Ion pairs of 5,5-dimethyl-2-(2-hydroxy-3,5-disulfophenylhydrazo)cyclohexane-1,3-dione with cationic...

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Ion Pairs of 5,5-dimethyl-2-(2-hydroxy-3,5-disulfophenylhydrazo)cyclohexane-1,3-dione with Cationic Surface-ActiveSubstances as Analytical Reagent for Determination of Copper(II)Kamran T. Mahmudovab; Abel M. Maharramova; Rafiga A. Aliyevaa; Ismayil A. Aliyeva; Maximilian N.Kopylovichb; Armando J. L. Pombeirob

a Baku State University, Department of Chemistry, Baku, Azerbaijan b Centro de Química Estrutural,Complexo I, Instituto Superior Técnico, TU Lisbon, Lisbon, Portugal

Online publication date: 13 December 2010

To cite this Article Mahmudov, Kamran T. , Maharramov, Abel M. , Aliyeva, Rafiga A. , Aliyev, Ismayil A. , Kopylovich,Maximilian N. and Pombeiro, Armando J. L.(2010) 'Ion Pairs of 5,5-dimethyl-2-(2-hydroxy-3,5-disulfophenylhydrazo)cyclohexane-1,3-dione with Cationic Surface-Active Substances as Analytical Reagent forDetermination of Copper(II)', Analytical Letters, 43: 18, 2923 — 2938To link to this Article: DOI: 10.1080/00032711003763665URL: http://dx.doi.org/10.1080/00032711003763665

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Spectrophotometry

ION PAIRS OF 5,5-DIMETHYL-2-(2-HYDROXY-3,5-DISULFOPHENYLHYDRAZO)CYCLOHEXANE-1,3-DIONEWITH CATIONIC SURFACE-ACTIVE SUBSTANCES ASANALYTICAL REAGENT FOR DETERMINATION OFCOPPER(II)

Kamran T. Mahmudov,1,2 Abel M. Maharramov,1

Rafiga A. Aliyeva,1 Ismayil A. Aliyev,1

Maximilian N. Kopylovich,2 and Armando J. L. Pombeiro21Baku State University, Department of Chemistry, Baku, Azerbaijan2Centro de Quımica Estrutural, Complexo I, Instituto Superior Tecnico,TU Lisbon, Lisbon, Portugal

A new organic reagent, 5,5-dimethyl-2-(2-hydroxy-3,5-disulfophenylhydrazo)cyclo-hexane-1,3-dione (H2L), was synthesized by azo coupling of diazonium salts of 2-hydroxy-

3,5-disulfoaniline with dimedone. The dissociation constants of H2L were determined by

potentiometric titration, being pK1¼ 5.90� 0.03 and pK2¼ 9.67� 0.04. The interaction

in systems of H2L and cationic surface-active substances (CSAS), cetylpyridinium chloride

(CPCl), cetylpyridinium bromide (CPBr), or cetyltrimethylammonium bromide (CTABr)

was studied in the presence and absence of Cu(II). It was found that the detection limit of

Cu(II) using H2L–CSAS pairs decreases in accord with the stability of associates

H2L(CPCl)2>H2L(CPBr)2>H2L(CTABr)2 and their copper(II) complexes Cu[(HL)

(CPCl)2]2>Cu[(HL)(CPBr)2]2>Cu[(HL)(CTABr)2]2. The effects of foreign ions

and masking substances on the complexation were studied and showed that the reaction

of Cu(II) with H2L in the presence of CSAS is more selective. Based on these observations,

a procedure for the spectrophotometric determination of copper(II) in soils polluted by oil,

seawater, igneous rock, and nickel-based alloys was developed.

Keywords: Azo derivatives of b-diketones; Copper complexes; 5,5-Dimethyl-2-(2-hydroxy-3,5-disulfophe-

nylhydrazo) cyclohexane-1,3-dione; Nickel-based alloys analysis; Seawater igneous rock; Soils polluted

by oil

Received 29 July 2009; accepted 11 November 2009.

This work has been partially supported by the Foundation for Science and Technology (FCT),

Portugal, and its PPCDT (FEDER funded), and ‘‘Science 2007’’ programs. K. T. Mahmudov and

M. N. Kopylovich express gratitude to the FCT for their post-doctoral fellowship and working contract.

The authors also acknowledge the Portuguese NMR Network (IST-UTL Center) for providing access to

the NMR facility.

