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SPECTROPHOTOMETRIC DETERMINATION OF Fe(III), Cu(II) AND UO2(II) IONS

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SPECTROPHOTOMETRIC DETERMINATION OF Fe(III), Cu(II) AND UO2(II) IONS
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     Bulletin of the Chemists and Technologists of Macedonia , Vol. 24 , No. 1, pp. 11–19 (2005)GHTMDD –456 ISSN 0350 – 0136Received: April 19, 2004 UDC: 546-4 : 543.48Accepted: March 3, 2005 Original scientific paper  SPECTROPHOTOMETRIC DETERMINATION OF Fe(III), Cu(II) AND UO 2 (II)   IONSBY A NEW ANALYTICAL REAGENT DERIVED FROM CONDENSATIONOF MONOETHANOLAMINE AND ACETYL ACETONE Adel S. Orabi 1 , Adel El Marghany 2 , Medhat A. Shaker 3 , Alaa E. Ali 3   1 Chemistry Department, Faculty of Science, Suez Canal University, Ismailia, Egypt  2 Chemisty Department, Faculty of Education, Suez Canal University, Suez, Egypt  3 Physics & Chemistry Department, Faculty of Education “Damanhour”, Alexandria, Egypt  dralaa@yahoo.com   A highly sensitive and selective spectrophotometric method is proposed for direct trace determination of Fe(III), Cu(II) and UO 2 (II) in aqueous solutions. The method is based on the reaction of those cations with a newanalytical reagent 2-ethanolimino-2-pentylidino-4-one (B3). Under the optimum reaction conditions and other impor-tant analytic parameters, B3 reacts with the investigated cations and forms colored complexes. The optimum pH forcomplex formation has been adjusted. The color reaction is rapidly completed and the absorbance remains stable forat least a week at room temperature. The Fe(III) complex is detected at λ  max = 440 nm and pH = 3.5, the Cu(II) com-plex is detected at λ  max = 340 nm and pH = 6.0, while that of UO 2 (II) is detected at λ  max = 370 nm and pH = 4.0. Bear-Lambert’s law is obeyed in the concentration range = 0.5 – 3.0·10 –4 M (2 – 17 µ g/ml for Fe(III), 3 – 9 µ g/ml forCu(II) and 13 – 81 µ g/ml for UO 2 (II)   complexes. The stoichiometries of the formed complexes are determined usingdifferent spectrophotometric methods. The conditions for the complexation were determined. The rate of the reactionbetween Fe(III)   ion and the ligand has been evaluated under pseudo first order condition. The ability of the presentligand to determine micrograms of Fe(III), Cu(II) and UO 2 (II) ions is tested and the resulted data are analyzed usingstatistical parameter to obtain the minimum error. The effect of various substances on the determination of the inves-tigated cations is also investigated in detail. The results indicate that most of the studied co-existing substances couldbe tolerated in considerable amounts. The proposed method offers the advantages of sensitivity, rapidity, selectivityand simplicity without any prior separation or extraction. It has been applied to the analytic samples with satisfactoryresults. Keywords: ethanolamine; Schiff base; spectrophotometry; acetyl acetone; condensation INTRODUCTIONThe separation and determination of heavymetal ions in the environmental and biochemicalresearch have been one of the most important top-ics of analytical chemistry. As compared with theother techniques, spectrophotometry is very sim-ple, rapid and less expensive for determination of elements in a variety of samples. Developinghighly functional chelating agents such as Schiff bases has been a great concern of many analyticalchemists. Many investigations have been centeredon the structure and bonding in Schiff bases butfew have been directly concerned with analyticalapplications [1–6]. Copper is essential for life butis highly toxic above certain limits to organismslike certain algae, fungi and many bacteria or vi-ruses [7, 8]. In addition, the accumulation of cop-per in the human liver is a characteristic of Wil-son’s disease, which produces neurological andpsychiatric defects [9]. There are conventionalmethods for copper(II)   determination [10–12].However, the colorimetric methods are often pre-ferred due to the fact that they involve less expen-sive instruments and show rapid results. Iron is themost important nutrient in the human diet as it iscomplexed with hemoglobin and plays a majorrole in respiratory enzymes such as cytochromes  12    A. S. Orabi, A. El Marghany, M. A. Shaker, A. E. Ali    Bull. Chem. Technol. Macedonia , 24 , 1, 11–19 (2005) [13]. Several methods for the analysis of iron inpharmaceuticals and environmental samples havebeen reported [14–20]. Considerable interest hasdeveloped in the determination of trace uranium inenvironmental sites as well as in facilities of thenuclear industry. Electroanalytical