Spect rophoto metric Dete rminatio n of T ha IIium(III) with 3-Hydroxy-l,3=DiphenyItriazine in 70% Alcohol S. C. SHOME, H. R. DAS, and 8. DAS Chemical laboratory, Presidency College, Calcutta, India
b The color reaction between thallium(lll) and 3-hydroxy-l,3-diphenyltriazine has been studied to determine the optimum conditions for the analytical use of this reagent. Because the orange-red colored complex is insoluble in water but soluble in 70% alcohol, the spectrophotometric measurements are carried out in 70% alcoholic medium. Full color is developed within the pH range from 5.0 to 8.0. The complex in alcohol shows maximum absorption at 422 mp and the mole ratio of thallium to the reagent in the complex is 1 :3. The absorbance of the solutions at 422 mp obeys Beer's law in the thallium concentration range investigated-i.e., 2 0 to 160 pg. per ml. Determination of thallium can be carried out spectrophotometrically in the presence of a large number of foreign ions.
0
phenylhydroxylamine derivatives have been used for the gravimetric estimation of metals. Shome (4) suggested the suitability of 3-hydroxy-l,3-diphenyltriazine as an improved analytical reagent in which the nitroso group of cupferron was replaced by --N=NCeHs group. Sogani and Bhattacharya (6) used this reagent for the gravimetric determination of pallsr dium, copper, and nickel. Later, various workers of this laboratory mployed this reagent successfully in the gravimetric estimation of gallium, indium, beryllium, molybdenum, and vanadium and for the spectrophotometric determination of copper, iron, cobalt, nickel, palladium, and molybdenum; the results of these investigations will be reported in the future. I n the present investigation, 3-hydroxy-l,3diphenyltriazine was used for the colorimetric determination of thallium in 70% alcohol. Spectrophotometric data for solutions of the thallium 3-hydroxy-l,3diphenyltriazine compound in 70% alcohol are presented in this paper. Appreciable amounts of aluminum, gallium, and thorium do not interfere with the determination of the metal. The interferences of iron, titanium, thorium, zirconium, etc., are avoided by complexing the foreign ions with fluoride. Indium and copper form insoluble preNLY A FEW
1522
ANALYTICAL CHEMISTRY
cipitates with 3-hydroxy-l,3-diphenyltriazine in 70% alcohol which are filtered before the spectrophotometric determination of thallium. EXPERIMENTAL
Apparatus. A Carl-Zeiss spectrophotometer PMQ I1 type with 1-cm. quartz cells was used for the transmittance measurements. All the p H measurements were carried out with a Cambridge p H meter (Bench Model). Reagents and Chemicals. 3-HyDROXY-1,3-DIPHENYLTRIAZINE SOLUTION. The organic reagent was crystallized from alcoholic solution twice and a weighed amount of the dried reagent was dissolved in alcohol (4, 6). A 0.02M solution of the reagent was employed in the study of the color reaction. THALLIUMSOLUTION. A known quantity of thallic oxide was dissolved in nitric acid and then made to volume with water. The solution was standardized gravimetrically by the Tl2CrO4 method. Weaker solutions were prepared by proper dilution. SOLUTIONS OF DIVERSEIONS. Stock solutions were prepared by dissolving measured amounts of nitrates, chlorides, or sulfates of the corresponding metal. I n some cases, dilute acids were added to prevent hydrolysis. To study the effect of anions, the corresponding alkali metal salts were dissolved in distilled water.
