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AZERBAIJAN CHEMICAL JOURNAL No 1 2020 ISSN 2522-1841 (Online)
ISSN 0005-2531 (Print)
UDC 543.4:542.61:546.812
NEW SIMPLE AND RAPID SPECTROPHOTOMETRY METHODS FOR THE DETERMINATION OF TRACE LEVEL GOLD(III) USING 2,2',3,4-TETRAHYDROXY-3'-SULPHO-5'-CHLORAZOBENZENE PRESENCE OF THE CATIONIC SURFACTANTS
P.R.Mammadov
Baku State University [email protected] Received 05.03.2019 Accepted 22.08.2019
It is shown that gold(III) with 2,2',3,4-tetrahydroxy-3'-sulpho-5'-chlorazobenzene (TSXAB) the rapid reacts in pH 5-6 acidic solution to form brownish-yellow complex and in pH 4-5 acidic solution to form brownish complexes in the presence of the cationic surfactants - cetylpyridinium chloride (CPCl), cetylpyridinium bromide (CPBr) and cetyltrymethylammonium bromide (CTMABr). The absorption spectra of the Au(III)-TSXAB system is a curve with the maximum absorbance at 490 nm and molar absorption coefficient of 2.3104 l mol-1 cm-1 in aqueous media. The absorption spectra of the Au(III)-TSXAB-CPCl, Au(III)-TSXAB-CPBr and Au(III)-TSXAB-CTMABr systems is a curves with the maximum ab-sorbances at 520, 520 and 540 nm and molar absorption coefficients of 3.78 104, 3.67.104 and 3.81104 l mol-1 cm-1 in micellar media respectively. The absorbance was linear for 0.584-5.61 mkg/ml of Au(III) in the Au(III)-TSXAB-CPCl, Au(III)-TSXAB system and 0.428-6.362, 0.435-6.221, 0.436-6.832 mkg/ml of Au(III) in the Au(III)-TSXAB-CPCl, Au(III)-TSXAB-CPBr and Au(III)-TSXAB-CTMABr systems, respectively. The Sandell's sensitivity for Au(III) were found to be 7 mkg cm-2 in Au(III)-TSXAB system and 5, 6, 5 mkg/cm in the Au(III)-TSXAB-CPCl, Au(III)-TSXAB-CPBr, Au(III)-TSXAB-CTMABr systems. The proposed methods was successfully used in the determination of Au(III) in several synthetic mixtures. The relative standard deviation (n = 5) was (0-2.0)%, for Au(III) indicating that this methods are highly precise and reproducible. The results obtained agree well with synthetic mixture samples analyzed by inductively coupled plasma optical emission spectrometry.
Keywords: spectrophotometric, Au(III), determination, 2,2',3,4-tetrahydroxy-3-sulpho-5'-chlorazoben-zene, cationic surfactants.
doi.org/10.32737/0005-2531-2020-1-20-25 Introduction
The large amounts of gold are still used in the manufacture of coins, medals, jewelry, art and also has a number of uses in industry, medicine, and other fields [1]. Therefore, it is clear that in the arsenal of analysts there must be simple and rapid methods to determine Au(III) in a wide concentration range with the highest possible sensitivity accuracy. Although many modern techniques, such as inductively coupled plasma atomic emission spectrometry (ICP-AES) [2], inductively coupled plasma mass spectrometry (ICP-MS) [3, 4], electrothermal atomic absorption spectrophotometry (EAAS) [5, 6], graphite furnace atomic absorption spectrophotometry (GFAAS) [7] are available for the determination of silver at trace levels in numerous complex materials.