Address correspondence to Kamran T. Mahmudov or Armando J. L. Pombeiro, Centro de Quı-

mica Estrutural, Complexo I, Instituto Superior Tecnico, TU Lisbon, Av. Rovisco Pais, 1049-001 Lisbon,

Portugal. E-mail: [email protected] or [email protected]

Analytical Letters, 43: 2923–2938, 2010

Copyright # Taylor & Francis Group, LLC

ISSN: 0003-2719 print=1532-236X online

DOI: 10.1080/00032711003763665

2923

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INTRODUCTION

The determination of the composite content of natural and industrial objectsrequires selective, sensitive, fast, and accurate methods for their analysis, the costof which also plays an important role (Christian 1994; Harvey 2000; Chan 2004;Vogel 1979). Copper is an essential element that is also toxic at elevated concentra-tions. The toxicity is generally attributed to the aquo complexed ‘‘free’’ copper(II)ion rather than its organic or inorganic complex (Nolan 1983). Analytical methodshave been proposed for determination of copper including atomic absorptionspectrometry (AAS) (Mashhadizadeh et al. 2008; Cassella et al. 2005), cold vaporAAS or flame AAS with electrothermal atomization (Almeida, Jun, and Lima2000; Campos, Santos, and Grinberg 2002), inductively coupled plasma emissionspectrometry (Ferreira et al. 2002), gravimetry (Potts 1987), chromatography (Ali,Shen, and Yin 1998), and anodic stripping voltammetry (Mohadesi and Taher2007), but most of these methods have one or more of the following disadvantages:high costs of equipment and expensive materials, time-consuming and complicatedoperation. Thus these methods are generally unsuitable for simple, low cost andremote determination of copper especially in field and domestic conditions. Differentanalytical reagents have already been used for the spectrophotometric determinationof copper(II) (Podchainova and Simonova 1990), but the analytical properties formost of them are rather moderate. Hence, we decided to search for a different, moreselective and sensitive reagent for this type of determination.

Complexes of azoderivatives of b-diketones (ADB) are of fundamental andapplied importance (Sokolnicki et al. 1999; Jeong et al. 2006; Chen et al. 2008). TheADB and their metal complexes are known to exist in different tautomeric forms, whichcan substantially complicate their study (Gadjieva, Pashaev et al. 2007; Gadjieva et al.2008; Alieva et al. 2009). In addition, since the tautomers of a compound usually differin thermodynamic stability, the equilibrium constants of complexation should differ fordifferent tautomers of a ligand (Gadjieva, Mursalov, Mahmudov, and Chyragov 2006;Gadjieva, Mursalov, Mahmudov, Pashaev et al. 2006). Meanwhile, the close values ofM–O bond lengths in chelating rings of b-diketone complexes usually prevent the esti-mate of the contribution of a certain tautomeric form (Garnovskii et al. 2004; Skopenkoet al. 2004). Earlier we attempted tomodify ADB in such amanner that the correspond-ing shift of the tautomeric equilibrium would allow to improve the sensitivity and sel-ectivity of the analysis (Alieva et al. 2005; Mahmudov et al. 2008). The importance ofthe quantitative study of the effects of the structure of the reagents on the propertiesof the formed complexes and their physico-chemical characteristics was also recognized,e.g., for developing direct spectrophotometric procedures without element pre-separation (Mahmudov et al. 2008; Gadjieva, Chyragov, and Mahmudov 2007; Gad-jieva, Pashaev et al. 2007; Gadjieva, Mursalov, Mahmudov, Pashaev et al. 2006).

On the other hand, it is known that when associates of cationic surface-activesubstances (CSAS) and acidic chromophoric reagents are formed, the degree of reagentprotonation decreases; therefore, the range of interaction between such reagents andmetals broadens and shifts to more acidic medium (Savvin, Chernova, and Shtykov1991; Pilipenko and Tananaiko 1983; Ivanov and Mamedova 2006). Taking in mindthe aforementioned considerations, we decided to study, from analytical and coordi-nation points of view, the interaction between a reagent containing two sulfonate

2924 K. T. MAHMUDOV ET AL.


groups and existing in several tautomeric forms—5,5-dimethyl-2-(2-hydroxy-3,5-disulfophenylhydrazo)cyclohexane-1,3-dione (H2L)—and CSAS [cetylpyridiniumchloride (CPCl), cetylpyridinium bromide (CPBr), and cetyltrimethylammoniumbromide (CTABr)], in the presence and absence of Cu(II). The results of this studyare reported herein.

EXPERIMENTAL

Chemicals and Instrumentation

All the chemicals were obtained from commercial sources (Aldrich) and used asreceived. The 1H and 13C NMR spectra were recorded at ambient temperature onBruker Avance IIþ 300 (UltraShieldTM Magnet) spectrometer operating at 300.130and 75.468MHz for proton and carbon-13, respectively. Infrared spectra (4000–400 cm�1) were recorded on a BIO-RAD FTS 3000MX instrument in KBr pellets.Carbon, hydrogen, and nitrogen elemental analyses were carried out by the Microa-nalytical Service of the Instituto Superior Tecnico. To create the necessary pH values,a commercial volumetric concentrate (fixanal) of HCl (pH 1–2) and an ammoniumacetate buffer solution (pH 3–11) were used. In dissolutions of samples, the concen-trated acids (HF 35%w=w, HCl 33%w=w, HNO3 65%w=w) were used. The acidity ofthe solutions was measured using an I-130 potentiometer with an ESL-43-07 glasselectrode adjusted by standard buffer solutions and an EVL-1M3.1 silver-silver chlor-ide reference electrode. The absorbance of the solutions was measured on a Lambda40 spectrophotometer (Perkin Elmer) in 1 cm quartz cells. 1.00� 10�3M aqueoussolutions of H2L and 1.00� 10�3M aqueous-ethanol (v=v 40=60) solutions of cetyl-pyridinium chloride and bromide, and cetyltrimethylammonium bromide were used.A starting 1.00� 10�1M solution of copper(II) was prepared by dissolving metalliccopper (99.99%) as described (Korostelev 1964) and the concentration of Cu(II)was determined by atomic absorption spectroscopy (Broekaert 2002).

