научная статья по теме APPLICATION OF TARTRAZINE FOR SENSITIVE AND SELECTIVE KINETIC DETERMINATION OF CU(II) TRACES Химия

Текст научной статьи на тему «APPLICATION OF TARTRAZINE FOR SENSITIVE AND SELECTIVE KINETIC DETERMINATION OF CU(II) TRACES»

ЖУРНАЛ АНАЛИТИЧЕСКОЙ ХИМИИ, 2014, том 69, № 12, с. 1260-1265

ОРИГИНАЛЬНЫЕ СТАТЬИ

УДК 543

APPLICATION OF TARTRAZINE FOR SENSITIVE AND SELECTIVE KINETIC

DETERMINATION OF Cu(II) TRACES

© 2014 R. J. Micic*, S. S. Mitic**, A. N. Pavlovic**, D. A. Kostic**, M. N. Mitic**

*Faculty of Sciences and Mathematics, Department of Chemistry, University of Pristina 38220 Kosovska Mitrovica, Lole Ribara 29, Serbia 1E-mail: ruzica.micic@pr.ac.rs **Faculty of Sciences and Mathematics, Department of Chemistry, University of Nis Visegradska 33, 18000 Nis, Serbia Received 10.10.2012; in final form 27.12.2013

An efficient, highly sensitive, fast and selective kinetic method for determination of traces of Cu(II) was developed and applied for its quantification in different real samples. The method was based on the catalytic effect of Cu(II) traces on the redox reaction of artificial azo-dye tartrazine (tri-sodium-5-hydroxy-1-(4-sul-fophenyl)-4-[(4-sulfophenyl)azo]pyrazole-3-carboxylate) with H2O2- The optimum operating conditions regarding reagent concentration were examined and established. Linearity of the method was obtained in the concentration range from 13 to 318 ng/mL of Cu(II), with a detection limit (LOD) (3sb/m ) of 2 ng/mL, and limit of quantification (LOQ) (10sb/m) of 7 ng/mL. Obtained results for Cu(II) determination in analyzed samples, as well as the development and validation of the proposed analytical procedure have given and discussed.

Keywords: copper, kinetic determination, tartrazine, food samples. DOI: 10.7868/S004445021412010X

Cu(II) is essential trace element in human body, having close relationship with human health, and its over-intake could cause several toxicological effects. Copper ion, also might play a central role in initiating wine non-enzymatic browning, leading to lightening of red wine and darkening of white wine, and this fact has an important implication for the determination of copper(II) in wines [1, 2]. High concentration of Cu may cause instability and turbidity of wine. The total copper concentration in red and white wines must be 0.3 and 0.5 mg/L. The main sources of copper in wines are equipment used in the wine production, addition of copper salts (CuSO4) and pesticides employed during growth. The maximum allowed level of copper in wine is 1.0 mg/L [3]. Hydrogen peroxide may be formed during the oxidation of wine phenols, and in association with copper it tends to generate reactive oxygen species such as hydroxyl radical ("OH), which is known as the Fenton reaction [3]. Most of the 'OH radicals generated in wine and non-fresh fruit come from the metal-catalyzed decomposition of hydrogen peroxide according to Fenton-type reaction. In light of this it is useful to know copper concentration in fruit, wine and honey samples.

Tartrazine (TZ) can cause the most allergic and intolerance reactions among all the azo-dyes, particu-

larly among asthmatics and those with an aspirin intolerance. Symptoms from TZ sensitivity can occur by either ingestion or cutaneous exposure to a substance containing TZ [3]. This work is a part of investigation of kinetic effect of trace metal ions on widely used additives azo-dyes: sunset yellow and tartrazine—H2O2 redox reaction, followed by spectrophotometry, in order to develop new kinetic methods for trace metal determination [4]. Various analytical methods have also been reported for the determination of copper, which include spectrophotometry [5], atomic absorption spectrophotometry [6—9], and flow system with inline separation—preconcentration, coupled to graphic furnace atomic absorption spectrometry [10]. High pressure liquid chromatography [11, 12], and anodic stripping voltammetry [13, 14] have also been used for the determination of copper with high sensitivity and selectivity. In recently reported literature, Cu(II) was determined by thermospray flame furnace atomic absorption spectrometry [15], inductively coupled plasma optical emission spectrometry (ICP—OES) [16] and inductively coupled plasma mass spectrometry [17].

Among them, the kinetic-catalytic methods give high sensitivity and accuracy, without the need for expensive and special equipment, connected with usage of different masking reagents or liquid/solid extraction, to improve their selectivity. In spite of the instru-

mental improvements in the previous decades [18], kinetic-catalytic method are still attractive since they are sensitive and simple [19—31]. Almost, all kinetic-catalytic methods for Cu(II) trace determination published in last decades used various types of indicator reactions. But some of these methods imply application of complicated synthetic procedure of indicator substance, sometimes high working temperature, time-consuming sample throughput, expensive reagents, providing similar sensitivity or even lower selectivity, and time-consuming sample throughput.

