Table IV. Replicate Analyses of Tentative U 3 0 8Standard Sample NBL 95
Determination
Parts Per RIilIion PresStandard enta Foundb deviation 50
Tin
49.7
0.95
50 49.8 0.56 Molybdenum a Quantity added. * Average of eight determinations.
shown to be due to some tin(1V) in the solution. No special steps are necessary to ensure the correct oxidation state. With every type of sample analyzed, the dissolution and fuming steps result in complete conversion of any tin(I1) to tin(1V).
LITERATURE CITED
(2) Gentry, C. H. R., Sherrington, L. G., Analyst 75, 17 (1950). (3) Hamaguchi, H., Ikeda, N., Osawa, K., Bull. Chem. SOC.Japan 32, 656 (1959). ( 4 ) Menis, O., Manning, D. L., Ball, R. G., U . S. Atomic Energy Comm. Rept. ORNL-2111, August 1956. (5) Motojima, K., Hashitani, H., ANAL. CHEM.33, 48 (1961). (6) Motojima, K., Hashitani, H., Bunseki Kagaku 9, 151 (1960). (7) ROSS,W. J., White, J. C , h A L . CHEM. 33, 421, 424 (1961). (8) Ruf, E., 2. anal. C h p . 162, 9 (1958). (9) Sandell, E. B., Colorimetric Determination of Traces of Metals,” 3rd ed., Interscience, New York, 1959. (10) Wakamatsu, S., Bunseki Kogaku 9 , 858 (1960). (11) Wyatt, P. F., Analyst 80, 368 (1955).
(1) Farnsworth, M.,Pekola, J., ASAL. CHEM.26, 735 (1954).
RECEIVED for review November 15, 1961. Accepted March 1, 1962.
No study was made of possible hydrolysis of tin before the extraction could be made. I n the usual elapsed time of a t least 30 minutes between the final pH adjustment and the extraction, no evidence of hydrolysis was found in the analysis of samples. Both the tin and molybdenum osine complexes appear to form immediately, and the extraction coefficients for the chloroform-aqueous system appear to be large. The extractions are complete within 30 seconds despite the unfavorable organic to aqueous volume ratio used.
Spectrophotometric Determination of Copper with Ethylenediamine E. A. TOMlC and J. L. BERNARD Explosives Departmenf, E. 1. du font de Nemours & Co., Wilmington 98, Del.
b The purpose of this study is to utilize the chelation of Cu by ethylenediamine (en) in a rapid and simple analytical method for the determination of copper. Copper(l1) reacts with ethylenediamine in aqueous solution to and (Cu form the blue (Cu chelates. The aqueous solutions of the chelates conform to Beer’s Law and are stable for several weeks. As described, the method is designed to determine copper in the concentration range of 20 to 1000 p.p.m. in solution when 1-cm. cells are used. It is particularly useful for the analysis of ores and alloys which contain several per cent copper.