Synthesis of H2L

The ligand was synthesized via the Japp-Klingemann reaction (Japp andKlingemann 1888) between the respective aromatic diazonium salt and pentane-2,4-dione in an ethanolic solution containing sodium acetate.

Diazotization

A 6.7250 g (0.0250mol) portion of 2-hydroxy-3,5-disulfoaniline was dissolvedin 50.00mL of water while gently heating upon addition of 1.00 g of crystallineKOH. Then, the solution was cooled down on an ice bath to 0�C and 1.7250 g(0.0250mol) NaNO2 was added, where after 5.00mL 33% HCl was added in portionsfor 40min. The temperature of the mixture should not exceed þ5�C. A suspensionof the unstable 2-hydroxy-3,5-disulfobenzodiazonium chloride [N�N{CC(OH)C(SO3H)CHC(SO3H)CH}]þCl� was obtained (Japp and Klingemann 1888) whichthen was used as such for the next stage (see as follows).

CATIONIC ANALYTICAL REAGENT/DETERMINATION OF COPPER(II) 2925


Azo Coupling

An amount of 5.0000g CH3COONa were added to a mixture of 3.5000g(0.0250mol) of 5,5-dimethylcyclohexane-1,3-dione with 25.00mL of ethanol. The sol-ution was cooled on an ice bath, and a suspension of 2-hydroxy-3,5-disulfobenzodiazo-nium chloride (see the aforementioned) was added in portions. In the azo coupling, thepH should be maintained in the range of 8–10; crystalline CH3COONamust be added ifneeded. On the next day, the precipitated reagent was filtered off, washed with ethanol,and dried in air. The formation of only one compound in the synthesis was confirmed bypaper chromatography; the identity of the new obtained compound as 5,5-dimethyl-2-(2-hydroxy-3,5-disulfophenylhydrazo)cyclohexane-1,3-dione (H2L) (Scheme 1) wasdemonstrated by elemental analysis, IR and 1H, and 13C NMR spectrometry.

Yield 74.00% (based on 5,5-dimethylcyclohexane-1,3-dione), red brown pow-der, soluble in water, DMSO, methanol, and insoluble in chloroform. Anal. Calcdfor C14H16N2O9S2 (M¼ 420): C, 40.00; H, 3.81; N, 6.67. Found: C, 39.96; H, 3.78;N, 6.65%. IR, cm�1: 3447 n(OH), 2957 n(NH), 1648 n(C=O), 1590 n(C=O ��H),1561 n(C=N), 779 n(Ar). 1H NMR (DMSO): d¼ 0.96 (s, 3H, CH3), 1.27 (s, 3H,CH3), 2.48 (s, 2H, CH2), 2.48 (s, 2H, CH2), 7.69–7.71 (s, 2H, Ar-H), 11.73 (s, 1H,OH), 14.17 (s, 1H, NH). 13C{1H} (DMSO): d¼ 28.12 (CH3), 30.69 (CH3), 51.86(2CH2), 114.30 (Ar-H), 114.54 (Ar-H), 125.34 (Ar-SO3H), 124.60 (Ar-SO3H),128.40 (Ar-OH), 133.47 (Ar-NH-N), 175.60 (C=N), 206.58 (C=O), 206.90 (C=O).

ANALYTICAL APPLICATIONS

Determination of Copper(II) in Soils Polluted by Oil

A sample of soils polluted by oil (Surakhany region of Azerbaijan) was analyzedusing the spectrophotometric method. A portion (2.000 g) of a sample was placed in aglassy carbon casserole and dissolved in a mixture of HF (35%, 38.00mL), HCl (33%,24.00mL), and HNO3 (65%, 8.00mL). The obtained paste was treated with12.00–16.00mL of conc. HNO3 at 60–70�C to distill off HF. The obtained residuewas dissolved in distilled water, filtered off, and diluted to 50.00mL with water. Analiquot portion of the solution was placed into a 25.00mL volumetric flask, then2.00mL of 1.00� 10�3M H2L, 2.00mL of 1.00� 10�3M CPCl and 1.00mL of1.00� 10�1M thiocarbamide solutions were added and the mixture was diluted upto the mark with 0.01M HCl. After 15min the absorbance of the solution was

Scheme 1. 5,5-Dimethyl-2-(2-hydroxy-3,5-disulfophenylhydrazo)cyclohexane-1,3-dione (H2L).



measured at 483 nm against the blank experiment. The concentrations of copperfound by the described method and by atomic absorption spectrophotometry (usedfor reference) were (6.75� 0.02)� 10�4 (RSD, 3.61%), and (6.77� 0.01)� 10�4%(RSD, 3.28%), respectively (n¼ 5, P¼ 0.95).

