FI64012C - JONSELEKTIV ELEKTROD OCH FOERFARANDE FOER DESS FRAMSTAELLNING - Google Patents

Description

6401 2

ION-SELECTIVE ELECTRODE AND METHOD FOR ITS MANUFACTURE

ELECTRICAL EQUIPMENT FOR THE FRAMEWORK OF THE FRAMEWORK

The present invention relates to an ion-selective electrode comprising a conductor or semiconductor body and a membrane of polymeric material which, in the measurement at the electrode, separates the conductor or semiconductor body from the solution to be measured.

An ion-selective electrode is an analytical instrument used to determine the concentration of a particular ion in solution. The determination is based on the fact that the potential of the electrode is, within certain limits, directly proportional to the logarithm of the activity of the ion in question. The most important feature of an ion-selective electrode is selectivity, i.e. that the results obtained are as independent as possible from the other ions present.

Ion-selective electrodes are now known which comprise a liquid membrane consisting of a sparingly water-soluble organic liquid and a compound dissolved therein, a sensor which forms either a complex or an ion pair with the ion to be determined and thus increases the ion distribution coefficient between the organic phase and the aqueous phase. However, the disadvantage of these electrodes is that the gradual dissolution of the sensor and / or organic solvent in the aqueous phase limits the life of the electrode, and in addition a suitable organic compound must be found for each ion, which in the absence of an exact theory must be done experimentally.

Further known is an ion-selective electrode in which the membrane is formed from a polymeric material containing active functional groups instead of an organic liquid. For example, a calcium selective electrode is constructed of F, C4012 by grafting triallyl phosphate into a polystyrene-butadiene backbone and then bis hydrolyzing the phosphate ester groups to the acid form. These electrodes are mechanically durable and do not undergo dissolution which reduces the life of the electrode, but e.g. the selectivity of said calcium selective electrode with respect to sodium is insufficient for clinical purposes.

It is an object of the present invention to provide an ion-selective electrode comprising a membrane of polymeric material in which the above disadvantages are avoided and which has an even better selectivity. The electrode according to the invention is characterized in that the membrane is a polymeric material made of a polymerized, ion-containing substance or mixture of substances from which said ions have been removed after the polymerization step, so that openings corresponding to the removed ions have formed in the material.

The method of manufacturing the membrane belonging to the electrode according to the invention could be referred to as "template polymerization", in which case the "ion" to be determined must be removed from the membrane at the final stage, e.g. by extraction. The openings in the membrane corresponding to the removed ions are such that the ions to be determined in the electrode measurement fit them like a key to the lock. A particular advantage of the invention is thus that electrodes selective for different ions can be prepared by exchanging only the template ion contained in the polymerizable mixture during the preparation of the membrane.

The membrane of the ion-selective electrode of the invention is preferably a cross-linked polymeric material prepared by polymerizing a mixture of a bifunctional polymerizable compound and a salt containing 3 64012 ions to be determined. In preparing such a membrane, the degree of crosslinking can be easily adjusted by the duration of the polymerization reaction.

It is possible to construct the electrode according to the invention in such a way that the polymer membrane is located between the solution to be measured and the internal reference solution of the electrode. However, a more advantageous solution in terms of the mechanical properties of the electrode is that the membrane is on the surface of the conductor or semiconductor body as a layer of material covering the body, in which case no internal reference solution is required. Such an insoluble electrode is suitable, for example, for automatic analyzers. Although the shadow side of the insoluble electrodes has been the indeterminate interface potential of the metallic conductor and the membrane, which has caused instability, this can be reduced by replacing the metal with an n-type oxide semiconductor, tin oxide. In addition, the stability of the insoluble electrode can be improved by copolymerizing redox centers in the membrane. These can be achieved, for example, by adding vinyl ferrocene to the polymerizable mixture during membrane formation.

The invention further relates to a method for manufacturing the ion-selective electrode described above. According to the method, a membrane of polymeric material is formed, which is connected to a conductor or semiconductor body so that, in the case of electrode measurement, the membrane separates the conductor or semiconductor body from the solution to be measured. The method is characterized in that the membrane is formed of a polymeric material made of a polymerizable substance or mixture containing the ion to be determined and from which said ions are removed after the polymerization step so that openings corresponding to the leaving ions are formed in the material.

4 6401 2

A preferred embodiment of the method according to the invention is characterized in that the polymeric material is prepared by polymerizing a mixture of a polyfunctional polymerizable compound 11a and a salt containing a ion to be determined which reacts with it. The polymerization can be effected by means of heat, and the degree of crosslinking of the polymer can then be adjusted by adjusting the heating time.

Another preferred embodiment of the method according to the invention is characterized in that the polymerizable substance or mixture of substances is applied to the surface of a conductor or semiconductor body where it is polymerized. as a membrane-forming polymer layer covering the body. In this way, a mechanically strong, internally insoluble electrode suitable for automatic analyzers is provided.

In order to illustrate the invention, the preparation of a calcium-selective electrode according to the invention and the measurements performed on the electrode are described below by way of example. In connection with the description, reference is made to the accompanying drawing, which graphically shows the potential of the electrode as a function of calcium concentration.

