Reference electrode for ion activity measurement, especially for ph measurement

The invention relates to a reference electrode for a measuring chain for measuring the ionic activity, such as the pH, according to the preamble of claim 1.

For electrochemical potential measurements such as the pH measurement, a measuring electrode which is responsive to the ions to be measured and a reference electrode is provided. Both electrodes are immersed in the medium to be measured. By a measuring device (mV meter, pH meter), the potential difference between the two electrodes is measured. The display unit is a measure of the ion concentration. In the hydrogen ion activity measurement (pH measurement), in which a measuring electrode is used which responds to hydrogen ions, which means that the potential dependent with respect to the reference electrode of the hydrogen ion concentration, the potential of the reference electrode but is independent constant, typically a pH -Wertmessgerät used. The pH meter is an mV meter, which is calibrated in pH values. The object of the reference electrode is to be independent of the state and the nature of the medium to be measured in an ion-conducting contact on the medium to be measured to the measuring electrode and to have an independent on the ion concentration constant self-potential. Such a reference electrode, for example, is known from DE-OS 30 36 354th In this known reference electrode a downwardly open chamber is provided with a coating of glass. The lower open end is closed by a porous plug, which ensured an ion-conducting contact on the medium to be measured to the measuring electrode, the chamber is filled with a saturated aqueous solution of potassium chloride and silver chloride. Inside the chamber, surrounded by the chloride solution, there is a galvanically chlorinated silver wire or silver plate, of or connected with a cable to the encoder.

Such an arrangement is not only expensive to manufacture, but also has the following disadvantages: The porous plug (diaphragm) leaking potassium chloride and silver chloride chemical reactions with the medium to be measured may occur that clog the diaphragm and can interrupt the ion-conducting contact.

This known arrangement is pressure resistant to diffusion of the medium to be measured to avoid only by an expensive pressure equalization valve inside the electrode through which the operational reliability may be affected.

The Elektolytvorrat inside the chamber is reduced due to the flow during the measurement process through the diaphragm. Topping up is essential.

This known arrangement has only limited temperature resistance.

In a further known from DE-A 32 28 647 the known reference electrode, a glass tube is provided as a reference element is provided whose one end is closed with a stopper, and that is filled with an electrolyte, in which a wire extends. The glass tube of the reference element is surrounded by a porous material consisting of a sheath, in whose pores a liquid solution is. The cladding is surrounded by a tube having a plurality of openings through which the contact between the test medium and the liquid solution in the pores of the envelope, and from this is made to the electrolyte of the reference element. This reference electrode is only limited temperature resistance. It can be with her not prevent that the said openings in the outer tube are gradually added under certain circumstances due to contamination, so that the operability of the electrode is severely limited. Purification of the openings in the supporting tube with considerable difficulties.

It is therefore an object of the invention to provide a reference electrode, which is simple in construction, has a higher reliability and a larger contact area with the test medium than in known electrodes.

The solution of the problem is inventively characterized in that the polymer of the material of the envelope of Polyvinylesther, polypropylene, polyvinylchloride or epoxy resin is with an addition of crystalline potassium chloride or another electrically conductive additive and the entire surface of Umhullung is freely accessible. The polymer is mixed prior to the curing process or the polymerization using the conductive additive.

An electrode with the electrode of the invention comprises a further, known per se, measuring electrode, as this example is known from DE-AS 23 56 719th Between the reference electrode and the measuring electrode a measuring device (mV meter, pH meter) is connected with high input resistance. The scale of the meter is calibrated in mV or pH.

An electrode with the electrode of the invention has a more well-known in itself, separate measuring electrode. This electrode can be designed as single-rod or as a two-rod measuring chain. The reference electrode and the measuring electrode are (, pH meter mV meter) connected to a measuring device, the scale of which is calibrated in mV or pH values.

The reference electrode of the invention is generally suitable for ion activity measurement. It is suitable as described for the measurement of the hydrogen ion activity (pH), as well as for any other anions such cations using for suitable measuring electrodes, which are not to be described in more detail here. In addition, there is the choice of the conductive additive in the polymer is important because a washout by the medium to be measured of the conductive additive in the form of salts can not be avoided, whereby the measurement can be influenced itself. It is therefore recommended as a conductive additive for the measurement of, for example chlorine, bromine, iodine, silver, mercury, potassium cyanate and a conductive additive potassium nitrate or sodium nitrate.

It show the<dl id="dl0001"><dt>Fig. 1</dt><dd>A reference electrode according to the invention in a longitudinal section;</dd><dt>FIG. 2</dt><dd>a Double electrode for the pH measurement to the reference electrode of the invention,</dd><dt>Fig. 3</dt><dd>a combination electrode for pH measurement with the reference electrode of the invention,</dd></dl> The proportions of the individual components in the drawings do not correspond to real conditions in order to allow a good visibility.

In the drawings, the reference electrode 2, a glass tube 22 with the same, with 21, which consists of conductive plastic jacket surrounding the glass tube concentrically, respectively. The glass tube 22 is closed at its lower end by an existing porous ceramic plug 25th In the glass tube 22, an electrolyte 24 is contained, as well as a supply of powdered silver chloride 26, to ensure saturation of the consisting of potassium chloride and silver chloride aqueous electrolyte 24th In these electrolyte of the galvanically chlorinated silver wire immersed 23 and establishes the electrical contact with the connection cable third

When Double electrode shown in Fig. 2 except the reference electrode 2 a measuring electrode 1 is provided, both of which are immersed in the process medium. 7 The measuring electrode 1 has a glass tube 10, the lower spherical member 13 consists of electrically conductive glass, and responsive to the measured hydrogen ion. The glass tube 10 is filled with an electrolyte, in which a galvanically chlorinated silver wire 11 is located which is like the galvanically chlorinated silver wire 23 is connected via connection cable 3 to the measuring device 5, the scale is calibrated in mV / pH.

In the illustrated in Fig. 3 electrode with a reference electrode 2 according to the invention is in turn with 10, the glass tube of the measuring electrode, referred to be spherical member made of electrically conductive glass, with 11 of the galvanically chlorinated silver wire 13, which is immersed in the electrolyte is filled in the glass tube 10 and is connected to the connecting cable 3 to the measuring device. The glass tube 10 is surrounded by an existing conductive plastic sheath 21st Within the jacket 21, the glass tube 22 is disposed. The chlorinated silver wire 23 is also connected via connection cable 3 to the measuring device.