SU1124214A1 - Composition of ion-selective electrode membrane for determination of magnesium ions - Google Patents

Abstract

COMPOSITION OF MEMBRANE OF IONOSELECTIVE ELECTRODE FOR DETERMINING THE ACTIVITY OF MAGNESIUM IONS, Injecting a membrane-active substance and solvent, characterized in that, in order to increase the selectivity, the complex, magnesium compound with phenanthroline, modified tetraphylenylphenyl, is modified borate, a as a solvent ortonitrophenyl lactyl ester in the following ratio, wt.%: Magnesium complex compound with phenanthroline modified with tetraphenyl borate, 0 Ortonitrophenyl lactyl ether Rest

Description

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Financial instrument

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The invention relates to methods of physico-chemical analysis, and more precisely to ion-selective membrane electrodes, and can be used for potentiometric measurements of the activity of magnesium ions in aqueous solutions in order to control the composition of liquid media in various areas of national economy, as well as in biomedical research x

The composition of the membrane of the ion-selective electrode for determining the hardness of water is known, with which it is possible to determine the total

.2 concentration concentration of Ca and Mg2CH11 ions.

The disadvantage of this electrode is the lack of a selectivity of the membrane for the magnesium ion; therefore, it can be determined only in the absence of Ca in the solution.

Closest to the proposed membrane ion-selective electrode composition for determining the activity of magnesium ions, including a membrane active substance and a solvent. Lime magnesium selective electrode is used to measure the intracellular activity of magnesium ions. The liquid membrane of this electrode is a solution of a 20% neutral ligand of 1% sodium tetraphenylborate in 2j propylene carbonate.

The electrode is characterized by the following selectivity to the magnesium cation in the presence of a number of foreign ions:

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This electrode is not selective for the magnesium cation in the presence of even comparable quantities of calcium. Moreover, it cannot be used to control the activity of magnesium ions in solutions containing a significant excess of calcium ions as compared with magnesium. In addition, the electrode does not have selectivity in the presence of lithium ions and hydrogen. The purpose of the invention is to increase the selectivity of determining the activity of magnesium ions.

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This goal is achieved by the fact that the composition of the membrane of the ion-selective electrode to determine the activity of magnesium ions, including the membrane-active substance and solvent, used the complex compound of magnesium with phenanthroline as the membrane-active substance. modified 10 tetraphenylborate, and as a solvent - ortonitrophenylamine ether in the following ratio, wt.%:

Magnesium complex compound J5 with phenanthroline, modified by tetraphenylborate 0.5-1.0 Ortonitrophenyl lactyl ester Remaining 20 FIG. Figure 1 shows the calibration curve of the magnesium selective electrode based on the pre / halogen composition of the membrane in standard solutions of magnesium chloride i in FIG. 2 25 the same 5 with a constant background of 0.1 M

NaCIj in FIG. 3 - the same, with a constant background of 0.01 M CaC.

The membrane is a solution of the complex in a solvent; at jQ, the decrease in the content of the complex below 0.5% leads to a decrease in the selectivity in the presence of extraneous ions. An increase in the content of the complex above 1% is not advisable, since the solvent is already saturated with this amount of the complex, and an increase in the precipitate amount does not affect the electrode properties.

Example 1. The complex compound was synthesized for the first time. It is prepared as follows: phenanthroline, sodium tetraphenylborate and magnesium chloride are taken in amounts corresponding to the stoichiometric composition of the complex (Mg (Ph) j (TBF)) per 1 mmol of the complex (0.594 g of phenanthroline, 0.684 g of sodium tetraphenylborate and 0.095 g of chloride magnesium). Weights were dissolved in a petri dish in 40 ml of ethanol and stirred on a magnetic stirrer. The alcohol is then evaporated. The slightly yellowish precipitate is transferred to a beaker, and 500 ml of distilled water is poured. stirred on a magnetic stirrer. The remaining precipitate is filtered and dried in a drying oven at. As a solvent for the complex, Pd 1 ortho-phenyloctyl ether was used. The liquid ion exchanger for the magnesium selective electrode is prepared by dissolving the complex compound in ortonitrophenyloctyl ether at the rate of 6 mg per 1 g. Electrode design - fluoroplastic tube hermetically closed EMF of this element E% f Е Е - standard EMF, V - 2,303 RT / F at t 25С, “1 ,, is the activity of the magnesium ion. In practice, the determination of the activity (concentration) of a magnesium ion is carried out using a calibration curve constructed from the emf values of the element in standard solutions. In the interval of concentrations 1–10–10 m MgClj, the graphical dependence of E on € ga M has an angular coefficient (cC 28 mV), which is close to the theoretical (29 mV). The proposed electrode, in contrast to the proto type, has a significantly greater selectivity for magnesium cations in the presence of calcium, sodium, and lithium ions: Li Na-K. NHt Ca -2.4 -1.0-0.5-2.5 Ba Sr2 one

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, 1 4 4 at the end with a plastic film using a special fluoroplastic washer. A 5–7 mm thick layer of liquid ion exchanger is poured inside the tube and a layer of a solution of 0.1 ha is applied on top of it. MgCl2, in which the chlorine-retarded current lead electrode is immersed. The study of electrodes was carried out in the following galvanic cell: The magnesium function of the electrode is maintained in the range of pH 6-8. Example 2. 5 mg of the complex compound are taken and dissolved in 1 g of orthonitrophenyloctyl ether, which is 0.5 and 99.5%. accordingly. Based on the obtained liquid ion exchanger, an electrode is made by construction similar to Example 1. Electrode characteristics are similar to those shown in Example 1. Example 3. Take 10 mg of the complex compound and dissolve in 1 g of orthonitrophenyloctyl ether, which is 1.0 and 99.0%, respectively . Based on the obtained liquid ion exchanger, an electrode was made (as in example 1). Electrode characteristics are similar to those in example t. From the obtained results it can be seen that an increase in the selectivity of the electrode is achieved in the presence of an excess of calcium ions. The selectivity constant makes it possible to determine the activity of magnesium in solution: containing even 10% excess calcium ions. In addition, the constant for Na is increased by more than an order of magnitude, by almost two orders for Ba, Li.

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Claims (1)

COMPOSITION OF AN ION-SELECTIVE ELECTRODE MEMBRANE FOR DETERMINING THE ACTIVITY OF MAGNESIUM IONS, including a membrane-active substance and a solvent, characterized in that, in order to increase selectivity, a complex membrane-like substance is used. a magnesium compound with phenanthroline / modified tetraphenyl-, borate, and, as a solvent, orthonitrophenylactyl ether in the following ratio of components, wt.%: The complex compound of magnesium with phenanthroline modified with tetraphenylborate 0; 5-1.0 Ortonitrophenylactyl ether Else Ί W 1 11