Factors such as the low cost of instrument, technical know-how, consumable and costly maintenance of technique restrict the wider applicability of these techniques, particularly in laborato-
ries with limited budget in developing countries and for field work lack of any requirement for consumables and almost no maintenance, have caused spectrophotometric methods to remain a popular technique. The wide variety of spectro-photometric methods for determination of Au(III) have been reported, each chromogenic system has its advantages and disadvantages with respect to sensitivity, selectivity and convenience [8-12]. The azocompounds on the basis of pyroghallol had widely been applied for the determination of noble metal ions, this type of reagent has higher sensitivity and high selectivity [13]. In the search for more sensitive azocompounds on the base of pyroghallol reagent, in this work, a reagent 2,2',3,4-tetrahydroxy-3'-sulpho-5'-chlorazobenzene (TSXAB) was synthesized according to the method of [13] and a color reaction of TSXAB with Au(III) in aqueous and in the presence of the cationic surfactants was carefully studied. The aim of present study is to develop a simple direct spectrophotometric method
for the trace determination of Au with TSXAB in aqueous solutions, and in the presence of cationic surfactants, such as cetylpyridinium chloride, ce-tylpyridine bromide and cetyltrimethylammonium bromide in aqueous solutions.
Experimental part
Instrumentation
The absorbance of solutions was measured with a Perkin Elmer (United States) (Model: Lambda-40) double-beam UV/VIS spectrophotometer and with a KFK-2 photoelectrocolorime-ter (Russia), with 1 cm matched quartz cells.
The pH values of solutions was controlled on the Ionomer i-121 (Russia) with glass electrode customized by standart bufer solutions.
A Perkin Elmer (United States) (Model: Optima-2100DV) Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES) was used for comparing the results.
Standard solutions
A 10 2 M 100 ml standard solution of Au was prepared by dissolving 1.967 g of Au (purity 99.99%) in aqua regia by warming, evaporating the solution to dryness, dissolving the residue in hydrochloric acid, evaporating the solution to half its volume, cooling and diluting with water to 100 ml in calibrated flask. Working solutions were prepared by appropriate dilution of standard solution. The gravimetric method (using hydrogen peroxide) was used for controlling of gold(III) concentration in the standard solution [1].
2,2',3,4-tetrahydroxy-3'-sulpho-5'-chlo-razobenzene (TSXAB) (210-3 M). The reagent was synthesized according to the method [13]. The solution was prepared by dissolving the requisite amount of TSXAB in a known volume of distilled water and ethanol (1:1). More dilute solution of the reagent was prepared as required.
Cationic surface-active substances (CSAS). M0-2 M
cationic surface-active substances (surfactants) - cetylpyridine chloride (CPCl), cetylpyridine bromide (CPBr) and cetyl-trymethylammonium bromide (CTMABr) was preparing by dissolving the requisite amounts of surfactants in distilled water.
Aqueous ammonia solution. A 100 ml solution of aqueous ammonia was prepared by
diluting 10 mL of concentrated NH3 (28%-30%) ACS grade with distilled water. The solution was stored in a glass bottle.
EDTA solution. A 100 ml stock solution of EDTA (0.1% w/v) was prepared by dissolving 128 mg of ethylenediaminetetraacetic acid, disodium salt dehydrate in 100 ml distilled water.
Other solutions. Solutions of a large number of inorganic ions and complexing agents were prepared from their grade, or equivalent grade, water soluble salts.
Results and discussion
Au(III) with 2,2',3,4-tetrahydroxy-3'-sulpho-5'-chlorazobenzene rapidly reacts in pH 5-6 acidic solution to form brownish-yellow complex and in pH 4-5 acidic solution to form brownish complexes in presence of the cationic surfactants.
Absorption spectra. The absorption spectra of the Au(III)-TSXAB- is a curve with the maximum absorbance at 490 nm and an average molar absorption coefficient of 2.3.104 l mol-1 cm-1 in aqueous media. The absorption spectra of the Au(III)-TSXAB- CPCl, Au(III)-TSXAB-CPBr and Au(III)-TSXAB- CTMABr systems is a curve with the maximum absor-bances at 520, 520 and 540 nm and average molar absorption coefficients of 3.78 104, 3.67104 and 3.81104 l mol-1 cm-1 in micellar media, respectively (Figure).
