CA2208597A1 - Device for measuring the partial pressure of gases dissolved in liquids - Google Patents

Device for measuring the partial pressure of gases dissolved in liquids

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Publication number
CA2208597A1
CA2208597A1 CA002208597A CA2208597A CA2208597A1 CA 2208597 A1 CA2208597 A1 CA 2208597A1 CA 002208597 A CA002208597 A CA 002208597A CA 2208597 A CA2208597 A CA 2208597A CA 2208597 A1 CA2208597 A1 CA 2208597A1
Authority
CA
Canada
Prior art keywords
measuring
light
gas
measuring chamber
membrane
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.)
Abandoned
Application number
CA002208597A
Other languages
French (fr)
Inventor
Michael Dieckmann
Rainer Buchholz
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.)
EUROFERM GESELLSCHAFT fur FERMENTATION und MESSTECHNIK MBH
Original Assignee
Individual
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 Individual filed Critical Individual
Publication of CA2208597A1 publication Critical patent/CA2208597A1/en
Abandoned legal-status Critical Current

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Classifications

    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/35Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
    • G01N21/3504Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing gases, e.g. multi-gas analysis
    • CCHEMISTRY; METALLURGY
    • C12BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12MAPPARATUS FOR ENZYMOLOGY OR MICROBIOLOGY; APPARATUS FOR CULTURING MICROORGANISMS FOR PRODUCING BIOMASS, FOR GROWING CELLS OR FOR OBTAINING FERMENTATION OR METABOLIC PRODUCTS, i.e. BIOREACTORS OR FERMENTERS
    • C12M41/00Means for regulation, monitoring, measurement or control, e.g. flow regulation
    • C12M41/30Means for regulation, monitoring, measurement or control, e.g. flow regulation of concentration
    • C12M41/32Means for regulation, monitoring, measurement or control, e.g. flow regulation of concentration of substances in solution
    • CCHEMISTRY; METALLURGY
    • C12BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12MAPPARATUS FOR ENZYMOLOGY OR MICROBIOLOGY; APPARATUS FOR CULTURING MICROORGANISMS FOR PRODUCING BIOMASS, FOR GROWING CELLS OR FOR OBTAINING FERMENTATION OR METABOLIC PRODUCTS, i.e. BIOREACTORS OR FERMENTERS
    • C12M41/00Means for regulation, monitoring, measurement or control, e.g. flow regulation
    • C12M41/40Means for regulation, monitoring, measurement or control, e.g. flow regulation of pressure
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84Systems specially adapted for particular applications
    • G01N21/85Investigating moving fluids or granular solids
    • G01N21/8507Probe photometers, i.e. with optical measuring part dipped into fluid sample
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/0004Gaseous mixtures, e.g. polluted air
    • G01N33/0009General constructional details of gas analysers, e.g. portable test equipment
    • G01N33/0011Sample conditioning
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84Systems specially adapted for particular applications
    • G01N21/85Investigating moving fluids or granular solids
    • G01N2021/8578Gaseous flow
    • G01N2021/8585Gaseous flow using porous sheets, e.g. for separating aerosols

Abstract

The present invention concerns a device for measuring the partial pressure of gases dissolved in liquids. The device comprises (a) a measurement chamber (14) which is separated by a gas-permeable membrane (11) permeable to the dissolved gas from a sample chamber (10) containing the liquid with the dissolved gas; (b) a light emission source (6) for producing a light beam which passes through the measurement chamber (14) and is of a wavelength absorbed by the dissolved gas; (c) a measurement device (7) for determining the intensity of the light beam leaving the measurement chamber.