Determination of Copper(II) in Seawater

One liter of water taken from Caspian Sea near Turkan village was evaporatedat 50�C to dryness. The residue was then dissolved in 5.00mL of HNO3 (65%) anddiluted to 50.00mL with water. To determine copper(II) by spectrophotometry,1.00mL of its solution obtained as described previously was placed into a 25mL volu-metric flask in which 2.00mL of 1.00� 10�3M H2L, 2.00mL of 1.00� 10�3M CPCland 1.00mL of 1.00� 10�1M thiocarbamide solutions were added, and the solutionwas diluted to the mark with 0.010M HCl. The absorbance of solutions was mea-sured with respect to a blank solution after 15min at 483 nm. The concentrationsof copper found by the described method and by atomic absorption spectrophotome-try were (3.82� 0.02)� 10�5 (RSD, 4.37%), and (3.84� 0.01)� 10�5% (RSD, 3.96%),respectively (n¼ 5, P¼ 0.95).

Determination of Copper(II) in Igneous Rock

Three different samples of igneous rock of Little Caucasus (Kelbedzhar region ofAzerbaijan) were analyzed using the spectrophotometric method. A portion (1.000 g) ofa sample [I (%) – SiO2 57.750; TiO2 0.750; Al2O3 17.750; Fe2O3 4.520; FeO 0.880; CaO5.880; MgO 1.500; P2O5 0.720; MnO <0.020; CuO 0.039; K2O 4.000; Na2O 5.400; SO3

0.050; rare earth metals 0.070; H2O 0.290; R 99.550; II (%) – SiO2 58.000; TiO2 0.700;Al2O3 18.000; Fe2O3 4.680; FeO 0.740; CaO 5.880; MgO 1.100; P2O5 0.710; MnO<0.020; CuO 0.033; K2O 3.920; Na2O 5.600; SO3 0.050; rare earth metals 0.030;H2O 0.130; R 99.560; III (%) – SiO2 55.250; TiO2 1.350; Al2O3 16.250; Fe2O3 5.580;FeO 2.400; CaO 6.430; MgO 2.950; P2O5 1.310; MnO 0.020; CuO 0.036; K2O 4.400;Na2O 3.200; SO3 0.270; rare earth metals 0.030; H2O 0.340; R 99.790] was placed ina glassy carbon casserole and dissolved in a mixture of HF (35%, 16.00mL), HCl(33%, 12.00mL), and HNO3 (65%, 4.00mL). The obtained paste was treated with6.00–8.00mL of conc. HNO3 at 60–70

�C to distill off HF. The obtained residue wasdissolved in distilled water, filtered off and diluted to 50.00mL with water. An aliquotportion of the solution was placed into a 25.00mL volumetric flask, then 2.00mL of1.00� 10�3M H2L, 2.00mL of 1.00� 10�3M CPCl and 1.00mL of 1.00� 10�1Mthiocarbamide solutions were added and the mixture was diluted up to the mark with0.01M HCl. After 15min the absorbance of the solution was measured at 483 nmagainst the blank experiment. In igneous rocks I, II and III 0.038� 0.001 (S¼ 0.001,RSD, 2.63%), 0.032� 0.001 (S¼ 0.001, RSD, 3.12%) and 0.035� 0.001% (S¼ 0.001,RSD, 2.86%) of Cu was found, respectively (n¼ 5, P¼ 0.95).

Determination of Copper(II) in Nickel-Based Alloys

A 0.5000 g portion of a sample (M 115–1 containing Cr 8.100, Co 1.450, Fe0.500, Si 0.500, Mg 0.030, Mn 0.350, Cu 0.250, Pb 0.001, Bi 0.004, Sb 0.001,



P 0.005, Al 0.250, C 0.050, Ti 0.005, Zr 0.150, As 0.001%, and the rest of Ni or M115–2 containing Cr 9.200, Co 0.870, Fe 0.350, Si 0.250, Mg 0.050, Mn 0.250, Cu0.180, Pb 0.003, Bi 0.002, Sb 0.002, P 0.003, Al 0.150, C 0.250, Ti 0.050, Zr 0.050,As 0.0025%, and the rest of Ni) was dissolved in a mixture of 10.00mL of H2O,12.00mL of HCl (33%), and 4.00mL of HNO3 (65%) in a chemical beaker at 70�C.The solution was transferred into a 50.00-mL volumetric flask and diluted to the markwith water. One mL of the thus obtained solution was placed into a 25.00mL flask,where 2.00mL of 1.00� 10�3M H2L and 2.00mL of 1.00� 10�3M CPCl and1.00mL of 1.00�10�1M thiocarbamide solutions were added; the mixture was diluted up to the markwith 0.01M HCl. After 15min, the absorbance of the solutions was measured at483 nm against a blank solution. In alloys M 115–1 and M 115–2, 0.25� 0.01%(S¼ 0.006, RSD, 2.40%) and 0.18� 0.01% (S¼ 0.006, RSD, 3.33%) of Cu was found,respectively (n¼ 5, P¼ 0.95).

