EP1917521A1 - Systeme d'electrode de reference pour capteur potentiometrique, et capteur potentiometrique comprenant un tel systeme d'electrode de reference - Google Patents

Systeme d'electrode de reference pour capteur potentiometrique, et capteur potentiometrique comprenant un tel systeme d'electrode de reference

Info

Publication number
EP1917521A1
EP1917521A1 EP06777765A EP06777765A EP1917521A1 EP 1917521 A1 EP1917521 A1 EP 1917521A1 EP 06777765 A EP06777765 A EP 06777765A EP 06777765 A EP06777765 A EP 06777765A EP 1917521 A1 EP1917521 A1 EP 1917521A1
Authority
EP
European Patent Office
Prior art keywords
container
reference electrode
glass tube
opening
electrode assembly
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.)
Withdrawn
Application number
EP06777765A
Other languages
German (de)
English (en)
Inventor
Katrin Scholz
Reiner Franzheld
Robert Scholz
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Endress and Hauser Conducta GmbH and Co KG
Original Assignee
Endress and Hauser Conducta Gesellschaft fuer Mess und Regeltechnik mbH and Co KG
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Endress and Hauser Conducta Gesellschaft fuer Mess und Regeltechnik mbH and Co KG filed Critical Endress and Hauser Conducta Gesellschaft fuer Mess und Regeltechnik mbH and Co KG
Publication of EP1917521A1 publication Critical patent/EP1917521A1/fr
Withdrawn legal-status Critical Current

Links

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
    • G01N27/403—Cells and electrode assemblies
    • G01N27/4035—Combination of a single ion-sensing electrode and a single reference electrode
    • 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
    • G01N27/401—Salt-bridge leaks; Liquid junctions

