WO1985004482A1 - Electrochemical assembly - Google Patents
Electrochemical assembly Download PDFInfo
- Publication number
- WO1985004482A1 WO1985004482A1 PCT/GB1985/000101 GB8500101W WO8504482A1 WO 1985004482 A1 WO1985004482 A1 WO 1985004482A1 GB 8500101 W GB8500101 W GB 8500101W WO 8504482 A1 WO8504482 A1 WO 8504482A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- assembly
- housing
- membrane
- outer membrane
- glass
- Prior art date
Links
- 239000012528 membrane Substances 0.000 claims abstract description 57
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 claims abstract description 38
- 239000011521 glass Substances 0.000 claims abstract description 24
- 229910021529 ammonia Inorganic materials 0.000 claims abstract description 17
- 239000008151 electrolyte solution Substances 0.000 claims abstract description 10
- 150000001768 cations Chemical class 0.000 claims abstract description 7
- 238000012544 monitoring process Methods 0.000 claims abstract description 7
- 229920002379 silicone rubber Polymers 0.000 claims description 6
- 239000004945 silicone rubber Substances 0.000 claims description 6
- 238000004659 sterilization and disinfection Methods 0.000 claims description 6
- 239000000203 mixture Substances 0.000 claims description 5
- 239000004809 Teflon Substances 0.000 claims description 3
- 229920006362 Teflon® Polymers 0.000 claims description 3
- 239000006174 pH buffer Substances 0.000 claims description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 3
- 230000007704 transition Effects 0.000 claims description 2
- 239000010408 film Substances 0.000 description 12
- 239000007789 gas Substances 0.000 description 8
- 239000000243 solution Substances 0.000 description 8
- 239000003792 electrolyte Substances 0.000 description 7
- 229940021013 electrolyte solution Drugs 0.000 description 7
- 230000004044 response Effects 0.000 description 6
- -1 ammonium ions Chemical class 0.000 description 5
- 229910021607 Silver chloride Inorganic materials 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- HKZLPVFGJNLROG-UHFFFAOYSA-M silver monochloride Chemical compound [Cl-].[Ag+] HKZLPVFGJNLROG-UHFFFAOYSA-M 0.000 description 4
- QGZKDVFQNNGYKY-UHFFFAOYSA-O Ammonium Chemical compound [NH4+] QGZKDVFQNNGYKY-UHFFFAOYSA-O 0.000 description 3
- 239000007864 aqueous solution Substances 0.000 description 3
- 230000004888 barrier function Effects 0.000 description 3
- 239000000872 buffer Substances 0.000 description 3
- 230000036512 infertility Effects 0.000 description 3
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- 239000004471 Glycine Substances 0.000 description 2
- TWRXJAOTZQYOKJ-UHFFFAOYSA-L Magnesium chloride Chemical compound [Mg+2].[Cl-].[Cl-] TWRXJAOTZQYOKJ-UHFFFAOYSA-L 0.000 description 2
- 150000001412 amines Chemical class 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 239000000356 contaminant Substances 0.000 description 2
- 238000011109 contamination Methods 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 229920001971 elastomer Polymers 0.000 description 2
- 150000002500 ions Chemical class 0.000 description 2
- 239000011777 magnesium Substances 0.000 description 2
- 239000004033 plastic Substances 0.000 description 2
- 229910001220 stainless steel Inorganic materials 0.000 description 2
- 239000010935 stainless steel Substances 0.000 description 2
- BTBUEUYNUDRHOZ-UHFFFAOYSA-N Borate Chemical compound [O-]B([O-])[O-] BTBUEUYNUDRHOZ-UHFFFAOYSA-N 0.000 description 1
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 1
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 1
- JLVVSXFLKOJNIY-UHFFFAOYSA-N Magnesium ion Chemical compound [Mg+2] JLVVSXFLKOJNIY-UHFFFAOYSA-N 0.000 description 1
- ZLMJMSJWJFRBEC-UHFFFAOYSA-N Potassium Chemical compound [K] ZLMJMSJWJFRBEC-UHFFFAOYSA-N 0.000 description 1
- NPYPAHLBTDXSSS-UHFFFAOYSA-N Potassium ion Chemical compound [K+] NPYPAHLBTDXSSS-UHFFFAOYSA-N 0.000 description 1
- 230000002378 acidificating effect Effects 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 150000001450 anions Chemical class 0.000 description 1
- 230000004323 axial length Effects 0.000 description 1
- 229910002092 carbon dioxide Inorganic materials 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- HFNQLYDPNAZRCH-UHFFFAOYSA-N carbonic acid Chemical compound OC(O)=O.OC(O)=O HFNQLYDPNAZRCH-UHFFFAOYSA-N 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 238000000855 fermentation Methods 0.000 description 1