techniques havefrequently been used for this purpose. In particu-lar, adsorptive stripping voltammetry is becoming awidely accepted tool for ultra-trace measurement of uranium [21–25]. This work has been aimed todevelop a highly sensitive and efficient spectro-photometric method for iron, copper and uranylcations determination, based on the formation of colored complexes which were formed by the reac-tion of those cations with 2-ethanolimino-2-pentyl-idino-4-one (B3) (Fig. 1). Various factors influencethe sensitivity of the proposed method such aswavelength, pH, effect of foreign ions, and rangesof applicability of the Beer’s law in the determina-tion of the investigated cations are also included.The method has been applied to some pharmaceu-tical and environmental water samples. H 3 CCH 2 CCH 3 CONCH 2 CH 2 OHH 3 CCHCCH 3 COHNCH 2 CH 2 OH   Fig. 1. The structural formulae of the tridentate ligand2-ethanolimino-2-pentylidino-4-one. EXPERIMENTAL  Reagents All chemicals were of analytical-grade qual-ity and freshly doubly distilled deionized waterwas used throughout the course of the investiga-tion. Synthesis of the ligand, B3 The 2-ethanolimino-2-pentylidino-4-one (B3)as shown in Fig. 1 was prepared as reported before[26]. The purity of the ligand was checked by theelemental analysis and physicochemical methods.  Apparatus The pH measurements were carried out usingthe Fischer Scientific Accument pH-meter model825 MP, fitted with the Fischer combined elec-trode and calibrated by a standard buffer solutionat the desired temperature. All uv-visible spectraof the investigated compounds were obtained atroom temperature by the uv-visible spectrophotometermodel Perkin-Elmer 550 S using 1 cm quartz cells.  Analytical method  A solution containing less than 30 µ g of eachof the iron(III), copper(II) and uranyl(II)   cationswas transferred into a 25 ml calibrated flask, 5.0ml of either 0.1 M KOH or HNO 3 solution to reachthe optimum value of pH (3.5 for Fe(III), 6.0 forCu(II) and 4.0 for UO 2 (II)) and 6.0 ml of 0.3 % 2-ethanolimino-2-pentylidino-4-one solution wereadded successively, the solution was diluted to themark with water and mixed well. It was waited 90min and the absorbance at the required wavelength(440 for Fe(III), 340 for Cu(II) and 370 nm forUO 2 (II)) in a 1 cm quartz cell against the reagentblank was measured. All absorbance measure-ments were carried out with a model Perkin-Elmer550 S.  Reference method  The measurements were carried out with stan-dard methods. Iron(III) was determined spectropho-tometrically [20, 27, 28]. The copper(II)   determina-tion was determined by the conventional spectropho-tometry method [10]. The recommended procedurefor the detection of uranyl(II) determination was car-ried out by the conventional method [29, 30].RESULTS AND DISCUSSION Optimal conditions for formation of the complexes This work was carried out on the complexesof Fe(III), Cu(II) and UO 2 (II) with the entitledligand due to the great tendency of these ions toform chelate compounds with characteristic colors.The effect of pH on the absorption spectra of Fe(III), Cu(II) and UO 2 (II)-ligand mixtures were  Sectrophotometric determination of Fe(III), Cu(II) and UO 2 (II) ions by a new analytical reagent … 13         UO 2 (II) + B30.00.51.01.52.00.01.02.03.04.0 380 nm375 nm370 nm365 nm360 nm studied by mixing 1·10 –5 M of the metal ions with3·10 –5 M  ligand under controlled pH values. ThepH’s were adjusted to the required values usingportions of 0.1 M HNO 3 and 0.1 M KOH and theabsorbance values of the solutions were measuredin the range of  λ  = 300 – 500 nm. It is evidentfrom the results, that the absorbance gave maxi-mum value at pH = 6.0 for Cu(II) – ligand mixtureat λ  = 340 nm, at pH 4.0 for UO 2 (II)-ligand mix-ture at λ  = 370 nm and at pH 3.5 for Fe(III)-ligandmixture at λ  = 440 nm. The validity of the Beer’slaw checked under the optimum condition gave agood straight line and the molar absorptivity wascalculated for each mixture at different λ    (Fig. 2). Fe(III) + B300.10.20.30.01.02.03.0[Fe 3+ ] · 10 4 mol/L       A      b     s     o     r      b     a     n     c     e   Cu(II) + B30.02.04.06.08.00.01.02.03.04.0[Cu 2+ ] · 10 4 mol/L    A   b  s  o  r   b  a  n  c  e 350 nm345 nm340 nm335 nm Cu 2+ + B34.0E+026.0E+028.0E+021.0E+031.2E+031.4E+03335340345350 λ  ( nm) UO 22+ + B34.7E+035.2E+035.7E+036.2E+036.7E+03360370380 λ  ( nm) Fe(III) + B38.5E+029.0E+029.5E+021.0E+031.1E+03425435445455 λ  ( nm)      ε    (   L  m  o   l   –   1   c  m   –   1    )      ε    (   L  m  o   l   –   1   c  m   –   1    )      ε    (   L  m  o   l   –   1   