Definitions

  • the present invention relates to a reference electrode arrangement for a potentiometric sensor and a potentiometric sensor with such a reference electrode arrangement.
  • Potentiometric sensors such as pH sensors, in addition to the actual working or measuring electrode, a reference electrode arrangement, against whose potential the potential of the working electrode is measured.
  • a generic reference electrode assembly usually also includes a container filled with a reference electrolyte; an electrical conductor in electrical contact with the reference electrolyte in the container to derive a reference potential; and a power key for establishing a first connection between the reference electrolyte and a medium to be analyzed, the analyte, in the vicinity of the reference electrode assembly.
  • This so-called power key often has a diaphragm, which is arranged in a wall of the container, and which, for example, a porous ceramic material or a porous plastic, such as Teflon, has. If these diaphragms are immersed in the analyte, due to the concentration differences, the ions of the reference electrolyte diffuse from the inside to the outside and vice versa, the ions of the analyte from the outside into the container of the reference electrode. Different diffusion rates lead to time-varying excess charges and thus to undesirable measurement errors. Normally, however, stationary diffusion profiles are formed in a relatively short time, the size of which depends on the selected combination of diaphragm and electrolyte. On the other hand, if the reference electrode arrangement is immersed in a moving analyte, the formation of constant concentration profiles over time is prevented. The measurement is constantly subject to a time-varying or shifted measurement error, the so-called stirring effect.
  • the stirrer is switched off, for example, before the measurement of a stirred substance, which of course is not suitable for continuous measurements during operation of a system.
  • the stirring effect can be minimized by using a liquid reference electrolyte in conjunction with a sufficiently large-pored ceramic diaphragm.
  • the geometric arrangement of Diaphragms have an additional influence.
  • measurements in a flow-calmed bypass or in a separate measuring chamber are known, the latter for example as E + H PuriSys CPF201.
  • the described arrangements are associated with an increased design effort, since additional valves, lines and branches are provided.
  • a so-called bridge electrolyte is provided, which corresponds in its chemical composition substantially the measured medium, and the first via a diaphragm with the reference electrolyte in combination stands and via a second diaphragm with the measuring medium.
  • the similarity of the bridge electrolyte to the measuring medium the diffusion processes through the second diaphragm are correspondingly low, so that the associated stirring effect is negligible with a moving measuring medium.
  • This approach naturally depends on the similarity of the bridge electrolyte to the medium. In other words, with highly variable measuring media, this procedure is unsuitable.
  • Another problem associated with reference measurements relates to contamination of the diaphragm by a sample medium with a contaminant load.
  • the diffusion through the diaphragm of dirt that clogged the pores of the diaphragm can be interrupted.
  • the reference electrode arrangement according to the invention is characterized compared to generic reference electrode arrangements by a second container, which adjoins the container for the reference electrolyte or surrounding this at least in sections, wherein
  • the current key is arranged in a volume surrounded by the second container, the second container has at least one first opening and at least one second opening, each communicating with a volume which is filled with a liquid medium, wherein at least the first opening communicates with a volume surrounding the reference electrode assembly.
  • the combination electrode according to the invention comprises a pH measuring cell with
  • a measuring cell tube a pH membrane which is attached media-tightly to one end of the measuring cell tube, a buffer solution, with which the measuring cell tube is affected, and an electrical conductor which is in contact with the buffer solution to derive a pH-dependent potential, and a reference electrode arrangement according to the invention, wherein the measuring cell tube is at least partially surrounded by the first container of the reference electrode arrangement, wherein the pH membrane outside of the second Container is arranged.
  • the measuring cell tube preferably has a measuring cell glass tube.
  • the at least one first opening on a simple hole whose contour is not important in detail. It may, for example, have a circular, elliptical or polygonal cross section.
  • the minimum diameter of the hole is, for example, not less than 0.1 mm, preferably not less than 0.2 mm, more preferably not less than 0.4 mm, and particularly preferably not less than 0.6 mm.
  • the maximum diameter of the first opening is for example not more than 2 mm, preferably not more than 1 mm and more preferably not more than 0.8 mm.
  • the second opening is also substantially dimensioned according to these requirements.
  • one of the openings has an annular gap between the shaft of the measuring or working electrode of a combination electrode and the second container surrounding the shaft.
  • the annular gap has, for example, a width of not less than 0.1 mm, preferably not less than 0.2 mm, more preferably not less than 0.4 mm, and particularly preferably not less than 0.6 mm.
  • the maximum width of the annular gap is, for example, not more than 2 mm, preferably not more than 1 mm, and more preferably not more than 0.8 mm.
  • the first and second openings are spaced apart by not less than 0.5 times the third root of the volume of the second container, preferably not less than the third root of the volume of the second container and farther preferably not less than 1.5 times the third root of the volume of the second container.
  • a plurality of smaller openings may be provided, wherein the openings must be dimensioned so that they have in total with respect to the medium such a flow resistance as the hole-shaped first or second openings with the previously defined dimensions.
  • the first opening has a diameter which leads to a sufficient flow calming of the medium, which is surrounded by the second container.
  • the reference electrode arrangement as a container, a glass tube, wherein the second container also has a glass tube which surrounds the first glass tube at least in sections.
  • both glass tubes are substantially cylindrical glass tubes which are coaxially aligned. It is presently preferred that the position of the flow key in the wall of the first container is axially spaced from the positions of the first and second openings in the second container.
  • the reference electrode assembly comprises a substantially cylindrical glass tube, which is separated by a partition in a first axial portion and a second axial portion.
  • a ceramic diaphragm is disposed as a power key in the partition wall between the first axial portion and the second axial portion.
  • a porous partition for example made of a plastic, in particular Teflon.
  • the first axial section also has a reference electrolyte and a working electrode in electrical contact with the reference electrolyte to derive the reference potential.
  • the second axial section has the first and second openings.
  • first axial portion serves as a first container and the second axial portion as a second container.
  • the reference electrode assembly is part of a combination electrode.
  • the reference electrode assembly extends through the first glass tube described above with the reference electrode assembly and the second container coaxially a second glass tube, which has a smaller radius than the first glass tube, and which has on a Meßmedien departmenten end portion of a pH membrane, the protrudes the second container, and can be exposed to the measuring medium.
