DE3242456A1 - Electrode arrangement with an ion-sensitive electrode having a polymer membrane - Google Patents

Abstract

In the electrode arrangement, the essentially planar, separately produced membrane is held by an annularly closed support element which has stop surfaces and/or sealing surfaces in the region of the front side of the membrane, which surfaces form a liquid connection to at least one opening located on the annular support element as a connection to a throughflow system, and the rear electrical contacting of the membrane is effected by mechanical pressure with a takeoff element.

Description

description

The invention relates to an electrode arrangement in the preamble of claim 1. Such electrode arrangements are used for potentiometric Measurement of ion concentrations in a flowing sample liquid.

Recently, electrolyte determinations in biological Liquids (as well as similar measuring media with basically known chemical Matrix composition) increasingly analyzing devices with ion-sensitive measuring systems used because the potentiometric determination of the electrolyte compared to the conventional Method of flame photometry offers clear advantages. The sensors of one of these Analyzer are ion-sensitive electrodes (ISE), which in principle consist of the actual Sensor - the so-called ion-sensitive "membrane" - and an electrical working system exist.

A distinction is made between the structure and composition of their membrane Glass membrane, solid or crystal membrane, liquid membrane and matrix or Polymer membrane ISE. In the last few years the analyzers described have been used Art increasingly using poly-membrane sensors, since such membranes are considerably better Provide properties with regard to the desired application than other membrane types. The manufacture and use of ion-sensitive polymer membranes are fundamental known and have been discussed for years in the relevant literature animals (see e.g. W.E. Morf and W.Simon in "Ion-Selective Electrodes Based on Neutral Carriers", as well as G.J.Moody and J.D.R.Thomas in "Poly (Vinyl Chloride) Matrix Membrane Ion-Selective Electrodes "; both in" Ion-Selective Electrodes in Analytical Chemistry ", Volume 1 by Henry Freiser (Ed.) Plenum Press New York 1978). The appropriate procedures are in principle prior art and not part of this invention.

In general, ion-sensitive polymer membranes consist of three lipophilic ones Main components: a polymeric support material (e.g. PVC), an ion-sensitive Carrier substance ("carrier", "ionophore") or a corresponding selective ion exchanger, and a solvent for the carrier substance (or the ion exchanger). That Solvent mostly acts as a plasticizer for the polymer at the same time. In use All ion-sensitive polymer membranes are more or less subject to a gradual Aging, which is caused by minor "bleeding" of the carrier substance and the solvent.

The speed of this aging depends on the original one Concentration of the "bleeding" components in the membrane, from the lipophilicity these substances as well as the size of the membrane / sample material contact surface active sensor area and the frequency of analysis. Either way, it is the most effective Lifetime of polymer membranes limited, so that aged sensors in an analyzer have to be replaced by "fresh" sensors after a certain period of operation.

The replacement of the aged sensors should be carried out by users of the analyzer can be carried out quickly and easily without prior training. Although in As a rule, only the ion-sensitive membrane of an ISE is subject to aging (not however, their electrical discharge system) requires the user to change the membrane often great manual dexterity and is therefore hardly reasonable in most cases. For this reason it is state of the art to provide such polymer membrane sensors as complete Replace units (i.e. together with the electrical discharge system). As a disposable As a result, polymer ISE (PME) or replacement items are becoming a significant cost factor for the user.

Conventional discharge systems for PME contain liquid internal electrolytes, Exchangeable PME with liquid drainage systems are known and have been e.g. EP-A1 00 27 256 and EP-Al 00 42 157 are disclosed. The one caused by sealing problems relatively complicated structure of such PME with liquid discharge, as well as the resulting difficult manual manufacturing processes and the associated ones In recent years, high manufacturing costs have led to the development of so-called "All-solid-state" or fixed contact polymer membrane electrodes (FK-PME). At acquaintances Austasch PME of this type (e.g.

