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ISSN 2522-1841 (Online) AZERBAIJAN CHEMICAL JOURNAL № 4 2022 ISSN 0005-2531 (Print)
UDC 541.543.42
EXTRACTION AND ATOMIC-ABSORPTION DETERMINATION OF TUNGSTEN (VI) WITH 2-HYDROXY-5-T-BUTYLPHENOL-4'-NITROAZOBENZENE
A.M.Pashajanov, T.M.Ismailov*, N.I.Ismayilov, M.M.Agamaliyeva, Sh.M.Bayramov, Z.A.Mamedova
M.Nagiyev Institute of Catalysis and Inorganic Chemistry, NAS of Azerbaijan
*Azerbaijan Medical University
Received 10.05.2022 Accepted 14.06.2022
The complexation of tungsten (VI) with an azo compound synthesized from para-tret-butylphenol (2-hydroxy-5-Tr-butylphenol-4-nitro-asobenzene) has been studied spectrophotometrically. The optimum pH values of the solution are 2.0-3.0. The maximum light absorption of the complexes in n-butanol is in the range 460-470nm, and that of the reagent at 360-370; complex formation is accompanied by a bathochromic shift. The spectrophotometry characteristics of the complex have been calculated and the composition of the complex was determined by various methods. Using the equilibrium shift and isomolar series methods it has been found that the W:R ratio is 1:2. By the Sommer method it has been found that during complex formation one proton is released from each reagent molecule. The complex stability constant pk = 9.04 1 08 and the complex formation reaction equilibrium constant (4.2 104) have been calculated by the method of Komar. The molar absorption coefficient is (3.4±4.2)104. The graduation diagram is linear at a tungsten concentration of 1.0-10 ^g/ml, n-butanol has been used as an extractant. A single extraction with n-butanol 97% of tungsten as a complex is extracted. Methods of extraction-atomic-absorption and extraction-photometric determination of tungsten have been developed and the influence of a number of extraneous ions on the determination of tungsten has been revealed. The correctness of the results obtained has been controlled by analysing the State Standard Alloy Reference Materials.
Keywords: tungsten, atomic-absorption method, extraction, complexation.
doi.org/10.32 73 7/0005-2531-2022-4-109-113 Introduction
It is known that azo compounds based on para-tret-butylphenol are promising reagents in analytical chemistry for the determination of metal ions, this is due to the fact that the hydrox-yl group of para-tret-butylphenol creates the possibility of complex formation with the direct participation of the nitrogen atom of the azo group with the appearance of metal-nitrogen bond [14]. Study of analytical properties of azo-tert-butylphenol derivatives showed that their use for spectrophotometric determination of metal ions increases not only sensitivity, in some cases, the selectivity of determination. Therefore, the discovery of new analytical capabilities of azo compounds synthesized on the basis of para-tret-butylphenol, is of practical interest.
The determination of tungsten by atomic absorption method has not yet become widespread. The direct atomic absorption method is often used to determine tungsten at 1.010%. Di-
rect atomic absorption determination of lower concentrations of tungsten in complex objects is not always possible due to the influence of accompanying elements on the analytical signal. More promising to increase the selectivity and sensitivity of AA method, combining it with extraction [5-9].
A number of reagents have been proposed for extraction concentration of tungsten: bromo-pyrogallol red, cetylpyridinium chloride, rhodamine B dithiol [10-13].
In the present work, the conditions of tungsten extraction with 2-hydroxy-5-tp-butyl-phenol-4-nitroasobenzene (HR) were studied, and a method of extraction-atomic-absorption determination of tungsten in various objects was developed.
Experimental part
Reagents: Initial solution of tungsten (VI) was prepared by dissolution of Na2WO4 to 0.5M NaOH [14]. Solutions with lower content
of tungsten were prepared by diluting initial solution. Concentrated HCl, 1n of CH3COOH and NH4OH were used for creating necessary acidity. 1M KCl was used to create ionic power of solution. Chloroform, dichloroethane, carbo tetrachloride, benzene, toluene, hexane, n-butanol and butylacetate were used as organic solvents.
