denum was found to be 35 ng; precision in the submicrogram region was 10 to 2 0 z . The detection limit for nickel was considerably poorer and was found to be about 1 pg for an exciter source strength of approximately 10 mCi. An examination of the factors affecting the analytical sensitivity of the system showed that it is limited primarily by poor detector geometry and background. The poor detector geometry results from the small size of the detector. Background results from electronic noise, instrumental artifacts, and backscatter of the exciter source radiation. However, background in the region of the X-ray spectrum above about 12 keV was due almost entirely to backscatter. Sensitivity of the system can be improved by increase in source intensity and reduction in background. (High de-
tector geometries cannot be achieved because large highresolution semiconductor detectors are not currently available.) Although electronic noise and instrumental artifacts cannot be readily reduced, backscatter can be reduced by selection of an exciter source whose backscatter peak will be far removed from that of the measured X-ray and by reduction in the mass of material placed in front of the detector and source. A major reduction in mass can be accomplished by operation of the spectrometer in a vacuum or in a helium atmosphere. RECEIVED for review July 24, 1968. Accepted October 7, 1968. Division of Nuclear Chemistry and Technology, 155th National Meeting, ACS, San Francisco, Calif., April 1968.
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Rapid Extraction and Direct Spectrophotometric Determination of Copper with Thiothenoyltrifluoroacetone V. M. Shinde and S. M. Khopkar Department of Chemistry, Indian Institute of Technology, Bombay, Bombay 76, India A procedure is described for the extractive photometric determination of copper(l1) with thiothenoyltrifluoroacetone (STTA) in carbon tetrachloride. The olive brown Cu(lI)-STTA chelate solution in carbon tetrachloride obeys Beer’s law over the concentration range of 1.23 to 12.35 pg of Cu per ml. Between pH 2 to 5, quantitative extraction is feasible with 0.001M STTA in carbon tetrachloride. The color of the complex is stable to 72 hours. Copper(l1) can be extracted rapidly and determined in the presence of large numbers of cations as well as anions.
THE CHELATING AGFNT thiothenoyltrifluoroacetone (STTA) was used for the extraction of transition elements ( I ) . From slightly acidic solution it gives, with copper, an olive brown complex in carbon tetrachloride measurable spectrophotornetrically at 490 mp. Acetylacetone (2-4) forms a complex with copper at pH 2 to 5, whereas benzoylacetone (5) can extract copper between pH 4 to 9. Furoyltrifluoroacetone (6, 7) gives a green complex in hexone which can be measured at 660 mp. 2-Thenoyltrifluoroacetone (8-10) was capable of extracting copper in benzene at pH 3 to 4. Such a complex can be measured spectrophotometrically at 430 mp. Chaston et al. (11, 12) synthesized the thio derivative of thenoyltrifluoroacetone, whereas Berg (t) V. M. Shinde and S. M. Khopkar, Chem. Ind., 1967, 1785. (2) T. Shigematsu and M. Tabushi, Bull. Inst. Chem. Res., Kyoto Unic., 39, 35 (1961). (3) A. H . I. BenBassat and Kupfer G. Frydman, Chemist Analyst, 51, 44 (1962). (4) Zbid., 52, 8 (1963). (5) J. Stary and E. Hladk?, Anal. Chim. Asfa, 28,227 (1963). (6) E. W. Berg and M. C. Day, ibid., 18, 578 (1958). (7) R. T. McIntyre, E. W. Berg, and D. N. Campbell, ANAL. CHEM., 28, 1316 (1956). (8) S. M. Khopkar and A. K. De, Z. Anal. Chem., 171,241 (1959). (9) R. A. Bolomey and L. Wish, J . Anier. Chem. SOC.,72, 4483 (1950). (10) E. W. Berg and R. T. McIntyre, ANAL.CHEM., 27, 195 (1955). (11) S. H. Chaston and S. E. Livingstone,Proc. Roy. SOC.(London), 111 (1964). (12) S. H. Chaston, S. E. Livingstone, T. N Lockyer, V. A. Pickles, and J . S. Shannon, Aust. J. Chem., 18,673 (1965).