- 230000004151 fermentation Effects 0.000 description 1
- 238000009472 formulation Methods 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 229910052744 lithium Inorganic materials 0.000 description 1
- 229910001629 magnesium chloride Inorganic materials 0.000 description 1
- 229910001425 magnesium ion Inorganic materials 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 230000007483 microbial process Effects 0.000 description 1
- 229910000069 nitrogen hydride Inorganic materials 0.000 description 1
- 238000005192 partition Methods 0.000 description 1
- 230000000149 penetrating effect Effects 0.000 description 1
- 150000002989 phenols Chemical class 0.000 description 1
- 229910052700 potassium Inorganic materials 0.000 description 1
- 239000011591 potassium Substances 0.000 description 1
- 229910001414 potassium ion Inorganic materials 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 239000011734 sodium Substances 0.000 description 1
- 229910052708 sodium Inorganic materials 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- QEMXHQIAXOOASZ-UHFFFAOYSA-N tetramethylammonium Chemical compound C[N+](C)(C)C QEMXHQIAXOOASZ-UHFFFAOYSA-N 0.000 description 1
- 239000010409 thin film Substances 0.000 description 1
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
- G01N27/416—Systems
- G01N27/4162—Systems investigating the composition of gases, by the influence exerted on ionic conductivity in a liquid
Definitions
- This invention relates to an electrochemical assembly for continuously monitoring the level of ammonia in a fermenting medium.
- an electrochemical assembly for continuously monitoring the level of ammonia in a fermenting medium, said assembly comprising a housing having a portion in the form of a gas- permeable ion-impermeable outer membrane for transmitting into said housing ammonia from said medium, a monitor electrode located within said housing and comprising an electrode container having a portion in the form of a monovalent cation-sensitive-glass inner membrane, a reference electrode located within said housing, a body of aqueous electrolyte solution containing a pH buffer located within said housing and forming a thin aqueous film in areal contiguity with both of said membranes, and means forming an electrical connection between said body of aqueous electrolyte solution and said reference electrode.
- the assembly being sufficiently robust as to be capable of withstanding sterilisation by water and/or steam under pressure at temperatures of 115 C and higher.
- the inner membrane by virtue of being of the monovalent-cation-sensitive-glass type is sensitive to the limited range of monovalent cations which are physically small, such as sodium, potassium, lithium, hydrogen and ammonium ions. Accordingly volatile species, although traversing the outer membrane, are in- capable of producing cations in the thin aqueous film to which the monitor electrode is sensitive. As regards ammonia and ammonium ions in the fermenting medium ammonia gas traverses the outer membrane and in the thin aqueous film forms ammonium ions which alter the electrochemical potential of the monovalent-cation-sensi ive glass inner membrane and this is measured electrically relative to the reference electrode.
- aqueous electrolyte solution within the housing of the assembly of the present invention is pH buffered (at a predetermined level) measurement of the ammonium ion therein (as previously explained) provides also a measure of the ammonia therein and under equilibrium conditions the concentration or activity level of the ammonia in the aqueous electrolyte body is the same as that in the fermenting medium. Furthermore, if the pH of the fermenting medium is known, as is usually the case, the respective concentrations of ammonia and of ammonium ion in the fermenting medium can be easily derived.
- the outer membrane may be made of silicone rubber or teflon and may have a thickness in the range 5 to 100 ⁇ _ ⁇ _ra. A thickness in the range 10-20.um is preferred in order to provide sufficient mechanical strength whilst maintaining sufficiently small response time.
- the outer membrane may be mechanically supported over its external face by open meshwork.