The aim of this study was the development and application of a simple and fast kinetic-spectrophoto-metric procedure, based on usage an inexpensive and stable substance tartrazine as a kinetic indicator. Catalytic selectivity of the kinetic method proposed in this work is excellent: the indicator reaction of oxidation of TZ by H2O2 is catalyzed strongly and only in presence of Cu(II) traces. Analytical selectivity is reduced by influence of several ions, which are present mostly in smaller concentrations in real samples (Pb, Co, Cd, Ni), aside from Fe, which can be simply and successfully eliminated by adding of masking reagent.

EXPERIMENTAL

Instrumentation. Spectrophotometric measurements were performed on Perkin-Elmer Lambda 15 UV-Vis spectrophotometer. The pH measurements were carried out using a Hanna Instruments pH meter. High precision measuring for laboratory applications were performed using an analytical balance (Mettler Toledo, AB204-S, Switzerland). ICP-OES measurements were done by means of a iCAP 6000 inductively coupled plasma optical emission spectrometer (Thermo Scientific, Cambridge, United Kingdom) which use an Echelle optical design and a Charge Injection Device (CID) solid state-detector. A Julabo MP-5A model thermostatic bath was used to maintain the reaction temperature at 25.0 ± 0.1°C.

Materials. Analytical grade chemicals and deion-ized water (MicroMed high purity water system, TKA Wasseraufbereitungssysteme GmbH) were used for the preparation of all solutions. A 1.000 g/L Cu(II) (Merck) was used as stock solution. A 1 x 10-4 M Cu(II) working solutions were made by suitable dilutions of the stock solution. A 1 x 10-3 M solution of TZ (Fluka) was prepared by weighing 0.0267 g of the substance, and dissolving it with deionized water in a calibrated volumetric flask of 50 mL. A 2 M solution of H2O2 was prepared by dilution of 10.2 mL of 30% H2O2 solution (Merck) with deionized water up to 50 mL. A 100 mL of borate buffer was prepared by mixing of 47.2 mL of 0.1 M NaOH with 52.8 mL of 0.05 M of Na2B4O7 ■ • 10H2O [32]. All working solutions were kept in a thermostated water-bath at 25.0 ± 0.1 °C before the beginning of the reactions. All the glassware used were washed with aqueous solution of

Table 1. ICP-OES operating conditions

Parameter Value

Flush pump rate 100 rpm

Analysis pump rate 50 rpm

RF power 1150 W

Nebulizer gas flow 0.7 L/min

Coolant gas flow 12 L/min

Auxiliary gas flow 0.5 L/min

Plasma view Axial

Detection wavelength 324.754 nm

HCl (1 : 1) and then thoroughly rinsed with running and distilled water, and then with deionized water.

Kinetic and ICP-OES procedure. In a standard flask (Bouderin) with four separated compartments, a suitable aliquot of working Cu(II) solution and an ap-roppriate volume of deionised water were placed in one part, 0.2 mL of 1 x 10-3 M solution of TZ in the second, 2 mL of borate buffer pH of 10.5 in the third, and 1 mL of 2 M H2O2 (total volume of 5 mL) in the fourth part. The flask was kept at 25.0 ± 0.1°C in the thermostated bath, and then was vigorously shaken and the reaction was initiated by mixing of reagents. Simultaneously, with start of reaction (mixing of reagents) a chronometer was turned on for monitoring the rate of the reaction. The spectrophotometric cell was rinsed well and filled with the reaction mixture. The absorbance at 428.4 nm was measured every 30 s over a period of 6 min after mixing, against the reagent blank.

All ICP-OES measurements were carried out on a iCAP 6000 inductively coupled plasma optical emission spectrometer (Thermo Scientific, Cambridge, United Kingdom) which use an Echelle optical design and a CID as solid state-detector. The instrumental conditions are given in Table 1.

Working parameters were controlled and altered using software package Smart Analyzer Vision. Calibration was performed using external standard prepared from 1.000 g/L stock of Cu(II), made up as appropriate with 2% nitric acid.

Sample preparation. An aliquot of 25 mL of each wine sample or 15 g of squeezed and homogenized fruit sample was placed in a porcelan vessel and heated. The vessels with the residues obtained after the vaporization were than ashed in a furnace at 450-500°C during 12 h. The residues were treated with 1 mL conc. HNO3 and heated in a furnace again. The obtained residues were dissolved in 5% (v/v) HNO3 to total volumes of 50 mL. Honey samples were prepared in accordance to the procedure given by Terrab et al [33]. The ashes were obtained by calcination (600° C) of 5 g honey samples to constant weight. Nitric acid (5 mL of 0.1 M) was added to the resultant ashes, and the mix-

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MICIC и др.

12

10

х о ft

а

10.5 pH

Fig. 1. Dependence of the reaction rates on pH; Ctz = 4 x x 10-5 M, cH2O2 = 0.4 M, pH 10.5, 25.0 ± 0.1°C, cCu(II) = = 254 ng/mL (Rc — catalytic, Ru— uncatalytic reaction and A(Rc-Ru) net reaction).

12 -

10

8 -

x

<D p

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Й 4

6 -

2 -

Kbuf, mL

Fig. 2. Dependence of the reaction rate on buffer volume; pH 10.5, Ctz = 4 X 10-5M, ch2o2 = 0.4 M, CCu(II) = = 254 ng/mL, 25.0 ± 0.1°C.

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