IONOMETRIC DETERMINATION OF MAGNESIUM IONS IN NATURAL OBJECTS

ABSTRACT

In this article, membrane selection for liquid membrane magnesium ion selective electrode, its preparation for analysis, material selection for the electrode body, provision of internal standard and background electrolyte of the electrode, and groundwater and surface water, agriculture using the developed magnesium ion selective electrode are discussed. Ionometric results for determining the concentration of magnesium ions in the soil used in the field and some of the cultivated products were obtained, and the results of comparison with the analysis indicators obtained by other methods were presented.

АННОТАЦИЯ

В данной статье рассмотрен выбор мембраны жидкого мембранного магниево-селективного электрода, ее подготовка к анализу, выбор материала корпуса электрода, обеспечение внутренним стандартом и фоновым электролитом электрода, а также грунтовые и поверхностные воды, сельское хозяйство с использованием разработанного магниево-селективного электрода. электрод обсуждается. Получены ионометрические результаты определения концентрации ионов магния в почве, используемой в поле, и некоторых возделываемых продуктах, а также представлены результаты сравнения с показателями анализа, полученными другими методами.

Keywords: magnesium, ion selective electrode, selectivity, ionometry, membrane, electrolyte, synthesis, X-ray spectroscopy, water.

Ключевые слова: магний, ион селективный электрод, селективность, ионометрия, мембрана, электролит, синтез, рентгеновская спектроскопия, вода.

Currently, protection of the environment, rational use of natural resources, preservation of human health by ensuring environmental safety is the most important urgent problem in our country. The main of such problems are the rational use of underground and surface water and ensuring their purity, maintaining the composition and productivity of the soil used in agriculture, maintaining the composition and productivity of the soil cultivated in it, ensuring that all types of products grown in it meet the quality and standards. consists of riding. The constitution of our country states that "Citizens are obliged to treat the natural environment with care", land, underground resources, water, flora and fauna and other natural resources are national wealth, they must be used wisely and are under the protection of the state.

The role of continuous analytical control in solving the mentioned problems and tasks is incomparable. The main goal and task of analysts is to automate analysis methods, to increase the possibilities of using the measurement tools created on their basis in field conditions, and to increase the sensitivity, selectivity and accuracy of analysis methods.

In this regard, one of the methods that can meet the requirements of the electrochemical analysis methods is the ionometric analysis method of potentiometry. The article focuses on the development of an ion selective electrode for ionometry, including a magnesium selective electrode.

Literature review

Some notable works on the creation of sensors for magnetic selective electrodes have been published only in recent years. One of the first such works, in the work labeled ETH 1117, it was possible to determine the micromolar concentration of magnesium ions in the presence of other monovalent and divalent cations. According to reports, the ones created after the developed macroelectrodes, labeled as ETH 5506 and ETH 5504, can detect magnesium ions by ionometric methods even in the presence of millimolar concentration solutions of calcium ions.

The composition of ion-selective electrode membrane for determining the activity of magnesium ions is published. The discovery is related to ionometry, and various solutions containing magnesium are used in the analysis. The purpose of the work is the selective determination of magnesium ions in the presence of singly and doubly charged cations. Diphenylphenanthroline and tetraphenylborate anion of magnesium complex compound are used as an electroactive component of the membrane. In addition, polyvinyl chloride and o-nitrophenyloctyl ether were used in the membrane. The detection range of magnesium is 3·10-6 M. A ten-fold excess of calcium, barium and strontium ions and a hundred-fold excess of Na+ and Li+ ions do not interfere with the determination of magnesium ions. The thickness of the membrane film is 1 mm. The selectivity of liquid membrane electrodes is determined by the formation of a complex between the electrolyte solution and the membrane. Therefore, the main requirement for the membrane is that it should be able to pass only the same ions through it. But it always passes some destructive ions. The conductivity specific to the main ion is estimated by the selectivity coefficient of the electrode. The potential of the ion selective electrode is measured against the reference electrode.

It is known that the equipment used in ionometry does not have any effect on the object of analysis. Currently, the selectivity of liquid membrane electrodes is sufficient for most ions. The stability of the membrane is also related to the high viscosity of the organic liquid used in its development and increases accordingly. The low dielectric constant of liquid organic matter allows the association of ions in the membrane phase. The modern design of such electrodes is made on the basis of plasticized membranes. To prepare them, the electrode active substance is mixed with a volatile organic solvent, polyvinyl chloride and plasticizer in certain proportions, a disc of the required diameter is cut from the resulting film and glued to a Teflon case [1-6].

According to information from scientific sources, cocoa powder contains 5.2 g/kg, walnuts 1.6-1.8 g/kg, cabbage 1-1.2 g/kg, dried figs 0.06 -0.075 g/kg, while dried apricots contain magnesium ions in amounts of 0.04-0.055 g/kg and so on. Therefore, we used the analytical capabilities of the inometric method based on the use of a new type of magnesium selective electrode as an indicator electrode in the determination of magnesium ions in analytical samples of underground drinking water and soil samples from which some agricultural products are grown [7-8].