Description

-CA 02208~97 1997-06-23 .
~LE, ~!N T~5~S
TE~TR~SLA~

Device for measuring the partial pre~ure of ga~es olved in liguids The present invention relates to a novel device for measuring gas partial pre~sure in liquid m~
There is an increasing need, primarily in the field of fermentation technology, to measure gases by determ; n; ng their partial pressure. Special probes have therefore been developed for det~rm;n;ng the partial pressure of oxyye~ and carbon dioxide. A common example of these is constituted, for example, by so-called Severinghaus electrodes. These devices operate with membrane-covered single-rod pH electrodes (DE-A 25 08 637, Biotechnol. Bioeng. 22 (1980), 2411-2416, Biotechnol. Bioeng. 23 (1981), 461-466). In this system, there is an electrolyte solution or paste between the gas-selective membrane and the -pH electrode. The measuring principle is based on the fact that, in aqueous solution, carbon dioxide forms carbonic acid, which dissociates into a bicarbonate anion and a proton. This process cause~ a change in the pH in the electrolyte solution, and this change is measured using the pH probe.
A disadvantage of this measuring principle is the fact that carbon dioxide is measured not directly, but in its ionic form. Since the ionic form is present in a propor-tion of less than 0.1%, this method is not sufficientlyaccurate. Apart from this, other acidic or basic volatile gases vitiate the measurement of the pH. Furthermore, very high outlay on maintenance is needed.
PCO2 optodes are also known from the prior art.
Once again, these involve a membrane-covered sensor system (SPIE vol. 798 Fiber Optic Sensors II (1987) pp. 249-252; Anal. Chim. Acta 160 (1984) pp. 305-309;
Proc. Int. Meeting on Chemical Sensors, Fllkllok~, Japan, Elsevier, pp. 609-619, 1983, Talanta 35 (1988) 2 pp. 109-112, Anal. Chem. 65 (1993) pp. 331-337, Fresenius Z.
Anal. Chem. 325 (1986) pp. 387-392). In pH optodes, pH
indicators, which change the-ir absorption or fluorescence properties as a function of the proton concentration, are used as indicator phase (Anal. Chem. 52 (1980) pp. 864-CA 02208~97 1997-06-23 869, DE-A 3 343 636 and 3 343 637, US Pat. Appl.
855 384). If a gas-permeable membrane is used to separate the indicator from the substance to be mea~ured, only gases, for example carbon dioxide, can penetrate the membrane to reach the indicator phase, where they cause a change in the pH through hydrolysis. Carbon dioxide optodes of this type operate in similar fashion to Severinghaus electrodes. The disadvantages of optical pH
and therefore PC02 measurements reside in the very limited analytical measuring range and the dep~n~nce on ionic strengths. This, as well as the disadvantages already mentioned with regard to the Severinghaus elec-trodes, is a hindrance to wide application of optodes.
It is also known to det~rm;ne the CO2 concentra-tion in liquids using attenuated total reflection (TheChemical Engineer 498 (1991) p. 18) In a continuous measuring cell for fluid substances, for example beer, a sapphire ATR (Attenuated Total Reflectance) crystal is arranged perpendicularly to the flow direction. The infrared light fed to one side of the crystal passes through the crystal and undergoes repeated total reflec-tion. On each reflection, the radiation travels several ~m into the sample liquid and is attenuated by the carbon dioxide which is present. The residual light intensity at the other end of the crystal is measured. A disadvantage with this method is that it is not possible to measure partial pressures. Furthermore, in the case of fluids which undergo changes, variations in the reflection properties can lead to errors in the results.
DE-A 2435493 discloses a differential-pressure measuring instrument for the determ;n~tion of carbonic acid. However, it is only possible to use this instrument in flowing media. It is therefore unsuitable, in particu-lar, for conventional stirred or fixed-bed reactors, as used, in particular, in the fermentation industry.
DE-A 2926138 discloses a device for continuously measuring the dissolved carbon dioxide content in liquids. The measuring principle is based on det~rm;n;ng conductivity difference. The instrument is equipped with CA 02208~97 1997-06-23 a membrane, one side of which has the liquid cont~;n;ng dissolved carbon dioxide flowing over it, and the other side of which ha~ a neutral or basic measuring liquid flowing over it. There i~ a con~llctivity meter arranged in the flow path of the measuring liquid both before and after the p~rm~hle membrane. A disadvantage with the measurement is that it is unsuitable for liquids whose chemical and physical properties are not constant.
Furth~more, European Patent Application 0462755 discloses the det~rr;n~tion of gases, for example CO2, by measuring infrared absorption. In this case, the infrared light beam is passed through the fluid to be measured.
The light beam i~ split into two or more components.
These split light beams are then measured. A disadvantage with this measuring arrangement i8 that it does not allow partial pressures to be determ;n~ and it is sensitive to scattering particles in the sample liquid.
Splitting into two beam paths has already been disclosed by GB 2194333. In this method, only one of the light beams is guided through the substance to be measured. The rest of the radiation is used as reference light, so as likewise to increase the accuracy.
A further publication discloses a so-called chopped gas analyzer, which likewise operates using light-emitting diodes (Laser und Optoelektronik 17 (1985) 3, p. 308-310, Wiegleb, G.: Einsatz von LED-Strahlungs-quellen in Analysengeraten [Use of LED Radiation Sources in Analyzers]).
These instruments and methods have in common the fact that they only determine concentrations. The sub-stance to be measured is placed and measured directly in the beam path. This is possible for gases and liquids which do not contain scattering particles and have constant physical composition, in which noise can be quantified using a blank measurement. However, partial pressures cannot be det~m;ne~ using the described optical methods. Neither i~ it pos~ible to use them for varying physical composition and liquids cont~ining particles giving rise to turbidity.