c  m   –   1    )   A   b  s  o  r   b  a  n  c  e  14 A. S. Orabi, A. El. Marghany, M.A. Shaker, A. E. Ali Bull. Chem. Technol. Macedonia , 24 , 1, 11–19 (2005) Fig. 2. Confirmation of the Beer’s law for the investigated complexes  Absorption spectra The entitled ligand B3 reacts with trivalentiron to form a yellow complex which has an ab-sorption maximum at 440 nm at optimum pH =3.5. The Beer’s law was valid over a range of con-centrations from 5 – 60 ppm. Determination of Fe(III) was also carried out using the standardmethod [28]. The iron in clay and limestone wasdetermined using the present ligand where it gavenearly a similar result to that obtained with EDTA[31–33]. The Fe(III) % obtained by the new re-agent had an error in the range of 0.01 %. Theformed green Cu-ligand complex had an absorp-tion maximum at 340 nm at pH = 6.0. The Beer’slaw was valid in the range of concentrations from6 – 70 ppm [34–39]. The yellow orange UO 2 (II)-ligand complex obeyed the Beer’s law in a widerange of concentration (27–270 ppm) at optimumpH = 4.0 and λ = 370 nm [40–42]. Characteristics of the complexes The colored ligand-metal complexes could beformed rapidly at 10 – 40 o C and their absorbancesremained stable for at least a week at 25 o C. Thecompositions of these complexes were determinedby different methods such as the molar ratio method[43], the method of continuous variation (the Job’smethod) [44, 45], the Haymann’s method [46] andthe straight-line method [47]. The molar ratiomethod carried out on a series of 50 ml solutionwhich was previously prepared by mixing 1·10 –5 Mmetal ions with ligand of concentration range 2·10 –6  – 3.0·10 –5 M at the optimum pH for each complexand the graphs plotted for the molar ratio methodwere shown in Fig. 3. The data indicated that thecomposition of the formed complexes was as 1:1and 1:2 (metal ions : ligand). The continuous varia-tion method proceeded on a series of constant con-centrations (6·10 –5 M) at the optimum pH (Fig. 4).The results confirmed the composition of theformed complexes as 1:1 and 1:2. The Haymann’smethod was discussed using a series of 20 ml solu-tion which was prepared by mixing the metal ionsand ligand keeping the ratio of metal ions : ligand1:2 and the concentration of metal ions regularlyincreased from 2.5·10 –21 M to 3.0·10 –3 at desiredpH. The plotting C M .C L  /A λ Vs. (C L + C M ), whereC L and C M were the concentration of the ligandand the metal ions respectively, A λ was the absorp-tion at certain λ , gave a good straight line which con-firmed 1:2 composition (Fig. 5). Fe(III) + B30.20.40.60.81.01.20.01.02.03.04.05.0[B3]/[Fe 3+ ]       A      b    s    o    r      b    a    n    c    e 450 nm445 nm440 nm435 nm Cu(II) + B30.00.40.81.21.60.01.02.03.04.0[B3]/[Cu 2+ ]       A      b    s    o    r      b    a    n    c    e 335 nm340 nm345 nm350 nm    Sectrophotometric determination of Fe(III), Cu(II) and UO 2 (II) ions by a new analytical reagent …   15         Fig. 3. Determination of the formed M-B3 complexesby the molar ratio method The straight-line method was carried out us-ing constant metal ions concentration at 1·10 –3 Mwhile the ligand concentration varied from 0.6·10 –3  to 3·10 –3 M and the pH of solution was adjusted atthe optimum value for each complex. The plot1/  V  n , (where V  = volume of ligand added and n =1, 2, 3), vs. 1/   A λ  gave a linear relationship, when n = 1,2 indicating 1:1 and 1:2 complexes and alsoplotting log V   L vs. log  A λ  gave straight lines whichconfirmed the 1:1 and 1:2 complexes. Fig. 4. Determination of the stoichiometries of the metalcomplexes by the Job's method UO 2 (II) + B30.00.10.30.40.50.70.80.01.02.03.04.05.0[B3]/[UO 22+ ]       A      b    s    o    r      b    a    n    c    e 365 nm370 nm375 nm380 nm Cu(II) + B30.00.40.81.21.60.02.04.06.0[B3]·10 –3 340 nm345 nm355 nm350 nm Fe(III) + B30.20.61.01.40.02.04.06.0[B3]·10 –3 450 nm445 nm440 nm435 nm330 nm UO 2 (II) + B30.00.10.20.30.40.50.60.70.01.02.03.04.05.06.0[B3]·10 –3 365 nm370 nm375 nm380 nm360 nm ε   A λ    ε   A λ    ε   A λ    0102030405060345678910([Cu(II)] +[B3])10 -3 340 nm345 nm350 nm355 nm    (   [   C  u   (   I   I   )   ]   [   B   3   ]   /       A        λ    )  ·   1   0   –   6     (   [   F  e   (   I   I   I   )   ]   [   B   3   ]   /       A        λ    )  ·   1   0   –   6   4.06.08.010.012.014.016.018.00.02.04.06.08.010.0([UO 2 (II)] +[B3])10 -3 360 nm365 nm370 nm375 nm380 nm    I   )   ]   [   B   3   ]   /       A        λ    )  ·   1   0   –   6   12345678012345678([Fe(III)] +[B3])10 -3 450 nm445 nm440 nm435 nm430 nm
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