- the inner membrane may be made of a glass having the composition 27% Na 2 0; 5% Al 2 0 3 ; 68% Si0 2 and may have a thickness in the range 0.05 to 1.00 mm although a thickness in the range 0.2-0.6 mm is preferred. Conveniently the surface of the inner membrane which is in areal contact with the thin aqueous film is either flat (planar) or convex towards the outer membrane.
- the body of aqueous electrolyte solution provides electrical conductance by the presence of ions therein.
- the preferred anion is chloride ion and preferred cations include tetramethylammonium and magnesium ions.
- the preferred pH buffer species forming part of the body of • aqueous electrolyte are non-volatile organic amines, phenols, borate, or carbonate bicarbonate ions. It will of course be understood that the content of the body of aqueous electrolyte must not adversely affect operation of the inner membrane or in the reference electrode or in the means forming the electrical connection between the electrolyte body and the reference electrode.
- the means forming the electrical connection between the electrolyte body and the reference electrode may be a liquid junction in the form of a porous plug in an otherwise impermeable wall separating the reference electrode from the electrolyte body.
- the reference electrode may conveniently be an
- the monitor electrode may conveniently be an Ag/AgCl rod immersed in a solution of 0.1M KC1.
- the outer membrane itself constitutes a sterility barrier preventing contaminants entering the fermenting medium via the interior of the electrode assembly, but, preferably the assembly additionally comprises means forming a sterility barrier around said body of electrolyte solution and within said housing to prevent contaminants entering said body so that in the event of mechanical failure of the thin outer membrane contamination of the fermenting medium is prevented.
- Fig. 1 is a cross sectional view of an electrochemical assembly according to the present invention.
- Fig. 2 is an enlarged view of a detail of Fig. 1.
- the assembly 30 comprises a generally cylindrical stainless-steel housing 14 across the lower open end of which is located an outer membrane 21 made of. silicone rubber, membrane 21 ' being held in place by a rubber 0-ring 18 and a threaded collar 9 threadedly engaging housing 14.
- Membrane 21 is gas-permeable and ion-impermeable as previously explained.
- a monitor electrode comprising a container in the form of a generally cylindrical glass tube 3 the lowermost end of which is closed by the inner membrane 19.
- Membrane 19 is formed of monovalent- cation-sensi ive glass having a formulation 27% Na_0; 5% Al_0 3 ; 68% Si0 2 whereas tube 3 is made of an ion- insensitive glass such as a borosilicate.
- the glasses of tube 3 and membrane 19 are joined by an annular joint 22 comprising five annular zones of intermediate glass composition for the purpose of providing a gradual transition between the two glass forms so that stresses due to differential thermal expansion are constrained to a tolerable level for the purpose of withstanding sterilisation.
- a body of 0.1M KCl solution 6 immersing electrode rod 15 which is Ag/AgCl.
- a reference electrode comprising glass tube 3A concentrically surrounding tube 3 and united with tube 3 at the lower end of tube 3A so as to form a container for a solution
- Solution 7 immerses rod electrode 16 which is Ag/AgCl.
- tube 3 is closed and provides a glass seal for exit of rod 15 which is provided with an electrically insulating plastic sleeve 11 the exterior of which has a conductive screen 12 connected directly to rod 16.
- the upper end of glass tube 3A forms a glass seal for components 10,11 and 12 and externally of the glass seal a plastic seal 13 is provided for integrity.
- Tube 3A at its upper end incorporates an integral collar against which a rubber
- inner membrane 19 is biassed towards outer membrane 21 and by virtue of the axial lengths of housing 14 and tubes 3, 3A being matched inner membrane 19 is capable of engaging outer membrane 21 and causing limited stretch therein. For this reason it is preferred that the surface of inner membrane 19 proximal outer membrane 21 is either flat or slightly convex (towards membrane 21) .
- a body 8 of aqueous electrolyte solution which is pH buffered is provided within the annular space between housing 14 and glass tube 3A so that the region between the membranes 19, 21 is flooded with this solution and, when top collar 1 is appropriately adjusted, a thin aqueous film 20 is formed between membranes 19, 21 being in areal contiguity with both membranes 19, 21.
- the body 8 has the same composition as the solution 7 and in conjunction with porous plug 17 in the wall of tube 3A provides an electrical connection between the reference electrode and the thin film 20.