Analysis  аnd  results

The membrane of liquid membrane ion-selective electrodes should have minimum resistance. After pouring a 0.1 N standard solution of MgCl2 into the tube of the Mg selective electrode, one of the Pt or Ag/AgCl electrodes is lowered. Magnesium phosphomolybdate, polyvinyl chloride, dioctyl phthalate plasticizer and electrode active compounds were dissolved in tetrahydrofuran. The magnesium selective membrane electrode consists of a Teflon body in the form of a cylinder, and the plasticized selective membrane is attached to the end of it in a polyvinyl chloride tube with a glue made from a mixture of 0.5 g of dibutyl phthalate, 5 ml of cyclohexanone, and 0.25 g of polyvinyl chloride. A 0.1 N KCl solution is also added as a background electrolyte to the 0.1 N standard solution of MgCl2 inside the magnesium selective electrode. The prepared magnesium selective electrode is stored in a 1·10–3 m MgCl2 solution before and after analysis.

The obtained results and their discussion

The signal (E, mV) of the magnesium selective electrode depends on the concentration of magnesium ions in the solution. Table 1 and Fig. 1 show the range of performance of the magnesium selective electrode.

Table 1.

Magnesium in solution of magnesium selective electrode potential depending on the concentration of ions

Figure 1. Electrode function performance interval

(Dependence of the signal of the ion-selective electrode developed on the basis of phosphorus molybdate on the detectable ion concentration in the solution)

From the results of determining the performance interval of the electrode function (Fig. 1), we see that the developed electrodes have the ability to detect magnesium ions in the range of 10-4-10-6 mol/l, depending on the ionophore content. It was observed that the highest detection range corresponds to ion selective electrodes developed on the basis of Mg+2 phosphonomolybdate acid.

Using the developed magnesium selective electrode, the concentration of magnesium ions in five districts of Samarkand region, which are considered the most important natural objects, and two underground waters recommended as mineral drinking water, using ionometric and chemical analysis methods selected as a comparison method, are presented in Table 2 below.

Table 2.

Results of determining the concentration of magnesium ions in underground and surface drinking water by ionometric and chemical methods.

n=3,  =0,95, 2023

Analytical samples taken from groundwater selected for determining the amount of magnesium ions by ionometric and chemical methods were taken from a depth of approximately 32 to 750 meters from the surface of the earth. The differences between the quantitative determination results obtained by both methods ranged from 0.12 to 14.7 mg/l. It can be seen from the results of the table that the relative standard deviation values ​​of the ionometric detection results obtained using the developed magnesium selective electrode are from 0.011 to 1.23 percent. It was recalculated with the help of mathematical statistics methods that the reliability values ​​ranged from 0.0038 to 0.055. In addition, in order to check the accuracy of the results of ionometric determination of the concentration of magnesium ions in natural objects based on the developed magnesium selective electrode, the energy dispersive X-ray spectroscopy (EDS) method was compared with the results obtained by scanning electron microscopy or transmission electron microscopy. The object of analysis examined by the EDS method is based on examination using high-energy electron beams.

It can be seen from table 3 below that the differences between the results of comparing the results of ionometric determination of the concentration of magnesium ions in natural underground drinking water taken from three districts of the Samarkand region selected as an analytical sample using the newly developed magnesium selective electrode with the quantitative determination results obtained by the EDS method are not higher than the required level. can be seen.

Table 3.

Results of ionometric and EDS determination of the amount of magnesium ions in underground water samples taken from Nurabad, Koshrabot and Pastdargham districts.

n=3,  =0,95, 2022

The differences between the average arithmetic values ​​of the concentrations of magnesium ions obtained by these two methods also meet the requirements for such analyzes and range from 0.14 to 0.85 mg/l.

The concentrations and EDS spectra of magnesium ions in the samples of underground drinking water in the mixture with other ions in the analytical samples are shown in the following figures 2-3

Figure 2                                                                          Figure 3

In the above-mentioned 2-3 pictures, Solpi M.F.Y., Koshrabot district. (Fig. 2) and EDS spectra taken to determine the concentration of magnesium ions from the mixture of various ions in groundwater from Zarkent town of Koshrabot district (Fig. 3) are presented.

Conclusion/Recommendations

Based on the results of scientific research related to the development of a magnesium-selective electrode from complex salts based on phosphoro-molybdate acid for the analytical control of the concentration of magnesium ions in solutions, chemical and energy methods are used to ionometrically assess the amount of magnesium ions in underground drinking water and their accuracy. the results of comparison with the values ​​obtained by the X-ray dispersive spectroscopy (EDS) method in scanning electron microscopy or transmission electron microscopy are presented.

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