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and Reed (13) indicated the possibility of utilizing it as a chelating agent for the transition elements. Thiothenoyltrifluoroacetone can be used as the extracting and colorimetric reagent for the transition elements ( I ) , including copper. This paper describes systematic studies on the solvent extraction of copper with thiothenoyltrifluoroacetone. The method is simple and rapid, and effects clean-cut separation and simultaneous spectrophotometric determination of copper at tracer level. EXPERIMENTAL
Apparatus and Reagents. A Type C44 quartz spectrophotometer, a Cambridge pH meter, and a wrist action flask shaker were used. Thiothenoyltrifluoroacetone (STTA) was synthesized from 2-thenoyltrifluoroacetone (Fluka A. G.)by the procedure of Berg and Reed (13). About 0.001M reagent was used in carbon tetrachloride and was usually preserved in a refrigerator. A stock solution of copper sulfate was prepared by dissolving about 0.9818 gram of copper sulfate pentahydrate (B.D.H. AnalaR) in 1 liter of distilled water. The solution was standardized iodometrically and contained 0.99 mg of copper per ml. The solutions of lower concentration were prepared by volumetric dilution of the stock solution. General Procedure. An aliquot of copper sulfate solution (containing about 49.4 pg of copper) was taken and adjusted to pH 4 with 0.01N sodium hydroxide and 0,OlN sulfuric acid in a 25-ml volume. The solution was then introduced into a separatory funnel and shaken with 10 ml of 0.001M S P A in carbon tetrachloride for 10 minutes, Layers were allowed to separate. The organic phase was withdrawn in a 10-ml volumetric flask and measured at 490 mp against the reagent blank. The amount of copper was then obtained from the calibration curve. RESULTS AND DISCUSSION
Absorption Curve. The absorption spectrum of a solution of the Cu(I1)-STTA complex (49.4 pg of copper) extracted at pH 4.0 against the reagent blank as a reference is shown in (13) E. W. Berg and K. P. Reed, Anal. Chim. Acta, 36,372 (1966).
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Table I. Extraction of Copper(I1)-Thiothenoyltrifluoroacetonate between Carbon Tetrachloride and Aqueous Solution as a Function of pH Percentage of copper extracted in CCld D,distribution ratio PH 1.0 28.70 1.01 1.5 69.10 5.50 2.0-5.0 100.00 m 5.5 89.30 20.70 6.0 88.80 10.50 7.0 61.70 4.00 8.0 48.90 2.30 9.0 48.90 2.30
'igure 1. Absorption spectra of ( A ) copper(II)-thiothenoyltrifluorocetonate in carbon tetrachloride, and ( B ) reagent blank us. carbon strachloride [CUI = 7.716 X 10-5M, [STTA] = 1.0 X 10-aM, pH -4
Figure 1. The spectrum of the reagent blank us. carbon tetrachloride is also given. The difference of absorbance between the Cu(I1)-STTA complex and the reagent blank appears to be maximum at 490 mp; hence, all absorbance measurements were carried out at 490 mp. The absorptivity of the complex was 6 x lo3 when the absorbance was 0.470 at 490 rnp, the copper concentration was 49.4 pg/lO ml, and the effective cell width was 1 cm.
Figure 2. Calibration curve at ( A ) 490 mp and ( B )500 mp
Table II. Effect of Reagent Concentration 49.4 p g of Cum) after extraction by SlTA-CCI4 at pH 4.0 gives an absorbance of 0.470 =k 0,010 in 10 ml of CC14 STI'A concentration, STTA Absorbance molar added, ml at 490 mp 0.00025 10 0.330 0.00050 10 0.390 0.00075 10 0.470 0.0010 10 0.470 0.0010 7.5 0.460 0.0010 5 0.370 0.0010 2.5 0.270
Table 111. Effect of Diverse Ions CU(II) = 49.4 pg; pH 4.0; STTA = O.OO1M Tolerance Foreign limit, p g ion 1000 T1+ None Ag+ 2500 Pb2+ None Hg2+ 50 CdZ+ 1000 Sb 3+ 2500 Bi 3+ 1000 Snz+ 1000 Pt4+ None Pdz+ 130 Os6+ 50 Ru3+ 78 Rh 3+ 49 Fea+ 1000 Cr 3+ ~ 1 3 + 500 500 Mn2+ 50 Nil+ 50 U6+ None Th4+ 50 Zr (+ Ce3+ 750 Bel+ 5000 Ca *+ 1000 Sr2+ 500 None Au3+ 1000 MO~0sr'1000 vos 2000 wor22500 CHsCOO50 CitaNone CNNone OxalatesNone &Oa2HPOda2500 5000 Seo3'~~~
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Effect of pH. The extraction of copper was studied at p H 1 t o 7 (Table I). The results showed that extraction is quantitative between p H 2 t o 5. However, the extraction is incomplete beyond this p H ; hence, the optimum p H for quantitative extraction of copper is 2.0 to 5.0. Calibration Curve. Different amounts of copper(I1) were taken and extracted at p H 4.0 and measured at various wavelengths, as shown in Figure 2. The Cu(I1)-STTA system conforms to Beer’s law over the concentration range of 1.23 to 12.35 pg of copper per ml at 490 mp only. Furthermore, at this wavelength there is a maximum difference in absorbance between the complex and the reagent blank. Stability of the Color. As per the general procedure, the absorbance of the Cu(I1)-STTA complex was measured at elapsed intervals of 0, 1,24,48,72, and 118hours. The absorbance was stable t o 72 hours. Hence, the complex should be measured within 72 hours of the extraction. Reagent Concentration. The extraction of copper was carried out with varying concentrations of the reagent (Table 11). The results show that a single extraction with 10 ml of 0.001M reagent is adequate for quantitative extraction. There is insignificant enhancement in the extraction of copper with a greater volume of reagent at this concentration and, with dilute solutions, the extraction is incomplete.
