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54 AZ9RBAYCAN KIMYA JURNALI № 4 2018 ISSN 2522-1841 (Online)
ISSN 0005-2531 (Print)
UDC 543.4:542.61:546.851
NEW SPECTROPHOTOMETRY METHOD FOR THE DETERMINATION OF TRACE LEVEL OF SILVER USING 2,2-DI(2,3,4-TRIHYDROXYPHENILAZO)BIPHENYL
A.R.Guliyeva, A.M.Maharramov, F.M.Chiragov, P.R.Mammadov
Baku State University [email protected] Received 04.06.2018
A very simple, sensitive, highly selective and non-extractive spectrophotometry method for the determination of trace amounts of silver(I) has been developed. 2,2-di(2,3,4-trihydroxyphenilazo)biphenil (DTFAB) has been proposed as a new analytical reagent for the direct non-extractive spectrophotomet-ric determination of silver(I). In the water media DTFAB reacts with silver to give a highly absorbent greenish yellow chelate with a molar ratio 2:1 (Ag:DTFAB). The reaction was instantaneous and the maximum absorption was obtained at 540 nm and remains stable for 24 h. The average molar absorptivity and Sandell's sensitivity were found to be 4.3 •Ш4 l mol-1 cm-1 and 5.0 mkg/cm2 of silver(I), respectively. Linear calibration graphs were obtained for 0.1-30 mkg/ml of silver(I). A large excess of over 30 cations, anions and complexing agents do not interfere in the determination. The method is highly selective for silver and was successfully applied to synthetic mixtures. The method has high precision and accuracy (s = ± 0.01 for 0.5 mkg/l).
Keywords: spectrophotometry; silver; 2,2-di(2,3,4-trihydroxyphenilazo)biphenil; determination; synthetic mixtures.
was synthesized according to the method of [3] and a color reaction of DTFAB with Ag(I) in aqueous media was carefully studied.
Although many sophisticated techniques, such as electrothermal AAS [4], flame AAS [5, 6], graphite furnace AAS [7], liquid chromatog-raphy [8], electrophoresis [8], are available for the determination of silver at trace levels in numerous complex materials, factors such as the low cost of the instrument, easy handling, portable, lack of any requirement for consumables and almost no maintenance, have caused spectropho-tometry to remain a popular technique.
The aim of the present study is to develop a simpler direct spectrophotometric method for the trace determination of silver(I) with DTFAB in aqueous solutions. The method described here has recorded for the first time the non-extractive direct spectrophotometric determination of silver(I) in aqueous media without the recourse of any clean-up step. This method is far more selective, sensitive, non-extractive, simple and rapid than all of the existing spec-trophotometric methods [9-12].
Experimental section Instruments
The absorbance of solutions was measured with a Perkin Elmer (United States) (Model: Lambda-40) double-beam UV/VIS spectropho-
Introduction
Silver is precious metal, used in solar panels, water filtration, jewellery, silverware, in electrical contacts and conductors, in catalysis of chemical reactions [1]. Separation, precon-centration and sensitive determination of silver ion is of increasing interest.
1,5-Diphenylthiocarbazone is one of the most widely used photometric reagents and forms colored water-insoluble complexes with silver ions. Silver-dithizone complexes are water insoluble and thus their determination requires a prior solvent extraction step into CHCl3 or CCl4, followed by spectrophotometry determinations [2]. Since these methods involve solvent extraction are lengthy and time-consuming and lack selectivity due to much interference, CHCl3 and CCl4 have been listed as toxic. This problem has been overcome in recent years and a new analytical reagent for the direct non-extractive spectrophotometric determination of silver(I) has been proposed. The azocompounds on the base of pyroghallol have widely been applied for the determination of noble metal ions, this type of reagent has higher sensitivity and high selectivity [3]. In the search for more sensitive azocompounds on the base of pyro-ghallol reagent, in this work, a reagent 2,2'-di(2,3,4-trihydroxyphenilazo)biphenil (DTFAB)
tometer and with a KFK-2 photoelectrocolori-meter (Russia), with 1 cm matched quartz cells. The pH values of solutions was controlled hh the ionomer I-121 with glass electrode customized by standard buffer solutions.
Chemicals and Reagents
All of the chemicals used were of analytical reagent grade or the highest purity available. Distilled deionized water, which is non-absorbent under ultraviolet radiation, was used throughout. Glass vessels were cleaned by soaking in acidified solution of KMnO4 or K2Cr2O7 followed by washing with concentrated HNO3 and rinsed several times with deionized water. Stock solutions and environmental water samples (1000 ml each) were kept in polypropylene bottles containing 1ml of concentrated HNO3. More rigorous contamination control was applied when the silver levels in the specimens were low.
