EXTRACTION-SPECTROPHOTOMETRIC DETERMINATION OF SCANDIUM (III) ION WITH 1-(2-HYDROXY-1-NAPHTOYAZO)-2-NAPHTHOL-4-SULFOCID SOLUTION

АННОТАЦИЯ

Рекомендована экстракционно-спектрофотометрическая методика определения ионов скандия раствором 1-(2-гидрокси-1-нафтойазо)-2-нафтол-4-сульфоновой кислоты. Найдены оптимальные условия: соотношение объемов органической и водной фаз равно 1:9, коэффициент распределения равен 0,93. Светопоглащение комплекса 420 нм, поглощение реагента 500 нм, контрастность равна 80 нм, это доказывает высокую чувствительность разработанного метода. Показано, что определение ионов скандия обладает высоку точностью с нижним пределом обнаружения 1,14 мкг/л и коэффициентом корреляции равным 0,9999.  Разработанная методика определения ионов скандия применены к анализу модельные смесей и относительное стандартное отклонения не превышает 0,0015.

ABSTRACT

Recommended an extraction-spectrophotometric method for determining scandium ions with a solution of 1-(2-hydroxy-1-naphthoiazo)-2-naphthol-4-sulfonic acid. Found optimal conditions: the volume ratio of the organic and aqueous phases is 1:9, the distribution coefficient is 0.93. The light absorption of the complex is 420 nm, the absorption of the reagent is 500 nm, the contrast is 80 nm, this proves the high sensitivity of the developed method. It has been shown that the determination of scandium ions is highly accurate with a lower detection limit of 1.14 μg/L and a correlation coefficient of 0.9999. The developed method for determining scandium ions is applied to the analysis of model mixtures and the relative standard deviation does not exceed 0.0015.

Ключевые слова: экстракционно-спектрофотометрия, коэффициент распределения, 1-(2-гидрокси-1-нафтоязо)-2-нафтол-4-сульфоновая кислота, скандий.

Keywords: extraction-spectrophotometry, distribution coefficient, 1-(2-hydroxy-1-naphthoyazo)-2-naphthol-4-sulfonic acid, scandium.

Introduction

Scandium, considered a rare earth element, is used in the production of ligatures, high-power metal halide lamps, analytical standards, medical devices, household appliances and lasers. In nature, scandium is found in minerals and ores, and in the waste waters and waste of factory process of gold, silver and copper. Therefore, development of scandium ion detection and extraction methods is one of the actual problems. In the literature, scandium ion were studied by extraction spectrophotometric methods with phosphorus-organic compounds-dioxide methylenediphosphine [1], oxides (dialkylcarbamoylmethyl) diarylphosphine (KMFO) [2], XAD-4 [3], eriochromcyanine [4], chlorocyanogenformazan [5], phosphorylated calixarenes [6], 2-amino-4-(m-tolyazo)pyridine-3-ol (ATAP) [7], polyethylene glycol PEG-3000 (C₃H₇OH)–NaNO₃ (NaNO₃ + KSCN)–H₂O [8], phosphoryl stored podands [9], 2-hydroxy-5-T-butylphenol-4¢-metoxyazobenzene (HR) [10], antipyrine - sulfosalicylic acid [11] by forming a complex. Methods for the extraction-conductometric determination of scandium in kaolin with 2,7-dinitroso-1,8-dihydroxynaphthalene-3,6-disulfonic acid with tributyl phosphate and trioctylphosphine oxide have also been developed [12,13]. In addition, selective and rapid determination procedure for Th, Zr and Sc in rock samples using adsorbent silica modified with arsenazo-III (SAR-III) was synthesised by a single step process in presence of cationic surfactant cetyltrimethylammonium bromide. [14]. The most effective extractants of scandium are organophosphate compounds, but their re-extraction process is difficult.

Currently, the search for effective and economically convenient extraction agents for the extraction of this metal remains an actual problem.

The purpose of this work is to develop a methodology for the extraction-spectrophotometric detection of scandium (III) ion with 1-(2-hydroxy-1-naphthoyazo)-2-naphthol-4-sulfonic acid reagent. For this, the effect of the nature of the solvent, the acidity of the solution, and the partition coefficient of Sc(III) between the aqueous and organic phases was studied.

