ЖУРНАЛ АНАЛИТИЧЕСКОЙ ХИМИИ, 2007, том 62, № 11, с. 1147-1154
^=ОРИГИНАЛЬНЫЕ СТАТЬИ
УДК 543
SPECTROPHOTOMETRIC DETERMINATION OF TELLURIUM(IV) IN ENVIRONMENTAL AND TELLURIDE FILM SAMPLES
© 2007 г. K. Suvardhanb, K. Suresh Kumarb, D. Rekhab, B. Krishna Priyab, P. Subrahmanyamb, P. Reddy Prasadb, J. Dilip Kumarb , P. Murali Krishna", E. T. Puttaiahc,
B. Jayaraja, P. Chiranjeevib
a Department of Mathematics, S.V. University Tirupati-517502, A.P., India b Environmental Monitoring Laboratories, Department of Chemistry, S.V. University
Tirupati-517502., India c Dept of Environmental Sciences, Kuvempu University Sankaragatta-577451, Karnataka, India Received 26.05.2006; in final form 20.12.2006
Three simple, rapid and sensitive spectrophotometric methods for the determination of traces and ultra traces of tellurium (IV) were studied. These methods were based on either the oxidation of 4-bromophenylhydra-zine (4-BPH) by tellurium in basic medium and coupling with N-(1-naphthyl)ethylenediamine dihydrochlo-ride (NEDA) to give purple colored product, or the oxidation of 3-methyl-2-benzothazoline hydrazone hydrochloride (MBTH) by tellurium in basic medium and coupling with chromotropic acid (CA) to yield a red colored species, or the oxidation of 2,3-dimethoxy strychnidin-10-one (2,3-DMSO) by tellurium in acid medium to yield orange colored derivative. Beer's law were obeyed in the range 1.0-25 |g/mL (purple colored product), 0.7-20 |g/mL (red colored species) and 0.3-15 |g/mL (orange colored derivative). The reaction conditions and other analytical parameters were investigated to enhance the sensitivity of the proposed methods. The tolerance limit of various ions has been studied. The methods were applied to the analysis of tellurium in water samples (waste, river, lake, spring), plant materials, soil samples and telluride thin films. The results obtained were superior to those obtained by the reported method. The performances of proposed methods were evaluated in terms of 't'-test and variance ratio 'f'-test which indicate the advances of proposed methods over reported methods.
Tellurium and its compounds are widely used in thin films, rechargeable batteries, charge transfer systems, etc. The tellurium exposure may result in garlic-like breath. The tellurium aerosol irritates the eyes and the respiratory tract. The substance may cause abdominal pain, constipation, vomiting effects on the liver and central nervous system. Tellurium is widely used as semiconductors and occurs abdominal in small quantities in inorganic materials and biological samples. It is also a potential environmental pollutant. Tellurium enters into natural water through seepage from soils and industrial waste. Many analytical techniques such as voltammetry [1], flame atomic absorption spectrometry [2], atomic absorption spectrometry [3, 4], inductively coupled plasma-mass spectroscopy [5-7], inductively coupled plasma-atomic emission spectroscopy [8, 9], X-ray fluorescence [10, 11] and electrophoresis [12] have been employed for tellurium determination in various environmental matrices. This increases the interest in developing rapid, sensitive and simple methods for the determination of traces of tellurium.
Several reagents like bismuthiol [13], N-phenylben-zohydroxamic acid [14], tetra methylthiourea [15], xy-
lenol orange [16], salicylfluorone [17] have been employed for the spectrophotometric determination of tellurium in various matrices. Ion association complex such as TeIV-Cl- - cationic violet [18], TeIV-Br - butyl rhodormin-B [19], TeIV-Br- - acridine [20], TeIV-I- -rhodormin B-polyvinyl alcohol [21] and TeIV-I- -rhodormin B-poly vinyl alcohol - OP [22] systems have been used for the determination of tellurium(IV) by ion pair complex methods. The above reported methods suffer from several drawbacks such as low sensitivity and low selectivity and require extraction steps [18-20]. The sensitivity of TeIV-I- - rhodormin B-polyvinyl alcohol [21], TeIV-I- - rhodormin B-polyvinyl alcohol - OP [22] and TeIV - tungstate-basic dyes-polyvinyl alcohol [23] was moderate, however, the stability of ion-pair complexes was very poor. So, it is desirable to develop a simple, sensitive, reliable, rapid and reproducible method for the determination of tellurium in environmental samples.
A survey of literature reveals that a few spectropho-tometric methods associated with ion-pair complexes were proposed for the determination of tellurium in environmental samples. Here, for first time the, author's
reported three simple, rapid and sensitive methods for the determination of traces of tellurium with oxidation process in various environmental samples. The reactions are oxidative coupling and the products are highly stable. The experimental variables affecting color formation and possible tolerance of foreign ions were thoroughly studied. The optimum conditions established were incorporated in the investigation of tellurium (IV) in various environmental samples.