Effect of acidity. Of the various pH 0-12 studied, pH 5.0-6.0 found to be the best acid environment for the Au(III)-TSXAB system and pH 4.0-5.0 for the Au(III)-TSXAB- CPCl, Au(III)-TSXAB-CPBr and Au(III)-TSXAB-CTMABr systems at room temperature (25±5)0C. The ab-sorbance of the reagent solution and the all systems depends on the medium pH; therefore, the absorption spectra are studied relatively to a blank experiment against the background of control experiment (R and R+CSAS), which was prepared in the same conditions.
Effect of time. The reaction is fast. Constant maximum absorbance was obtained after 10 min for Au(III)-TSXAB system in aqueous media and 5 min for Au(III)-TSXAB- CPCl, Au(III)-TSXAB-CPBr and Au(III)-TSXAB-CTMABr systems in micellar media, respectively.
Absorption spectra of Au(III)-TSXAB (1), Au(III)-TSXAB-CPCl (2), Au(III)-TSXAB-CPBr (3) and Au(III)-TSXAB-CTMABr (4).
Effect of temperature. The absorbance at different temperatures, 0-800C, of a 25 ml solution of all systems was measured according to the standard procedure. The absorbance was found to be strictly unaltered through-out the temperature range of 10-400C. Therefore, all measurements were performed at room temperature (25±5)0C.
Stoichiometry. The component ratio in the complexes was found using the method of isomolar series, the Starik and Barbanel relative yield method and the equilibrium shift method. All the methods showed that the component ratio were 1:2 in the double Au(III)-TSXAB system and 1:2:2 in the triple Au(III)-TSXAB-CPCl, Au(III)-TSXAB-CPBr, Au(III)-TSXAB-
CTMABr systems. The number of protons displaced upon complexation was determined by the Astakhovs method, and the indicated component ratio in the complexes was confirmed [14].
Effect of the reagent and cationic surfactants concentration. Different molar excesses of TSXAB and cationic surfactants were added to a fixed Au(III) concentration and the absorbance was measured according to the standard procedure. It was observed that a 1 mkg/ml of silver metal (optical path 1 cm in length), the reagent and cationic surfactants molar ratios produced a constant absorbance of Au(III)-TSXAB- CPCl, Au(III)-TSXAB-CPBr, Au(III)-TSXAB-
CTMABr systems. For all subsequent measurements, 2 ml of 210-4 M TSXAB reagent and 4 ml of 210-4 M cationic surfactants was added.
Analytical performance of the methods
Calibration graph. The effect of metal concentration was studied in the range of 0.01100 mkg/ml, distributed in four different sets (0.01-0.1, 0.1-1, 1-10 mkg/ml) for convenience of the measurement. The absorbance was linear for 0.584-5.61 mkg/ml of Au(III) in the Au(III)-TSXAB system and 0.428-6.362 mkg/ml, 0.435-6.221 mkg/ml, 0.436-6.832 mkg/ml of Au(III) in the Au(III)-TSXAB-CPCl, Au(III)-TSXAB-CPBr, Au(III)-TSXAB-CTMABr systems respectively. From the slope of the calibration graph, the average molar absorption coefficient was found to be 2.3104 l mol-1 cm-1 for Au(III)- TSXAB system and 3.78 104 l mol-1 cm-1 , 3.67104 l mol-1 cm-1 and 3.81104 l mol-1 cm-1 in the Au(III)-TSXAB-CPCl, Au(III)-TSXAB-CPBr, Au(III)-TSXAB-CTMABr systems respectively. The selected analytical parameters obtained as a result of the optimization experiments are summarized in Table 1.
Precision and accuracy. The precision of the present method was evaluated by determining different concentrations of Au (each analyzed at least five times). The relative standard deviation (n =5) was (0-2.0) %, for 0.1-8 mkg of Au(III), indicating that this method is highly precise and reproducible. The Sandell's sensitivity for Au(III) made up 7 mkg/cm-2 in Au(III)-TSXAB system and 5mkg cm-2, 6 mkg cm-2, 5 mkg cm-2 in the Au(III)-TSXAB- CPCl, Au(III)-TSXAB-CPBr, Au(III)-TSXAB-CTMABr systems respectively.