Preparation of starting materials for membrane polymerization

Allyl-ilsi8Hb-substituted

A solution of 50 g of allyl glycidyl ether (Aldrich, 99.5%) and boron trifluoride diethyl etherate (BDH, distilled under reduced pressure over calcium hydride) dissolved in 3 g of 100 ml of hexane was refluxed for 3 h. The hexane was evaporated off, the product was dissolved in ether. . Evaporation of the ether gave 40 g of a viscous, pale yellow product. The formula for the product is 5 64012 CH0 = CHCH0

0, I

CH- I 1 f-CH-CH2O-Jn

Kal Si ^ ^ ^ p ^ UMB iall.y ^ .li.'PHsfaatti

Phosphoric acid diallyl ester (4 g) was dissolved in 50 ml of water and excess calcium carbonate was added. After completion of the reaction, it was filtered and the filtrate was evaporated to dryness on a rotary evaporator. The product was crystallized twice from ethanol-water. Yield 2.3 g of needle-like crystals. The product formula is

[(CH2 »CHCH2O) 2PG2] 2Ca II

Electrode fabrication Ele ktrodi ^ _poh2amateriaal_i

The electrode was based on glass made electrically conductive on one side with a thin layer of tin dioxide (Libbey-Owens-Ford Company, Glass Division, Ohio, U.S.A.). The size of the glass plate was about 20x50 mm. Tin dioxide was removed from three edges a few mm wide using photolithography and electrolytic etching. Electrical contact was made by mechanical compression from the non-corrosive edge.

The membrane can i_n_v £ lmi_stu_s

To 100 ml of an ethanol-methanol mixture (15: 1) was dissolved 2.0 g of telomer (Compound I) and 60 mg of calcium bisdiallyl phosphate (Compound II). The base plate of the electrode was coated with a spin coating technique so that 1 ml of the above solution was added to the surface of the rotating plate three times and the plate was occasionally dried in an oven. Finally, the plate was kept for 60 h in an oven at 100 ° C.

2ajsa a £ ^ £ p noti

The electrode was equilibrated by keeping it for 3 days in a solution of -3 M relative to 10 M calcium chloride. In this connection, Ca ions were removed from the polymer material of the electrode, so that openings corresponding to the removed ions were formed in the material.

Measurements L data

Measurements were performed in a thermostated (25.0 ° C) 50 ml measuring cell (Metrohm). The reference electrode was a silver-silver chloride electrode connected to the cell via a 0.1 M NaCl salt bridge. The potential was measured using a preamplifier (AD515L, Analog Devices) with an input resistance> 10 -O connected to a 4 1/2 digit digital voltmeter.

M i_t background input kset

The response of the electrode to calcium ion and selectivity to sodium ion were determined by measuring the cell potential as a function of calcium ion concentration in pure water and G, 1 M aqueous sodium chloride solution. The following table shows the results of a series of measurements as an example.

Cell potential (mV) c [Ml

Ca in water in 0.1 M NaCl solution 10'6 57.2 103.0 10'5 70.1 107.1 10 "4 94.8 114.5 10" 3 123.0 130.1 10 ~ 2 150.3 157 , 5 10 “1,176.5 195.6 7 64012

The accompanying drawing shows the cell potentials as a function of the logarithm of the calcium ion concentration. From the curve measured in pure water, the amount of calcium electrode can be estimated.

“6 3 the rolling limit with this electrode is about 10 mol / dm. From the curve measured in sodium chloride 1 solution, the selectivity factor is 2 to 10. The selectivity of the electrode is thus sufficient e.g. clinical analyzes.

It will be clear to a person skilled in the art that the various embodiments of the invention are not limited to the example given above but may vary within the scope of the appended claims. Thus, in addition to the calcium-selective electrode, it is also possible to prepare electrodes selective for other ions, such as, for example, Mg, K, Na, etc. This is done simply by using the desired ion instead of calcium as a "template" in the membrane preparation. In addition, in addition to the polymerizable compounds shown, other polymerizable compounds can be used in the preparation of the membrane, in which case it is essential that the polymer formed is sufficiently polar and mechanically strong enough. In addition to heating, other methods, such as plasma polymerization or UV polymerization, can then be used in the polymerization. It is also not necessary for the electrode to be insoluble, but a conventional electrode structure with an internal reference solution between the membrane and the conductive metal body may also be considered.

Claims (7)

1. Ion selective electrode, consisting of a conductor or semiconductor piece · and of a membrane of polymeric material, which, when measured with the electrode, separates the conductor or semiconductor piece from the solution provided for the measurement, characterized in that the membrane consists of a polymeric material made of a polymerizable substance or mixture containing the ion to be determined, from which said ions are removed after the polymerization phase, so that heels have formed in the material corresponding to the removed ions. 2. An electrode according to claim 1, characterized in that the membrane consists of a cross-linked polymeric material made by polymerizing a mixture consisting of a polyfunctional polymerizable compound and one with the reacting site containing the ion to be determined. 3. Potassium selective electrode according to claim 2, characterized in that the membrane consists of a polymeric material made by polymerization of a mixture consisting of allylocis-substituted propylene glycol telomeres and calcium bisdiallyl phosphate. 4. An electrode according to any one of claims 1-3 · characterized in that the membrane consists of a polymeric layer covering the conductor or semiconductor piece. 5. An electrode according to claim * J, characterized in that the electrode comprises a semiconducting peneoxide piece and a covering polymeric layer, in which are polymerized redox centers. A method of producing an ion-selective electrode according to any of claims 1-5, wherein