DEVELOPMENT OF BUFFER SOLUTIONS WITH NEW COMPOSITIONS AND INVESTIGATION OF THEIR PROPERTIES

ABSTRACT

The article is based on the preparation of secondary buffer solutions and the study of their stability and density changes under increasing temperature. For the preparation of secondary buffer solutions, 0.04 N solutions of glycine (containing an NH₂ group), boric acid, and phosphoric acid, as well as 0.1 N sodium hydroxide solutions, were used. The prepared secondary buffer solutions were applied to various sorption processes, and the results were calculated. The densities of the buffer solutions were studied using an Anton Paar Density Meter (DMA 4500M).

АННОТАЦИЯ

Статья посвящена приготовлению вторичных буферных растворов и изучению их стабильности и изменения плотности при повышении температуры. Для приготовления вторичных буферных растворов использовались 0,04 N растворы аминоуксусной кислоты, содержащей NH₂-группу, борной кислоты и фосфорной кислоты, а также 0,1 N раствор гидроксида натрия. Приготовленные вторичные буферные растворы применялись в различных процессах сорбции, и были рассчитаны полученные результаты. Плотности буферных растворов исследовались с использованием прибора Anton Paar Density Meter (DMA 4500M).

Keywords: Glycine, phosphoric acid, boric acid, sodium hydroxide, Anton Paar Density Meter (DMA 4500M), universal buffer solution.

Ключевые слова: глицин, фосфорная кислота, борная кислота, гидроксид натрия, Anton Paar Density Meter (DMA 4500M), универсальный буферный раствор.

Introduction

Buffer solutions are widely used in chemistry, biology, and pharmaceuticals, ensuring the efficient course of various processes by stabilizing the pH balance. Secondary buffers are distinguished by their ability to provide stability over a wide pH range and by their use in instrument calibration [1]. For example, the interaction of L-histidine and uracil in an aqueous medium has been studied using calorimetry and UV spectroscopy, where potassium phosphate buffers provided the necessary pH stability for the accuracy of protein–ligand interactions. In addition, the dependence of buffer density on temperature and concentration plays an important role in enhancing the reliability of research results [2]. Although the phosphate buffer solution (PBS) based on physiological saline is one of the most commonly used systems, it can increase the water content in tissues, reduce mechanical strength, and affect the results of mechanical testing [3]. At the same time, changes in pH during heat treatment yield different results in various buffer solutions and trigger additional reactions in the preservation of food products [4]. The Britton–Robinson buffer, which covers a wide pH range, is effectively used for calibrating ion-selective electrodes and for detecting low-concentration ions [5]. However, certain chemical compounds can significantly affect the long-term stability of buffer solutions as well as enzymatic processes. For example, the sodium bicarbonate-based McDougall buffer requires additional CO₂ to stabilize the pH, while the potassium phosphate-based Kansas buffer provides higher stability through simple mixtures, thereby simplifying the process and reducing both time and costs [6,7]. In addition, in obtaining hydroxyapatite coatings on Ti₆Al₄V alloy by a biomimetic method, a glycine–sodium glycinate buffer system was used, resulting in coatings with high hardness, elasticity, and adhesion strength that are compatible with human blood plasma [8]. Overall, the main advantage of buffer solutions is their ability to maintain a stable pH. This ensures the stability of substances in various scientific and practical studies and allows their effective application over a wide pH range [9]. In phosphate buffer solutions, the ratio of mono- and dibasic phosphate salts and the concentration of electrolytes in the solution are of great importance. The presence of calcium ions may lead to phosphate precipitation; therefore, these factors should be taken into account when selecting optimal conditions for biological and medical applications [10]. The interaction of glycine with sodium phosphate buffer (NaPB) has been studied using density measurements and UV spectroscopy, and molecular-level interactions have been identified [11]. At the same time, glycine-grafted pectin (Gly-Pe) possesses high viscosity and gel-forming properties and has been proposed as a promising biomaterial for providing sustained drug release [12]. Buffer solutions of boric acid have been used as an effective medium for studying the formation of passive films on pure iron surfaces and their electrochemical properties [13]. The preparation of inexpensive and stable buffer solutions that can be stored for a long time without changing their composition, as well as the study of their practical applications, is considered a promising scientific direction. Therefore, based on the data presented in the literature, the aim was to develop secondary buffer solutions with a wide pH range and high stability, and solutions composed of glycine, boric acid, and phosphoric acid were prepared.