CA 02208~97 1997-06-23 The object of the present invention is therefore to provide a device for mea~uring the partial pressure of gase~ dissolved in liquids using optical methods which does not have the abG~ ~ntioned disadvantages of the devices known from the prior art, and which, in particular, allows the partial pressures of gases to be measured accurately, with extended long-term stability for the device, and in meA; A whose physico-chemical composition may change, as well as in clear or turbid media or media whose turbidity varies.
This object is achieved in that the device consists of a) a measuring chamber which is separated, by means of a gas-permeable membrane which is perme~hle to the gas to be determ;neA, from a sample space which contains the li~uid and, dissolved therein, the gas Io be ~e~P~m.nP~, b) a light-emission source for generating a light beam which passes through the measuring chamber and has a wavelength which is absorbed by the gas to be determ; n~A, and ~ _ c) a measuring arrangement for det~rm; n; ng the light beam emerging from the measuring chA~ber.
According to the invention, the measuring chamber, the light-emission source and the measuring arrangement are arranged in a rod-shaped probe. When it is intended to be used in the field of biotechnology, for example for fermentation, the production of drinks or waste-water purification, it is designed as a sterilizable device. Since, in the field of fermentation technology, sterilization is pr~m;nAntly carried out using steam, the materials of the probe should be tailored to such conditions. For this reason, membrane materials which are tried and tested in this field are also primarily to be used here. In particular, these include polytetrafluoroethylene (silicone and other fluoride polymers). Gas-selective membranes which have proved successful according to the invention are solubility membranes. When they are introducted into the CA 02208~97 1997-06-23 , sample space (10), they can establish equilibrium between the ~ample liquid and the internal mixture.
According to the invention, the measuring chamber is preferably filled with a chemically and biologically inert fluid. This fluid is selected in such a way that it absorbs the gas to be determ;ne~, which diffuses through the membrane into the measuring chamber. To this end, suitable liquid~ or gases may equally well be used. The nature of the said fluids is dictated by the gases which are to be measured.
According to the invention, light-emitting diodes are preferably used as the light source. Using these device~ has the following advantages: -The emission has a relati~ely narrow band, which means that it is not absolutely necessary to use inter-ference filters in order to determ;ne the correspo~A;ng gas selectively. By virtue of the relatively low power consumption, it is in principle possible to design the measuring structure as portable with battery operation.
A decisive advantage over conventional infrared ~ources is that the power is extremely constant. It may therefore be possible to make do without comparison paths or to construct compensation circuits without moving parts. A
system of this type is mechanically robust. At the same time, the fact that the power is very constant ensures extended operation without recalibration. The light-emitting diodes are small enough for the injection of light into optical waveguides to be straightforward. The sensitive parts can thus be located externally, and are not subjected to the ~h~rm~l and merh~n;cal stresses of steam sterilization.
In the method according to the invention, it is also possible to operate with different wavelengths, for example two different wavelengths, in order to increase the accuracy. The methods for increasing the accuracy of the measurement and for compensating for fluctuations in the electronic components are widely known and published (Meas. Sci. Technol. 3 (1992) 2 191-195, Sean F.
Johnston: Gas Monitors Employing Infrared LEDs).