Reagent (2-hydroxy-5-tret-butylphenol-4'-nitroazobenzene) was synthesized by the method [15-16]. Reagent is a monoacid which has a general structural formula:
H9C4
O
N=N
O
NO2
OH
Additional treatment of the reagent was performed by recrystallization from ethyl alcohol. Composition and structure of the reagent were established with elemental analysis, IR-, UV-spectroscopy. IR-spectra 3450 cm-1 (O-H arom.); 2960 cm-1 (C-H from CH3), 3030 cm-1 (C-H arom.); 1592, 1496 cm-1 (C=C arom), 1408 cm-1 (N=N). 1168 cm-1 (C-C), 1264 cm-1 (C-N), 1136 cm-1, 1104 cm-1 (arom. O-C), 1302 cm-1 (arom. NO2). 4.210-4 M of reagent solution was prepared by dissolution of weighed samples in ethanol.
Instruments: Optical density was measured with spectrophotometer SF-46 and photoe-lectrocalorimeter KFK-2.
pH value was controlled by universal ionomer (pH/mV/Temp.meter-86501).
Atomic absorption of tungsten was measured on atomic-absorption spectrophotometer AAS-1N (Germany). As light sources standard hollow cathode lamps were used. Optimum measurement conditions are listed in Table 1.
Table 1. Atomic-absorption determination of tungsten
Wavelength, nm Slot width, nm Lamp current, mA Consumption of acetylene, l/hr Consumption of nitrogen oxide, l/hr
255.1 0.5 25 200 180
Technique: A certain amount of standard solution of tungsten, necessary amount of HCl, 0.5 ml of HR were poured into a separatory funnel, shaken and aqueous phase was diluted with distilled water to 20 ml. After 1-2 minutes 10 ml of n-butanol was added and extracted 1 minute. After complete separation of phases extract was sprayed into the acetylene-nitrogen oxide flame and atomic absorption of tungsten was measured under optimum conditions.
Results and discussion
Spectrophotometry study of the reaction.
The effect of acidity on complexation of tungsten is given in Figure 1. In acidic medium tungsten with HR forms colored complex. Influence of HCl and H2SO4 on complexation of tungsten with HR is not the same. For full extraction of the complex the use of 1.5-2.5 ml 0.8 M of HCl or 0.5-0.8 ml 0.4 M of H2SO4 is necessary. pH of these solutions is found to be 2.0-3.0. At lower acidity optical density decreases, that is probably related to the formation of wolframic acid.
Extraction of the complex
Chloroform, dichloroethane, carbo tetrachloride, benzene, toluene, xylene, hexane and n-butanol were used to extract the complex from organic solutions. Organic solvent must be combustible in direct atomization of extracts to burner flame.
The highest recovery of tungsten (96%) was obtained during extraction with chloroform and n-butanol. Studies show that atomic absorption of tungsten decreases with the use of halogen-containing solvents. n-Butanol is found to be most suitable for atomic-absorption analysis. It does not change combustion mode of flame and does not form a background in analytical line of tungsten. n-Butanol supports stable burning flame which allows us to determine tungsten in direct spraying the extract into flame.
Extractability of the complex was evaluated by diffusion coefficient and degree of extraction. Equilibrium densities of tungsten in aqueous phase were determined by using atomic-absorption method. Amount of tungsten in organic phase was found by the difference. Degree of single extraction of tungsten complex with n-butanol equals to 96-98%.
The effect of aqueous phase volume and hold time on formation and completeness of extraction of tungsten complex was studied. The increase of the aqueous phase volume up to 20 ml does not significantly influence on optical density of butanol extract. When holding colored complex of tungsten with HR for 2 minutes maximum optical density of solvent is achieved. The complex was stable for two days.
A
Effect of reagent concentration
A series of experiments with constant concentrations of tungsten and variable concentrations of HR reagent were carried out to study the influence of HR on formation of the complex. When concentration of HR increases up to 0.8 ml (4.210-4M) extraction of tungsten increases and further increase of its concentration does not influence on extraction of tungsten. 4.210-4M HR is needed for the formation of the complex W-R.
