HU219329B - Ph-electrode based on glass material - Google Patents

Abstract

The object of the invention is to determine the pH value of pH electrode solutions, which contain 0.05-2 mol% platinum and/or palladium silicate, also lanthanide silicate, optionally barium silicate, and 0.04-0.8 mol% nickel - or lithium glass sensor element (2) containing cobalt silicate, the hollow electrode body (1) carrying the sensor element (2), and the electrolyte solution (3) placed in the cavity, and the reference electrode (4) located in the latter. ŕ

Description

FIELD OF THE INVENTION The present invention relates to a pH electrode with platinum and / or palladium silicate as well as lanthanide silicate, optionally barium silicate and synergistic additive lithium glass sensor, which is capable of rapid determination of pH by a single calibration over a long period (several months). wide pH range. The pH electrode is particularly useful for controlling industrial processes.

Nowadays, glass-based pH electrodes are widely used not only in analytical chemistry but also in industry and the environment.

The glass-based pH electrode is essentially a tube of glass (the so-called electrode body) with one end usually closed by a spherical glass sensor. Inside the electrode body is an internal reference solution and an internal reference electrode is immersed therein. The latter is connected to a potential outlet at the other end of the electrode body. The pH electrode is often integrated with an external reference electrode, thereby obtaining a so-called combination pH electrode that is convenient to use.

There are several descriptions of a pH electrode formed with a glass-based sensor element. The first of these is the Hungarian Patent Application No. 172,894 and US Patent No. 4,297,193. The Hungarian patent discloses a mixed alkali oxide, titanium, neodymium and tantalum oxide sensing element, the US patent discloses lithium, cerium and rubidium oxide, and lanthanum, praseodymium, neodymium and uranium oxide. contains a sensor element. Both pH electrodes described herein exhibit near-theoretical behavior over a wide pH range, but lose their selectivity in solutions containing more than 0.1 mol / dm ^{3 of} alkali ion.

The Hungarian patent application No. 52,466 differs from the Hungarian patent specification No. 172,894 in that the sensor element contains only lithium oxide and lanthanum oxide instead of titanium oxide. The properties of the pH electrode of this invention are the same as those described above for the two patents described above.

Also mentioned in the literature are the German Patent No. 3 607522, which has a pH electrode with a sensing element containing sodium and magnesium oxide and lanthanum oxide, and CA 105: 23368j - lithium oxide and titanium. containing barium, lanthanum, cerium, alumina - and CA 111: 12607e - which also contains lithium oxide and lanthanum fluoride, barium, uranium oxide and aluminum, cerium describes a pH electrode with a sensor element containing lanthanum and lead oxide. Electrodes exhibit noble (i.e., theoretical) behavior over a wide pH range, but lose their selectivity in solutions with a pH greater than 12.

The detector element of the pH electrode according to Hungarian Patent Application No. 204,927 is a lithium silicate glass containing praseodymium and optionally barium and / or zirconium and / or lead oxide and also containing bismuth oxide. These pH electrodes are distinguished by their low internal resistance.

All known alkaline-silicate-based glass electrodes with glass sensing elements have the disadvantage that their basal potential (potential measured with a symmetric cell) and its sensitivity change significantly over time (e.g., the change in _the basal potential E at ± 23 ° C). 5 mV / 50 days, the sensitivity change at 23 ° C is 58.76 mV ± 1.2 mV / pH / 50 days) and should therefore usually be calibrated with one standard solution per hour, two standard solutions every 2-3 hours, usually with buffer. More accurate measurements require more frequent calibrations.

An indirect disadvantage of the known glass-based pH electrodes is that the expensive platinum crucible used for melting the sensor element is highly soluble in the glass and, after fifty to seventy digestions, the platinum crucible is thinned and sometimes pierced. The puncture jar cannot be repaired, but requires re-metallurgical production.

During the experimental work it was proved that the weak potential of the pH electrodes in the crosslinked structure of the glass sensor element after the glass processing is due to the weak connections in the sensor element. the outer surface of the sensor element is in direct contact with the flame, while the inner surface is not). Due to the uneven distribution of weak bonds, the thickness of the hollow surface layer permeable to hydrogen ions does not vary uniformly after hydration in the inner and outer surface layers of the sensor element. The different degrees of swelling correspond to different surface ion activity and Galvani potential values.

It is an object of the present invention to provide a glass-based pH electrode with a negligible change in the basal potential and sensitivity over time.