DE-OS 28 54 444 and DE-OS 29 22 884) the contact is made ion-sensitive polymer membrane via a solidified intermediate electrolyte to form a metallic conduction system. In the manufacture of such sensors, first of all the components of the ion-sensitive membrane are dissolved in a suitable solvent. This liquid Polymer solution is then desired by potting in the Shaped and then dried by evaporation of the organic solvent and hardened. This is followed by an initially gel-like discharge electrolyte contacted the membrane and at the same time with a metallic dissipation system in Connected. After the gel has solidified, there is a "solid" connection made of membrane and electrical discharge. It can be seen that the Production of such sensors inevitably takes place in several production steps, and thus the manufacturing costs are very high.

In clinical-chemical analysis devices there is usually a simultaneous measurement of different parameters with several different ISEs for same time. Since there is usually only a small amount of sample available for this purpose the active sensor surface - i.e. the contact surface between the sensor and the material to be measured - must be as close as possible can be made small in order to simultaneously handle several PMEs with the small amount of sample (usually less than 500 / ul). In the preparation of the described FK-PME therefore result in particular manufacturing difficulties from the fact that, on the one hand, the ion-sensitive membrane has a very small area on the sample side and should be of reproducible geometry, but on the other hand the production Such reproducible membranes are made more difficult by the casting of the membrane solution in liquid state. As a result, a high reject rate has to be accepted, because a reproducible drying and hardening of the previously liquid components (Membrane and solidified discharge electrolyte) difficult to reach is, and possible malfunctions of the finished sensor (due to curing and drying errors, such as.

Air bubbles etc.) only recognized during a later function check can be. Since the membrane and drainage system cannot be removed after drying and hardening are connected, faulty sensors can only be completely discarded what with the usual use of precious metals (especially silver or platinum) as an electrical arrester as well as a process-related high reject rate leads to a considerable increase in the cost of such FK-PME.

In contrast, a method is described in DE-OS 29 41 083, analogous to the production of so-called "coated wire" electrodes (see e.g. H. Freiser in "Coated Wire Ion-Selective Electrodes" in "Ion-Selective Electrodes in Analytical Chemistry ", Volume 2, by Henry Freiser (Ed.) Plenum Press, New York 1980) enables the production of FK-PME in just one operation. It will with the omission of a solidified discharge electrolyte, an ion-sensitive polymer solution connected directly to a metallic drainage system and dried on it.

A reproducible coating of the leakage contact with the ion-sensitive Membrane is guaranteed that in a specially constructed Overpressure chamber the drying of the membrane at controlled overpressure and / or reduced temperature takes place, creating a reproducible, trouble-free contact zone Membrane / leakage contact by avoiding the formation of bubbles achieved can be. It can be seen that in such a way the possible reject rate is reduced, but only with the aid of a very complex process. In addition, sensors identified as faulty in quality control even if this method is used, they can only be discarded in full, i.e. including of the expensive precious metal dissipation system.

Another disadvantage of the manufacturing process described for FK-PME is based on the fact that as a result of the respective contacting process and the required small active sensor surface (contact zone membrane / sample) the ratio of the total membrane volume to the active sensor area is not very large is. "Bleeding" membrane components can therefore not leave other membrane zones (which are not in contact with the sample) are replaced. This will the possible service life of such membranes is severely restricted.

The invention specified in claim 1 is therefore based on the object a durable and firmly contacted ion-sensitive polymer membrane electrode assembly of the type specified at the beginning for use in an ion-sensitive analyzer to create that can be manufactured inexpensively.

Furthermore, a more favorable ratio of the total membrane volume should be achieved too active sensor surface can be achieved in order to improve the service life of such sensors.

Another object of the present invention is design a measuring system for recording this Sensors, on the one hand a easy and quick interchangeability of the described electrodes ensures, and on the other hand is designed so small that even small amounts of sample are still reliable can be measured.

With electrode assemblies manufactured according to the invention, first it can be demonstrated that - contrary to the techniques previously used - a "dry" Connection between membrane and deflection surface, which under a certain mechanical Contact pressure is sufficient to maintain the ion-sensitive properties of the membrane element to have an effect.

In particular, the invention has the following advantages: Prefabricated Membranes can be used in batches (i.e.

representative) even before contacting, regardless of the lead system to be tried out. Even if the membrane is defective (e.g. due to a faulty setting or incorrect Recipe of the membrane polymer solution) completely manufactured electrodes do not work lost more.

