion-sensitive pH
~o electrodes. The method of manufacture, as described above, permits virtually flat membrane wall thicknesses as low as .005 inches and therefore allows the use of much higher resistivity materials for flat membranes than those available previously. Thus, high performance materials, desirable for the reduced sodium interference effects which characterize them but hithereto 1 ~ ~ 2~ ~ ~ D23-014 contraindicated by their high resistivity which led to increased electerical noise pickup, can now advantageously be used to form pH electrodes operable ~ over a wide pH range.
This process of manufacture also makes advantageous use of the highly uniform wall thicknesses that can be achieved in blowing glass bulbs. The bulb 32 of membrane material is blown to a uniform desired wall thickness; as a result the membrane formed on the tube 12 also possesses a uniform wall thickness. This avoids the unoesirable electroae resistance variations discussed in reference to figure 1.
The membrane is also structurally im~roved by the use of this process. The uniform joint between the tube boay 12 and membrane 14 is quite strong and less likely to separate than the joints formed by previous methods.
Further, microscratches and stresses which are induced by conventional grinding of a membrane surface to the proper thicknesses for flat membranes are completely eliminated by this process. The membraneoùs bulb needs no further processing after its fusing to the ~ubular body of the electrode probe. ~his results in an improved membrane surface with less likelihood of electrode cracking.
Finally, it should be noted that the process used in the manufacture of this improved ion sensitive electrode substantially reduces the cost of manufacture~ Since ~Z~27~
hand grinding and polishing is largely eliminated, the most time consuminy and delicate operation in the construction of flat sur-face ion sensitive electrodes has been eliminated. Further, waste caused by membrane breakage during grinding and polishing is also eliminated.
While the invention has been particularly shown and described with reference to the preferred embodiment thereof, it will be understood by those skilled in the art, that various changes in form and de-tail may be made therein without departing from the spirit and scope of the invention as defined by the append-ed claims. It is possible, for example, to utilize other electxo-magnetic energy sources such as ultraviolet light to fuse the material of the body to the membrane material. Further, the materials used to construct the probe need not be llmited to glass-es: ceramic and epoxy materials have also been used in ion sensitive electrode devices with good results. In appropriate cases, an intermediate meltable bonding material, compatible with both the tubular wall material and the membrane material, may be used to effectuate the desired bond in cases where the membrane material and the tubular wall material may not themselves be sufficiently compatible.
Claims (10)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. For manufacturing an ion-sensitive-electrode body having a portion formed of an ion-selective membrane material, a method comprising the steps of:
A. inserting an end of a tube, which tube consists essen-tially of material that absorbs radiation of a predetermined wave-length, into a bulb consisting essentially of an ion-selective membrane material that is substantially transparent to radiation of the predetermined wavelength so that the end of said tube con-tacts an inner surface of said bulb; and B. shining radiation of the predetermined wavelength through said bulb onto the end of said tube in contact with said bulb to fuse said end of said tube to the inner surface of said bulb.
A. inserting an end of a tube, which tube consists essen-tially of material that absorbs radiation of a predetermined wave-length, into a bulb consisting essentially of an ion-selective membrane material that is substantially transparent to radiation of the predetermined wavelength so that the end of said tube con-tacts an inner surface of said bulb; and B. shining radiation of the predetermined wavelength through said bulb onto the end of said tube in contact with said bulb to fuse said end of said tube to the inner surface of said bulb.
2. The method of claim 1 wherein the predetermined wavelength lies in the infrared region.
3. The method of claim 1 wherein said bulb is less than 0.025 inch thick.
4. The method of manufacturing an electrode body of claim 1 further comprising the step of:
slightly pressurizing said electrode body after fusing said tube to said bulb in order to eliminate internal stresses in said infrared tube.
slightly pressurizing said electrode body after fusing said tube to said bulb in order to eliminate internal stresses in said infrared tube.
5. The method of manufacturing an electrode body of claim 1 wherein said ion-selective membrane material is selectively per-meable to hydrogen ions.
6. The method of manufacturing an electrode body of claim 1 wherein said ion-selective membrane material comprises a limited portion of the surface of said bulb to thereby form a substantially flat surface.
7. The method of claim 6 wherein the said bulb has a radius of at least twice the radius of said tube.
8. An ion-sensitive electrode formed according to a method comprising the steps of:
a. forming a bulb of ion-sensitive membrane material which is transparent to radiation;
b. resting said bulb upon a tube of radiation absorbtive material; and c. irradiating said bulb and said tube in order to form a bond therebetween.
a. forming a bulb of ion-sensitive membrane material which is transparent to radiation;
b. resting said bulb upon a tube of radiation absorbtive material; and c. irradiating said bulb and said tube in order to form a bond therebetween.