+’
all metal ions, C U + is ~ probably the one for which the largest number of photometric determinations have been published. Most of these methods (12) are designed to determine copper in trace amounts. The determination of copper with HBr (3, 7 ) has been adopted widely for the determination of relatively large amounts of copper although molybdenum, vanadium, chromium, cobalt, gold, and platinum metals can interfere. The classic cupric ammonia method (6) and its modifications (10, 11, 1:) provide the means to measure copper concentrations in the range of 40 to 600 p.p.m. However, these methods suffer especially from dependence of color intensity on reagent MOSG
632
ANALYTICAL CHEMISTRY
concentration, volatility of reagent, and interference by foreign metal ions. Ethylenediamine (en) forms complexes with C U + of ~ comparable absorptivity. Therefore, substitution of en for ammonia as the reagent for Cu t2promised to overcome some of the disadvantages. EXPERIMENTAL
Apparatus. Absorption spectra were obtained with a Perkin-Elmer recording spectrophotometer, Model 4000A. Routine measurements were made in a Beckman, Model B spectrophotometer. One-centimeter cells were used in both instruments. Spectrographic metal analyses were obtained with a 3.4-meter Ebert Type (Jarrell--4sh Co.) emission spectrograph. Measurements of p H were made with a Beckman Model H2 pH meter equipped with a glass and reference electrode couple. Reagents. COPPER SOLUTIOSS. Stock solution was prepared by dissolving 120 grams of cupric nitrate (trihydrate) in 500 ml. of mater containing 1 ml. of concentrated nitric acid. The solution, standardized by electrolytic deposition, contained 61.70 mg. of Cu+*per ml. Standard copper solution containing 10 mg. of C U + per ~ ml. was prepared by diluting 81.04 ml. of the stock solution to 500 ml. A 0.5M cupric nitrate solution was prepared by diluting 51.5 ml. of the cupric nitrate stock solution to 100 ml. ETHYLENEDIAMINE REAGENT SOLUTION. An ethylenediamine solution-
en reagent solution-was prepared by diluting redistilled 98% ethylenediamine with an equal volume of water. Ethylenediamine solutions, 0.5iIf and 5M, were prepared by diluting appropriate amounts of the redistilled 98y0 ethylenediamine with water. SOLUTIONSOF OTHER METAL IONS. Reagent grade nitrates of the following metals were dissolved in water with the aid of concentrated H?;Oa to give approximately 1M solutions of p H ‘v 1: Th4-4, Fef3, Crf3, Ti+*, Mn+2, Ca+2, Sn+21 UOz+2, Xif2, and Co+2. Reagent grade sodium salts of W04+, MOO^-^, VOs-, and Crz0,-2 were dissolved in water to give 1M solutions. These solutions were standardized by titration with EDTA or by conventional gravimetric analyses. Copper-Ethylenediamine
System.
The copper-ethylenediamine chelates were studied by several authors by means of different techniques (4, 5, .9, l S ) , and the existence of the complexes (Cu en)fZJ (Cu enz)+2,and (Cu en3)+? with the respective formation constants of log kl = 10.75, log kz = 9.28, and log k3 = 0.90, was established. Figure 1 compares the absorption spectra of copper(I1) nitrate solutions which contain no ethylenediamine, the stoichiometric amount of ethylenediamine to form the (Cu enz)+2 complex, and a large excess of ethylenediamine. These spectra show the existence of two different complexes with absorption maxima a t 550 mfi and 610 m p , respectively. Job’s plots (8) a t these n-ave-
PH
1.2425
'
450
I
475
I 500
525
l
l
5 5 0 575 600
I
650
1
700 750
WAVELENGTH rnp
Figure 1. system
Figure 2. Dependence of absorbance of copper(l1)-ethylenediamine system on pH, measured a t 540 mp
Absorption spectra of copper(l1)-ethylenediamine