For quality control, defective sensors do not need to be complete be destroyed. After replacing the membrane, the drainage system can be used again.

All plastic parts can be designed as molded parts, so that no manual reworking is necessary.

Mechanically self-adjusting and self-sealing systems during assembly the electrode and when changing electrodes allow a quick and uncomplicated Handling.

The ratio of the membrane volume to the active sensor area is in an advantageous embodiment of the invention about 1.6 mm compared to the known electrodes of less than 0.5 mm.

Accordingly, the diaphragms can have an approximately three times longer service life to be expected.

In the solution according to the invention, the necessary mechanical Apply contact pressure in a simple manner by coil springs, which on the Apply the necessary pressure to the edge area of the membrane or the discharge element. the Together with the ring-shaped support element, the electrode arrangement forms an easily replaceable one Unit that can be inserted between the sample channel and the electrical connection. the Unit is - with a correspondingly closed design of the liquid chamber - secured against mechanical damage and can be operated by the operator without special knowledge and skills are exchanged. A cylindrical one The edge of the electrode element serves as a grip sleeve.

Preferred developments of the invention are set out in the subclaims specified or are based on the embodiment shown in the figure is described in more detail.

The single figure shows a side view of the electrode arrangement according to the invention.

In the embodiment shown in the figure of the invention The electrode arrangement is a base body 1 fixed in a not shown in detail Device for ion-sensitive analysis installed to accommodate multiple electrodes. The base body is designed as a thermoplastic injection-molded part. The liquid to be examined arrives in the direction of the arrow to an inflow opening 2 and from there in a straight line via an attachment 3 into the exchangeable electrode arrangement 4.

The connection path (sample channel) for the analysis liquid to the outlet opening runs within and encloses a removable electrode element Connection element 5 in turn to the base body 1, which by means of a straight Direction running hole 6 the connection to the following (not shown) Manufactures electrode assembly.

It can be seen that the path for the liquid is extremely short, so that the tests in question can be carried out with a very small amount of substance are. In addition, the electrodes are individually accessible and from the base body are easily removable. The liquid to be analyzed leaves after Flow through the ion-sensitive electrodes including the reference electrode Base body through an outlet port 10. The structure of a single electrode is intended are presented in more detail below.

An annular carrier element 11 forms the electrode head and closes a membrane 12 towards the outside in the shape of a cylinder jacket. The electrode head 11 has an inner cavity 13 for the liquid passing through, which the Diaphragm 12 is adjacent and thus forms a closed chamber. This measuring chamber stands through an inlet and outlet opening 14 and 15 with the corresponding connections the straight connection of the flow system in connection.

In this way the membrane is in the electrode head when changing of the head part is optimally protected, as they are involved in the handling required for this cannot be reached by the operator's fingers. Tools are exchangeable not mandatory.

The membrane is in the usual way - but as a separate element without any contacting and discharge elements in a homogeneous form as a disc - manufactured. The membrane can get a relatively large thickness, which their The service life is extended, as this increases the ratio of membrane volume to active Sensor area increases. With a membrane thickness of 0.3 mm, for example achieve a ratio of 2.95 mm.

By the illustrated angled course of the flow channel the tightness of the connections to the Ensure the base body, as this is perpendicular to the membrane and to the installation direction of the electrode so that they fix the electrode head in its position Forces a compressive force on the sealing surfaces surrounding the flow channel 16 and 17 exercise. The effect of the sealing surfaces is increased by the surrounding area O-rings 19. It should be noted that these sealing surfaces are the only support points Form for the electrodes on the base body, so that here a maximum pressure arises.

The membrane 12 is simply in the cylindrical during assembly Electrode head 11 inserted, whereby it is on a circumferential ring-shaped approach supports. With a corresponding contact pressure, the electrode arrangement is also sealed against the material to be measured in this area.

On the membrane 12, which is located on an inside of the electrode head supports circumferential annular projection, is an Ag disk 19, the The surface facing the membrane is provided with a chloride layer. These parts form together with the ring-shaped carrier representing the electrode head 12 an exchangeable one Unit, which is easily grasped manually at its edge area, from the one shown Subtracted position to the right (in the drawing) and replaced by a corresponding element can be replaced. Access is expediently done with the thumb and Index finger, which has sufficient space in the direction perpendicular to the plane of the drawing Find.

