DK150997B

DK150997B - ELECTRODE UNIT FOR MEASURING OXYGEN CONCENTRATION WITH PROTECTION MEMBRANE FOR THE REDUCTION ELECTRODE

Info

Publication number: DK150997B
Application number: DK300678AA
Authority: DK
Inventors: Manfred Kessler; Jens Hoeper
Original assignee: Manfred Kessler
Priority date: 1977-07-04
Filing date: 1978-07-03
Publication date: 1987-10-05
Also published as: DE2730143C3; DK150997C; AT381594B; DE2730143A1; DE2730143B2; JPS6129458B2; GB2000595A; JPS5440693A; FR2396972B1; CH629305A5; GB2000595B; FR2396972A1; DK300678A; USRE31299E; ATA484378A

Description

150997150997

Opfindelsen angår et elektrodeaggregat til måling af en oxygenkoncentration bestående af en referenceelektrode, en reduktionselektrode af ædelmetal, en elektrolyt, en afslutningsmembran, der er gennemtrængelig for oxy-5 gen, men uigennemtrængelig for vand, og som afslutter aggregatet mod det omgivende rum, og yderligere en oxy-gengennemtrængelig membran, der er placeret i elektrolytten umiddelbart foran reduktionselektroden.The invention relates to an electrode assembly for measuring an oxygen concentration consisting of a reference electrode, a reduction electrode of precious metal, an electrolyte, an oxygen-permeable but impervious termination membrane, and terminating the assembly against the surrounding space, and further an oxy-permeable membrane located in the electrolyte immediately in front of the reduction electrode.

10 De kendte aggregater har to væsentlige ulemper. For det første kan en transport af urenheder dannet på elektroderne ikke forhindres selv ved valg af særlig egnede ædelmetaller til elektroderne, således at elektroderne viser driftssymptomer, som forhindrer en ubegrænset le-15 vetid. For det andet er oxygenforbruget som følge af selve målingen så højt, at det principielt fører til forstyrrelser af diffusionsfeltet i de for det meste målte organiske væv. For at forhindre dette er det forsøgt at forhøje diffusionsmodstanden. Til dette formål 20 er det i henhold til USA patentskrift nr. 3 985 633 foreslået at anbringe en yderligere membran mellem afslutningsmembranen og reduktionselektroden. Ved at forhøje diffusionsmodstanden bliver måletiden dog også betydelig længere. Derfor kan den sande oxygenkoncentration ikke 25 bestemmes eller kun bestemmes med lange måletider.The known assemblies have two major disadvantages. First, the transport of impurities formed on the electrodes cannot be prevented even by the choice of particularly suitable precious metals for the electrodes, so that the electrodes show operating symptoms which prevent an unlimited life. Second, as a result of the measurement itself, oxygen consumption is so high that, in principle, it causes disturbance of the diffusion field in the mostly measured organic tissues. To prevent this, an attempt has been made to increase the diffusion resistance. For this purpose, in accordance with United States Patent No. 3,985,633, it is proposed to place an additional membrane between the termination membrane and the reduction electrode. However, by increasing the diffusion resistance, the measurement time also becomes considerably longer. Therefore, the true oxygen concentration cannot be determined or only determined with long measurement times.

Disse ulemper kan med et aggregat ifølge opfindelsen nedsættes ved,at den oxygengennemtrængelige membran er gennemtrængelig for hydrogenioner og indeholder en kati-30 onligand, og at elektrolytten indeholder ligandkationer.These disadvantages can be mitigated by an aggregate according to the invention in that the oxygen-permeable membrane is permeable to hydrogen ions and contains a cationic ligand and that the electrolyte contains ligand cations.

I dette aggregat kommer kun reaktionsmaterialer og ikke også materialet fra elektrolytten eller modelektroden i berøring med reduktionselektroden på grund af ligandmem-35 2 150997 branens selektivitet, således at fysiske og kemiske ændringer ved reduktionselektroden udebliver, og holdbarheden forøges væsentligt. Ligandmembranen er gennemtræn-gelig for oxygen, men nedsætter oxygenets diffusionshas-5 tighed væsentligt, hvorfor ændringen af oxygenkoncentrationen som følge af målingen bliver ringe.In this aggregate, only reaction materials, and not also the material of the electrolyte or model electrode, come into contact with the reduction electrode due to the selectivity of the ligand membrane, so that physical and chemical changes at the reduction electrode fail and the durability is significantly increased. The ligand membrane is permeable to oxygen but substantially reduces the rate of diffusion of oxygen, which is why the change in oxygen concentration due to the measurement becomes small.

For at udnyttte denne fordel har forstærkeren, som måler indgangssignalet, en indgangsmodstand med en værdi på 10 omkring 1012 ohm. Særlige gunstige forhold foreligger, når liganden er natriumionselektiv. Det har nemlig vist sig, at. der så fremkommer et let tydeligt og med oxygenkoncentrationen proportionalt signal. Som ligand tjener fortrinsvis 3,6-dioxaoctandisyre-bis-diphenylamin.To take advantage of this advantage, the amplifier which measures the input signal has an input resistance with a value of about 1012 ohms. Particularly favorable conditions exist when the ligand is sodium ion selective. For it has been found that. a signal that is clearly visible and proportional to the oxygen concentration appears. Preferably, as the ligand, 3,6-dioxaoctanedioic acid bis-diphenylamine is used.

1515

Ifølge en særlig hensigtsmæssig udførelsesform for opfindelsen består elektrolytten af 10 mM NaCl og 0,1 M HC1.According to a particularly convenient embodiment of the invention, the electrolyte consists of 10 mM NaCl and 0.1 M HCl.