Effect of foreign ions. The effect of over an absorbance value varying by more than 5%
30 cations, anions and complexing agents on from the expected value for Au(III) alone. The
the determination of only 1 mkg/ml of Au(III) results are given in Table 2. was studied. The criterion for interference was
Table 1. Selected analytical parameters obtained by optimization experiments
Parameters Studied range Selected value
Au(III)-TSXAB Au(III)-TSXAB-CPCl Au(III)-TSXAB-CPBr Au(III)-TSXAB-CTMABr
Wavelength/Xmax, nm 200-800 490 520 520 540
Wavelength/XODt, nm - 490 540 540 540
pH 0-12 5-6 4-5 4-5 4-5
Time, h 1 - 24h 5-10 min 5-6 min 5-6 min 5-6 min
Temperature, 0C 0-800C 25 ± 50C 25 ± 50C 25 ± 50C 25 ± 50C
Au(III):TSXAB:CSAS 1:10-10:1 1:2 1:2:2 1:2:2 1:2:2
Molar absorption coefficient, l mol-1 cm-1 - 2.30104 3.78^104 3.67-104 3.81104
Linear range/mkg l-1 0.01-10 0.584-5.61 0.428-6.362 0.435-6.221 0.436-6.832
IfiP - 8.58 11.58 11.26 12.88
Sandell's sensitivity/mkg cm-2 0.1-10 7 5 6 5
Relative Standard 0-5 0-2 0-2 0-2 0-2
Table 2. Tolerance limits of foreign ions,tolerance ratio lons(x)]/Au (w/w)
Ions X Au(III)-TSXAB Au(III)-TSXAB-CPCl Au(III)-TSXAB- CPBr Au(III)-TSXAB- CTMABr [12]
Na(I) 100 110 115 150 100
K(I) 100 145 150 180 100
Mg(II) 120 160 160 180 100
Ca(II) 120 170 170 180 100
Cr(III) 120 175 175 185 100
Fe(III) 30 45 45 55 25
Cu(II) 60 80 80 95 50
Cd(II) 100 130 130 140 100
Hg(II) 105 145 145 160 100
Mo(II) 105 135 145 160 100
Co(III) 110 150 150 165 100
Zn(II) 115 140 150 160 100
Be(III) 110 150 150 155 100
Sn(IV) 25 35 35 40 25
Mn(II) 120 155 155 155 100
V(V) 30 50 50 60 25
Ag (I) 25 45 45 45 25
Ga(III) 100 120 120 130 100
La(III) 110 140 140 150 100
Ta(IV) 110 140 140 150 100
Ni(II) 120 155 155 165 100
Pb(II) 25 35 35 45 25
NO 3 250 270 270 285 200
SO 4" 110 1250 1250 1250 1000
Cl" 1150 1220 1220 1240 1000
F" 120 125 135 145 100
HCO 3 130 145 155 170 100
C2O43 1100 1140 1140 1250 1000
EDTA 650 730 760 780 500
C4H4O 2 260 280 280 300 200
CH3COO" 110 130 130 140 75
Table 3. Determination of Au(III) in synthetic mixtures
Sample Composition of mixture (mkq/ml) Proposed method ICP-OES
Au(III) mkq/ml Recovery ± sb (%) Au(III) mkq/ml Recovery ± 5 (%)
Added Founda Found
A Au3+ 1.5 2.0 1.52 2.04 102 ± 0.3 104 ± 0.2 1.51 2.02 101 ± 0.3 102 ± 0.2
B As in A + Cu2+(25)+ Fe3+(25) 1.5 2.0 0.51 2.03 101 ± 0.4 103 ± 0.2 0.52 2.02 102 ± 0.4 102 ± 0.2
C As in B+Mg2+ (25)+Co3+ (25) 1.5 2.0 1.51 2.02 101 ± 0.2 102 ± 0.2 1.50 2.01 100 ± 0.2 101 ± 0.2
D As in C +Cr 3+(25)+Ca2+ (25) 1.5 2.0 1.49 2.02 98 ± 0.2 102 ± 0.1 1.495 2.025 99 ± 0.1 101 ± 0.1
E As in D +Ag+(25)+Hg22+ (25) 1.5 2.0 1.48 2.02 97 ± 0.3 102 ± 0.2 1.49 2.01 97 ± 0.3 101 ± 0.2
a Average of five analysis of each sample; The measure of precision is the standard deviation (5).
