WO2010056101A1

WO2010056101A1 - An oxygen sensor

Info

Publication number: WO2010056101A1
Application number: PCT/MY2008/000134
Authority: WO
Inventors: Ekhson Holmuhamedov
Original assignee: Advanced Bio-Med Tools Sdn. Bhd.
Priority date: 2008-11-13
Filing date: 2008-11-13
Publication date: 2010-05-20

Abstract

A sensor (10) for measuring concentration of dissolved oxygen in a sample solution, comprising potentiometric electrodes, comprising a cathode and a reference electrode, characterized in that the sensor comprises natural rubber latex membrane (22) which separates external probe cylinder (30) and the internal probe cylinder (36) separating the electrolyte in the internal probe cylinder from the sample solution.

Description

AN OXYGEN SENSOR

FIELD OF INVENTION

The invention relates to an oxygen sensor comprising membrane. More particularly it relates to an oxygen sensor with a natural rubber latex membrane.

BACKGROUND OF INVENTION

There are various types of instruments available for sensing, recording, monitoring changes in the biological/physiological processes with respect to time, A basic recording setup includes a measurement device, a processing or coupling device, and a recorder. In a polarographic system the measurement device (transducer) is a Clark-style oxygen electrode, the processing/coupling device is an oxygen monitor and the recording device is a flatbed strip chart recorder, or perhaps a computer-assisted data acquisition system.

In such a system the biological solution or suspension to be assayed is placed into the sealed chamber and dissolved oxygen is measured with Clark oxygen electrode which acts as the measurement device. The dissolved oxygen (D.O.) chamber contains one or more access ports for adding/removing materials. The medium is stirred to ensure homogeneity and to ensure that oxygen can freely diffuse into the electrode. The presence of oxygen causes the electrode to deliver a current to the oxygen monitor, which amplifies the current and converts it to a voltage output that is directly proportional to the concentration of oxygen in the chamber. This allows the oxygen to be measured. The recorder moves a paper chart at constant speed, so that when the recorder pen moves in response to voltage changes, oxygen content is recorded as a function of time.

US 2004/0211242 A1 discloses a multipurpose monitoring system that provides instantaneous, simultaneous and continuous monitoring, acquisition and storage of the information on biological processes occurring in a variety of aqueous solutions such as biological samples including mitochondria, nuclei, bacteria, fungi, suspension of mammalian cells and others. One of the parameters continuously measured and monitored is oxygen concentration which is done using Clark-style oxygen sensor. Ionic composition and dissolved oxygen in the aqueous solution are measured.

The Clark-style oxygen sensor utilizes a gas permeable membrane which separates internal electrolyte of the oxygen sensor from incubation medium and should also provide electrical insulation of a powered (-65OmV) negative Pt electrode from incubation medium, thus preventing electrical contact between Pt electrode and other ion-selective electrodes through biological sample.

Various membranes associated with sensors are described in the prior art. US 5,595,646 discloses a membrane that serves the purpose of protecting electrolyte and electrodes from species such as metal ions, battery metals and liquid water, while passing species such as water vapor and oxygen necessary for sensor operation. US 4,484,987 discloses a membrane applicable to implantable sensor and can be used in oxygen sensor device. The membrane is a combination of a body of hydrophilic material and a body or bodies of hydrophobic material.

Oxygen sensor with conventional membrane such of polypropylene, teflon, butylacetate or flourinated ethylene-propylene (FEP), is not compatible when used in multichannel monitoring apparatus where potentiometric electrodes, such as tetraphenylphosphonium (TPP) electrodes, pH electrodes, calcium electrodes, or potassium electrodes were used.

Thus the prior art membranes used in oxygen sensors in single volume chambers did not yield useful or reliable results in multipurpose monitoring system. Accordingly there is a need to provide a suitable oxygen sensor membrane, which prevents interference with measurements supported by potentiometric electrodes placed into the same sample volume as oxygen sensor with acceptable degree of accuracy in the detection of the concentrations of soluble ions in sample.

SUMMARY OF INVENTION

The invention discloses a sensor for measuring concentration of dissolved oxygen in a sample solution, comprising a cathode and a reference electrode, characterized in that the sensor comprises natural rubber latex membrane which separates external probe cylinder and the internal probe cylinder separating the electrolyte in the internal probe cylinder from the sample solution.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is an exploded perspective view of an oxygen sensor according to the preferred embodiments of the present invention.

Fig. 2 is a diagrammatic view of the Pt and Ag/AgCI electrode.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to the present invention the oxygen sensor comprises a membrane formed of natural rubber latex. The sensor is for use in a device for measuring the oxygen content in a sample. The device with a sensor for measuring concentration of oxygen includes potentiometric electrodes of any kind. The electrolyte is separated from the aqueous solution by a natural rubber membrane. The potentiometric electrodes such as the TPP electrodes, pH electrodes, calcium electrodes, or potassium electrodes include electrodes to measure concentration of various parameters.

In the following description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural, logical and electrical changes may be made without departing from the scope of the present invention. The following description is, therefore, not to be taken in a limited sense, and the scope of the present invention is defined by the appended claims.

The oxygen sensor used in the multi-purpose monitoring system as that disclosed in US 2004/0211242 A1 requires external negative 650 mV applied between reference and measuring electrodes. This electrode uses substantially large current values as compared with conventional potentiometric electrodes, which makes it a source of disturbance and noise to the sensors measuring various parameters.