9. An ion-sensitive electrode formed according to a method comprising the steps of:
a. forming a bulb of ion-sensitive membrane material which is transparent to radiation and comprises glass having a resistivity value greater than 105 ohm-centimeters;
b. resting said bulb upon a tube of radiation absorbtive material; and c. irradiating said bulb and said tube in order to form a bond therebetween.
a. forming a bulb of ion-sensitive membrane material which is transparent to radiation and comprises glass having a resistivity value greater than 105 ohm-centimeters;
b. resting said bulb upon a tube of radiation absorbtive material; and c. irradiating said bulb and said tube in order to form a bond therebetween.
10. An ion-sensitive electrode formed according to a method comprising the steps of:
a. forming a bulb of ion sensitive membrane material which is transparent to radiation;
b. resting said bulb upon a tube of radiation absorbtive material; and c. irradiating said bulb and said tube in order to form a bond therebetween, wherein the portion of the bulb surface enclosed by the bond is substantially flat.
a. forming a bulb of ion sensitive membrane material which is transparent to radiation;
b. resting said bulb upon a tube of radiation absorbtive material; and c. irradiating said bulb and said tube in order to form a bond therebetween, wherein the portion of the bulb surface enclosed by the bond is substantially flat.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US64759984A | 1984-09-05 | 1984-09-05 | |
| US647,599 | 1984-09-05 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1242764A true CA1242764A (en) | 1988-10-04 |
Family
ID=24597599
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000489961A Expired CA1242764A (en) | 1984-09-05 | 1985-09-04 | Ion-sensitive electrode |
Country Status (5)
| Country | Link |
|---|---|
| CA (1) | CA1242764A (en) |
| CH (1) | CH671466A5 (en) |
| DE (2) | DE3590404T1 (en) |
| GB (1) | GB2176898B (en) |
| WO (1) | WO1986001601A1 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5208887A (en) * | 1990-01-22 | 1993-05-04 | Amp Incorporated | Method and apparatus for terminating a fiber-optic cable without adhesive |
| DE102018118792A1 (en) * | 2017-08-14 | 2019-02-14 | Endress+Hauser Conducta Gmbh+Co. Kg | Method for manufacturing an ISE half cell, ISE half cell, sensor and multiparameter sensor |
Family Cites Families (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3282817A (en) * | 1963-02-20 | 1966-11-01 | Corning Glass Works | Glass electrode and method of making the same |
| US3282818A (en) * | 1963-03-12 | 1966-11-01 | Beckman Instruments Inc | Electrochemical liquid junction structure and method for producing same |
| US3855095A (en) * | 1966-01-03 | 1974-12-17 | Beckman Instruments Inc | Electrochemical electrode assembly and method of making same |
| US3523777A (en) * | 1967-06-29 | 1970-08-11 | Beckman Instruments Inc | Method of making electrochemical glass electrode assembly |
| US3923625A (en) * | 1971-06-30 | 1975-12-02 | Corning Glass Works | Reinforced glass electrode structure |
| US3741884A (en) * | 1972-05-04 | 1973-06-26 | Beckman Instruments Inc | Electrochemical electrode liquid junction structure and method for producing same |
| US3853731A (en) * | 1973-03-12 | 1974-12-10 | Owens Illinois Inc | Solid state junction glass electrode and method of making said electrode |
| US4162211A (en) * | 1977-02-25 | 1979-07-24 | Beckman Instruments, Inc. | Combination electrode assembly |
| US4328082A (en) * | 1980-06-26 | 1982-05-04 | Beckman Instruments, Inc. | Solid state ion-sensitive electrode and method of making said electrode |
| US4485001A (en) * | 1984-02-21 | 1984-11-27 | Beckman Instruments, Inc. | Sterilizable pH electrode and method for producing the same |
-
1985
- 1985-09-03 GB GB08610242A patent/GB2176898B/en not_active Expired
- 1985-09-03 DE DE19853590404 patent/DE3590404T1/de active Pending
- 1985-09-03 DE DE3590404A patent/DE3590404C2/en not_active Expired - Fee Related
- 1985-09-03 WO PCT/US1985/001682 patent/WO1986001601A1/en active Application Filing
- 1985-09-04 CA CA000489961A patent/CA1242764A/en not_active Expired
-
1986
- 1986-09-03 CH CH189086A patent/CH671466A5/de not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| WO1986001601A1 (en) | 1986-03-13 |
| GB2176898B (en) | 1988-06-08 |
| DE3590404T1 (en) | 1987-01-29 |
| GB2176898A (en) | 1987-01-07 |
| GB8610242D0 (en) | 1986-05-29 |
| CH671466A5 (en) | 1989-08-31 |
| DE3590404C2 (en) | 1998-04-16 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |