DE3000886A1 - Anion-selective electrode for anion determn. in urine - has polymer coating permeable for inorganic ions on measuring membrane to minimise errors - Google Patents

Abstract

Anion-selective electrode has an inner electrode immersed in a soln. (I) in a container (II) and a polymer measuring membrane (III) on the end of (II), which is in contact with (I), a substance (IV) responding to anions being dispersed in (III). The novelty is that a layer of polymer resin (V), which is permeable for inorganic ions, covers one side of (III) and can be brought into contact with the sample. (II) consists of PVC. (III) contains a phenyl alkyl alcohol and consists of PVC, whilst (IV) is a quat. ammonium salt with alkyl gps. (V) is 30-50 um thick and is a cellulosic polymer, esp. acetylcellulose (with 1-3 acetyl gps.) coated on (III) by drying a soln.; or polycarbonate, PMMA and/or silicone rubber. Analytic errors are small.

Description

Anion selective electrode

The invention relates to a selective anion electrode arrangement or Anion electrode. In particular, the invention relates to a selective anion electrode, which is suitable for the determination of anion concentrations in body fluids.

Electrodes that respond selectively to ions are used for determination of ion concentrations by taking advantage of the reaction that occurs between the surface of a measuring membrane of the electrode and a certain ion in one Liquid sample runs out into which the electrode is immersed. Such ion-selective Electrodes are currently used extensively in diagnostics as the measurements are very simple.

As an example of such anion selective electrodes for diagnostic purposes electrodes with a polymer membrane are known, which have a measuring membrane made of a polymer resin have, by dispersing an ion-responsive substance and a Plasticizer was formed in a polymeric resin base material, the measuring membrane placed in a container charged with an inner filling solution; such electrodes with polymer membrane are already in practice for determination from Cation concentrations, such as sodium or potassium ion concentrations, or anion concentrations have been used, e.g.

Chloride ion concentrations. An anion-selective electrode with a polymer membrane, as used e.g. for the determination of chloride ion- "-sonzenxraslonen wira una consists of a quaternary metal compound, plasticizer and polyvinyl chloride, works reproducible when examining serum samples; such a measuring electrode ensures high measurement accuracy when measuring serum samples and delivers results, which agree well with the results obtained in the determination of chloride according to the coulometric method. However, if you have a urine sample with such a selective chloride electrode, a value is obtained that is 20 to 40% greater than is the value obtained by the coulometric method; the reproducibility the measurements are not as good as in the case of the serum.

As a result of studies preceding the invention, assumed that the analytical errors of the measured values of urine samples in the case of anion-selective Electrodes are so strikingly large that organic anions are in relatively large quantities are contained in the urine samples.

In further investigations it was found that the influence of such Interfering components in urine samples can be eliminated if you have a laminated one or coated membrane used for anion-selective electrodes.

It is known that coated membranes are used for purposes which have nothing in common with the present invention.

For example, U.S. Patent 3,847,777 suggests coated membranes to be used for oxygen electrodes. This creates a porous, gas-permeable membrane placed on the surface of an oxygen-permeable membrane, whereby on traces of water located in the oxygen-permeable membrane are eliminated and a immediate response is achieved.

Another example of a coated membrane is in JA-OS 107 295/74 (= DE-OS 2 400 817 = CA-PS 986 184). It is suggested that to form a reinforced measuring diaphragm by adding layers of polyvinyl chloride with are impregnated with a selectively ion-responsive substance, e.g. valinomycin, on both the top and bottom of an acetyl cellulose sheet applied with a selectively ion-responsive substance such as vanilomycin, is impregnated, so that the impregnated acetyl cellulose film with the impregnated Polyvinyl chloride films is coated in a sandwich-like manner.

The object of the invention is to provide an anion-selective electrode, delivers the measured values with very small analytical errors if the anion electrode used to measure anion concentrations in urine samples.

According to the invention, an anion-selective electrode with a measuring membrane is used made of a polymer resin, which is characterized in that one side the measuring membrane with a polymer resin layer permeable to inorganic ions is coated and that the measuring membrane is arranged so that it is with the inner Rinsing solution is in contact, and that the inorganic anions permeable Polymer resin layer is on the outside.

The measuring membrane contains a quaternary ammonium salt as the measuring substance. Usually a quaternary ammonium salt is used with 1 to 4 alkyl chains each with 7 to 16 carbon atoms used as the measuring substance. As the basic material for the The measuring membrane is made of polyvinyl chloride, polycarbonate and / or polymethyl methacrylate used. Used as a polymer resin material permeable to inorganic ions acetyl cellulose, polycarbonate, silicone rubber and / or polymethyl methacrylate.

In a preferred embodiment of the invention, the Measuring membrane formed from polyvinyl chloride in which a quaternary ammonium salt is dispersed; the layer permeable to inorganic ions is made of acetyl cellulose with a Formed content of 1 to 3 acetyl groups.

DRAWING The invention is explained in more detail below by aie /.

The figures show: FIG. 1 a sectional view which schematically shows an embodiment Figure 9 shows an anion selective electrode according to the invention; Figure 2 is a diagram that is, the results of measurements of chloride ion concentrations in urine samples with an anion-selective electrode according to the invention and in comparison the results the measurements of chloride ion concentrations of the same urine samples according to the coulometric Method reproduces; Figure 3 is a diagram showing the reproducibility of the measurements of chloride ion concentrations; Figure 4 is a graph showing the response speed compared to urine samples with an electrode according to the invention and in comparison the Represents the speed of response to urine samples for a conventional electrode; Figure 5 is a graph showing the relationship between the influence of inhibiting components and represents the thickness of the acetyl cellulose layer; Figure 6 is a diagram showing the Shows the influence of immersion in water and drying on the measured values; and Figure 7 is a graph showing the results of measurements of chloride ion concentrations in serum samples according to the invention in comparison with results of measurements of the Chloride ion concentrations in the same serum samples by the coulometric method reproduces.

According to Figure 1, which shows a longitudinal section of an anion-selective electrode According to one embodiment of the invention, is the top of a container of polyvinyl chloride, e.g.

a cylindrical, tubular container 2, through a lid 5 closed; an inner filling solution 3 is located inside the container 2. An inner electrode 4 is immersed in the inner filling solution 3. A lead wire is denoted by 6.

In operation, this lead wire 6 is connected to an amplifier. When measuring a sample, the anion-selective electrode 10 is related to the sample immersed with a reference electrode connected to the amplifier. A The electrical signal from the amplifier is sent to an evaluation circuit (computing circuit) and after the necessary operations, the ion concentration displayed on a display device.

A membrane 1 is arranged at the lower end of the container 2; the Membrane 1 comprises a relatively thick inner layer 11 and a thin outer layer 12; the inner layer 11 is in contact with the inner filling solution 3. In the When measuring a sample, the electrode according to FIG. 1 becomes the lower end section immersing the electrode in the sample solution to be tested; this is where the outer layer stands 12 in direct contact with the sample solution.

This embodiment is in the following with reference to an electrode for Measuring chloride ion concentrations in sample solutions of a living body explained by way of example.

The inner layer 11 consists of polyvinyl chloride in which a quaternary Dispersed ammonium salt with 1 to 4 alkyl chains each having 7 to 16 carbon atoms is, for example, methyltridodecylammonium chloride. A quaternary ammonium salt with ethyl groups instead of methyl groups can also be used. The training of the The inner layer of the end portion of the container 2 is made according to the following procedure achieved.

First is a mixture of 20-25% by weight methyltridodecylammonium chloride and 75 to 80 wt .- <10% polyvinyl chloride in tetrahydrofuran as solvent solved; the solution is in a container with a flat, level Poured soil and the solvent evaporates, leaving a sheet-like measuring membrane is formed. A piece of a size corresponding to the size of the electrode on which the membrane is to be attached is cut out of the sheet-like membrane; the cut piece is placed with a container 2 made of the same material connected like the basic material of the membrane, using tetrahydrofuran.

Thereafter, an outer layer 12 is attached to the outside of the in this way formed inner layer 11 bound. Acetyl cellulose with 1 to 3 acetyl groups is preferred as the base material for the outer layer 12.

Acetyl cellulose is dissolved in tetrahydrofuran, making a solution is formed with an acetyl cellulose concentration of 2 to 3% by weight; the lower End section of the container 2 to which the inner layer or inner membrane 11 is attached has been, we & immersed in the solution thus formed. After that, the Container 2 is withdrawn from the solution and the tetrahydrofuran evaporates, creating a thin outer layer 12 is formed on the inner layer or inner membrane 11. the Outer layer 12 can also be made by using a solution of acetyl cellulose sprayed in tetrahydrofuran onto the inner layer 11 and the sprayed-on solution dries with evaporation of tetrahydrofuran. If the two layers according to are connected to one another according to the procedure specified, has the outer layer formed 12 a thickness of 10 to 50 µm.

In the membrane 1 formed in this way with a unit forming inner and outer layer leaves the outer layer 12 in an anoralized state with ions relatively small ionic radius in hydrati- / by, however, organic ions or Proteins with a large hydration radius are hardly allowed to pass through the outer layer 12. Accordingly, it can be considered that only inorganic ions selectively from the inner layer 11 can be detected.

The following is another embodiment of an anion-selective According to the electrode of the invention described.

To form the inner layer 11 of the membrane 1 according to FIG a mixture of 20 to 24 wt .-% methyltridodecylammonium chloride, 5 to \) GewO-jU Phenylalkyl alcohol and 60 to 79% by weight of polyvinyl chloride dissolved in tetrahydrofuran In this embodiment, the mixture with methyltridodecylammonium chloride, Polyvinyl chloride and phenylalkyl alcohol instead of a mixture of methyltridodecylammonium chloride and polyvinyl chloride of the first embodiment are used. The inner layer 11 and the outer layer 12 are formed by the solution thus prepared in the manner indicated above for the first embodiment used according to the invention a selectivity for inorganic ions is achieved that with that of the first embodiment 9 is the response speed of the present embodiment however, higher than that of the first embodiment.

In FIG. 2, results of the measurement of chloride ion concentrations are shown with a diagram in urine samples with an anion-selective electrode according to the invention in comparison with results of measurement of chloride ion concentrations in the same urine samples explained according to the coulometric method As can be seen from FIG the compliance with the coulometric method by applying the invention The values obtained by measuring with a single-layer membrane electrode are noticeably improved outside the scope of the present invention9 are much larger than that Values obtained by the coulometric method; the match is very bad Figure 2 shows the values of a measurement of 24 urine samples of each abscissa or ordinate value corresponds to the measured value of a measuring device.

Figure 3 illustrates the relationship between the measured value of the chloride ion concentration in a urine sample of a first measurement and the measurement value for the chloride ion concentration in the same Urine sample during a second measurement. So explained FIG. 3 shows the reproducibility of measurements of the chloride ion concentrations in Urine samples. From the results of Figure 3 it can easily be seen that even in the case of urine samples, a high level of analytical accuracy with good reproducibility according to the invention can be reached.

In Figure 4, the diagram explains the response speed Urine samples with an electrode according to the invention compared with the speed of response on urine samples with a common electrode. The final values (21 in Figure 4) of the measurement according to the coulometric method are shown in Figure 4 independently of the abscissa In FIG. 4, the ordinate value applies to the value displayed on a measuring device, where the abscissa indicates the response time from when the electrode in a urine sample was immersed values (22 in Figure 4) of measurements with a usual electrode are unstable even after 30 s and much larger than the values (21 in Figure 4 obtained by the coulometric method, on the other hand are values (23 in Figure 4) of measurements with an electrode according to the invention stable after about 11 seconds Figure 5 illustrates the relationship between the thickness of the acetyl cellulose layer and the reduction in measurement error9 observed when measuring on a Urine sample with a chloride ion concentration of 150 indole is carried out From the results of Figure 5 it can be easily seen that with a strength of Ace / cylcelluloseschicht- of more than 30 pm the influence of inhibiting components can be almost completely eliminated. However, the response speed becomes the thickness of the acetylcellulone layer decreases with increasing; if the strength was more than 100 µm, the response speed is reduced in such a way that that the electrode can practically no longer be used Practice thicknesses of the acrylic cellulose of 30 to 50 µm are not preferred figure 6 explains results of examinations 9 which were intended to establish9 whether the performance of electrodes according to the invention is impaired, when they are immersed in water and then dried. If a common single-layer membrane electrode is immersed in water and then dried, the membrane9 shrinks so that stable operation or reproducible measurements cannot be expected. However, the results of FIG. 6 can be used for an anion-selective electrode According to the invention infer 9 that the performance by immersion in water and subsequent drying is hardly affected. Figure 6 shows results, those with an electrode that is immersed in water for 15 days and natural Way was air dried for days when testing various urine specimens different concentrations were obtained using the same dried electrode was used. For comparison, the values of a measurement based on the coulometric Method shown in Figure 6. From the results of Figure 6 it can be seen that the electrode according to the invention even after immersion in water and drying can be used satisfactorily. Therefore, the operational problems with usual Electrodes, doh, the constant moisturizing of the electrodes, should be avoided9 if electrodes according to the invention are used; so the handleability according to the invention noticeably improved.

FIG. 7 explains the results of measurements of the chloride ion concentration in serum samples according to the invention in comparison with results of measurements of the Chloride ion concentrations in the same serum samples by the coulometric method. It cannot be inferred from the results in FIG. 7 that also in the case of serum samples the measurements according to the invention can be carried out with high accuracy.

The above embodiments were used to measure chloride ion concentrations described. However, the anion-selective electrodes according to the invention can generally used to measure concentrations of anions, e.g.

N03, Clo4, C103, SCN, I, Br and Cl From the description above of the invention it follows that with the anion-selective electrode according to the invention the influences of interfering components are remarkable even when measuring urine samples Way can be turned off. Thus, according to the present invention, a large one becomes more practical Advantage achieved.

In summary, the invention relates to anion-selective electrodes, in particular, among other things, a selective chloride ion electrode, with an ion-selective, For example, membrane made of polyvinyl chloride that responds to chloride ions and in which a quaternary Ammonium salt is dispersed, and an acetyl cellulose layer on one side the polyvinyl chloride membrane is formed. When this ion selective electrode is immersed in a urine sample, the acetyloilulose layer is in immediate Brought into contact with the urine sample.

The electrodes according to the invention allow, for example, a very accurate determination of the chloride ion concentration in urine samples without interference inhibiting components.

Claims (11)

Claims 1.% Anion-selective electrode with - a container, which contains an inner filling solution - an inner electrode which is inserted into the inner filling solution immersed, and - a measuring membrane made of a polymer resin, which on the end section of the container is arranged and is in contact with the inner filling solution, a substance that responds to anions is dispersed in the measuring membrane, g e k e k e n n -marked by a layer of one for inorganic ions permeable polymer resin that covers one side of the measuring membrane and with the sample can be brought into contact. 2. Anion-selective electrode according to claim 1, characterized by a quaternary ammonium salt as an anion-responsive substance. 3. Anion-selective electrode according to claim 1 or 2, characterized by a cellulose type polymer as the inorganic ion permeable polymer resin. 4. Anion-selective electrode according to claim 1 or 2, characterized by polycarbonate, polymethyl methacrylate and / or silicone rubber than for inorganic ones Ion permeable polymer resin. 5. Anion-selective electrode according to one of the preceding claims, characterized in that the polymer resin of the measuring membrane is a Pherlylalkylalkohc) l contains. 6. Anion-selective electrode according to one of the preceding claims, characterized in that the layer of the inorganic ions permeable Polymer resin is 30 to 50 µm thick. 7. Anion-selective electrode according to one of the preceding Expectations, characterized by a measuring membrane made of polyvinyl chloride in which a quaternary Ammonium salt is dispersed with alkyl groups and covered with a layer of acetyl cellulose coated as a polymer resin permeable to inorganic ions. 8. Anion-selective electrode according to claim 7, characterized by an acetyl cellulose layer obtained by drying a solution of acetyl cellulose is received on the measuring membrane. 9. Anion-selective electrode according to one of the preceding claims, characterized in that the container is made of polyvinyl chloride. 10. Anion-selective electrode according to claim 7, characterized in that that the acetyl cellulose contains 1 to 3 acetyl groups. 11. Use of the anion-selective electrode according to one of the claims 1 to 10 for the determination of anions in urine samples.