CA 02208~97 1997-06-23 Furthermore, according to the inventionr the detectors which are compatible with the light-emitting diodes are used. Suitable examples are, in particular, photodiodes, photoresistors and lead selenide photo-detectors (PbSe detectors). The latter operate predomi-nantly in the infrared range and are suitable, above all, for the determination of carbon dioxide.
Optical waveguides are used to guide the light waves from the light-emission source to the measuring chamber. The same is true for guiding the light from the measuring chamber to the measuring arrangement for deterr;n;ng the unabsorbed light intensity. According to the invention, the measuring arrangement is preferably connected to a special circuit for evaluating, storing and displaying the signals. Because of this, the device according to the invention is suitable, in particular, for the automation of systems. When an integrated evalua-tion unit is used, all the data can be acquired automatically and a control process can be carried out.
A further advantage according to the invention is the possibility of the device having a pressure-proof design. It is merely necessary to tailor the design of the housing of the probe accordingly. In this way, the device according to the invention can be used at pres-sures of 200 bar. ~referably, the probe is used at pressures of up to 20 bar. In the case of use for fermen-tation processes, it is merely necessary to ensure that the probe withstands the elevated pressures which occur under sterilization conditions.
A further subject of the present invention is a method for measuring the partial pressure of gases dissolved in liquids. In this method, the device accord-ing to the invention is immersed in the liquid present in the sample space in such a way that the m~hrane is fully wetted with sample liquid. Because of this, the gas which is to be determined can then diffuse selectively through the membrane into the measuring chamber. Using the light-emission source, a light beam is guided through the measuring chamber via optical w~ve~uides. The gas diffus-CA 02208~97 1997-06-23 ing into the latter absorbs ~ome of the radiation. The unabsorbed part of the light beam is fed to the measuring arrangement, via an optical wd~e~uide, for det~m;n;ng the partial pressure of the gas. Using correspo~;ng evaluation, storage and display devices, the measurement of the unabsorbed light beam can be used to determ;ne and evaluate the partial pre~sure of the gas.
According to the invention, use is preferably made of electromagnetic radiation generated by light-emitting diodes. The infrared range is quite particularlypreferred.
The device according to the invention and the method according to the invention are suitable, in particular, for use in measuring the partial pre~sure of carbon dioxide. Carbon dioxide represents a considerable production factor in the food industry, in particular in the drinks industry. In the drinks themselves, carbon dioxide is responsible for the shelf life and the refr~sh;ng taste. Most deterr;n~tions are currently carried out with simultaneous pressure and temperature monitoring.
For optimum process control of biotechnology processes, measurement of the partial pressure of carbon dioxide is likewise al~o necessary. An important fact in connection with this is that the supply of the micro-organisms with gases and their inhibitory properties are a function of the corresps~;ng partial pressures rather than of the concentrations. In spite of this knowledge, the partial pressure of carbon dioxide has not to date been taken into account sufficiently. A satisfactory solution to its determ;n~tion has not yet been found. The main problems in choosing a suitable determination method are the lack of available equipment and the high chemical stability of carbon dioxide. Carbon dioxide represents the highest oxidation state of carbon and is therefore very unreactive at room temperature. In contrast to other heterogeneous gases, it does not form hydrogen bonds in its dissolved form. With a dissociation constant for carbonic acid equal to 2 x 10-4 M, only a very small - CA 02208~97 1997-06-23 proportion is present in the form of dissolved ions. A