EXPERIMENTAL PART

Instruments and Reagents

For measuring the pH of buffer solutions, a potentiometer (pH meter, Mettler Toledo) and an Anton Paar Density Meter (DMA 4500M) were used. The reagents included glycine, boric acid, phosphoric acid, sodium hydroxide 0.05 N, bidistilled water (GFL 2102), distilled water (GOST 6709), and bidistilled water (GOST 6710).

Preparation of Secondary Buffer Solution

Within the scope of our study, a buffer solution containing glycine (NH₂CH₂COOH), orthophosphoric acid (H₃PO₄), boric acid (H₃BO₃), and sodium hydroxide (NaOH) was prepared. Its time- and temperature-dependent properties were investigated. To prepare the solution, the following components were used: 0.0826 g of boric acid (H₃BO₃) and 0.3 g of glycine (NH₂CH₂COOH), which were placed in a 100 ml volumetric flask. From a 98% solution of orthophosphoric acid, 1 ml was taken, and bidistilled water was added to bring the total volume to 250 ml. From the obtained solutions, 0.04 N solutions were prepared. In addition, using a Mohr pipette, 33.3 ml of each solution was taken and placed into a 100 ml flask to prepare a solution containing all three components. The resulting solution was then mixed with 0.1000 N NaOH solution in various ratios.

OBTAINED RESULTS AND THEIR SELECTION

As a result of the study, samples with various values were obtained: 2.48; 5.57; 7.01; 11.05; 12.35; 12.53. The pH values of each sample were measured after 24, 48, 72, and 120 hours. The obtained results are presented in Table 1. Time dependence of the pH changes of the buffer solution.

Table 1.

Time Dependence of the pH Values of Buffer Solutions

According to the table analysis, the prepared buffer solutions fully meet the main requirements for secondary buffer systems. The differences in pH values between the samples did not exceed ±0.05, confirming their high stability. The obtained results demonstrate the reliability of the buffer solutions and show that the pH values remain almost unchanged over time. In buffer solutions with pH = 4.01 and pH = 10.03, changes in density with increasing temperature were studied, and their dependence on pH was determined. The obtained results are shown in Figures 1–2.

The density values of the newly prepared standard secondary buffer solutions were measured using an Anton Paar DMA 4500M vibrating tube densimeter, and the interval of possible pH changes was determined based on the density values of the buffer solutions.

Figures 1 and 2 show the temperature dependence of the density values, obtained using an Anton Paar DMA 4500M vibrating tube densimeter, for the secondary buffer solutions composed of glycine, boric acid, and phosphoric acid with pH = 4.01 and pH = 10.03.

As can be seen from the figures, with the increase in temperature, a decrease in density values is observed, and they did not differ significantly from the density value of pure water, which indicates that the composition of the buffer solution and the new pH value remain unchanged.

The prepared pH 10.03 buffer solution and the LiCl–NH₃·H₂O–NH₄Cl buffer solution [14] were used to support the adsorption of lithium ions onto the sorbent, and the static ion-exchange capacity of lithium ions was determined, with the results compared. It was found that the adsorption of lithium ions was higher.

In conclusion, it can be observed that the densities of all the prepared secondary buffer solutions decrease with increasing temperature. The pH variation range deviates from the actual value with an error of 0.05, which indicates that the measurement errors are minor.

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