lengths identified the complexes as (Cu en,)+? and (Cu ena)+,, which is in agreement with Bjerrum and Xielson's findings (a). Figure 1 also shoas that the absorption curves of the (Cu en.JT2 and the (Cu en3)+? complexes intercept a t 540 nip. This suggests that the determinaticn of C u T 2by ethylenediamine might be possible a t this wavelength irrespective to the reagent concentration. Observance of Beer's Law and Precision. To determine whether absorbance of the Cu-en system increases linearly n i t h copper concentration, t h e folloning solutions were prepai ctl :ind measured spectrophotonietrically :it 510 nip, sensitivity setting 3 -1 copper solution containing 1 nig. of Cut2 per ml. was prepared from the standard copper solution. Volumes of 0.5, 1, 2, 5 , 7 , and 10 ml. of this solution were transferred into 25-ml. volumetric flasks. One milliliter of the en reagent solution was added to each. The solutions were brought to volume with water. A second set of solutions was prepared by transferring 0.5, 1, 2, 5, 7, and 10 ml. portions of the standard copper solution into 100-ml. volumetric flasks. The en reagent solution, 3 nil., n a s added to each flask, and the solutions were made u p to volume n i t h water. The absorbance of these solutions n a s measured a t 540 mp. Plots of absorbance us. concentration for solutions containing 0.5 to 10 mg. of copper (11) in 25 ml. and 5 to 100 mg. of copper (TI) in 100 ml. shoned straight lines. Aqueous solutions containing 10, 50, and 100 mg. of Cuf2 and 1 ml. of en reagent solution in 25 ml. were prepared in triplicate. Dilutions were made by transferring 10 ml. of each solution into a 100-ml. flask, adding 4 ml. of en reagent solution, and diluting to volume n i t h water. The standard deviation of these measurements was 0.08. Influence of Experimental VariO F REAGENT CONCENables. EFFECT TILATIOX. T o determine t h e effect of ethylenediamine concentration on ab-
sorbance, measurements were made on 13 solutions containing 0.5 to 1460 moles of ethylenediamine per mole of copper. The absorption spectra of these solutions were recorded between 450 and 750 mp against water. Solutions containing 2 to 1000 moles en per mole of Cu+2 showed the same absorbance at 540 mp, although the formation of (Cu en3jL2was detected in the presence of a 100-fold excess of ethylenediamine (200 moles of en per mole of C U + ~as ) characterized by the shift of the absorption maximum from 540 mp to higher wavelengths. Therefore, the determination of 0.5 to 10 mg. of CuL2 with 1 ml. of en reagent solution and of 5 to 100 mg. of Cu+? with 5 nil. of en reagent solution is possible a t 540 mp. ii 500-fold excess of ethylenediamine should not be exceeded. EFFECT OF PH. Each of five samples n-as prepared by diluting 5-ml. samples of standard copper solution to approximately 7 5 ml. with nater. To each solution, 5 ml. of en reagent solution was added. The p H n a s adjusted to 10, 8, 6, 4 and 3, respectively, n-ith nitric acid. The solutions were transferred into 100-ml. volumetric flasks and diluted to volume with water. The spectra were recorded b e h e e n 450 and 790 mp, against water. Figure 2 shows that free acid, sufficient t o a t least partially neutralize ethylenediamine, interferes with the color formation. Therefore, the determination of C U +with ~ ethylenediamine should be carried out a t a p H of a t least 5, preferably 7-10. EFFECTS OF ORGAKIC SOLYEKTS.Attempts to extract the copper-ethylenediamine complex from aqueous solution with a variety of organic solvents, such as chlorocarbons, ketones, and ethers, failed. Solutions of the (Cu complex, formed by addition of 5 ml. of en reagent solution t o 5 ml. of the standard copper nitrate solution lvere diluted to 100 ml. using various ratios of either ethyl alcohol and water or acetone and water. Deviations observed by comparing
absorbances of the solutions a t 540 nip n i t h the absorbances of solutions made up to volume with water alone Ivere 15 ithin experimental error. E F F E C T OF TEhIPERATLTRE. Ternperature effects were investigated by measuring the absorbances of solutions prepared from 5 nil. of en reagent solution and 5 ml. of standard copper solution diluted to 100 ml. a t lo", 2 j 0 , 40°, 60". and 70" C. A slight increase in absorbance with temperature above 40" C. was observed n hich was well within experimental error. A 1.3% increase in absorbance was observed for the solution at 70" C. Between 10" and 40" C., no influence of tpmperature on absorbance could be seen, hon ever. EFFECTOF TINE. A solution prepared from 5 ml. of the standard copper solution and 3 ml. of the en reagent solution diluted to 100 ml. was measured immediately after dilution. The measurement was repeated hours, sex era1 days, and 3 neeks later. No change in absorbance R'BS observed. EFFECTS OF L 4 N ~ ~ K s To . 