The pH electrode of the present invention is based on the discovery that if the composition of a known lanthanide sensing element having a known advantageous electrode property and optionally containing barium silicate is selected to include platinum and / or palladium silicate, a glass is obtained from which the structure of the sensing element contains only negligible amount of weak bonds, its direct structure practically remains unchanged under the influence of heat, and therefore its basic potential and sensitivity are practically unchanged during the measurements. The pH sensing element of the pH electrode of the present invention also has the surprising novelty that, being "saturated" with the relatively inexpensive platinum and / or palladium compound, the platinum crucible used during digestion is less damaging, thus increasing the life of the sensing element. it is cheaper to produce.

We chose the trivalent and tetravalent platinum and palladium because our preliminary experiments proved that the lithium glass is made of SiO ₄ tetrahedrons

EN 219 329 Β chemical resistance and thermal stability without altering the original advantageous properties of the known sensor element.

It has also been demonstrated in the experimental work that the described advantageous properties of platinum and / or palladium silicate glasses can be enhanced if the glass also contains a so-called synergizing additive of nickel and / or cobalt silicate.

In one embodiment of the pH electrode according to the invention, the glass sensing element is a lithium glass containing lanthanide, optionally barium silicate, containing 0.05 to 2 mol% of platinum and / or palladium silicate.

In another embodiment of the pH electrode of the present invention, the glass sensing element further comprises 0.04-0.8 mol% of a nickel or cobalt silicate synergizing additive.

Any of the above-described pH electrodes may also be implemented with an external reference electrode.

The main advantages of the pH electrode according to the invention are as follows:

(a) Very small change in baseline potential (value of E _a change at 23 ° C ± 2.6 mV / 100 days).

b) Only sensitivity changes within the limits of experimental errors (value measured at 23 ° C is 58.76 mV ± 0.8 mV / pH / 100 days).

(c) Insignificant damage to platinum digestion vessel during manufacture (one jar also capable of 200-250 melting).

A simple and combined version of the pH electrode of the present invention is illustrated in detail in Examples 1 and 2, and Figures 1 and 2 illustrate schematically the structure of the electrodes.

Example 1

In Figure 1, a sensor element 2 is attached to the glass electrode body 1 and has the following initial composition in mode:

67.5 SiO ₂ , 24 Li ₂ O, 4 BaO, 0.3 Er ₂ O ₃ , 4 La ₂ O ₃ and 0.2 PtO ₂ or 0.2 PdO ₂ .

The sensor element ² contacts a solution of potassium chloride saturated with silver chloride at a molar / dm ^{2 3} concentration and a pH 7.0 electrolyte solution into which a silver reference silver electrode 4 is immersed.

Example 2

In Figure 2, the sensor element is attached to the glass electrode body 1 and has the following initial composition in mole%:

67.5 SiO ₂ , 24 Li ₂ O, 4 BaO, 0.3 Er ₂ O ₃ , 4 La ₂ O ₃ , 0.1 CoO and 0.1 PtO ₂ or 0.1 PdO ₂ .

The sensor element 2 contacts a 3 mol / dm ³ potassium chloride solution saturated with silver chloride, a pH 7 phosphate buffer solution 3 into which a silver / silver chloride 4 internal reference electrode is immersed. The electrode body 1 of the pH electrode is coaxially integrated with the tubular glass body 6 of the outer reference electrode 5 of silver / silver chloride. Inside the glass body 6 is an external reference solution of potassium chloride (3 mol / dm ³ ). In the glass body 6, an ion conductor 8 is attached to the ceramic filter.

The sensing element for the pH electrodes shown in the examples is made by melting in a platinum crucible, and the electrode is made in a manner known per art. The pH electrodes of the Examples also determine the pH after calibration with buffer solutions of a given pH in a known manner.

The change in baseline potential and sensitivity of the pH electrodes shown in Examples 1 and 2 was determined over a long period (100 days). These were as follows:

Baseline change at 23 ° C: ± 1.7 mV / 100 days. Sensitivity change at 23 ° C: 58.76 ± 0.5 mV / pH / 100 days.

As can be seen, our measurements have shown that the basal and sensitivity changes of the pH electrodes of the present invention are significantly improved compared to known pH electrodes, and the properties of the electrodes tested are about four times better than those known.

Thus, the primary advantage of the electrodes of the invention is that it is sufficient to calibrate them every 100-120 days at a pH accuracy of ± 0.03.

Claims (2)

PATENT CLAIMS 1. To determine the pH of a glass-based pH electrode solution consisting of a hollow electrode body containing a lanthanide silicate, optionally a lithium glass sensor element containing barium silicate, and an electrolyte solution housed in the cavity, characterized in that the sensor element ( 2) 0.05 to 2 mol% of platinum and / or palladium silicate. The pH electrode according to claim 1, characterized in that the sensing element (2) contains 0.04-0.8 mol% of a nickel or cobalt silicate additive.