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A highly sensitive fluorescent reaction for tellurium(VI) application to the determination of tellurium in selenium
Analytica Chimica Acta, 80(1976)180-182 0 Elsevier Scientific Publishing Company, Amsterdam -Printed
in The Netherlands
Short Communication ____ -_. .--
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A HIGHLY SENSITIVE FLUORESCENT REACTION FOR TELLURIUM(V1) APPLICATION TO THE DETERMINATION OF TELLURIUM IN SELENIUM M. BOVAY
nnd M. MARCANTONATOS
Department (Swilxcrland)
of Inorganic
and Analytical
Chemistry.
University
of Geneva,
221 l-Geneva-4
(Received 8th May 1975)
Numerous spectrophotometric methods have been proposed for the determination of tellurium, but the highly sensitive photoluminescence techniques have only found a few applications. Most of the calorimetric methods are based on the formation of complexes with ligands having oxygen, sulfur or 0,s coordination sites; a few methods involve the formation of colored ionic associates between acid tellurium complexes and organic bases [ 11. Fluorescent associates have been obtained with rhodamine S derivatives [l(a)] and these, like the coloured associates and the other absorbing complexes, permit the determination of tellurium in the pg ml-’ range. The formation of fluorescent tellurium chelates does not seem to have been reported; the only fluorimetric method proposed so far for the determination of tellurium is based on the formation of ion associates with rhodamine S (or derivatives). l,l’-Dianthrimide reacts with tellurium species in concentrated sulfuric acid, to give a 1 :l coloured complex [ 2,3]. In this solvent, fluorescent chelates are formed between orthotelluric acid and hydroxy-2-benzophenone ligands, which also form highly luminescent chelates with the tetra(hydrogensulfato)borate monomeric anion 14-61. Most of the benzophenones studied in the present work gave coloured chelates with Te(OH)6 and two of them - 2-hydroxy-5methoxybenzophenone and 2,4,4&rihydroxybenzophenone (THE) -formed chelates which were also highly fluorescent. The THB ligand was found to be the most appropriate for analytical purposes, and permits the precise determination of tellurium in the ng ml-’ range. Boron-THB chelates, which are negligibly excited at 426 nm (maximum excitation of Te-THB), do not interfere. Expsrimen
tal
Reagent-grade orthotelluric acid and sulfuric acid (d 1.84; Merck) were used. 2,4,4-Trihydroxybenzophenone (Aldrich) was purified by double recrystallization with triple-distilled water-ethanol (70+30). Solutions of telluric acid in sulfuric acid were prepared from an aqueous 5 * lo-’ M solution. A Perkin-
181
Elmer MPF-2A spectrofluorimeter
was used.
Results and discussion Spectral investigations, as well as studies on the kinetics and equilibria of complex formation, showed that THB, in excess over Te(OH)6, forms successively 1:l and 2:l THB-Te(OH)6 fluorescent chelates [7]. The 1 :I chelate is readily formed at room temperature, while the 2: 1 chelate, on which the proposed analytical method is based, is formed by heating the THB-Te(OH)6 solutions in sulfuric acid at 90 “C for 120 min. This is due to the structure of the 1:l complex in which the tellurium moiety is deprived of sites capable of being readily coordinated by a second THB molecule. The formation of the 2:l chelate, therefore, requires opening of a probably highly stabilized ring in the 1:l complex. The maximum excitation and fluorescence emission wavelengths of the 2:l chelate lie at 426 and 465 nm, respectively. At these wavelengths, the apparent fluorescence emission efficiency, f#~~, , for a moderately sensitive arrangement of the fluorimeter, is of the order of 10M M-’ cm-’ , thus permitting ng ml-’ levels of tellurium to be determined with acceptable precision. The obl1 value of the 1:l chelate is about lo2 times lower than the @i2 value, showing the predominant intraligand transition character of the absorption and emission bands of these complexes. Analytical curves were determined by repeating single fluorescence measurements for each tellurium concentration over several weeks. Repeatability was satisfactory, and the straight-line slopes were reproducible. The linear regression coefficients were never lower than 0.995 and the relative errors did not exceed + 16% and + 3% for 9 ng Te ml-’ and 65 ng Te ml-’ , respectively. Foreign ions such as Li’, Mg2’, Ca2+, Sr2+, Bazc, B3’, Al’*, V4+, Mn2+, Fe2+, Co?*, Ni’*, Coz+, Zn2’, Cd2+, Sn”, Pb2+, Sb”, Bi”, NO;, NO, and CO