Absorption spectrum of complex
Under optimum conditions light absorb-ance spectrum was taken, maximum was observed in the range of 460-470 nm, reagent maximally absorbs in the range of 360-380 nm. Complexation is accompanied by bathochromic shift (Figure 2).
Composition and physical-chemical properties of the complex
Ratio of components in the complex equals to W(VI):HR=1:2 under optimum conditions found by method of equilibrium shift and straight-line method of Asmus [17].
The complex stability constant pk = 9.0410 and equilibrium constant of complexation reaction (3,2104 at pH 2.0) was calculated by spectrophotometric data for chloroform solvent with using dependence of light absorb-ance of solutions on pH. Molar absorption coefficient of tungsten calculated by Tolmachev method [17] equals to (2.1±0.1)104. Calibration curve is linear at concentrations of tungsten 110 mkg/ml. By Nazarenko method [18] it was established that complex forming form is WO(OH)2+.
rum of reagent extracts
=3,210-5M, Chr=4,210-4 KFK-2.
0.6
0.4
0.2
Fig.2. Absorption spect (1) and complex W; CW= M; Vorg=5ml; /=0,5 cm;
370 420 470 520 X,nm
2
Influence of foreign ions
Selectivity of extraction-atomic-absorption determination of tungsten with HR was studied. It was established that large amounts of alkali, alkali-earth elements and rare earth elements do not interfere with the determination of tungsten. Under optimum conditions up to 100 mkg of Co, Ni, Nb, Ta do not interfere with the determination of tungsten. Since tungsten forms complexes in more acidic medium than vanadium, determination of tungsten in the presence of less amounts of vanadium is possible. Effect of V and Mo was eliminated by the change of pH and oxalate-ions correspondingly. Interfering effect of the basis (iron) is eliminated by adding ascorbic acid. According to the studies of extraction-atomic-absorption method for determining microgram amounts of tungsten in steel was developed.
Determination of tungsten in steel Weighed sample of alloy (0.2 g) is dissolved at heating in 150 ml of H2SO4 (1:4). 3-5 ml of mixture (1:3) HNO3 and HCl is added and heated till release of nitrogen oxide. Nonsoluble residue is filtered and filtrate is moved to 100 ml of measuring flask. After cooling the solution is diluted with water up to the mark. Aliquot part of solution is moved to separatory funnel, 2.0 ml of 0.8 M HCl, and 0.5 ml of HR are added, is diluted with water up to 25 ml and 10 ml of n-butanol is extracted 1 minute. Organic phase is separated and sprayed into acetylene-nitrogen oxide flame, atomic absorption of tungsten is measured under optimum conditions.
Table 2. Results of extraction-atomic-absorption determination of tungsten (VI) in steel (n=5; P=0.95)_
Standard sample Content, W% Sr
by specification found
EI-69 0.40 0.39 0.012
EI-415 0.55 0.51 0.014
Amount of tungsten was found by calibration curve. Validity of results was confirmed by determination data of tungsten and standard sample of steel.
Conclusions
Complexation of W(VI) with 2-hydroxy-5-T-butylphanol-4'-nitroazobenzene (HR) was studied. Optimum conditions of formation of the
complex and its extraction with chloroform and n-butanol were found. Molar absorption coefficient equals to (3.4±4.2)104. Stability constant f the complex of tungsten in n-butanol is pk = 9.04 1 08. Beer's law is observed at concentrations of tungsten 1-10 mkg/ml. Determination technique of tungsten in soils was developed.