The structural formula of the selected organic reagent is as follows.

According to the Gaussian method electron densities of reagent were 0.203-0.247 of hydroxyl groups in the ring and 0.070-0.042 of -N=N- group. And this gives an opportunity to form a chemical bond with metal ions.

Experimental part

Newly synthesized 1-(2-hydroxy-1-naphthoiazo)-2-naphthol-4-sulfonic acid was used as an extractant to separate the scandium (III) ion in the solution. Toluene, chloroform and benzene "ch.c." or "c.f.a." certain organic solvents were used.

Solutions containing Sc (III) and other metals (Ce, Y, Pr, Te, Eu, Tm, Tb, Yb) with a concentration of 10^-5 mol/l were prepared by dissolving the appropriate salts.

Sc(III) ion concentrations in initial and equilibrium solutions were determined by spectrophotometry (EMC-30PC-UB spectrophotometer). The acidity of the solution was determined by potentiometric titration with KOH solution (pH meter / mV / TEMP meter P25 Ecomet (Korea)).

Results and discussions

Knowing the effect of the nature of the organic solvent on the extraction rate, the effect of different organic solvents was studied. The nature of the organic solvent has a strong influence on the distribution constants of the reagent and enhances complex formation. In this study, we used chloroform CHCl₃ (P=1.49), benzene C₆H₆ (toxic, P=0.88) and toluene C₆H₅CH₃ (P=0.87). The reason is that they are insoluble in water and differ from the dissociation constants of the reagent and the stability of the complex. Received data are shown in Figure 1.

First, the light absorption maximum of the 0.1% alcohol solution of 1-(2-hydroxy-1-naphthoyazo)-2-naphthol-4-sulfonic acid reagent was measured in a spectrophotometer. Then, 1.0 ml of 45 µg/ml scandium (III) solution, 2.0 ml solution of the 0.1% 1-(2-hydroxy-1-naphthoiso)-2-naphthol-4-sulfonic acid reagent in alcohol, 12.0 ml of distilled water and 2.0 ml of chloroform, toluene, benzene solution as an extractant were added to a 50 ml separatory funnel. The mixture was shaken for 2 min and allowed to stand. The organic layer was separated in a separatory funnel, and the optical density of the obtained complex was measured compared to the reference solution (λ_max= 420, l = 1,0 sm). The measurement results are presented in Figure 1. The same procedures were repeated with solutions of the reagent 1-(2-hydroxy-1-naphthoyazo)-2-naphthol-4-sulfonic acid in toluene and in benzene.

Figure 1. Light absorption spectra of 0.1 % alcohol solution of 1-(2-hydroxy-1-naphthazo)-2-naphthol-4-sulfonic acid reagent (1) and its mixtures in chloroform (2), toluene (3) and benzene (4)

According to the obtained results, the extraction rate of scandium was the highest in the mixture of 1-(2-hydroxy-1-naphthoyazo)-2-naphthol-4-sulfonic acid reagent in chloroform. For this reason, chloroform was chosen as the extractant for the 1-(2-hydroxy-1-naphthazo)-2-naphthol-4-sulfonic acid reagent for the extraction of scandium.

It can be seen from the above picture that 1-(2-hydroxy-1-naphthoiso)-2-naphthol-4-sulfonic acid extracted scandium(III) ion well in chloroform, which is due to its good solubility and high density in chloroform [15].

The influence of the volume ratio of the aqueous and organic phases on the level of extraction of metals in the extraction with a standard solution of scandium in a solution of 1-(2-hydroxy-1-naphthazo)-2-naphthol-4-sulfonic acid in chloroform was studied. The degree of separation of scandium was determined in the following proportions of volumes of organic and aqueous phases: 1:1; 1:2; 1:5; 1:8; 1:9; 1:10; 1:11; 1:15 a.m.; 1:20;. It was found that changing the volume ratio of organic and aqueous phases from 1:5 to 1:10 does not lead to a decrease in the level of extraction of elements.

Table 1 graphically shows the dependence of the degree of separation of scandium with a solution of 1-(2-hydroxy-1-naphthoyazo)-2-naphthol-4-sulfonic acid in chloroform on the ratio Vo:Vs.