RESULTS AND DISCUSSION

Determination of Dissociation Constants of the Reagent H2L

To determine the dissociation constants of the reagent H2L, we used pH-metrictitration in aqueous media. The ionic strength was maintained constant (I¼ 0.1) byadding a calculated amount of KCl. To calculate the dissociation constants of thereagents, the Schwarzenbach algebraic method was used (Dyatlova, Temkina, andKolpakova 1970):

K1 ¼½Hþ�facH2L þ ½Hþ� � ½OH��gð1� aÞcH2L � ½Hþ� þ ½OH�� ;

K2 ¼½Hþ�fða� 1ÞcH2L þ ½Hþ� � ½OH��g

ð2� aÞcH2L � ½Hþ� þ ½OH�� ;

where cH2L is total concentration of H2L and a is the neutralization point. Thedissociation constants of the reagent were found to be pK1¼ 5.90� 0.03 andpK2¼ 9.67� 0.04. Earlier, it was assumed (Gadjieva, Pashaev et al. 2007; Gadjievaet al. 2008; Alieva et al. 2009; Gadjieva, Mursalov, Mahmudov, and Chyragov2006; Gadjieva, Mursalov, Mahmudov, Pashaev et al. 2006) that ADB occurs inthree tautomeric forms (enol-azo, keto-azo and hydrazo, Scheme 2), and, accordingto quantum chemical calculations performed on similar compounds, pK1 charac-terizes the proton abstraction from the �OH group of the aromatic ring situated

Scheme 2. Possible tautomeric equilibria in H2L.



in the ortho position to the hydrazo group of the molecule, while pK2 concerns thedeprotonation of the hydrazone group (=N�NH�) (Gadjieva et al. 2008).

The 1H-NMR spectrum of H2L in dimethylsulfoxide-d6 solution at room tem-perature shows a signal at d 14.17 assigned to the proton of the protonated nitrogenatom adjacent to the aryl unit (=N�NH� hydrazone form) (Marten, Seichter, andWeber 2005). Moreover, the two methyl groups of the 5,5-dimethylcyclohexane-1,3-dione moiety yield separate singlets in the proton spectrum. Those data support theformation of the hydrazo form (Scheme 2) with a six-membered H-bonded ringinvolving one of the carbonyl groups and the protonated nitrogen moiety of thehydrazone structure. The IR spectrum of the isolated H2L shows the OH and NHvibrations at 3447 and 2957 cm�1, respectively. n(C=O) (1648 cm�1), n(C=O ��H)(1590 cm�1) and n(C=N) (1561 cm�1) also support the H-bonded hydrazone struc-ture in the solid state.

Complexation Conditions

In order to find the optimum conditions for complexation in solution andsubsequently for spectrophotometric analysis, the influences of concentration ofthe reagents, temperature, and basicity on the reaction rate were studied by the fixedtime method (Bulatov and Kalinkin 1972). The optimum conditions for the finalworking procedure were chosen as a compromise in order to ensure low blankvalues, an extended linearity, and a short measuring time. Experiments showed thatan aqueous H2L solution has an absorption band with 345 nm maximum at pH 2.Under these conditions, H2L forms a complex with copper(II) that exhibits anabsorption maximum at 467 nm. The study in a wide range of pH showed that theabsorbance of solutions of this complex increases significantly under the CSAS effect

Figure 1. Variation of the absorbance of the copper(II) complexes with pH: Cu(HL)2 (1); Cu[(HL)(C-

TABr)2]2 (2); Cu[(HL)(CPBr)2]2 (3); Cu[(HL)(CPCl)2]2 (4). k¼ 467nm, l¼ 1 cm, cCu¼ 1.50� 10�5M,

cL¼ 3.00� 10�5M, cCSAS¼ 6.00� 10�5M, blank solution contains H2L for experiment 1 and

H2LþCSAS for 2, 3, and 4 correspondingly.



at pH 2 (Figure 1). Therefore, to study the ligand–ligand interaction the absorptionspectra of H2L–CSAS were obtained at pH 2 (Table 1). To determine the stabilityconstants of the H2L–CSAS systems, the curve-crossing method was used (Bulatovand Kalinkin 1972).