Procedure. The p H of the standard thallic solution was adjusted t o 5.5-7.0 by adding 10% sodium acetate or sodium potassium tartrate solution (to obtain higher p H values the latter was employed). A known amount of the standard solution was then added to a 25-ml. volumetric flask, cooled in ice-cold water, and a few milliliters of alcohol were added followed by 0.02M 3-hydroxy-l,3-diphenyltriazine solution (2.0-4.0 ml.). The solution was mixed thoroughly, and water or a mixture of water and alcohol was added to make up the volume. The final concentration of alcohol in the solution was 70%. After 30 minutes, as the solutions attained the room temperature, the spectral transmittance measurements were made. The blank was prepared under the same conditions using the same quantity of organic reagent solution and at the same pH. RESULTS
Absorption Curves. Transmittance curves with different amounts of thallium(II1) - 3-hydroxy-l,3diphenyltriazine chelate (Tl+3 = 25.0, 62.5, 115.0 pg. per ml.) in 70% alcohol at pH 6.0 are shown in Figure 1. The transmittance measurements were made in the wavelength range of 200-540 mp. The curves showed maximum absorp tion at 270 mp (in dilute solutions) and at 422 mp; above 422 mp the absorption gradually decreases. The solutions
Wavelength, mp Figure 1. Transmittance curves of thallium(lll)-triazine complex in 70y0alcohol
o (A) 25.0
pg./rnl.
A
(C) 1 1 5 pg./ml.
(6) 62.5 pg./ml.
0
(D)Blank 10-'M
gave complete transmission from 330 rnp to 400 mp. The reagent blank showed maximum absorption from 330 t o 400 mp and was relatively negligible from 415 mp and onward. Transmittance measurements were made at 422 mp, and the wavelengths below 422 mp were avoided because of appreciable absorption by the reagent. The molar absorptivity at 422 mp was 477.5 f16.2. More work will be needed to explain the absorption peak at 270 mp for dilute solutions. Effect of pH. The variation of t h e transmittances of the color system (contains 100 pg./ml. of Tl+3) with the pH of the solution was also studied. The orange-red color formed by 3hydroxy-l,3-diphenyltriazine with thallium was fully developed within 5 minutes. The color reaction was independent of the acidity in the pH range 5.0 to 8.0. The solution decomposed a t pH 2.0 or below, and above pH 8.5. As the optimum pH range was between 5.5 and 7.5, the spectral transmittance measurements were carried out a t 422 mp in the pH range 6.0-7.0. Stability of Color. T h e orange-red color formed by 3-hydroxy-lJ3-diphenyltriazine with thallium in 70% alcohol was quite stable. The transmittance of alcoholic solution of thallium 3-hydroxy-l,3-diphenyltriazine complex (100 pg./ml. of thallium and 3 ml. of 0.02.M reagent at pH 6.4) was measured at different intervals of time. The color of the complex was quite stable for 5-6 hours, after which it faded somewhat and became stable after 12 hours for 3-4 days, again obeying Beer's 1aw . Conformity to Beer's Law. T h e absorbance of 700/, alcoholic solutions of thallium 3-hydroxy-l,3-diphenyltriazine complex of various concentrations, prepared according to the general procedure given as above a t p H 6.4, was measured at 422 mp against an appropriate reagent blank. The results showed that thallium ("-3hydroxy- lj3-diphenyltriaaine followed Beer's law at 422 mp over the concentration range investigated-Le., 20 to 160 pg./ml. Optimum Concentration Range. According t o Sandell (Z),the most favorable range for making absorbance measurements is from 0.2 to 0.7 absorbance unit. This corresponds to a concentration of thallium ranging from 90 to 300 pg./ml. Sensitivity. The sensitivity of the reaction, as defined by Sandell (S),was found t o be 0.45 pg. per sq. cm. Nature of the Complex. T h e empirical formula of the thallium complex was determined by the mole ratio method of Meyer and Ayres (1). il series of solutions were prepared, each of which contained 1.342 X lO-5M thallic ion and varying concentrations
0-02 0
I
I
I
I
I
1
I
1
I
I
2
4
6
8
10
I2
14
16
18
PO
Mole ratio of Figure 2. complex
[ R l Reagent to Metal [MI
Composition by mole ratio method applied to thallium(lll)-triazine
Effect of Diverse Ions Concn. of Tli3 = 200 pg. Sources Concn. tolerated
Table I,
Ions added Ga +3 In +a&
Ti + 4
uoz +z W +e
Mo +d
Fe +a
~ 1 + 3
5
(pg.)