measuring probe which relies on determination of the ionic form therefore has an inherent shortcoming. For an accurate method, it is therefore necessary to determ;ne the dissolved carbon dioxide directly. For a measurement at room temperatures, it is possible to measure the absorption of carbon dioxide. Measuring absorption in the infrared range is, with existing exhaust-gas analysis instruments, part of the prior art. However, det~rm;n~-tion from the waste air gives concentrations and notpartial pressures. Concentrations can be converted into partial pressures, and vice versa, using Henry-~s law. In contrast to oxy~e~ the conversion of concentrations into partial pressures proves more difficult for carbon dioxide, since Henry's constant is influenced by the pH
and the constituents of the media. Fluctuations in the pH
lead to variations in the concentration of carbon dioxide in the outlet air over time. In particular with basic fermentations, and in large reactors, the accumulation of carbon dioxide in the media leads to temporal overshoots of the measured signal when approaching a new equili-brium. Signals of this type can be misinterpreted as changes in metabolism.
When the device according to the invention is used, the abovementioned problems in measuring the partial pressure of carbon dioxide are solved in particular. In this case, the measuring chamber is filled with a carrier fluid for carbon dioxide. Carbon dioxide must be soluble in this fluid. A further prerequisite is for the fluid to be chemically and biologically inert.
For steam sterilization, it is furthermore advantageous if the fluid has a higher boiling point than the sub-stance to be measured, in order substantially to avoid pressure fluctuations. According to the invention, however, the device is not restricted to a particular carrier liquid. Instead, the composition and chemical nature of the latter are dictated by the type of gas to be measured and the working conditions for the probe.
The invention will be expl~;n~ in more detail CA 02208~97 1997-06-23 below with reference to the figure, according to which the device in accordance with the invention consists of the probe (1). In the example according to the invention, the body of the probe is made of stainless steel. It is, however, possible to make it from any other desired material, but in general the material ~hould not corrode.
The probe (1) has a connector (2) which makes it po~sible for the probe (1) to be fitted in pressure-proof fashion into the pipe or the wall (5) of a vessel. The connector (2) and the O-ring arrangement (3) allow the probe (1) to be fastened in leaktight fashion in an access tube (4) on the wall (5). The access tube (4) has the correspon~;ng connector to the connector (2).
This structure affords the possibility of sub-]ecting the probe head to steam sterilization and usingit in sterile operation.
A light source (6) and a measuring arrangement (7) are present inside the probe (1). In the example according to the invention, the light source (6) is a light-emitting diode and the measuring arrangement (7) is a photodetector. Both instrument parts are provided with electrical leads (8) and (9). The light-emitting diode (6) is supplied with electricity via the lead (8j. The photodetector (7) transmits a signal pulse, via the lead (9), to a means for amplifying and recording the signal.
The light-emitting diode (6) and the photo-detector (7) are arranged outside the liquid space (10).
They are used via the extrinsic optical waveguides (12) and (13), which serve to transmit the light (12) from the light-emitting diode (6) and the unabsorbed light to the photodetector (7). The optical waveguides may be made of any materials suitable for the transmission of light. In the example according to the invention, operation is carried out in the infrared range. Light guides made of transparent material, for example silver halides and chalcogenides, are therefore preferable.
These optical w~e~ides can withstand thermal stresses and are theretore suitable for use in a steam-sterilizable environment.