2,2'-di(2,3,4-trihydroxyphenilazo)biphe-
nil (2x10-3 M). The reagent was synthesized according to the method of [2]. The solution was prepared by dissolving the requisite amount of èzs-(2,3,4-trihydroxyfenilazo)biphenil in a known volume of absolute ethanol. More dilute solutions of the reagent were prepared as required.
Standard silver solution (1x10-2 M). A stock solution 1x10-2 M, 100 ml of silver(I) was prepared by dissolving 0.1575 g of silver nitrate in 100 ml of distilled deionized water and added 0.1 ml concentrated HNO3. The working standard of silver solution was prepared by suitable dilutions of this stock solution.
EDTA solution. A 100 mL stock solution of EDTA (0.01%) was prepared by dissolving 10 mg of A C S. grade (>90%) ethylenedi-aminetetraacetic acid, dissodium salt dehydrate in 100 ml deionized water.
Tartrate solution. A 100 ml stock solution of tartrate (0.01%) was prepared by dissolving 10 mg of A.C.S. grade (99%) potassium sodium tartrate tetrahydrate in 100 ml deionized water.
Ammonium hydroxide solution. All solutions of ammonium hydroxide was prepared by diluting some ml concentration NH4OH (2830% A.C.S. grade) to 100 l with deionized water. The solution was stored in a glass bottle.
Other solutions. Solutions of a great number of inorganic ions and complexing agents were prepared from their analytical grade or equivalent grade, water soluble salts. In the case of insoluble substances, special dissolution methods were adopted [12].
General Procedure. To 0.1-1.0 ml of a
3
slightly acidic solution containing 2*10 M of silver(I) in a 25-ml volumetric flask was mixed with 1.0-4.0 ml (preferably 2.0 ml ) of 1 *10-3 M ¿zs-(2,3,4-trihydroxyfenilazo)biphenil solution (preferably 2.0 ml). The mixture was diluted up to the mark with pH solution to attain the necessary acidity, acetate ammonia buffer solutions (pH 3-11) and H2SO4 (pH 0-2) were used. After 5 min the absorbance was measured at 540 nm against a corresponding reagent blank. The silver content in an unknown sample was determined using a concurrently prepared calibration graph.
Results and discussion
Absorption spectra
The absorption spectra of greenish yellow color of the silver-DTFAB system in presence of pH 8 solution were recorded using a spectrophotometer. The absorption spectra of the silver-DTFAB represent a symmetric curve with maximum absorbance at 540 nm and an average molar absorptivity of 4.3 x 104 l/mol cm (Figure). The reagent blank having maximum absorbance wavelength at 430 nm. In all instances, measurements were made at 540 nm against a corresponding reagent blank.
Absorption spectra of the reagent blank (1) and the Ag-DTFAB system (2).
Effect of acidity. Of the various pH 0-10 of the solution studied, pH 7-9 was found to be the optimum for the silver-DTFAB system. The maximum and constant absorbance of the silver-DTFAB system was obtained in the presence of pH 8 at room temperature (25±5)0C. The absorbance of the reagent solution and the silver-DTFAB system depends on the medium pH; therefore, the absorption spectra are studied relative to a blank experiment (DTFAB).
Effect of time. The reaction is fast. Constant maximum absorbance was obtained just after 5 min of the dilution to volume at room temperature (25±5)0C, and remained strictly unaltered for 24 h.
Effect of temperature. The absorbance at different temperatures, 0-800C, of a 25 ml solution of silver-DTFAB was measured according to the standard procedure. The absorb-ance was found to be strictly unaltered throughout the temperature range of 10-400C. Therefore, all measurements were performed at room temperature (25 ±5)0C.
Effect of the reagent concentration. Different molar excesses of DTFAB were added to a fixed metal-ion concentration and the absorb-ance 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 molar ratios of 1:10 to 1:50 produced a constant absorbance of Ag-DTFAB system. A greater excess of the reagent was not studied. For all subsequent measurements, 2 ml of 210-4 M DTFAB reagent was added.
Stoichiometry. The component ratio in the complexes was found using the isomolar series method, the relative yield method by Starik and Barbanel, and the equilibrium shift method [11]. All the methods showed that the component ratio was 2:1 in the silver-DTFAB system. The number of protons displaced upon complex-ation was determined by the Astakhovs method, and the indicated component ratio in the complexes was confirmed [12].
Analytical performance of the method
Calibration curve. The effect of silver (I) concentration was studied over 0.01-100 mkg/l, distributed in four different sets (0.01-
0.1, 0.1-1, 1-10, 10-100 mkg/l) for convenience of the measurement. The absorbance was linear for 0.1-30 mkg/l of silver(I) in aqueous media. From the slope of the calibration graph, the average molar absorption coefficient was found to be 4.3 104 l mol-1cm-1 in aqueous medium. The selected analytical parameters obtained with the optimization experiments are summarized in Table 1.