560
2000
1800 50 360 200 3 (linterf e r e ) 1800
280 Ce + 4 3a 160 CU+l" 2000 Th+4 200 Zr +4 Ni +la 100 2000 Zn +a tartrate >lo6 Tartrate ion FNaF >IO6 Interference of these ions is eliminated by filtering the solution.
of the chelating agent at pH 6.56. The ratio of the concentrations was varied from 0.3 to 14.0. The absorbances which were measured at 422 mp were plotted against the ratio of the number of moles of ligand to the number of moles of metal ion. The results are shown in Figure 2. From the figure it is evident that thallium formed a complex with 3-hydroxy1,3-diphenyltriazine in the ratio of metal: ligand = 1: 3. Effect of Diverse Ions. I n determining the effect of diverse ions, a known volume of standard thallium solution containing the ion in question was taken. The pH of the solution was adjusted to 6.0-6.5 with 10% sodium acetate solution or sodium potassium tartrate solution. An excess of t h e reagent solution and alcohol was added and the absorption was measured at 422 mp as described before.
Because 3-hydroxyl-l,3-diphenyltriazine formed precipitates with copper, indium, and nickel, thallium was determined in the presence of these ions by the following procedure: A measured quantity of the standard thallium solution was taken in a 50-ml. volumetric flask and the required amount of copper, indium, or nickel solution was added before the pH of the solution was adjusted to 6.0-6.5 with 10% sodium acetate solution. A few milliliters of alcohol was introduced, the solution was cooled, and 0.02M 3hydroxy-lI3-diphenyltriszine was added in excess. The solution containing the precipitate was made to volume with distilled water and thoroughly mixed. The precipitate was removed by filtration and the absorption of the colored filtrate was measured at 422 mp. The results are recorded in Table I. The estimation of Tl+3 with 3-hydroxy-lJ3-diphenyltriazinein 70% alcoVOL 38, NO. 11, OCTOBER 1966
1523
hol waa possible in the presence of tartrate and fluoride (> 100 mg.), thorium and zinc (2 mg.), titanium and aluminum (1.8 mg.), gallium (560 pg.), uranium (50 pg.), tungstate (360 pg.), molybdate (200 pg.), zirconium (200 wg.), and cerium (280 pg.) ions. Indium, copper, and nickel interfered due to the formation of insoluble precipitates with the reagent. The interferencesof C U +(160 ~ p g . ) , Ni+*(lOOpg.), In+3(2000pg.) could be eliminated by carrying out the absorption measurements after filtration. Traces of iron and vanadium produced interfering colors. It was observed that thallium could be estimated in the presence of appreciable amounts of fluoride ions. Attempts were, therefore, m d e to eliminate the interferences due to ferric, thorium, titanium, zirconium, and aluminum ions by adding sodium fluoride solution. The
Table 11.
Wed of Diverse Ions in Presence of Fluoride
Concn. of T1+’= 200 pg. added = 2.0 ml. of 5% F- soh.
Ions added
Concn. tolerated sources
(ag.)
Precision and Accuracy. Precision data were obtained from standard solutions prepared and estimated on different days. The precision varied from 3.2% at 144 pg. per ml. to 0.1% at 444 pg. per ml. Accuracy of the method wm justified by measuring some standard solutions. The relative error waa 1.5% at 144 pg. per ml. and 0.9% at 444 pg. per ml. LITERATURE CITED
results in Table I1 indicate that large amounts of iron, thorium, aluminum, titanium, and zirconium could be tolerated if the spectrophotometric measurements were carried out in the presence of fluoride ions.