EXPERIMENTAL Materials and methods
Apparatus. A HITACHI U 2001 Spectrophotometer with 1.0 cm path length and a Elico Li-129 model pH meter were used for electronic spectral studies and pH measurements, respectively.
Reagents. All reagents used were of analytical reagent grade. Doubly-deionised distilled water was used through out the experiments. Working solutions of tel-lurium(IV) oxide was prepared by dilution of the corresponding standard solutions (1000 mg/L, Merck, Mum-bai, India) with doubly-deionised distilled water. 1.5% 4-bromphenylhydrasine (4-BPH) - iV-(1-naphtyl)ethyl-enediaminedihydrochloride (NEDA) (1 : 2) reagent mixture was prepared by dissolving 1.0 g of 4-BPH and 0.5 g of NEDA (Sigma Chemicals, USA) in a few drops of concentrated HCl, was made up to mark with doubly- deionised distilled water in 100 mL standard flask and refrigerated. 1.0% 3-methyl-2-benzothazoline hydrazone hydrochloride (MBTH)-chromo tropic acid (CA) (1 : 1) (Merck, Mumbai, India) reagent mixture was prepared by dissolving 0.5 g of MBTH and 0.5 g of CA in 20 mL of doubly-deionised distilled water and was made up to mark in 100 mL standard flask. Solution of 2,3-dimethoxystrychnidin-10-one (2,3-DMSO) (0.5%) (G.V.K Pharmaceuticals, Hyderabad, India) was prepared by dissolving 0.5 g of 2,3-DMSO in 100 mL of doubly-distilled water. Finally, HCl and H2SO4 (both from S.D. fine Chemicals, Mumbai, India) were used for the present studies.
PROCEDURE
4-bromophenylhydrazine (4-BPH)-A^(1-naphth-yl)ethylenediamine dihydrochloride (NEDA) method. Stock solution containing 1 to 100 |g of tellurium (the volume of the test solution was restricted to 1 mL) were transferred into 25 mL calibrated flask and 5 mL of 4-BPH-NEDA reagent mixture were added followed by 3 mL of 4 M NaOH. The mixture was allowed to stand for 5 min for the completion of the reaction. The content was diluted up to the mark with doubly-deionised distilled water, the absorbance was measured
at 550 nm against the corresponding reagent blank and the calibration graph was constructed.
3-methyl-2-benzothazoline hydrazone hydrochloride (MBTH)-chromotropic acid (CA) method. Ali-quots of stock solution containing 2-60 |g (0.052.0 |g/mL) of tellurium were transferred into a series of 25 mL standard flasks, to which 2 mL of MBTH and 4 mL of CA (1.0%) were added followed by 6 mL of 4 M NaOH. The mixture was allowed to stand for 5 min with occasional shaking for the completion of reaction. The content was diluted to the mark with water, absor-bance was measured at 500 nm against the corresponding reagent blank and the calibration graph was constructed.
2,3-dimethoxystrychnidin-10-one (2,3-DMSO) method. Aliquots of stock solution containing 5-75 |g (0.08-3.2 |g/mL) of tellurium were transferred into series of 25 mL standard flasks, to which 5 mL of concentrated H2SO4 were added followed by 1 mL of 2,3-DMSO and heated up to 40°C in an microwave oven for 2 min. The content was diluted to the mark with water, absorbance was measured at 480 nm against the corresponding reagent blank and the calibration graph was constructed.
Determination of tellurium in spiked water samples. The spiked water samples were prepared with 500 mL of doubly-deionised distilled water by adding known amounts of tellurium(IV), preconcentrated as mentioned in literature [24], and the percentage recovery of tellurium(IV) was determined as explained in aforesaid procedure.
Determination of tellurium in natural water samples. The proposed methods were employed for different natural water samples (river, lake, spring) (200 mL each) collected around Tirupati area. The samples were used directly to measure tellurium(IV) contents by the proposed methods after filtered with cellulose membrane of pore size 0.45 |m as mentioned in literature [24].
Determination of tellurium in waste water samples. The distillation procedure for the determination of tellurium in waste water was as follows. To an aliquot (100 mL) of known sample taken in a distillation flask, 1 g of KBr and 10 mL of concentrated H2SO4 treated with 0.5 mL of saturated bromine water were added and the solution was then distilled under vacuum till copious white fumes of SO3 vapours were evolved. This process converts all other forms of tellurium into tellu-rium(IV). The distillate was collected in 10 mL of 5% hydroxyl ammonium chloride solution, then made up to a fixed volume and analyzed by the general procedure.
Determination of tellurium in vegetable samples.
5 g of each finely chopped fresh tomato and brinjal samples were placed in a 250 mL beaker and 10 mL of a 1 : 1 (v/v) mixture of concentrated sulfuric acid and nitric acid were added. This solution was heated, until the mixture was clear. Then, the solution was filtered and concentrated to 5 mL, cooled and diluted up to 50 mL with doubly-deionised distilled water. The general procedure was employed to 1 mL of this solution.
Determination of tellurium in soil sample. A
known
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