- a silicone rubber 0-ring seal " is provided between housing 14 and glass tube 3A above the body 8 of aqueous solution.
- the assembly 30 is constructed as has previously been explained to provide a measure of the ammonium ion level within aqueous fil 20 arising from the diffusion through outer membrane 21 of ammonia gas, such gas being present in a fermenting medium.
- the constructional details of the assembly 30 will be better understood in terms of quantita ⁇ tive analysis of its response at equilibrium of the diffusing gas (NH ⁇ ) , that is when the concentration or activity level of the ammonia on either side of the outer membrane 21 is equal.
- (pNH 4 ) 0 (pNH 4 ) I + (pH) Q - (pH #I (2) where the subscripts 0 and I respectively denote outside the assembly (i.e. in the fermenting medium) and inside the assembly (i.e. in the aqueous film 20) .
- the electrical potential of the monitor electrode is linearly related to (pNH. ). j . within the normal operating range of the inner membrane 19 whilst (pH) is maintained constant by the buffer within aqueous film 20 and (pH) _ is separately measurable (and may even be controlled at a' constant level) so that by measuring (pNH.)- a measure of (pNH.) 0 is also provided.
- the response rate of the assembly 30 is derivable from the equation given by J.W. Ross et al (Pure and Applied Chemistry, Vol. 36, pages 473-487 published 1973), namely
- the assembly 30 by virtue of having its components made of stainless steel, glass, silicone rubber and/or teflon in the construction shown in the drawing is sufficiently robust to be capable of withstanding sterilisation by water and/or steam under pressure of the order of 1 or 2 atmospheres at temperatures of 115 C up to 150 C.
- the.various electrolyte solutions are either relatively volatile .and held within a pressure vessel formed within the assembly 30 or relatively non ⁇ volatile so that there is no loss of electrolyte during sterilisation.
- collar 1 threadedly engages the uppermost end of housing 14 release of this collar permits tube 3A to be moved axially away from outer membrane 21 which enables sterilisation to be effected with minimum stress on outer membrane 21.
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Abstract
An electrochemical assembly (30) for continuously monitoring the level of ammonia in a fermenting medium comprises a housing (14) incorporating a gas-permeable ion-impermeable outer membrane (21) which is capable of transmitting ammonia from the medium into the housing (14). A monitor electrode is located within housing (14) and incorporates a monovalent cation-sensitive-glass inner membrane (19) the latter being separated from outer membrane (21) by a thin aqueous film (20) of electrolyte solution which is pH buffered. A reference electrode (16) is provided within housing (14) and an electrical connection (17) is provided between the film (20) and the reference electrode (16).
Description
ELECTROCHEMICAL ASSEMBLY
This invention relates to an electrochemical assembly for continuously monitoring the level of ammonia in a fermenting medium.
In many microbial processes such as occur in industria fermentations the presence and concentration or activity level of ammonia and ammonium ions is of practical significance. It is therefore desirable to monitor continuously the level of ammonia since this provides a measure of the concentration or activity level of ammonia and ammonium ions in the medium concerned. Known apparatus for this purpose has the disadvantage that it is also sensitive to the presence of substances such as carbon dioxide, volatile amines, acidic or basic volatile species, and monovalent cations such as the potassium ion, at least one or more of which is present in variable but significant concentrations in most fermenting media.
It is an object of the present invention to provide a new and improved form of electrochemical assembly for continuously monitoring the level of ammonia in a fermenting medium.
According to the present invention there is provided an electrochemical assembly for continuously monitoring the level of ammonia in a fermenting medium, said assembly comprising a housing having a portion in the form of a gas- permeable ion-impermeable outer membrane for transmitting into said housing ammonia from said medium, a monitor electrode located within said housing and comprising an electrode container having a portion in the form of a monovalent cation-sensitive-glass inner membrane, a reference electrode located within said housing, a body of aqueous electrolyte solution containing a pH buffer located within said housing and forming a thin aqueous film in areal contiguity with both of said membranes, and means forming an electrical connection between said body of aqueous electrolyte solution and said reference electrode.
the assembly being sufficiently robust as to be capable of withstanding sterilisation by water and/or steam under pressure at temperatures of 115 C and higher.