- CA 02208~97 1997-06-23 .

The measuring space (14) is located at the tip o$
the head of the probe (1). In the example according to the invention, this space i8 filled with a chemically and biologically inert fluid which has a high physical absorption capacity for carbon dioxide. In fermentation methods, the fluids chosen have a melting point which is selected in such a way that pressure fluctuations do not occur during the sterilization.
The measuring space (14) is separated from the sample space (10) by the gas-permeable membrane (11). In the example according to the invention, the membrane (11) is a thermally stable membrane which is made of steam-sterilizable material. According to the invention, poly-tetrafluoroethylene and/or silicone are preferred for this.
The dissolved gas diffuses through the membrane (;i) into the sample space (lû) unril an equilibrium is established. Since the diffusion of gases through a membrane is controlled by partial pressure, the probe (1) det~rm;ne the partial pressure. The probe therefore measures a biologically me~n;ngful parameter, since the supply to the microorganisms i8, like all transport processes out of or into cells, controlled by partial pressure rather than concentration.
The light-emitting diode (6) emits narrow-band light which is absorbed selectively by the gas to be determined. In accordance with the gas to be examined, the wavelength may be either in the W/VIS or in the infrared range. For carbon dioxide, this wavelength is preferably 4.3 ~m.
The emitted wavelength range can be restricted by a heat radiator with interference filter, or preferably by a narrow-band light-emitting diode. The particular advantage in using light-emitting diodes is that the radiation can be modulated, which ~nh~nces the detection and minimizes effects such as DC drift.
The emitted radiation is fed, via the optical waveguide (12), to the measuring space. The gas which is present specifically attenuates the emitted radiation.

-~ ~ . CA 02208~97 1997-06-23 Some of the attenuated light i8 picked up by the optical waveguide (13) and fed to the photodetector (7). The latter measures the attenuated light and produces an electrical signal proportional to the attenuated light.
If m~ ted light is used, the electrical signal may likewise be modulated.
The length of the measuring chamber (14) corre-sponds to the optical path length. An optimum optical path length is selected in the measuring space (14), 80 that the probe (1) acquires the entire measuring range.
The measuring range is inversely proportional to the path length. Thus, the smaller the path length o~ the measur-ing chamber (14) of the probe (1), the greater is the detectable range and the ~maller is the resolution.
The advantages achieved with the invention consist, in particular, in that, primarily in the case of measuring the partial pressure of carbon dioxide, separating the measuring space from the sample space avoids effects due to the presence of particles which give rise to turbidity and have a concentration which varies. Furthermore, implementation of the membrane ensures that the partial pressure is measured. Although it is in principle possible to use Henry's law to convert concentration into partial pressures, this requires simultaneous knowledge of temperature and pressure, as well as the properties of the media. The latter is difficult, in particular when using fer~enta-ion ~.edia.
Further~ore, the long-term stability, accuracy and measuring range are increased in comparison with pH-sensitive partial pressure probes.
The probe according to the invention can be used particularly well both in the drinks industry and in biotechnology. Probes for measuring ranges of up to 10 bar can be made for use in food technology.
For use in measuring the partial pressure of carbon dioxide in the field of fermentation technology, it is advantageous for precalibration to be possible.
This is because, in view of the inhibiting effect of carbon dioxide on most organisms, calibration can no CA 02208~97 1997-06-23 longer be carried out subsequently. A further advantage in this field of application is that, during steriliza-tion, the probe withstands therm~l stresses and is readily stable at temperatures of 150~C. Lastly, it is advantageous that, in contrast to the prior methods involving the measurement of absorption, interference by materials which likewise absorb in the infrared range is ruled out.