Table 1.

Dependence of the degree of separation (R%) in the extraction of scandium (III) ion on the volume ratio of aqueous and organic phases

Based on the obtained results, it was found that the extraction rate of scandium extraction was the highest when the ratio of aqueous and organic phases was 9:1.  For this reason, it was determined that the ratio of aqueous and organic phases was 9:1 for the extraction of scandium.

In order to study the effect of environmental acidity, HCl, H2SO4 and HNO3 acids were selected, and 1.0 ml of 45 μg/ml scandium (III) solution, 2.0 ml solution of the 0.1% 1-(2-hydroxy-1-naphthoiso)-2-naphthol-4-sulfonic acid reagent in alcohol, 3.0 ml of a 0.1 M nitric acid solution, 12 ml of distilled water and 2.0 ml of a chloroform solution were added to a 50 ml separatory funnel. The mixture was shaken in the separatory funnel for 2 minutes and then allowed to stand. The organic layer was separated in a separatory funnel, and the optical density of the obtained complex was measured compared to the reference solution (λ_max= 420, l = 1,0 sm). The measurement results are given in table 2. Based on this methodology, the work was performed several times with 0.1 M solutions of sulfuric and hydrochloric acids. Based on the obtained results, it was determined that nitric acid is the most optimal for extracting scandium. In the extraction of metals, the values of the degree of separation are different in different acids and reach a maximum level in certain acids.

Table 2.

Effect of aqueous phase acidity on scandium ion degree of separation (R%).

Based on the obtained results, the level of extraction of scandium in nitric acid environment had the highest value. For this reason, it was found that the use of nitric acid is effective in forming a complex of scandium (III) ion with 1-(2-hydroxy-1-naphthoyazo)-2-naphthol-4-sulfonic acid.

In order to study the effect of the amount of selected acid on the level of extraction, 1.0 ml of 45 μg/ml scandium (III) solution, 2.0 ml solution of the 0.1% 1-(2-hydroxy-1-naphthoiso)-2-naphthol-4-sulfonic acid reagent in alcohol, 3.0 ml of different concentrations solutions of the nitric acid solution at 0.025 M; 0.05 M; 0.1 M; 0.125 M; 0.15 M, 12 ml of distilled water and 2.0 ml of chloroform solution were added to a 50 ml separatory funnel, and then optical densities were measured. The measurement results are shown in Table 3, Figure 2 below.

Table 3.

Effect of nitric acid concentration on degree of separation in scandium extraction

Figure 2. Dependence of concentration of nitric acid on degree of separation of scandium (III) ion

As can be seen from the obtained results, the degree of separation (R%) of scandium with 0.1 M nitric acid solution has reached the maximum value.

In order to study the dependence of the complex compound on the amount of added reagent, 1.0 ml of 45 μg/ml scandium (III) solution, different volumes of 0.1% 1-(2-hydroxy-1-naphthoiso)-2-naphthol-4-sulfonic acid reagent in alcohol (0.5; 1.0; 1.5; 2.0; 2.50; 3.0 ml), 3, 0 ml  of 0.1 M nitric acid solution, 12 ml of distilled water and 2.0 ml of chloroform solution as an extractant were added to a 50 ml separatory funnel and the optical densities were studied and is given in Table 4 and Figure 4.

Based on this methodology was done several times with 0.50; 1.0; 1.50; 2.0; 2.50; 3.0 mL solutions. Based on the obtained results, it was determined that the optimal volume of the reagent for the extraction of scandium (III) ion is 2.0 ml.

Table 4.

Dependence of the optical density on the amount of reagent ((λ _max =420 nm , l = 1.0 cm, extragen= chloroform, C_M = 0. 1 HNO₃ )

Figure 3. Dependence of the amount of reagent on the formation of a complex compound

From the results of the research, it can be observed that the optical density increased with the increase in the amount of reagent in the composition of the mixture. As a result of interaction with 1.0 ml solution containing 45 µg/ml scandium and 2.0 ml solution containing 0.1% reagent, the optical density reached the highest value. A decrease in optical density was observed when the amount of reagent exceeded 2.0 ml.