(1) Meyer, A. S., Ayrea, G. H.,J . Am. Chem. SOC.79,49 (1957). (2)Sandell E. B., “Colorimetric De termination of Traces of Metals,” p. 97,Interscience, New York, 1959. (3) Ibid., p. 83. (4) Shome, S. C., Current Sa‘. (India) 13, 257 (1944). (5) Sogani, N. C., Bhattacharya, S. C., ANAL.CHEM.28, 81, 1616 (1956). RECEIVEDfor review January 13, 1966. Accepted June 28, 1966.
Spectrophotometric Investigation and Analytical Application of the Synergic Solvent Extraction of Rare Earths with Mixtures of 2 -Thenoyltriflu o roaceto ne and Tri-n-octyI Phosphine Oxide TOMITSUGU TAKETATSU and CHARLES V. BANKS Institute for Atomic Research and Department of Chemistry, lowa State University, Ames, lowa The absorption spectra of rare earth-TTA-TOP0 complexes, that were synergically extracted into toluene from an aqueous solution, were measured from 430 through 800 mp. One absorption band each for neodymium, holmium, and erbium was remarkably enhanced and the molar absorptivities at the wavelengths of maximum absorption were about 7, 26, and 22 times greater, respectively, than the same quantities in chloride medium. The formulae of these complexes were estimated spectroF1lotometrically to be LII(TTA)~ TOPO and Ln(TTA)a 2TOPO. The spectrophotometric determination of neodymium, holmium, and erbium was investigated using the analytically significant absorption bands at 584.1, 451 -8,and 520.2 mM, respectively. a
I
that the sharpness and complexity of absorption spectra of solutions of rare earths arise from pure electronic transitions involving the 4f subshell, which is shielded by the 5s and 5p outer shells from interaction with the ionic field in the solutions. If the strength of the ionic field surrounding T IS WELL KNOWN
1524
ANALYTICAL CHEMISTRY
the rare earth ions is sufficient to penetrate the shielding, some absorp tion bands may be shifted in wavelength and enhanced in sensitivity. Such effects have been observed with rare earth complexes of (ethylenedinitrilo) tetraacetic acid (EDTA) (6, 9, IO) and of related compounds (IO) in aqueous solutions. Rare earth complexes with 5,7-dichloro-8-quinolinol (6) in chloroform also show these same effects. Recently, it has been observed that the absorption bands of the complexes of the rare earths are particularly enhanced in the following cases: with acetylacetone in chloroform and benzene (7), with carbonate in aqueous solution (8),with nitrate in tetrabutylammonium nitrate-nitroethane (a), and with thenoyltrifluoroacetone in benzene ( 4 ) . It is expected that strong enhancement of the intensity and a shift in wavelength of certain bands in the absorption spectra would be observed for cases in which synergic complexation of the rare earths influences the ionic field surrounding the metal ions more than would the chelating acid or the neutral donor done. Healy and Ferraro (1) studied the absorption spectra of the uranyl,
thorium, and neodymium complexes extracted into organic solvents containing a mixture of 2-thenoyltrifluoroacetone (TTA) and tri-n-octyl phosphine oxide (TOPO) or tri-nbutyl phosphate (TBP); and Ihle et al. (8) reported a spectrophotometric study of the uranyl-di(2-ethylhexy1)phosphoric acid-TOP0 complex. The absorption spectra of the TTATOPO complexes of rare earths which are synergically extracted into toluene from aqueous acetate solution and which show significant absorption in the visible region are recorded in this paper. The formulae and spectrophotometric analytical applications of the neodymium, holmium, and erbium TTATOPO complexes are discussed. EXPERIMENTAL
Reagents. Standard solutions of scandium and the rare earths, except cerium, were prepared by dissolving in dilute hydrochloric acid the 99.9% pure oxide, which had been purified by ion exchange and analyzed spectrographically in this laboratory. The solution of cerium(II1) was prepared by dissolving in dilute hydrochloric acid the reagenbgrade cerous chloride. The concentrations of these