It will be understood that the inner membrane by virtue of being of the monovalent-cation-sensitive-glass type is sensitive to the limited range of monovalent cations which are physically small, such as sodium, potassium, lithium, hydrogen and ammonium ions. Accordingly volatile species, although traversing the outer membrane, are in- capable of producing cations in the thin aqueous film to which the monitor electrode is sensitive. As regards ammonia and ammonium ions in the fermenting medium ammonia gas traverses the outer membrane and in the thin aqueous film forms ammonium ions which alter the electrochemical potential of the monovalent-cation-sensi ive glass inner membrane and this is measured electrically relative to the reference electrode.
It will be understood that in fermenting media and aqueous solutions ammonia and ammoniu 'ions co-exist in relative proportions determined by the pH of the media
(or solution) and because the body of aqueous electrolyte solution within the housing of the assembly of the present invention is pH buffered (at a predetermined level) measurement of the ammonium ion therein (as previously explained) provides also a measure of the ammonia therein and under equilibrium conditions the concentration or activity level of the ammonia in the aqueous electrolyte body is the same as that in the fermenting medium. Furthermore, if the pH of the fermenting medium is known, as is usually the case, the respective concentrations of ammonia and of ammonium ion in the fermenting medium can be easily derived.
The outer membrane may be made of silicone rubber or teflon and may have a thickness in the range 5 to 100^_ι_ra. A thickness in the range 10-20.um is preferred in order to
provide sufficient mechanical strength whilst maintaining sufficiently small response time. The outer membrane may be mechanically supported over its external face by open meshwork. The inner membrane may be made of a glass having the composition 27% Na20; 5% Al203; 68% Si02 and may have a thickness in the range 0.05 to 1.00 mm although a thickness in the range 0.2-0.6 mm is preferred. Conveniently the surface of the inner membrane which is in areal contact with the thin aqueous film is either flat (planar) or convex towards the outer membrane.
The body of aqueous electrolyte solution provides electrical conductance by the presence of ions therein. The preferred anion is chloride ion and preferred cations include tetramethylammonium and magnesium ions. The preferred pH buffer species forming part of the body of • aqueous electrolyte are non-volatile organic amines, phenols, borate, or carbonate bicarbonate ions. It will of course be understood that the content of the body of aqueous electrolyte must not adversely affect operation of the inner membrane or in the reference electrode or in the means forming the electrical connection between the electrolyte body and the reference electrode.
The means forming the electrical connection between the electrolyte body and the reference electrode may be a liquid junction in the form of a porous plug in an otherwise impermeable wall separating the reference electrode from the electrolyte body.
The reference electrode may conveniently be an
++ Ag/AgCl rod immersed in a solution of 1M Mg -glycine buffer pH9 containing 3M MgCl2.
The monitor electrode may conveniently be an Ag/AgCl rod immersed in a solution of 0.1M KC1.
The outer membrane itself constitutes a sterility barrier preventing contaminants entering the fermenting
medium via the interior of the electrode assembly, but, preferably the assembly additionally comprises means forming a sterility barrier around said body of electrolyte solution and within said housing to prevent contaminants entering said body so that in the event of mechanical failure of the thin outer membrane contamination of the fermenting medium is prevented.
An embodiment of the present invention will now be described by way of example with reference to the accompanying drawing, in which:
Fig. 1 is a cross sectional view of an electrochemical assembly according to the present invention; and
Fig. 2 is an enlarged view of a detail of Fig. 1. In the drawing the assembly 30 comprises a generally cylindrical stainless-steel housing 14 across the lower open end of which is located an outer membrane 21 made of. silicone rubber, membrane 21' being held in place by a rubber 0-ring 18 and a threaded collar 9 threadedly engaging housing 14. Membrane 21 is gas-permeable and ion-impermeable as previously explained.
Within housing 14 there is located a monitor electrode comprising a container in the form of a generally cylindrical glass tube 3 the lowermost end of which is closed by the inner membrane 19. Membrane 19 is formed of monovalent- cation-sensi ive glass having a formulation 27% Na_0; 5% Al_03; 68% Si02 whereas tube 3 is made of an ion- insensitive glass such as a borosilicate. The glasses of tube 3 and membrane 19 are joined by an annular joint 22 comprising five annular zones of intermediate glass composition for the purpose of providing a gradual transition between the two glass forms so that stresses due to differential thermal expansion are constrained to a tolerable level for the purpose of withstanding sterilisation. Within container tube 3 is a body of 0.1M KCl solution 6 immersing electrode rod 15 which is Ag/AgCl.