Kn ¼ci:p

ðcH2L � ci:pÞðcCSAS � nci:pÞn; ci;p ¼ cH2L

DADAlim

� �;

where ci.p is the concentration of the ion pair, DA is the difference of the absorbancesof the solution with an ion pair (H2L–CSAS), and the solution with only H2L(cH2L

¼ 4.00� 10�4M), and DAlim is the limiting value of DA reached for high CSASconcentrations, measured at pH 2 and kmax. The ratios of H2L:CSAS were found bythe Starik–Barbanel relative yield method, the slope method, and the isomolar seriesmethod (Bulatov and Kalinkin 1972) showing the same results (Table 1). Theobserved variation in the stability of the associates (Table 1) is probably dependenton the mobility of chloride and bromide ions and the partial charge (þd) on the Natom in the �N(CH3)3 and �NC5H5 groups of CSAS.

The delocalization of the p-electron system of the H2L reagent causes a bath-ochromic shift of the absorption band upon formation of the H2L–CSAS associate(Table 1), which is stable for at least a few days. This also can be accounted for bythe increase of the negative inductive effect of the sulfonate group under the influ-ence of CSAS. Besides, the dissociation constants of H2L, pK1¼ 5.90� 0.03 andpK2¼ 9.67� 0.04, show that CSAS affects �SO�

3 rather than the HO-group ofH2L (Scheme 3). All this indicates that ion pairs of CSAS and the sulfonate groupof H2L are formed in the solution.

The absorbance of the complex of copper(II) and H2L increases in the presenceof CSAS at pH 2 improving the analytical effect of H2L. The Astakhov method

Table 1. Characteristics of the H2L–CSAS systems (kH2L¼ 345 nm, H2L:CSAS¼ 1:2)

CSAS kCSAS, nm kH2L–CSAS, nm logK1 logK2

CPCl 259 353 3.75� 0.09 8.58� 0.07

CPBr 260 350 3.68� 0.08 8.51� 0.08

CTABr 206 348 3.53� 0.09 8.42� 0.06

Scheme 3. Reaction between H2L and CSAS at pH 2.



(Astakhov et al. 1961) was used to quantify this effect and it was found that in pres-ence and absence of CSAS the slope of dependence of pH from log[DA=(DAlim–DA)]equals 2 at pH 1–2 (i.e., Cu(II):H2L¼ 1:2); the molar ratios of the components inassociates Cu(II):H2L:CSAS were 1:2:4, respectively. This means that the mechanismof complexation between copper(II) and H2L is the same as for the H2L(CSAS)2 ionpairs and that most probably CSAS interacts electrostatically with the sulfonategroups of H2L:

Cu2þ þ 2H2L�!pH2CuðHLÞ2 þ 2Hþ

Cu2þ þ 2H2Lþ 4CSAS�!pH2Cu½ðHLÞðCSASÞ2�2 þ 2Hþ

The complex of copper(II) and H2L forms in 15min and remains stable for a longtime. Upon addition of CSAS, the rate of complexation increases, and the complexCu[(HL)(CSAS)2]2 is formed almost immediately.

To determine the stability constants of the mono-ligand and mixed-ligandcopper(II) complexes, the curve-crossing method was used with the followingmodifications (Bulatov and Kalinkin 1972):

Kn ¼cc

ðcCuðHLÞ2 � ccÞðcH2L � nccÞncc ¼ cCuðHLÞ2

DADAlim

� �;

where cc is the concentration of the mixed ligand complexes and DA is the differenceof the absorbances of the solution with the mixed ligand complex and the solutionH2L–CSAS, and DAlim is the limiting value of DA reached for high CSAS concentra-tions, measured for cCu(HL)2

¼ 4.00� 10�5M, at pH 2 and kmax (Table 2). Theseresults are also supported by the Job’s method (Bulatov and Kalinkin 1972). Theobtained data allow to conclude that addition of CSAS to H2L-copper(II) solutioncaused an increase in the stability constants (Table 2). A comparison of the stabilityconstants of the associates (Table 1) and the corresponding complexes (Table 2)shows that with increase of the stability of the associates (H2L(CPCl)2>H2L(CPBr)2>H2L(CTABr)2) their complexes become more stable in the same order(Cu[(HL)(CPCl)2]2>Cu[(HL)(CPBr)2]2>Cu[(HL)(CPABr)2]2) and the detectionlimit of copper(II) in the Cu[(HL)(CSAS)2]2 systems decreases. The additionalvariable-temperature spectrophotometric measurements show that stability of theformed complex is not dependent on the temperature until 70�C. We have also

Table 2. Characteristics of the Cu[(HL)(CSAS)2]2 systems (pH 2)

Complex

kmax,

nm

Dk,nm

emax� 10�4,

Lmol�1 cm�1Cu:H2L:

CSAS

Correspondence

to Beer’s law,

mgmL�1 logK1 logK2

Cu(HL)2 467 122 2.50� 0.01 1:2 0.23–2.56 4.79� 0.08 10.41� 0.09

Cu[(HL)(CPCl)2]2 483 130 2.95� 0.01 1:2:4 0.13–3.07 4.97� 0.06 10.59� 0.05

Cu[(HL)(CPBr)2]2 480 130 2.80� 0.01 1:2:4 0.19–2.94 4.90� 0.07 10.54� 0.09

Cu[(HL)(CTABr)2]2 474 126 2.73� 0.01 1:2:4 0.22–2.81 4.86� 0.09 10.49� 0.08



found that in the presence of anionic (sodium dodecyl sulfate and ammonium laurylsulfate) and nonionic (Triton X-100) surfactants the analytical parameters ofreactions do not increase.