In order to determine the ratio of metal and reagent 1.0 ml of 45 µg/ml scandium (III) solution, 2.0 ml solution of the 0.1% 1-(2-hydroxy-1-naphthoiso)-2-naphthol-4-sulfonic acid reagent in alcohol, 3.0 ml of 0.1 M nitric acid solution, 12 ml of distilled water and 2.0 ml of chloroform were added to a 50 ml separatory funnel. The mixture was shaken in the separatory funnel for 2 minutes and then allowed to stand. The organic layer was separated in a separatory funnel, and the optical density of the obtained complex was measured compared to the reference solution. The measurement results are given in Figure 4.

The resulting mixture was shaken continuously for 2 minutes and allowed to cool. The organic layer was separated by a separatory funnel and its optical density was measured against a standard solution. The obtained results are presented in Figure 4. To determine the stoichiometric proportions of the reacting components, Asmus' straight line graph method was used. If we set the dependence of 1/V_R along the ordinate axis and the corresponding optical density values along the abscissa axis, we get a set of curves in the coordinates.

Figure 4.  The graph for determining the ratio of moles of complex compounds using Asmus's method of straight lines

As can be seen from the graph in Figure 4, only the condition n=1 satisfies the requirement of correctness of the Asmus function. This straight line corresponds to a 1:1 mole ratio of scandium (III) and the reagent. Therefore, it was determined that scandium and the reagent reacted in a 1:1 ratio in the formation of a complex compound.

For the determine the scandium (III) ion correlation coefficient 2.0 ml solution of the 0.1% 1-(2-hydroxy-1-naphthoiso)-2-naphthol-4-sulfonic acid reagent in alcohol, from 2 μg to 50 μg/ml standard solution of scandium (III) were taken, 3.0 ml of 0.1 M nitric acid, 12 ml of distilled water and 2.0 ml of chloroform solution were added to a 50 ml separatory funnel then shaken and allowed to stand. The organic layer was separated in a separatory funnel, and the optical density of the obtained complex was measured compared to the reference solution (λ_max= 420, l = 1,0 sm).

The measurement results were given in Table 5, and mathematical calculations were made on this basis.

 Table 5.

Calculation of the parameters of the equation of a straight line by the method of least squares

Figure 5. A graduation graph for the determination of scandium(III) ion

According to these results, the graduated graph (graded graph) equation was Yi=a+bXi, i.e. y =a+bXi=0.0005+0.0072∙Xi. This shows that it has accuracy.

The lower detection limit was determined by the following formula:

e_x - true molar extinction coefficient;

V - solution volume , (25 ml);

V - the atomic mass of the element ( Sc = 44.95g);

l - sink thickness (1.0 cm);

M is complex to the composition entered of scandium defined atoms the number

-standard deviation, ( =0.00166);

Q _min. -lower limit of detection

As a result of the obtained results and calculations, it was determined that the Q_min.-lower detection limit of scandium ion is equal to 1.14 μg.

It was determined from the composition of the artificial mixture under selected optimal conditions using the complexation of scandium (III) ion with 1-(2-hydroxy-1-naphthoyazo)-2-naphthol-4-sulfoacid reagent. To carry out the determinations, 2.0 ml of a 0.1% alcoholic solution of 1-(2-hydroxy-1-naphthazo)-2-naphthol-4-sulfonic acid reagent, 1.0 ml of standard solution scandium (III) ion and a number of cations that do not interfere with the determination of scandium (III) ions were added in the required amount.

It was mixed and allowed to stand, and the optical density of the obtained complex was measured compared to the reference solution (λ_max= 420, l = 1,0 sm). The obtained results are given in table 5 .

Table 5.

Determination of scandium (III) ion from the composition of artificial mixture

The obtained results show that with the developed method it is possible to determine the scandium ion from the composition of the artificial mixture with an error not exceeding 0.0308. This allows the developed method to be used to determine the composition of natural objects.

Conclusion

The obtained results show that the developed extraction-spectrophotometric method is recommended for the detection and separation of scandium (III) ion from the composition of technological solutions with 1-(2-hydroxy-1-naphthoyazo)-2-naphthol-4-sulfoacid reagent in the presence of HNO₃ acid.

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