  • the second container may be tapered at its end facing the pH membrane, so that an annular gap remains between the second glass tube and the second container, which serves as one of the two openings of the second container.
  • the second glass tube as is common in many working electrodes, a buffered electrolyte solution and an electrode for deriving the measured potential, which is in electrical contact with the buffer solution in the second glass tube.
  • the second opening in the second container may in principle be provided at any position in the wall of the second container, in particular in the lateral surface of the second container, wherein in a preferred embodiment, the second opening of the container is positioned so that it at Combination electrodes with a diaphragm, based on the orientation of the diaphragm in the partition wall between the first container and the second container, is rotated by 180 ° about the longitudinal axis of the container. In this way, a direct flow of the diaphragm through liquid, which enters through the opening prevents, because the direct connection is blocked by the second glass tube.
  • the second opening of the second container is connected to a liquid supply, through which a bridge electrolyte flows into the second container, which leaves the second container through the first opening.
  • This embodiment of the invention is particularly advantageous if the measuring medium has heavy loads with dirt particles that can block the power key of the reference electrode assembly.
  • the injected countercurrent of the bridge electrolyte is namely prevented that the contaminant load of the measuring medium passes through the second container to the diaphragm or to the porous wall, which is provided for the realization of the current key in the wall of the differential container.
  • aqueous solutions can be introduced as bridging electrolyte at a sufficiently low flow rate that are not sufficient to contaminate the medium, but can prevent the flow key from being blocked by the contaminant load of the medium.
  • This embodiment of the differential electrode according to the invention is used in particular in combination electrodes, wherein coaxial with the first container and the second container which surrounds the first container at least in the region of the current key, a glass tube with a smaller radius than the radius of the reference container by the second Container and the reference container is guided. At a media-side end portion of the glass tube, which projects beyond the second container, a pH glass membrane is provided.
  • the first opening of the second container, through which the inflowing bridge electrolyte leaves the second container again, either as described above can be configured as an annular gap around the glass tube of the measuring electrode at the media-side end portion of the second container or as a hole in the lateral surface of the second Container, in which case a large axial distance of the hole to the power key is preferable.
  • FIG. 1 shows a longitudinal section through a first exemplary embodiment of a combination electrode according to the invention
  • FIG. 2 shows a longitudinal section through a second exemplary embodiment of a combination electrode according to the invention.
  • the combination electrode shown in Fig. 1 comprises a first glass tube 1, at theticiann broughtem end of a glass membrane 2 is mounted for pH measurement.
  • a working electrode 3 is provided, which has a chlorided silver wire.
  • the glass tube 1 is filled with a buffered KCl solution to complete the working electrode of the combination electrode.
  • a second glass tube 4 with a larger radius is arranged coaxially around the glass tube 1 of the working electrode, wherein the glass tube is tapered in its end facing the glass membrane 2 end, and ends in front of the pH glass membrane, so that the pH -Glasmembran can be washed freely by a medium.
  • an electrode wire 5 is arranged, which is in electrical contact with a reference electrolyte, such as a KCl solution, in the annular chamber between the first glass tube and the second glass tube.
  • a partition wall 6 is further provided which the annular chamber in a first axial portion 7, which serves as a reference electrolyte container, and a second axial portion 8, which serves as a second container Flow calming serves, divided.
  • the partition wall 6 has at least one porous passage, which can be, for example, a glass wall with a porous ceramic diaphragm or a Teflon plug, which is designed as a porous diaphragm.
  • a first opening 9 is provided, which is formed as an annular gap at the media-side end of the second glass tube between the second glass tube and the first glass tube, and a second opening 10, which adjacent as a bore in the lateral surface of the second glass tube is formed to the partition wall 6 in the second portion 8 of the second glass tube.
  • the second container through the first opening 9 and the second opening 10 are in fluid communication with the measuring medium, which surrounds the second container, wherein the measuring medium is flow-calmed in the second container, so that stable diffusion profiles between the measured medium and can form the second container and the reference electrolyte in the reference container. In this way, the so-called stirring effect is avoided or at least significantly reduced.
  • Measuring medium carries a heavy dirt load, which could block the power key between the reference cell and the measuring medium.
  • the electrode according to the invention is used according to the second embodiment.
  • Glass tube 51 at theticiann workedem end of a glass membrane 52 is provided for pH measurement, and which has in its interior a chlorided silver wire, which is in contact with a pH-7 buffered KCl solution in the first glass tube to a pH-dependent Derive potential.
  • the first glass tube 51 is at least partially surrounded by a second glass tube 54, wherein the first glass tube projects beyond the second glass tube in the media-side axial direction by a length of a plurality of diameters of the second glass tube 54.
  • the end of the second glass tube is media-tightly connected to the lateral surface of the first glass tube 51, for example by melting.
  • a chlorided silver wire for deriving a reference potential is provided in the second glass tube, the annular chamber between the first glass tube 51 and the second glass tube 54 being filled with a reference electrolyte (KCL) in electrical contact with the chlorided silver wire 55.
  • KCL reference electrolyte
  • a porous ceramic diaphragm is further provided as a power key.
  • the first glass tube 51 and the second glass tube 54 are coaxially surrounded by a third glass tube 58, wherein the third glass tube 58 has a larger diameter than the second glass tube 54 and the latter also projects beyond its medial end in the axial direction.
  • the third glass tube 58 extends in the axial direction until just before the pH membrane 52, where it is fused with the lateral surface of the first glass tube 51.
  • the third glass tube 58 has in its media-side end portion an opening 59 in its lateral surface, which serves as an outlet opening for a bridge electrolyte.
  • the inlet opening is provided in the embodiment in the lateral surface of the third glass tube 58 in an axial portion which is farther from the media-side end portion of the third glass tube than the axial position of the ceramic diaphragm 56 in the end portion of the second glass tube 54.
  • the inlet opening 60 may for example be designed as Schlaucholive, via which the annular chamber between the third glass tube and the second and first glass tube, a bridge electrolyte is regularly supplied to prevent the flushing of dirt particles into the annular chamber by a countercurrent.