Table 1. Selected analytical parameters obtained by optimization experiments_
Parameters Studied range Selected value
Wavelength / ■■,.max, nm 200-800 540
pH 0-1 8
Time, h 1-24h 5-10 min
Temperature, 0C 0-800C 25 ± 5 0C
Reagent (fold molar excess, M:R) 1:10-1:50 1:20
Molar absorption coefficient l mol-1cm-1 1.5104-5.8104 4.3 104
Linear range, mkg/l 0.001-100 0.1-30
Detection limit, mkg/l 0.01-100 1
Sandell's sensitivity, mkg/cm2 0.1-100 5
Relative Standard 0-2 0-2
Regression coefficient 0.998-0.9999 0.999
Effect of foreign ions. The effect of over 30 cations, anions and complexing agents on the determination of only 1 mkg/ml of silver was studied. The criterion for interference [24] was an absorbance value varying by more than 5% from the expected value for silver(I) alone. There was no interference from the following 1500-fold amount of EDTA and tartrate of a 100-fold amount. EDTA prevented the interference of a 40-fold excess of Al(III), 145-fold excess of Cr(VI), 120-fold excess of Pb(II), 140fold excess of Na or a 40-fold excess of Sn(IV) and tartrate prevented the interference of a 30fold excess of V(V) or Au(III) . During interference studies, if a precipitate was formed, it was removed by centrifugation. The quantities of these diverse ions mentioned were the actual amounts studied but not the tolerance limit. However, for those ions whose tolerance limit has been studied, the tolerance ratios are mentioned in Table 2.
Table 2. Tolerance limits of foreign ions, tolerance ratio [Species(x)]/Ag (w/w)
Species x Tolerance ratio [Species (x) /Ag (w/w)] Reference [12] Species x Tolerance ratio [Species (x) /Ag (w/w)] Reference [12]
Be(III) 140 50 Sr(II) 45 20
Ca(II) 160 20 Ta(IV) 150 100
Cd(II) 120 50 HCO3 170 100
Co(III) 150 100 tartarat 1500 1000
Cr(III) 145 200 Ni(II) 165 100
Cu(II) 70 50 Cl- 135 20
Fe(III) 40 25 Pb(II) 120 100
Hg(II) 135 50 c2O2~ 200 100
K(I) 140 10 Ga(III) 130 100
Mg(II) 170 100 La(III) 140 100
Mn(II) 150 100 cyanide 140 50
Mo(II) 145 100 EDTA 1500 1000
Na(I) 140 100 Au(III) 30 25
Sn(IV) 40 10 phosphate 130 100
V(V) 30 10 Al(III) 40 10
Zn(II) 155 10 CH3COO- 1300 1000
Precision and accuracy. The precision of the present method was evaluated by determining different concentrations of silver(I) (each analyzed at least five times). The relative standard deviation (n = 5) was (2-0)%, for 0.1-30 mkg of Ag(I) in 25 ml, indicates that this method is highly precise and reproducible. The detection limit (3s of the blank) and Sandell's sensitivity (concentration for 0.001 absorbance unit) for Ag(I) were found to be 1 mkg/ml, 5 mkg/cm2, respectively. The reliability of our Ag-chelate procedure was tested by recovery studies. Regression analysis of Beer's law plots at 540 nm revealed a good correlation. The method was also tested by analyzing several synthetic mixtures containing silver and diverse ions (Table 3). The results for silver recovery were in good agreement with added values. The average percentage recovery obtained for
Table 3. Determination of silver(I) in synthetic mixtures
the addition of silver spike to some drink and tap water samples were quantitative. Hence, the precision and accuracy of the method were found to be excellent.
Applications. The present method was successfully applied to the determination of silver in series of synthetic mixtures of various compositions and also in a number of drink water samples.
Determination of silver in synthetic mixtures. Several synthetic mixtures of varying compositions containing silver(I) and diverse ions of known concentrations were determined by the present method using EDTA as a masking agent and the results were found to be highly reproducible. The results are shown in Table 3. The accurate recoveries were achieved in all solutions.