The discharge element 19 made of silver lies with its chlorinated surface loosely on the membrane 12 and we use a helical spring 40 in the edge area pressed on. An inner sleeve 41 with a force is used to guide the helical spring. gene, on which the other end of the coil spring is supported. From the inner sleeve the force of the coil spring 40 is connected to the electrode head (carrier element) 11 elastic hooks passed over, which can be disengaged for dismantling.

A contacting unit is attached to the electrode head 20, which are pushed onto the electrode head 12 like a plug can and via a contact 21, which is guided in a hole and under the force a compression spring 22 is connected to a coaxial socket 23 by means of the the electrical connection to the electronic part of the device is established. The element that forms the cap and the element that receives the contact elements forms an insulating material housing, in the possibly required shielding elements against electromagnetic interference can be inserted.

The dimensioning is chosen such that when exerted on the housing 7 Pressure force, the electrode cap is supported on the electrode body.

The contact element 21 leading bore 23 holds in their area Front surfaces, however, a certain distance from the discharge element made of silver 19, so that the contact takes place exclusively via the compression spring 22 and the Contact forces can thus be controlled within specified limits.

It can be seen that the number of when changing with the electrode parts to be removed is minimal, so that the relevant spare part Can be produced inexpensively. In addition, there are also advantages in the manufacture itself occur, which result from the illustrated disk shape of the membrane, the is fixed solely by forces exerted on the loose membrane body. The silver plate is simply inserted, with the forces necessary for contacting can be safely applied and an operationally stable one State is reached.

With the arrangement shown according to the invention, the electrodes be provided extremely close together, so that only short lines are required are, although the handling necessary for replacement is easy are feasible and the actuating parts can be reached safely.

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Claims (10)

Electrode arrangement with an ion-sensitive one having a polymer membrane Electrode claims 1. An electrode arrangement with a polymer membrane having ion-sensitive electrode that the substantially flat, separately produced membrane (12) from an annular closed carrier element (11) is held in the area of the front side of the Membrane has stop and / or sealing surfaces (16, 17) which have a fluid connection to at least one opening located on the annular carrier element (11) as Form connection to a flow system (1), and that the rear electrical Contacting the membrane (11) with a discharge element (19) by mechanical pressure he follows. 2. Electrode arrangement according to claim 1, d a d u r c h g e k e n n it is clear that the membrane (12) is otherwise loose in the carrier element (11) is inserted and is supported on this only in its edge area. 3. Electrode arrangement according to one of the preceding claims, d a it is indicated that the ring-shaped, closed carrier element (11) has a helical spring (40), which in turn is at least indirectly supported on the carrier element (11) and on the disc-shaped discharge element a Exerts pressure force, which presses this against the membrane (12), which in turn is supported on the collar-shaped stop surface of the carrier element. 4. Electrode arrangement according to one of the preceding claims, d a d u r g e k e n n n z e i n e t that the annular support element a front electrode cover, each with a separate opening (14, 15) for has the inlet and outlet of the sample liquid. 5. Electrode arrangement according to one of the preceding claims, d a it is indicated that the discharge element (19) is also a forms a substantially flat surface. 6. Electrode arrangement according to claim 5, d a d u r c h g e k e n n shows that the discharge element (19) consists of a noble metal. 7. Electrode arrangement according to one of the preceding claims, d a It is indicated that the precious metal is silver. 8. Electrode arrangement according to claim 7, d a d u r c h g e k e n n z. e i c h n e t that the discharge element (19) made of silver membrane side with a Silver chloride layer is provided. 9. Electrode arrangement according to one of the preceding claims, d a d u r c h g e k e n n n z e i c h n e t that for the electrical connection of the discharge element (19) with a supply line in a cover cap for the Support element Resiliently mounted contact element (21) is provided, the cap itself supported in operation on the carrier element. 10. Electrode arrangement according to one of the preceding claims, d a d u r c h g e k e n n n z e i c h n e t that the outer edge area of the carrier element (11) is cylindrical and forms a handle element.