Also within housing 14 there is located a reference electrode comprising glass tube 3A concentrically surrounding tube 3 and united with tube 3 at the lower end of tube 3A so as to form a container for a solution
++ 7 which is 1M Mg -glycine buffer pH 9 containing 3M MgCl,.
Solution 7 immerses rod electrode 16 which is Ag/AgCl.
At the upper end of the assembly 30 tube 3 is closed and provides a glass seal for exit of rod 15 which is provided with an electrically insulating plastic sleeve 11 the exterior of which has a conductive screen 12 connected directly to rod 16. The upper end of glass tube 3A forms a glass seal for components 10,11 and 12 and externally of the glass seal a plastic seal 13 is provided for integrity. Tube 3A at its upper end incorporates an integral collar against which a rubber
0-ring 2 seats being held in place by a threaded collar 1 which threadedly engages, the uppermost end of housing 14. By this method inner membrane 19 is biassed towards outer membrane 21 and by virtue of the axial lengths of housing 14 and tubes 3, 3A being matched inner membrane 19 is capable of engaging outer membrane 21 and causing limited stretch therein. For this reason it is preferred that the surface of inner membrane 19 proximal outer membrane 21 is either flat or slightly convex (towards membrane 21) . In accordance with an important aspect of the present invention a body 8 of aqueous electrolyte solution which is pH buffered is provided within the annular space between housing 14 and glass tube 3A so that the region between the membranes 19, 21 is flooded with this solution and, when top collar 1 is appropriately adjusted, a thin aqueous film 20 is formed between membranes 19, 21 being in areal contiguity with both membranes 19, 21. The body 8 has the same composition as the solution 7 and in conjunction with porous plug 17 in the wall of tube 3A provides an electrical connection between the reference electrode and the thin film
20. Furthermore, in order to provide a sterility barrier preventing contamination entering the top of housing 14 penetrating downwardly and possibly out into a fermenting medium via a ruptured outer membrane 21 a silicone rubber 0-ring seal "is provided between housing 14 and glass tube 3A above the body 8 of aqueous solution.
The assembly 30 is constructed as has previously been explained to provide a measure of the ammonium ion level within aqueous fil 20 arising from the diffusion through outer membrane 21 of ammonia gas, such gas being present in a fermenting medium. The constructional details of the assembly 30 will be better understood in terms of quantita¬ tive analysis of its response at equilibrium of the diffusing gas (NH^) , that is when the concentration or activity level of the ammonia on either side of the outer membrane 21 is equal.
In an aqueous solution the equilibrium condition is given by κa " [NH3. [H+] (1)
where Ka = dissoci Kati.on constant of NH4..
Using the symbol pX to denote - log,QX equation (1) becomes pNH, = pK + pNH, - pH and since pNH___ and pKa have the same value on either side of the outer membrane 21 it follows that
(pNH4)0 = (pNH4)I + (pH)Q - (pH#I (2) where the subscripts 0 and I respectively denote outside the assembly (i.e. in the fermenting medium) and inside the assembly (i.e. in the aqueous film 20) . The electrical potential of the monitor electrode is linearly related to (pNH. ).j. within the normal operating range of the inner membrane 19 whilst (pH) is maintained constant by the buffer within aqueous film 20 and (pH) _ is separately measurable (and may even be controlled at a'
constant level) so that by measuring (pNH.)- a measure of (pNH.)0 is also provided.
The response rate of the assembly 30 is derivable from the equation given by J.W. Ross et al (Pure and Applied Chemistry, Vol. 36, pages 473-487 published 1973), namely
, , dCB . d .log 6 _ -D.K (3) dC dt e ~ Z. where C = concentration of diffusing gas in film 20;
C___> = concentration of the bound form of the gas in film 20 £ = fractional deviation from equilibrium relative to the final equilibrium concentration in film 20; D = diffusion coefficient of the gas in the outer membrane 21; K = partition coefficient of the gas into membrane 21; I - thickness of film 20; m = thickness of membrane 21; and t = time
It can be shown that for the assembly described, because dCB . 10(pKa - (PH)∑ ) = constant dC the response time T is given by
C- = final gas concentration after the ΔC change in the medium; and 6. =.the fractional deviation taken to define complete response.