Applications
The Au(III)-TSXAB-CTMABr system was successfully applied to the determination of Au(III) in a series of synthetic mixtures of various compositions (Table 3).
Determination of Au(III) in synthetic mixtures. Several synthetic mixtures of vary-ious compositions containing Au(III) and diverse ions of known concentrations were determined by the present method using EDTA as a masking agent; the results were found to be highly reproducible. The results of synthetic mixtures analysis by the spectrophotometric method were found to be in excellent agreement with those obtained by ICP-OES. The results are given in Table 3. Accurate recoveries were achieved in all solutions.
General Procedure
To synthetic mixtures samples of varyious compositions containing 1-2 mkg/ml Au(III) in 25 ml volumetric flask was mixed with 2 ml of 210-4 M TSXAB reagent solution and 4 ml of 210-4 CTMABr solution with subsequent followed by the addition of 5 ml initial solution of EDTA (0.1mass.% w/v). The mixture was diluted up to the mark with pH 5 buffer solutions. After 5 min the absorbance was measured at 540 nm against the background of the corresponding reagent. The gold(III) content in the synthetic mixtures sample was determined using a concurrently prepared calibration graph.
Conclusion
In the present work, a simple, rapid, sensitive and selective methods was developed for the determination of Au(III)) in difficult sample matrices. Therefore, this methods can be successful-
ly applied to the monitoring of trace amounts of Au(III) in industrial and natural samples.
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YENÍ SADO VO SÜROTLÍ SPEKTROFOTOMETRÍK ÜSULLARLA QIZILIN(III) 2,2', 3,4-
TETRAHÍDROKSÍ-3'-SULFO-5'-XLORAZOBENZOL ÍLO KATION TÍP SOTHÍ-AKTÍV MADDOLOR
ͧTÍRAKINDA TOYÍNÍ
P.RMammadov
Qizil(III) 2,2',3,4-tetrahidroksi-3'-sulfo-5'-xlorazobenzol (TSXAB) ils pH 5-6 turçuluqlu mühitda süratla reaksiyaya girarak qahvayi-sari rangli kompleks va pH 5-6 turçuluqlu mühitda kation tip sathi aktiv maddalar- cetilpiridin xlorid (CPCl), cetilpiridin bromid (CPBr) va cetiltrimetilammonium bromid (CTMABr) içtirakinda isa qahvayi rangli komplekslar amala gatirir. Au(III)- TSXAB sisteminin içiq udma spektrinda maksimum 490 nm-da va molyar udma amsalli 2.3104 l mol-1sm-1 mûçahida olunur. Au(III)-TSXAB-CPCl, Au(III)-TSXAB-CPBr va Au(III)-TSXAB-CTMABr TSXAB sistemlarinin içiq udma spektrlarinda maksimumlar 520, 520 va 540 nm dalga uzunluqlarinda mûçahida olunur va molyar udma amsallari isa uygun olaraq 3.l8104, 3.6l104 and 3.81104 l mol-1 sm-1 qiymatlar alir. Optiki sixligin xattiliyi Au(III) ûçûn 0.584-5.61 mkg/ml miqdannda Au(III)-TSXAB sisteminda va 0.428-6.362 mkg/ml, 0.435-6.221 mkg/ml, 0.436-6.832 mkg/ml miqdarlarinda isa uygun olaraq Au(III)-TSXAB-CPCl, Au(III)-TSXAB- va Au(III)-TSXAB-CTMABr sistemlarinda olur. Sendel hassasligi Au(III) ûçûn Au(III)-TSXAB sisteminda l mkg cm-2 va Au(III)-TSXAB-CPCl, Au(III)-TSXAB-CPBr va Au(III)-TSXAB-CTMABr TSXAB sistemlarinda isa 5, 6, 5 mkg/cm müayyan edilmiçdi. Taklif olunan metodlar qizilin (III) bir neça sintetik qançiqlarda tayininda ugurla tatbiq olunmuçdu. Nisbi standart kanara çixma Au(III) ûçûn (0-2.0)% olmagi, bu üsullarin yüksak daqiqliyinin va takrarliginin oldugunu göstarir. Alinan naticalar sintetik qariçiq nümunalarinin induktiv alaqali plazma optik emissiya spektrometriyasi üsulu ila analizinin naticalari ila müqayisa edilmiçdi.