Construction of calibration curves. To determine the concentration ofcopper(II) with H2L(CSAS)2, portions of 0.02–1.20mL of 1.00� 10�3M referencecopper(II) solution were placed into eight 25.00mL calibrated flasks. Then2.00mL of 1.00� 10�3M solutions of H2L and 2.00mL of 1.00� 10�3M solutionsof CSAS were added, and the mixtures were diluted up to the mark with 0.01M HCl.The absorbance of the solutions was measured (kmax nm, l¼ 1 cm) against the refer-ence solution. Beer’s law was obeyed in the range of 0.23–2.56 mgmL�1 Cu(HL)2,0.13–2.56 mgmL�1 Cu[(HL)(CPCl)2]2, 0.19–2.94 mgmL�1 Cu[(HL)(CPBr)2]2, 0.22–2.81 mgmL�1 Cu[(HL)(CTABr)2]2.

To reveal the effect of the stability of the associates and complexes on thedetection limit of copper(II) by the complexation reaction with H2L–CSAS, the coef-ficients of the calibration plot were determined by the least-squares method (Batunerand Pozin 1963):

PA ¼ a

Pcþ nbP

Ac ¼ aP

c2 þ bP

c;

�

where A is absorbance of complexes, c is concentration of copper(II) (mgmL�1), n isnumber of experiments. Thus, for complexation of copper(II) and H2L–CSAS, thefunction A¼ f(c) is described by the following linear equations:

A ¼ ð0:25� 0:02Þc� ð4:22� 0:09Þ � 10�3 ðr ¼ 0:999Þ; Cu½ðHLÞðCPClÞ2�2

A ¼ ð0:22� 0:01Þc� ð3:77� 0:10Þ � 10�3 ðr ¼ 0:997Þ; Cu½ðHLÞðCPBrÞ2�2

A ¼ ð0:19� 0:01Þc� ð3:45� 0:09Þ � 10�3 ðr ¼ 0:989Þ; Cu½ðHLÞðCTABrÞ2�2

A ¼ ð0:16� 0:01Þcþ ð1:06� 0:10Þ � 10�3 ðr ¼ 0:988Þ; CuðHLÞ2

As it can be seen, with an increase of the slope (a), both the molar absorption coef-ficient of the complexes and the stability constants of associates (Table 1), as well asthe stability constants of the corresponding complexes (Table 2), grow. Accordingly,the intercept on the ordinate axis (jbj) increases, meaning that the detection limit ofcopper(II) in the Cu-H2L-CSAS system is reduced.

Determination of the polymerization degree. The polymerization degreeof the mono-ligand and mixed-ligand complexes were determined by the equationpresented in (Novopol’tseva and Osipov 2006):

c ¼ ðlogAi=AkÞ=½ðqþ 1Þ logfðciel � AiÞ=ðckel � AkÞg�;



Table

3.Permissible

weightratiosofforeignspeciesandcopper(II)

initsdeterminationin

theform

ofCu[(HL)(CSAS) 2] 2(error<5%)

Ionorsubstance

H2L

H2L(C

PCl)2

H2L(C

PBr)2

H2L(C

TABr)2

Picramine-epsilon(Podchainova

andSim

onova1990)

N,N

-Di(2-carboxyethyl)-3,4-xylidine

(Neudachinaet

al.2005)

Na(I)

��

��

1000

K(I)

��

��

1000

Mg(II)

143

�374

187

370

Ca(II)

��

��

250

Ba(II)

��

��

1000

Zn(II)

305

�610

�200

Cd(II)

875

��

�1000

Mn(II)

��

��

500

Ni(II)

922

�922

�500

Co(II)

461

��

�750

Al(III)

354

�2110

2110

1

Sm(III)

1172

��

�

Fe(III)

987

44

44

0.01

Ga(III)

547

��

�60

In(III)

539

�1078

�

Bi(III)

326

652

��

Zr(IV

)558

��

1116

0.1

Sn(IV)

278

��

�

Hf(IV

)142

��

575

Ti(IV

)37

870

660

�

Mo(V

I)750

��

1500

3

W(V

I)144

�452

�100

C2O

2�4

628

��

�

EDTA

58

116

116

�

Carbamide

469

��

�

Thiocarbamide

59

��

188

Citricacid

1640

��

�

Na2HPO

4�12H

2O

560

�345

�

Tartaricacid

1171

��

�

F�

580

��

232

2933


where Ai and Ak are the absorbances of the complexes in experiments i and k, e is themolar absorption coefficient of the complex, l is the thickness of the cell (cm), ci andck are the concentration of copper in experiments i and k, and q is the number ofmolecules which form the complex. The polymerization coefficients of the complexeswere calculated and it was found that these complexes occurred as monomers ratherthan as polymers.