By way of example if I - 10 yum; m = 20 ,um; D.K = 10
2 cm /s (i.e. silicone rubber); pKa = 9.3; (pH)_ = 9.0; β = 0.01; __-C/Cf = 0.2; it follows that T = 240 seconds, a value which is acceptable for monitoring and control of fermenting media.
The choice of pH level for the film 20 is governed by two factors. Firstly, equation 4 shows that minimum- response time is achieved by maximising (pH)_. Secondly, the sensitivity of the inner membrane 19 to H. generally requires (pNH.)_ 6 to obtain a useful signal. For a typical fermenting media where (pNH.)- = 3 and (pH)_ = 6 it can be shown from equation 2 that (pH)_ must be less than or equal to 9. Therefore (pH)_ = 9 is the preferable value. The assembly 30 by virtue of having its components made of stainless steel, glass, silicone rubber and/or teflon in the construction shown in the drawing is sufficiently robust to be capable of withstanding sterilisation by water and/or steam under pressure of the order of 1 or 2 atmospheres at temperatures of 115 C up to 150 C. Furthermore the.various electrolyte solutions are either relatively volatile .and held within a pressure vessel formed within the assembly 30 or relatively non¬ volatile so that there is no loss of electrolyte during sterilisation. Additionally because collar 1 threadedly engages the uppermost end of housing 14 release of this collar permits tube 3A to be moved axially away from outer membrane 21 which enables sterilisation to be effected with minimum stress on outer membrane 21.
Claims
1. An electrochemical assembly for continuously monitoring the level of ammonia in a fermenting medium, said assembly (30) being qharacterised by the combination of a housing (14) having a portion in the form of a gas-permeable ion- impermeable outer membrane (21) for transmitting into said housing (14) ammonia from said medium, a monitor electrode located within said housing (14) and comprising an electrode container (3) having a portion in the form of a monovalent cation-sensitive-glass inner membrane (19) , a reference electrode (3A,7,16) located within said housing (14) , a body (8) of aqueous electrolyte solution containing a pH buffer located within said housing (14) and forming a thin aqueous film (20) in areal contiguity with both of said membranes (19,21) , and means (17) forming an electrical connection between said body (8) of aqueous electrolyte solution and said reference electrode (3A,7,16), the assembly (30) being sufficiently robust as to be capable of withstanding sterilisation by water and/or steam under pressure at temperatures of 115 C and higher.
2. An assembly as claimed in claim 1, characterised in that the outer membrane (21) is made of silicone rubber or teflon.
3. An assembly as claimed in claim 2, characterised in that the outer membrane (21) has a thickness in the range 5 to 100 μm.
4. An assembly as claimed in any preceding claim, characterised in that the outer membrane (21) is mechanicall supported over its external face by open meshwork.
5. An assembly as claimed in any preceding claim, characterised in that the inner membrane (19) is made of glass.
6. An assembly as claimed in claim 5, characterised in that the inner membrane (19) has a thickness in the range 0.05 to 1.00 mm.
7. An assembly as claimed in any preceding claim, characterised in that the surface of the inner membrane
(19) which is in areal contact with the thin aqueous film
(20) is either flat or convex towards the outer membrane (21).
8. An assembly as claimed in any one of claims 5-7, characterised in that the electrode container (3) is made of glass and the inner membrane (19) is joined to the electrode container (3) by a plurality of annular zones (22). of intermediate glass composition providing a gradual transition between the glass forms of inner membrane (19) and the container (3) .