Mixtures Composition of mixture, mkg/ml Silver, mkg/ml Recovery ± sb (%)
Added Found"
A Ag+ 1.5-2.0 1.49-2.02 98 ± 0.2 102 ± 0.1
B As in A + Mg2+ (25)+Fe3+(25) 1.5-2.0 1.48-1.98 97 ± 0.3 98 ± 0.2
C As in B + Mn2+ (25)+Co3+ (25) 1.5-2.0 1.51-2.02 101 ± 0.2 102 ± 0.2
D As in C + Cr 3+(25)+ Ca2+ (25) 1.5-2.0 1.52-2.04 102 ± 0.3 104 ± 0.2
E As in D + Cu2+(2 5 )+Ni2+25) 1.5-2.0 1.52-2.03 102 ± 0.4 103 ± 0.2
a Average of five analyses of each sample; the measure of precision is the standard deviation (s).
Conclusion
Developed by a new approach and alternative spectrophotometric determination method for silver(I). In the present work a simple sensitive, selective non-extractive and inexpensive method with silver-DTFAB system was developed for the determination of silver(I) in industrial and environmental samples. The method also offers a very efficient procedure for speciation analysis. Therefore, this method effectively the monitoring of trace amounts of silver(I) in drink and tap water samples.
References
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2,2'-Di(2,3,4-TRffliDROKSiFENiLAZO)BiFENiLDaN iSTiFADO EDOROK GUMU§UN iZ MiQDARININ TOYiN EDiLMOSi U£UN YENi SPEKTROFOTOMETRiK USUL
A.R.Quliyeva, A.M.M3h3rramov, F.M.^iraqov, P.RMammadov
Cox sada, hassas, yuksak selektiv va qeyri-ekstraksiyali spektrofotometrik metodla gumu§un(I) tayini nazarda tutulmu§dur. 2,2'-di(2,3,4-trihidroksifenilazo)bifenil (DTFAB) gumu§un(I) qeyri-ekstraksiyali spektrofotometrik tayini ugun yeni analitik reagent kimi taklif edilmi§dir. Su muhitinda DTFAB gumu§ ila 2:1 (Ag:DTFAB) molyar nisbati ila yuksak i§iqudmaya malik ya§imtil-sari xelat verir. Reaksiya ani olur va maksimum udulma 540 nm saviyyasinda mu§ahida edilir va 24 saat sabit qalir. Orta molyar udma amsali va Sandell hassasligi muvafiq olaraq 4.3 • 104 l mol-1 sm-1 va 5.0 mkq/sm gumu§(I) olub. Daracali qrafikda xattilik 0.1-3 mkq/ml Ag(I) intervalda mu§ahida olunur. Boyuk miqdarda 30-dan gox kation, anion va kompleks agentlari tayinata mane olmur. Metod gumu§ ugun yuksak selektivdir va sintetik qari§iqlara ugurla tatbiq olunur. Metod yuksak hassasliq va duzgunluya malikdir (s = ± 0.5 0 mkq/l ugun).
Agar sozlar: spektrofotometriya, gumu§, 2,2-di(2,3,4-trihidroksifenilazo)bifenil, tayin edilma, sintetik qari§iq.
A3EPEAH#^AHCKHH XHMHHECKHH ^YPHAH № 4 2018
НОВЫЙ СПЕКТРОФОТОМЕТРИЧЕСКИЙ МЕТОД ОПРЕДЕЛЕНИЯ СЛЕДОВЫХ КОЛИЧЕСТВ СЕРЕБРА С ИСПОЛЬЗОВАНИЕМ 2,2'-ДИ(2,3,4-ТРИГИДРОКСИФЕНИЛАЗО)БИФЕНИЛА
А.Р.Гулиева, А.М.Магеррамов, Ф.М.Чирагов, П.Р.Мамедов
Разработан простой, чувствительный, высокоселективный спектрофотометрический метод для определения следовых количества серебра(1). 2,2'-ди(2,3,4-тригидроксифенилазо)бифенил (ДТФАБ) предложен в качестве нового аналитического реагента для неэкстракционного спектрофотометрического определения серебра(1). В водных средах ДТФАБ реагирует с серебром, образуя высокопоглощающий зеленовато-желтого цвета хелат с молярным соотношением 2:1 (Ag:ДТФAБ). Реакция протекает мгновенно, и максимальное поглощение происходит при 540 нм и остается стабильным в течение 24 ч. Средняя молярная поглощающая способность и чувствительность Санделла оказались равными 4.3 104 л моль-1 см-1 и 5.0 мкг/см серебра(1) соответственно. Линейные калибровочные графики получены для 0.1-30 мкг/мл серебра(1). Большой избыток более 30 катионов, анионов и комплексообразователей не мешает определению последнего. Метод высоко селективен для серебра, обладает высокой точностью и чувствительностью (5 = ± 0.01 для 0.5 мкг/л). Успешное применение его показано на примере синтетических смесей.
Ключевые слова: спектрофотометрия, серебро, 2,2'-ди(2,3,4-тригидроксифенилазо)бифенил, определение, синтетические смеси.