Effect of interfering species. To elucidate the possibility of the quantitativedetermination of copper in various materials, the effect of foreign ions and maskingsubstances on the complexation of copper(II) with H2L–CSAS was studied. Theeffect of the interfering species upon the complex formation was investigated bythe use of the proposed method at optimum conditions. This effect was characterizedby the maximum permissible species-copper weight ratios for an error of determi-nation lower than 5% (Table 3). Thus, a comparison of the selectivity of the reagentsfor the determination of copper(II) listed in the assortment (Podchainova andSimonova 1990) and the recently published method (Neudachina et al. 2005) withthat of our H2L–CSAS system shows that H2L, in nearly all the cases, is more selec-tive in both the presence and absence of CSAS (Table 3), while the systems studiedhere increases the selectivity with modification of H2L with CSAS.

As can be seen from Table 3, the alkaline and alkali-earth metals cations, Zn(II),Cd(II), Mn(II), Ni(II), Co(II), Al(III), Sm(III), Ga(III), In(III), Zr(IV), Sn(IV),Hf(IV), Mo(VI), W(VI), Bi(III), and Ti(IV) almost create no interference with thedetermination of copper with H2L(CPCl)2, while Fe(III) ions significantly affect it.The influence of oxalic, citric, and tartaric acids, EDTA, carbamide, thiocarbamide,Na2HPO4 � 12H2O, and NH4F on the selectivity of determining copper was studied aswell, showing that the solution under analysis can contain all of these curtain sub-stances, with the exception of EDTA, which can be presented only in small amounts.Taking into consideration all these analytical parameters, one can conclude that theproposed method is more selective than other similar methods (Podchainova andSimonova 1990; Chimpalee et al. 1996; Li, Jiang, Lin 1997; Thakur and Deb 1999;Barreto Nozaki, and Barreto 1999; Karabocek et al. 2000; Yun and Choi 2000; Wink-ler and Arenhovel-Pacula 2000; Donglan et al. 2002; Neudachina et al. 2005; Du et al.2005; Kaur and Malik 2007; Sharma and Singh 2009).

Applications of the Method

First, the developed method was successfully applied to soils polluted by oil,seawater, and a comparison with the results of the reference atom-absorption analy-sis shows its high accuracy and precision. Second, the method was applied for threeigneous rock samples with diverse composition and also exhibited a high precision.Third, the determination of copper(II) was achieved in nickel-based alloys with thesame good results (See experimental section).

CONCLUSIONS

The new ligand 5,5-dimethyl-2-(2-hydroxy-3,5-disulfophenylhydrazo)cyclohexane-1,3-dione (H2L) was synthesized and applied to the spectrophotometric



determination of copper(II), separately and in combination with cationicsurface-active substances: cetylpyridinium chloride, cetylpyridinium bromide, andcetyltrimethylammonium bromide. The interactions in the systems H2L–CSAS werestudied in the presence and absence of copper(II), and it was shown that CSASelectrostatically interacts with the sulfonate groups of the H2L reagent leading tothe formation of ion pairs. The stoichiometry and the stability constants of theseion pairs were determined, and these systems were applied for the determinationof copper. It was found that alkaline and earth-alkaline metals, Zn(II), Cd(II),Mn(II), Ni(II), Co(II), Al(III), Sm(III), Ga(III), In(III), Zr(IV), Sn(IV), Hf(IV),Mo(VI), W(VI), C2O

2�4 , carbamide, thiocarbamide, citric and tartaric acids, Na2H-

PO4 � 12H2O, and F� do not interfere in this method. A procedure for the spectro-photometric determination of copper(II) in seawater, igneous rock, soils pollutedby oil and nickel-based alloys was thus developed. The developed method is moreselective, sensitive, reproducible, rapid, cheap, and simple than in most of theanalogous methods cited in literature (Nolan 1983; Potts 1987; Podchainova and Simo-nova 1990; Chimpalee et al. 1996; Li et al. 1997; Ali et al. 1998; Thakur and Deb 1999;Barreto et al. 1999; Almeida et al. 2000; Karabocek et al. 2000; Yun and Choi 2000;Winkler and Arenhovel-Pacula 2000; Campos et al. 2002; Donglan et al. 2002; Ferreiraat al. 2002; and Queiroz et al. 2002; Cassella et al. 2005; Du et al. 2005; Neudachinaet al. 2005; Kaur and Malik 2007; Mohadesi and Taher 2007; Mashhadizadeh et al.2008; Sharma and Singh 2009). For these reasons, it can be used in routine analysisand can be applied for the determination of copper in a diversity of objects.

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