Claims (18)

Claims
1. Device for measuring the partial pressure of gases dissolved in liquids, characterized in that it consists of a) a measuring chamber (14) which is separated by means of a gas-permeable membrane (11), which is permeable to the gas to be determined, from a sample space (10) which contains the liquid and, dissolved therein, the gas to be determined, b) a light-emission source (6) for generating a light beam which passes through the measuring chamber (14) and has a wavelength which is absorbed by the gas to be determined, and c) a measuring arrangement (7) for determining the light beam emerging from the measuring chamber (14).
2. Device according to Claim 1, characterized in that the measuring chamber (14), the light-emission source (6) and the measuring arrangement (7) are arranged in a rod-shaped probe (1).
3. Device according to Claim 2, characterized in that the probe (1) is sterilizable.
4. Device according to Claim 3, characterized in that the probe (1) can be sterilized using steam.
5. Device according to Claims 1 to 4, characterized in that the membrane consists of polytetrafluoroethylene.
6. Device according to Claims 1 to 5, characterized in that the membrane is a gas-selective solubility membrane, through which equilibrium is established between the sample space (10) and the measuring chamber (14).
7. Device according to Claims 1 to 6, characterized in that the measuring chamber (14) is filled with a chemically and biologically inert fluid for absorbing the gas to be determined.
8. Device according to Claim 7, characterized in that the fluid is a liquid or a gas.
9. Device according to Claims 1 to 7, characterized in that it contains an optical waveguide (12) for guiding the light beam from the light-emission source (6) to the measuring chamber (14) and an optical waveguide (13) for guiding the light from the measuring chamber (14) to the measuring arrangement (7).
10. Device according to Claims 1 to 9, characterized in that the light-emission source (6) is a light-emitting diode.
11. Device according to Claims 1 to 10, characterized in that the measuring arrangement (7) is a photodiode, a photoresistor or a lead selenide photo-detector.
12. Device according to Claims 1 to 11, characterized in that the measuring arrangement (7) is connected to a circuit arrangement for evaluating, storing and displaying the signals.
13. Device according to Claims 1 to 12, characterized in that it is of pressure-proof design.
14. Device according to Claim 13, characterized in that it is designed for operation under pressures of up to 200 bar, preferably up to 20 bar.
15. Method for measuring the partial pressure of gases dissolved in liquids using a device according to one of Claims 1 to 14, characterized in that a) the membrane (11) of this device is immersed in the liquid present in the sample space (10), b) the gas which is present in the liquid and is to be determined diffuses into the measuring chamber (14) through the membrane (11), c) a light beam having a wavelength which is absorbed by the gas to be determined is guided through the measuring chamber (14), and d) the unabsorbed light is fed to the measuring arrangement (7).
16. Method according to Claim 15, characterized in that the measurement is carried out using infrared radiation.
17. Use of the device according to one of Claims 1 to 14 for determining the partial pressure of oxygen or carbon dioxide.
18. Use of the device according to one of Claims 1 to 14 for measuring, controlling and regulating fermentation processes, methods for the production of drinks, and waste-water purification plants.
CA002208597A 1994-12-21 1995-12-20 Device for measuring the partial pressure of gases dissolved in liquids Abandoned CA2208597A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DEP4445668.9 1994-12-21
DE4445668A DE4445668C2 (en) 1994-12-21 1994-12-21 Device for measuring the partial pressure of gases dissolved in liquids in systems for carrying out biotechnological or food technology processes

Publications (1)

Publication Number Publication Date
CA2208597A1 true CA2208597A1 (en) 1996-06-27

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CA002208597A Abandoned CA2208597A1 (en) 1994-12-21 1995-12-20 Device for measuring the partial pressure of gases dissolved in liquids

Country Status (7)

Country Link
EP (1) EP0871865B1 (en)
JP (1) JPH10512668A (en)
AT (1) ATE232977T1 (en)
AU (1) AU695408B2 (en)
CA (1) CA2208597A1 (en)
DE (3) DE4445668C2 (en)
WO (1) WO1996019723A2 (en)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
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WO1996019723A3 (en) 1996-08-22
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EP0871865A2 (en) 1998-10-21
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JPH10512668A (en) 1998-12-02
WO1996019723A2 (en) 1996-06-27

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