182
contents of these elements in the sample were fax lower than the tolerance limits for the procedure. TABLE
1
Fluorimetric determination of tellurium in selenium (The selenium was a B.D.H. AnalaR sample with the maximum limits of impurity given as 0.05 % Te, 0.006 % Fe. P, initial sample solution in sulfuric acid; V,, volume of aliquot (total volume, 6 ml); F, fluorescence intensity.) --_. ---_--.--_..-.-.---.--_.-_-_____.--._________ P External standard Internal standnrd (II ml-’ ) 21) ----_ _..._ .._-_ __.________ % Te F S Te F _____.____.__ ._.___ __ ___-____..__.. .__. . .. . _....-.-... ...--..-..---..-. --.-- - ---.- ~--1.2765 1.2765 1.0361 1.0361 0.20722 0.20722
0.2 0.2 0.07 0.1 0.2 0.3
68 51 25 15 23
0.089 0.093 0.123 0.10 0.10
82 57 37 47 49 56
0.093 0.07 5 0.073 0.090 0.10 0.099
-_-._. -_._-
-_-__________
REFERENCES 1 1.1. Nazarenko and A.N. Ermakov, Analytical Chemistry of Selenium and Tellurium. Halsted Press, New Yorlc (1972), (a) page 3 15. 2 O.B. Sknar and F.J. Langmyhr, Anal. Chim. Acta, 23 (1960) 175. 3 F.J. Lnngmyhr and G. Norheim. Anal. Chim. Acta, 41 (1968) 341. 4 M. Marcantonatos, A. Mnrcantonatos nnd D. Monnier. Helv. Chim. Acta, 48 (1965) 194. 6 M. Marcantonatos and B. Liebiclc, Chimia, 24 (1970) 447. 6 M. Marcantonatos and C. Menzinger, Inorg. Chim. Acta (in press). 7 M. Marcantonatos and M. Bovay, unpublished results.
in The Netherlands
Short Communication ____ -_. .--
.._..___ --__- _._._. ----._
__.-.-.... --..-- ._.._.--.--.-
---- -
.--.-
A HIGHLY SENSITIVE FLUORESCENT REACTION FOR TELLURIUM(V1) APPLICATION TO THE DETERMINATION OF TELLURIUM IN SELENIUM M. BOVAY
nnd M. MARCANTONATOS
Department (Swilxcrland)
of Inorganic
and Analytical
Chemistry.
University
of Geneva,
221 l-Geneva-4
(Received 8th May 1975)
Numerous spectrophotometric methods have been proposed for the determination of tellurium, but the highly sensitive photoluminescence techniques have only found a few applications. Most of the calorimetric methods are based on the formation of complexes with ligands having oxygen, sulfur or 0,s coordination sites; a few methods involve the formation of colored ionic associates between acid tellurium complexes and organic bases [ 11. Fluorescent associates have been obtained with rhodamine S derivatives [l(a)] and these, like the coloured associates and the other absorbing complexes, permit the determination of tellurium in the pg ml-’ range. The formation of fluorescent tellurium chelates does not seem to have been reported; the only fluorimetric method proposed so far for the determination of tellurium is based on the formation of ion associates with rhodamine S (or derivatives). l,l’-Dianthrimide reacts with tellurium species in concentrated sulfuric acid, to give a 1 :l coloured complex [ 2,3]. In this solvent, fluorescent chelates are formed between orthotelluric acid and hydroxy-2-benzophenone ligands, which also form highly luminescent chelates with the tetra(hydrogensulfato)borate monomeric anion 14-61. Most of the benzophenones studied in the present work gave coloured chelates with Te(OH)6 and two of them - 2-hydroxy-5methoxybenzophenone and 2,4,4&rihydroxybenzophenone (THE) -formed chelates which were also highly fluorescent. The THB ligand was found to be the most appropriate for analytical purposes, and permits the precise determination of tellurium in the ng ml-’ range. Boron-THB chelates, which are negligibly excited at 426 nm (maximum excitation of Te-THB), do not interfere. Expsrimen
tal
Reagent-grade orthotelluric acid and sulfuric acid (d 1.84; Merck) were used. 2,4,4-Trihydroxybenzophenone (Aldrich) was purified by double recrystallization with triple-distilled water-ethanol (70+30). Solutions of telluric acid in sulfuric acid were prepared from an aqueous 5 * lo-’ M solution. A Perkin-
181
Elmer MPF-2A spectrofluorimeter
was used.