9. An electrochemical assembly for continuously monitoring the level of ammonia- in a fermenting medium substantially as hereinbefore described with reference to the accompanying drawing.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB8407835 | 1984-03-27 | ||
GB848407835A GB8407835D0 (en) | 1984-03-27 | 1984-03-27 | Electrochemical assembly |
Publications (1)
Publication Number | Publication Date |
---|---|
WO1985004482A1 true WO1985004482A1 (en) | 1985-10-10 |
Family
ID=10558708
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/GB1985/000101 WO1985004482A1 (en) | 1984-03-27 | 1985-03-15 | Electrochemical assembly |
Country Status (4)
Country | Link |
---|---|
EP (1) | EP0175732A1 (en) |
GB (1) | GB8407835D0 (en) |
IT (1) | IT8567294A0 (en) |
WO (1) | WO1985004482A1 (en) |
Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB2277378A (en) * | 1993-03-05 | 1994-10-26 | Mine Safety Appliances Co | Electrochemical membrane gas sensor |
GB2303710A (en) * | 1993-03-05 | 1997-02-26 | Mine Safety Appliances Co | Electrochemical toxic gas sensor with gas permeable membrane |
US5683989A (en) * | 1993-12-17 | 1997-11-04 | Novo Nordisk A/S | Treatment of ischemias by administration of 2,N6 -substituted adenosines |
WO1999053312A1 (en) * | 1998-04-15 | 1999-10-21 | Biofutura S.R.L. | Apparatus adapted to perform a plurality of determinations on wine samples or the like |
EP1929938A1 (en) * | 2006-12-04 | 2008-06-11 | Sentec AG | Device for measuring partial pressure of carbon dioxide |
Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3444068A (en) * | 1966-01-03 | 1969-05-13 | Beckman Instruments Inc | Electrode and method of making same |
US3689222A (en) * | 1969-09-24 | 1972-09-05 | Abbott Lab | Carbon dioxide monitor |
GB1388340A (en) * | 1973-03-22 | 1975-03-26 | Orion Research | Electrochemical cell |
GB1535361A (en) * | 1976-03-17 | 1978-12-13 | Owens Illinois Inc | Electrochemical cell |
-
1984
- 1984-03-27 GB GB848407835A patent/GB8407835D0/en active Pending
-
1985
- 1985-03-15 WO PCT/GB1985/000101 patent/WO1985004482A1/en unknown
- 1985-03-15 EP EP85901481A patent/EP0175732A1/en not_active Withdrawn
- 1985-03-26 IT IT8567294A patent/IT8567294A0/en unknown
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3444068A (en) * | 1966-01-03 | 1969-05-13 | Beckman Instruments Inc | Electrode and method of making same |
US3689222A (en) * | 1969-09-24 | 1972-09-05 | Abbott Lab | Carbon dioxide monitor |
GB1388340A (en) * | 1973-03-22 | 1975-03-26 | Orion Research | Electrochemical cell |
GB1535361A (en) * | 1976-03-17 | 1978-12-13 | Owens Illinois Inc | Electrochemical cell |
Cited By (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB2277378A (en) * | 1993-03-05 | 1994-10-26 | Mine Safety Appliances Co | Electrochemical membrane gas sensor |
GB2303710A (en) * | 1993-03-05 | 1997-02-26 | Mine Safety Appliances Co | Electrochemical toxic gas sensor with gas permeable membrane |
GB2277378B (en) * | 1993-03-05 | 1997-04-30 | Mine Safety Appliances Co | Electrochemical toxic gas sensor |
US5683989A (en) * | 1993-12-17 | 1997-11-04 | Novo Nordisk A/S | Treatment of ischemias by administration of 2,N6 -substituted adenosines |
WO1999053312A1 (en) * | 1998-04-15 | 1999-10-21 | Biofutura S.R.L. | Apparatus adapted to perform a plurality of determinations on wine samples or the like |
EP1929938A1 (en) * | 2006-12-04 | 2008-06-11 | Sentec AG | Device for measuring partial pressure of carbon dioxide |
WO2008068274A1 (en) * | 2006-12-04 | 2008-06-12 | Sentec Ag | Transcutaneous co2-sensor for measuring the partial pressure of carbon dioxide |
Also Published As
Publication number | Publication date |
---|---|
EP0175732A1 (en) | 1986-04-02 |
GB8407835D0 (en) | 1984-05-02 |
IT8567294A0 (en) | 1985-03-26 |
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AL | Designated countries for regional patents |
Designated state(s): AT BE CH DE FR GB LU NL SE |