Effect of Salting-Out Agent. The sulfates of ammonium, lithium, sodium, and magnesium (1 to 3M) were used as salting-out agents to study their effects on the extraction of copper with 0.001M STTA at p H 4.0. The results revealed that they d o not enhance the extraction. Diverse Ions. Results in Table 111 show the effect of various ions on the process of extraction. The tolerance limit was set at the amount required to cause =t2,0Z error in the copper recovery, Thallium, lead, antimony, bismuth, tin, platinum, chromium, beryllium, calcium, strontium, molybdate, tungstate, acetate, and selenite can be tolerated in the ratio of 1 t o 20, but ions such as cadmium, ruthenium, iron, nickel, and zirconium are tolerable in the ratio of 1 t o 1. Gold, mercury, oxalate, cyanide, and thiocyanate show serious interference. From eight determinations with 49.4 pg of copper, the ab0.010. Thus, the relative sorbance was found to be 0.470 standard deviation is approximately f1.02z. The total operation requires about 30 minutes.
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RECEIVED for review February 29,1968. Accepted September 13, 1968. This project was sponsored by the Council of Scientific and Industrial Research (India), which awarded a Junior Research Fellowship t o one of the authors (V.M.S.).
Spectrophotometric Determination of Copper in Alkali Metals and Hydroxides with 4,4‘-Dihydroxy2,2’-Biquinoline Alfred A. Schilt and William C . H o y l e Department of Chemistry, Northern Illinois University, Dekalb, Ill. 60115 Thirteen new symmetrically substituted derivatives of 2,2’-biquinoline were evaluated as chromogenic reagents. One of these, the 4,4’-dihydroxy derivative, is capable of complexing copper(1) directly in strongly alkaline solutions. A detailed study of the complex and its application for the determination of copper in sodium and potassium metals of hydroxides are reported. Simplicity is achieved in the determination since neutralization of base and pH adjustment are unnecessary. Sensitivity is favored by extractability of the complex. In common with other cuproine reagents, 4,4’-dihydroxy-2,2‘-biquinoline is a specific chromogenic reagent for copper(1).
stituted ferroin and cuproine reagents initiated by Professors Smith and Case (3, 4). The present investigation was undertaken to evaluate the chromogenic properties of the 13 newly synthesized biquinolines with regard to metal ion chelation. A detailed study was subsequently made of the reaction between copper(1) and the most promising of these, the 4,4’-dihydroxy derivative, from which practical procedures for the determination of copper in alkali metals and in concentrated alkaline solutions were established.
THEPREPARATION of 13 different 4,4’-disubstituted 2,2‘-biquinolines was recently described by Case and Lesser ( I ) . They report that the 4,4‘-dihydroxy derivative can complex copper(1) in concentrated alkaline solutions. This remarkable property was not unexpected, for an earlier study had revealed that hydroxy substituents in the 4,7-positions in 1, 10phenanthroline will impart greatly improved alkaline stability to the iron(I1) phenanthroline complex (2). It is fair to assert that 4,4’-dihydroxy-2,2‘-biquinoline was literally custom made by Case and Lesser for the purpose of chelating copper in strongly alkaline solutions. The appropriate design for its construction evolved through the systematic studies of sub-
Apparatus. A Cary Model 14 recording spectrophotometer was used for the absorbance and spectral measurements. A Corning Model 7 p H meter, with saturated calomel-glass electrode system, was used for the p H measurements. Reagents. Preparative and analytical details of the substituted 2,2’-biquinolines have been reported (1). Solutions, 0.004M, were prepared by adding a slight excess of concentrated hydrochloric acid to weighed amounts of the biquinolines, followed by measured volumes of ethanol. The 0.004M solution of 4,4‘-dihydroxy was prepared by adding 3 drops of 6 M sodium hydroxide to 0.115 gram of compound, followed by 100 ml of 9 5 z ethanol. A 10% solution of hydroxylamine hydrochloride, for use as a reductant for
(1) F. H. Case and J. M. Lesser, J . Heterocycl. Chem., 3, 170 (1966). (2) A. A. Schilt, G. F. Smith, and A. Heimbuch, ANAL.CHEM., 28, 809 (1956).
(3) G. F. Smith, ANAL.CHEM.,26, 1534 (1954). (4) F. H. Case, “A Review of Syntheses of Organic Compounds Containing the Ferroin Group,” G. Frederick Smith Chemical Co., Columbus, Ohio, 1960.
EXPERIMENTAL
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