Results and discussion Spectral investigations, as well as studies on the kinetics and equilibria of complex formation, showed that THB, in excess over Te(OH)6, forms successively 1:l and 2:l THB-Te(OH)6 fluorescent chelates [7]. The 1 :I chelate is readily formed at room temperature, while the 2: 1 chelate, on which the proposed analytical method is based, is formed by heating the THB-Te(OH)6 solutions in sulfuric acid at 90 “C for 120 min. This is due to the structure of the 1:l complex in which the tellurium moiety is deprived of sites capable of being readily coordinated by a second THB molecule. The formation of the 2:l chelate, therefore, requires opening of a probably highly stabilized ring in the 1:l complex. The maximum excitation and fluorescence emission wavelengths of the 2:l chelate lie at 426 and 465 nm, respectively. At these wavelengths, the apparent fluorescence emission efficiency, f#~~, , for a moderately sensitive arrangement of the fluorimeter, is of the order of 10M M-’ cm-’ , thus permitting ng ml-’ levels of tellurium to be determined with acceptable precision. The obl1 value of the 1:l chelate is about lo2 times lower than the @i2 value, showing the predominant intraligand transition character of the absorption and emission bands of these complexes. Analytical curves were determined by repeating single fluorescence measurements for each tellurium concentration over several weeks. Repeatability was satisfactory, and the straight-line slopes were reproducible. The linear regression coefficients were never lower than 0.995 and the relative errors did not exceed + 16% and + 3% for 9 ng Te ml-’ and 65 ng Te ml-’ , respectively. Foreign ions such as Li’, Mg2’, Ca2+, Sr2+, Bazc, B3’, Al’*, V4+, Mn2+, Fe2+, Co?*, Ni’*, Coz+, Zn2’, Cd2+, Sn”, Pb2+, Sb”, Bi”, NO;, NO, and CO
182
contents of these elements in the sample were fax lower than the tolerance limits for the procedure. TABLE
1
Fluorimetric determination of tellurium in selenium (The selenium was a B.D.H. AnalaR sample with the maximum limits of impurity given as 0.05 % Te, 0.006 % Fe. P, initial sample solution in sulfuric acid; V,, volume of aliquot (total volume, 6 ml); F, fluorescence intensity.) --_. ---_--.--_..-.-.---.--_.-_-_____.--._________ P External standard Internal standnrd (II ml-’ ) 21) ----_ _..._ .._-_ __.________ % Te F S Te F _____.____.__ ._.___ __ ___-____..__.. .__. . .. . _....-.-... ...--..-..---..-. --.-- - ---.- ~--1.2765 1.2765 1.0361 1.0361 0.20722 0.20722
0.2 0.2 0.07 0.1 0.2 0.3
68 51 25 15 23
0.089 0.093 0.123 0.10 0.10
82 57 37 47 49 56
0.093 0.07 5 0.073 0.090 0.10 0.099
-_-._. -_._-
-_-__________
REFERENCES 1 1.1. Nazarenko and A.N. Ermakov, Analytical Chemistry of Selenium and Tellurium. Halsted Press, New Yorlc (1972), (a) page 3 15. 2 O.B. Sknar and F.J. Langmyhr, Anal. Chim. Acta, 23 (1960) 175. 3 F.J. Lnngmyhr and G. Norheim. Anal. Chim. Acta, 41 (1968) 341. 4 M. Marcantonatos, A. Mnrcantonatos nnd D. Monnier. Helv. Chim. Acta, 48 (1965) 194. 6 M. Marcantonatos and B. Liebiclc, Chimia, 24 (1970) 447. 6 M. Marcantonatos and C. Menzinger, Inorg. Chim. Acta (in press). 7 M. Marcantonatos and M. Bovay, unpublished results.