20 I en anden videreudvikling af opfindelsen er referenceelektroden dækket af en ligandmembran, som indeholder en ligand, der er forskellig fra den ligand, der findes i den membran, som dækker reduktionselektroden. Derved forhindres også et fysisk eller kemisk angreb på refe-25 renceelektroden.In another further development of the invention, the reference electrode is covered by a ligand membrane which contains a ligand different from the ligand present in the membrane covering the reduction electrode. This also prevents a physical or chemical attack on the reference electrode.

Med aggregatet ifølge opfindelsen kan man også på i og for sig kendt måde måle amperometrisk, altså med en målemodstand på omkring 106 ohm, som frembringer en stati-30 onær partikelstrøm i målesystemet. Ved denne anvendelse består stadig den fordel, at elektroderne er fysisk og kemisk beskyttet.With the assembly according to the invention, it is also possible to measure, in a manner known per se, amperometric, ie with a measuring resistance of about 106 ohms, which produces a static particle flow in the measuring system. In this application, the advantage remains that the electrodes are physically and chemically protected.

35 150997 335 150997 3

Et aggregat ifølge opfindelsen er skematisk vist på tegningen.An assembly according to the invention is schematically shown in the drawing.

Elektrodeaggregatet omfatter en reduktionselektrode 2, 5 som påføres en polarisationsspænding fra en jævnspændingskilde 1, og en fortrinsvis ringformet omkring reduktionselektroden 2 liggende referenceelektrode 3. Foran reduktionselektroden er anbragt en membran 20 af PVC, som indeholder en ionselektiv kationligand og er gennem-10 trængelig over for såvel hydrogenioner som oxygen, og foran referenceelektroden er anbragt en ligandmembran 30, som indeholder en fra ligandmembranen 20 forskellig ligand. Ligandmembranen 30 kan også udelades. Ligandmembranen 20's ligand er fortrinsvis 3,6-dioxaoctan-disyre-15 bis-diphenylamin. En elektrolyt 5 dækker det samlede aggregat, som er afsluttet ved hjælp af en afslutningsmembran 6 imod det omgivende rum. Elektrolytten består af 10 mM NaCl og 0,1 M HC1, når der ikke er tilvejebragt nogen ligandmembran 30. Hvis en ligandmembran 30 er til-20 vejebragt, skal elektrolytten yderligere indeholde denne ligands ion.The electrode assembly comprises a reduction electrode 2, 5 applied to a polarization voltage from a DC voltage source 1, and a preferably annular reference electrode 3 located above the reduction electrode. A diaphragm 20 of PVC containing both hydrogen ions and oxygen, and in front of the reference electrode is a ligand membrane 30 which contains a ligand different from the ligand membrane 20. Ligand membrane 30 may also be omitted. The ligand of the ligand membrane 20 is preferably 3,6-dioxaoctane-diacetic acid bis-diphenylamine. An electrolyte 5 covers the overall assembly which is terminated by a terminating membrane 6 against the surrounding space. The electrolyte consists of 10 mM NaCl and 0.1 M HCl when no ligand membrane 30 is provided. If a ligand membrane 30 is provided, the electrolyte must further contain the ion of that ligand.

Hvis en bestemt oxygenkoncentration 7 foreligger i det omgivende rum, så diffunderer oxygen gennem teflonmem-25 branen 6 og yderligere sammen med hydrogenioner fra elektrolytten 5 gennem ligandmembranen 20. Der opstår vand efter oxygenets reduktion sammen med brintion ifølge ligningen 30 02+4e-> 20 + 4H+ = 2H20If a certain oxygen concentration 7 is present in the surrounding space, then oxygen diffuses through the teflon membrane 6 and further along with hydrogen ions from the electrolyte 5 through the ligand membrane 20. Water is produced after the reduction of oxygen along with hydrogen ion according to equation 30 02 + 4e-> 20 + 4H + = 2H20

Den ved denne fremgangsmåde opståede potentialændring af elektroden 2-20 i potentialkæden bestående af elektroderne 2-20, 3-30, elektrolytten 5 og polarisationsspæn-35The potential change of the electrode 2-20 in the potential chain resulting from this method consisting of electrodes 2-20, 3-30, electrolyte 5 and polarization voltage 35

Claims

The source 1 is measured by a measuring amplifier 4 with indicator. The measuring amplifier 4 has an input resistance of about 1012 ohms. An electrode assembly for measuring an oxygen concentration consisting of a reference electrode (3), a reduction electrode (2) of noble metal, an electrolyte (5), a terminating membrane (6) which is permeable to oxygen but impervious to water, and terminating the assembly against the surrounding space, and further an oxy-permeable membrane (20) located in the electrolyte (5) immediately in front of the reduction electrode (2), characterized in that the membrane (20) is permeable to hydrogen ion ex and contains a cation ligand, and that the electrolyte: (5j contains ligand cations ^

2. A unit according to claim 1, characterized in that an amplifier (4) measuring the signal of the unit has an input resistance of about 1012 ohms.

An aggregate according to claim 1, characterized in that the ligand is sodium ion selective.

An aggregate according to claim 3, characterized in that the ligand is 3,6-dioxaoctanedioic acid bis-diphenylamine.

An assembly according to claim 1, characterized in that the electrolyte (5) consists of 10 mM NaCl and 0.1 M HCl.

An assembly according to claim 1, characterized in that the reference electrode (3) is covered by a ligand membrane (30) containing a ligand different from the cation ligand of the ligand membrane (20). 150997

An assembly according to claim 1, characterized in that the ligand membranes (20, 30) consist of PVC.