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  • Chemical & Material Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Molecular Biology (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)

Abstract

La présente invention concerne un système d'électrode de référence qui comprend: un contenant (54) rempli d'un électrolyte de référence; un conducteur électrique (55) en contact électrique avec l'électrolyte de référence présent dans le contenant, pour prélever un potentiel de référence; et une liaison saline (56) présente dans une paroi du contenant. Selon l'invention, le système d'électrode de référence présente un second contenant (58), la liaison saline (56) se trouve dans un volume entouré par le second contenant, et le second contenant présente une première (59) et une seconde (60) ouverture qui communiquent respectivement avec le volume à l'extérieur du premier et du second contenant, au moins la première ouverture (59) communiquant en outre avec un volume qui entoure le système d'électrode de référence. Une électrode combinée comprend une cellule de mesure de pH et un système d'électrode de référence tel que décrit ci-dessus, un tube de verre de cellule de mesure (51) étant entouré au moins par sections par le premier contenant (54) du système d'électrode de référence, et la membrane à pH (52) se trouvant à l'extérieur du second contenant (58).
EP06777765A 2005-08-26 2006-07-13 Systeme d'electrode de reference pour capteur potentiometrique, et capteur potentiometrique comprenant un tel systeme d'electrode de reference Withdrawn EP1917521A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE200510040764 DE102005040764A1 (de) 2005-08-26 2005-08-26 Referenzelektrodenanordnung für einen potentiometrischen Sensor und potentiometrischer Sensor mit Referenzelektrodenanordnung
PCT/EP2006/064217 WO2007023031A1 (fr) 2005-08-26 2006-07-13 Systeme d'electrode de reference pour capteur potentiometrique, et capteur potentiometrique comprenant un tel systeme d'electrode de reference

Publications (1)

Publication Number Publication Date
EP1917521A1 true EP1917521A1 (fr) 2008-05-07

Family

ID=37492528

Family Applications (1)

Application Number Title Priority Date Filing Date
EP06777765A Withdrawn EP1917521A1 (fr) 2005-08-26 2006-07-13 Systeme d'electrode de reference pour capteur potentiometrique, et capteur potentiometrique comprenant un tel systeme d'electrode de reference

Country Status (3)

Country Link
EP (1) EP1917521A1 (fr)
DE (1) DE102005040764A1 (fr)
WO (1) WO2007023031A1 (fr)

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102008055084A1 (de) * 2008-12-22 2010-06-24 Endress + Hauser Conducta Gesellschaft für Mess- und Regeltechnik mbH + Co. KG Ionenselektive Elektrode
EP2293052B1 (fr) 2009-09-03 2014-03-12 Hach Lange GmbH Agencement de mesure d'analyse de l'eau
DE102018132131B4 (de) * 2018-12-13 2023-03-30 Hamilton Bonaduz Ag Einstabmesskette mit erweitertem Referenzraum und Verfahren zum Herstellen der Einstabmesskette

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4477330A (en) * 1981-10-01 1984-10-16 Radiometer A/S Electrochemical electrode device

Family Cites Families (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4401548A (en) * 1981-02-12 1983-08-30 Corning Glass Works Reference electrode with internal diffusion barrier
US4592823A (en) * 1985-08-15 1986-06-03 Rohm And Haas Company Flushable reference cell for potentiometric measurements
CA1286720C (fr) * 1986-08-25 1991-07-23 Moshe Hirshberg Ensemble d'electrode rincable
DE3840961A1 (de) * 1988-12-05 1990-06-07 Hellige Gmbh Ionensensitive elektrode und verfahren zur temperaturgangkompensation bei solchen elektroden
US5096565A (en) * 1989-07-10 1992-03-17 Cobe Laboratories, Inc. Safe failure ion selective combination electrode
US20030178305A1 (en) * 2000-03-31 2003-09-25 Catalano Lauren M. PH glass membrane and sensor
US6395158B1 (en) * 2000-11-06 2002-05-28 Gli International PH sensor with electrical noise immunity
DE10243930A1 (de) * 2002-03-08 2003-09-25 Conducta Endress & Hauser Vorrichtung zur Messung und Regelung des pH-Wertes eines Mediums

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4477330A (en) * 1981-10-01 1984-10-16 Radiometer A/S Electrochemical electrode device

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See also references of WO2007023031A1 *

Also Published As

Publication number Publication date
DE102005040764A1 (de) 2007-03-01
WO2007023031A1 (fr) 2007-03-01

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