Açar sözlzr: spektrofotometrik, Au(III), tayin, 2,2',3,4-tetrahidroksi-3'-sulfo-5'-klorazobenzen, kation tip sathi-aktiv maddalar.
НОВЫЙ ПРОСТОЙ И БЫСТРЫЙ СПЕКТРОФОТОМЕТРИЧЕСКИЙ МЕТОД ОПРЕДЕЛЕНИЯ
СЛЕДОВЫХ КОЛИЧЕСТВ ЗОЛОТО (III) С ИСПОЛЬЗОВАНИЕМ 2, 2',3,4-ТЕТРАГИДРОКСИ-3'-СУЛЬФО-5'-ХЛОРАЗОБЕНЗЕОЛА В ПРИСУТСТВИИ КАТИОННЫХ ПОВЕРХНОСТНО-АКТИВНЫХ ВЕЩЕСТВ
П.Р.Мамедов
Показано, что золото(Ш) с 2,2',3,4-тетрагидрокси-3'-сульфо-5'-хлоразобензолом (TCXAB) быстро реагирует в кислой среде при pH 5-6 с образованием коричневато-желтого комплекса и при pH 4-5 с образованием коричневатых комплексов в присутствии катионных поверхностно-активных веществ - хлорида цетилпиридиния (ЦПСГ), бромида цетилпиридиния (ЦПВг) и бромида цетилтриметиламмония (ЦTMABr). Спектры поглощения Au(III)-TСXAБ представляют собой кривую с максимальным свето поглощением при 490 нм и молярным коэффициентом поглощения 2,3 104 моль-1см-1 в водных средах. Спектры поглощения систем Au^IQ-TCXAE-CPCl, Au(III)-TСXAБ-ЦПBr и Au(III)-TСXAB-ЦТMABr представляют собой кривую с максимальными свето поглощением при 520, 520 и 540 нм. и молярные коэффициенты поглощения составляют 3.l8 104, 3.6l 104 и 3.81 104 моль-1см-1 соответственно. Подчиняемость закону Бера Au(III) в двойной системе Au(III)-TСXAБ соблюдалось в пределах 0.584-5.61 мкг/мл, а в тройных системах Au(III)-TСXAБ-ЦПCl, Au(III)-TСXAБ-ЦПBr, Au(III)-TСXAБ-ЦТMABr- в пределах 0.428-6.362, 0.435-6.221 и 0.436-6.832 мкг мл-1 соответственно. Чувствительность Сэнделла для Au(III) составила 7 мкг/см в системе Au(III)-TCXA, и 5, 6, 5 мкг/см в системах Au(III)-TСXAБ-ЦПCl, Au(III)-TСXAБ-ЦПBr и Au(III)-СXAБ-ЦTMABr. Предложенные методы были успешно использованы при определении Au(III) в нескольких искусственных смесях. Относительное стандартное отклонение составляло (0-2.0)% для Au(III), что свидетельствует о высокой точности и воспроизводимости этих методов. Полученные результаты хорошо согласуются с образцами искусственной смеси, проанализированными методом оптической эмиссионной спектрометрии с индуктивно связанной плазмой.
Ключевые слова: спектрофотометрический, Au(III), определение, 2,2',3,4-тетрагидрокси-3'-сульфо-5'-хлор-азобензол, катионные поверхностно-активные вещества.
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