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VOLFRAMIN(VI) 2- HÍDROKSÍ-5T-BUTÍLFENOL-4'-NÍTROAZOBENZOLLA
ekstraksíyasi va atom absorbsíya üsulu ílo toyíní
A.M.Paçacanov, T.M.Ísmayilov, N.Í.Ísmayilov, M.M.Agamaliyeva, §.M.Bayramov, Z.A.Mamm3dova
Volframin (VI) para-tret-butilfenol (2-hidroksi-5-Tr-butilfenol-4'-nitro-azobenzol) asasinda sintez edilmiç azo birlaçma ils kompleks amala galmasi spektrofotometrik üsulla tadqiq edilmiçdir. Mahlulun optimal pH 2.0-3.0 arasindadir. Kompleksin normal butanolda maksimum içiq udulmasi 460-470 nm, reagentin maksimumu isa 360-370; kompleksamalagalma batoxrom sürüjma ila mûçayiat olunur. Kompleksin spektrofotometrik xarakteristikasi hesablanmiç va tarkibi müxtalif üsullarla müayyan edilmiçdir. Tarazligin yerdayiçmasi va izomolyar sira üsullarindan istifada etmakla W:R nisbatinin 1:2 oldugu tastiq edilmiçdir. Sommer üsulu ila müayyan edilmiçdir ki, kompleksamalagalma prosesinda har bir reagent molekulundan bir proton aynlir. Kompleksinin dayaniqliq sabitini pk=9.04 108, hamçinin kompleksamalagalma reaksiyasinin tarazliq sabitini hesablamaq ûçûn Komar üsulundan istifada edilmiçdir (4.2104). Molyar udma amsali (3.4+4.2)104 taçkil edir. Kalibrlama qrafiki volframin 1,0-10 ^g/ml konsentrasiyasinda xattidir. Ekstragent kimi n-Butanol istifada edilmiçdir. N-butanol ila tak ekstraksiya ila volframin 97%-i kompleks çaklinda ayrilir. Volframin tayin edilmasina bir sira yad ionlarin tasiri ôrganilmaçdir. Volframin ekstraksiya-atom-absorbsiya va ekstraksiya-fotometrik tayini üsullari içlanib hazirlanmiçdir. içlanmiç üsulun düzgünlüyü tarkibi malum olan Dovlat standart nümunalarini analiz etmakla tastiq edilmiçdir.
Açar sozlzr: volfram, atom absorbsiya, ekstraksiya üsulu, kompleksamalagalma.
ЭКСТРАКЦИЯ И АТОМНО-АБСОРБЦИОННОЕ ОПРЕДЕЛЕНИЕ ВОЛЬФРАМА^Г) С 2-ГИДРОКСИ-5-Т-БУТИЛФЕНОЛ-4'-НИТРОАЗОБЕНЗОЛОМ
А.М.Пашаджанов, Т.М.Исмаилов, Н.И.Исмаилов, М.М.Агамалиева, Ш.М.Байрамов, З.А.Мамедова
Спектрофотометрическим методом изучено комплексообразование вольфрама (VI) с азосоединением, синтезированным на основе пара-трет-бутилфенола (2-гидрокси-5-Тр-бутилфенол-4'-нитро-азобензол). Оптимальные значения pH раствора 2.0-3.0. Максимум светопоглощения комплексов в н-бутаноле находится в пределах 460-470нм, а реагента - при 360-370; комплексобразование сопровождается батохромным сдвигом. Рассчитаны спектрофотометрические характеристики комплекса, определен состав комплекса различными методами. Методами сдвига равновесия и изомолярных серий установлено, что соотношение W:R равно 1:2 . Методом Соммера найдено, что в процессе комплексообразования из каждой молекулы реагента выделяется один протон. Методом Комаря рассчитаны константа устойчивости комплекса pk=9.04 108, а также константа равновесия реакции комплексообразования (4.2 104). Молярный коэффициент поглощения равен (3.4+4.2)104 Градуировочный график линеен при консентрации вольфрама 1.0-10 мкг\мл, В качестве экстрагента использовали н-бутанол. При однократной экстракции н-бутанолом извлекается 97% вольфрама в виде комплекса. Разработаны методики экстракционно-атомно-абсорбционного и экстракционно-фотометрического определения вольфрама и выявлено влияние ряда посторонних ионов на определение вольфрама. Контроль правильности полученных результатов осуществляли путем анализа Государственных стандартных образцов сплавов.
Ключевые слова: вольфрам, атомно-абсорбционный метод, экстракция, комплексообразование.