Electrical contact between oxygen and the measuring volume must be minimized to allow simultaneous use of potentiometric and oxygen sensors within the same volume. Membranes which are electrically conductive are not suitable for use in a oxygen sensor together with other potentiometric electrodes as they interrupt the measurement of various parameters. Accordingly the natural rubber membrane is used in the oxygen sensor of the present invention, where the oxygen sensor is used simultaneously with other potentiometric electrodes, so that it electrically insulates internal working part of oxygen sensor from incubation medium containing potentiometric electrodes.

Referring to Fig 1 , there is shown an exploded view of an oxygen sensor according to an embodiment of the invention. The main features of the oxygen sensor (10) consists of a plastic holder (12) and includes within its chamber, a platinum electrode (14) sealed and secured inside, preferably by use of high quality electrically insulating epoxy resin. Electrical contact between the platinum electrode (14) and a connector (16) is provided by connecting wire (18) and a first cable (19). The connecting wire (18) is soldered to a first cable (19) which in turn is soldered to the connector (16).

A reference (Ag/AgCI) electrode (20) is mounted on the plastic holder (12) and is electrically connected to the connector (16) by means of a second cable (19). Thus the completely assembled main features contain a mounted Pt and Ag/AgCI electrodes (14, 20), thereby producing a measuring insert.

The assembly of the remaining components of the oxygen sensor is described now. A natural rubber latex membrane (22) is rolled over a tip of a membrane holder (24) which is preferably of plastics. The latex membrane (22) is held in position over the membrane holder, by securing the membrane over a designated groove (26) in the membrane holder (24). The latex membrane (22) is attached and is mounted on a holder thus providing controlled stretch (and thickness) of the latex membrane (22). The sub-assembly of the latex membrane on the membrane holder is introduced into an opening port (28) of external probe cylinder (30). To connect the housing of the sub- assembly onto the opening port (28), the membrane holder (24) is provided with a pair of grooves to mate with a reciprocating tongue (34) on the opening port (28). For sake of clarity of diagram, grooves and tongue are not shown in the illustration.

External probe cylinder (30) now housing the latex membrane, which is mounted securely onto the membrane holder (24), is now introduced over a hollow internal probe cylinder (36). The external probe cylinder (30) and the internal probe cylinder (36) are secured in position by the provision of ears and notch joints (not shown in the illustration). During this operation it is necessary to ensure that the latex membrane (22) does not slip from the membrane holder (24) and that the membrane holder does not dislodge from the external probe cylinder (30). Internal chamber of the internal probe cylinder (36) is moistened with distilled water to facilitate the telescoping of the parts as explained above. Since this operation will stretch the latex membrane (22) and generate extra force, which will push the parts away from each other, the operator must keep both parts together with additional effort.

A holder nut (38) is introduced over the external probe cylinder (30) so as to engage over a threaded position at external base (40) of the internal probe cylinder (36). The chamber within the internal probe cylinder (36) is filled with 250 μl of electrolyte solution (solution of 3M KCI supplemented with saturated Ag/AgCI). Whilst ensuring there are no bubbles, the plastic holder (12) (with the electrodes within it) is introduced into the chamber in internal probe cylinder (36). Assembly so formed is secured by the use of a second holder nut (42). The chamber holding the electrolyte in the internal probe cylinder (36) is sealed by means of the head of insert (42). The sealing head of insert (42) also used to mount and secure the cables connecting Platinum and Ag/ AgCI parts of electrode (19) with connector (16). The platinum electrode (14) and a reference electrode are connected to -650 mV and +650 mV respectively.

The oxygen sensor (10) so constituted and assembled is calibrated as follows. For Clark style oxygen electrode a two-point calibration procedure is adopted. The sensor (10) is exposed to a solution and the tip of the oxygen sensor covered with the membrane is inserted into the sample volume using passages in the body of the measurement chamber with known concentration of dissolved oxygen and the system is allowed to stabilize and the current value is measured. This level of the current is defined as known concentration of dissolved oxygen (or as 100% point). At the next step of calibration the solution with known oxygen concentration is replaced with zero oxygen containing solution and the system is allowed to stabilize and the reading is taken as zero oxygen (or 0%) point.

These two points are used by the multi-purpose monitoring system with appropriate software to construct a calibration curve. For Clark style electrode the relationship between the concentration of dissolved oxygen and the current is linear.

In a similar manner the oxygen in the sample is measured and the reading taken.

Claims

1. A sensor (10) for measuring concentration of dissolved oxygen in a sample solution, a cathode and a reference electrode, characterized in that the sensor comprises natural rubber latex membrane (22) which separates an external probe cylinder (30) and an internal probe cylinder (36) separating the electrolyte in the internal probe cylinder from the sample solution..

2. The sensor as claimed in claim 1 wherein the latex membrane (22) is molded and is mounted on a holder and operatively connected to the external probe cylinder thus providing controlled stretch and thickness of the latex membrane (22).

3. A device comprising a sensor (10) for measuring concentration of dissolved oxygen in a sample solution and potentiometric electrodes comprising a cathode and a reference electrode, characterized in that the sensor comprises a natural rubber latex membrane (22) which separates external probe cylinder (30) from internal probe cylinder (36) thus separating electrolyte in the internal probe cylinder from the sample solution..

4. The device as claimed in claim 3 wherein the latex membrane (22) is molded and is mounted on a holder and operatively connected with the external probe cylinder thus providing controlled stretch and thickness of the latex membrane (22).

5. The device as claimed in claim 3 wherein the potentiometric electrodes are of any kind.

6. Use of a natural rubber membrane (22) in a sensor (10) for measuring concentration of dissolved oxygen in a sample solution, said device comprising potentiometric electrodes, comprising a cathode and a reference electrode and wherein the latex membrane (22) separates external probe cylinder from internal probe cylinder, thus separating electrolyte in internal probe cylinder from the sample solution.