5-nil. portions of the standard copper solution in 100-nil. volumetric flasks, 13.6 grains of sodium acetate (trihydrate), 8.5 grams of sodium nitrate, 5.8 grams of sodium chloride, 14.2 grams of sodium sulfate (anhydrous) , 29.4 grams of sodium citrate, and 15.0 grams of tartaric acid (neutralized with sodium hydroxide to pH = lo), respectively, were added. Sufficient \\-ater was added to each to dissolve the salt, 5 ml. of en reagent solution was added, and the solutions were made up to volume with water. Sbsorbance was measured a t 540 mp. Acetate, nitrate, sulfate, tartrate, and citrate in 1M concentrations did not influence the absorbance readings. -4 considerable increase in absorption of chloride-containing solutions n as noted, however. Measurements of solutions containing NaCl showed that a chloride concentration of 0.05M gave rise to relative error of $370 which increases with increasing chloride concentration. At a sodium chloride concentration of 0.5J1, the relative error was +12%. VOL. 34, NO. 6, MAY 1962
e
633
EFFECTS OF CATIOKS. To determine the effect of a number of the most commonly encountered metal ions in the determination of copper with ethylenediamine, spectrophotometric measurements were made on solutions containing Th+4, Fe+3, Al+3, Cr+3, Ti+3, Nn+2, Ca+2, hIg+2, Sn+Z, U02+2, Si+2, and Cofz, as nitrates, and 7V04-2, hI004-~, and VO3-I as sodium salts. Each was prepared by diluting 1 ml. of a n approximately 1 M solution of the salt to about 10 nil. and adding 1 ml. of en reagent solution. With the exception of tungstate, molybdate, and vanadate, which formed no precipitates and remained colorless, most metal ions precipitated as hydroxides. Nickel, cobalt, and chromate formed colored solutions with ethylenediamine (1) and were therefore investigated further. Solutions were prepared from 2 ml. of 1JI nickel nitrate, 2 ml. of 1-11cobalt nitrate, 2 ml. of 1%' sodium chromate, 5 ml. of en reagent solution, made up to 100 ml. with water. Absorbance was recorded against water. The spectra showed that chromate does not interfere with the spectrophotometric determination of copper a t 540 mp, whereas both nickel and cobalt shon ed absorption a t 540 mp. ISTERFERENCE BY KICKEL. Eleven solutions containing 11.5 t o 230 mg. of Xi+* as nickel nitrate and 5 ml of en reagent solution were diluted m ith n ater to 100 nil. and their absorbance was measured in 1-cm. cells at 540 q p . These measurements showed that the reaction of ethylenediamine with copper is 10 to 15 times more sensitive than the reaction with nickel. Concentrations up to 23 nig. of N i f 2 per 100 ml. did not interfere with the determination of copper by ethylenediamine under the described conditions. At equimolar concentrations of nickel and copper, a rchtive error of approuimately 10%
occurred, and at a tenfold molar excess of nickel, the relative error approached +85%. INTERFERENCE BY COBALT. The interference by cobalt in the copper determination employing ethylenediamine mas determined by measurements made on solutions prepared from 1, 2, 3, 4, 5.9, 59, and 590 mg. of cobalt as cobalt(I1) nitrate and 5 ml. of en reagent solution, made up to 100 ml. with water. Absorbance was measured in 1-cm. cells a t 540 mp. These measurements showed that as ~ in a solulittle as 1 mg. of C O +present tion containing 61.7 mg. of Cut2 per 100 ml. caused a relative error of approximately +4%. For the determination of copper by ethylenediamine, the sample solution, therefore, has to be free of cobalt. PROCEDURE
Analysis of Solutions. Aliquots of solutions containing 1 t o 100 mg. of copper, chloride ions, and metal ions listed in Effects of Cations and in Table I b u t no more than 23 nig. of nickel and no cobalt were added to a n equal volume of concentrated nitric acid. The solutions were evaporated to dryness on a steam table to remove most of the chloride. The residues were dissolved in 1 ml. of concentrated nitric acid with addition of 5 ml. of n-ater and transferred to a 25-ml. volumetric flask. After cooling to room temperature, 10% sodium hydroxide solution was added dropwise with shaking until the slight turbidity appeared which was dissolved by addition of dilute nitric acid. One milliliter of en reagent solution was ndded, and the flasks were stoppered and shaken well. Indicator paper \vas used to assure a pH greater than 8. The solutions were
+
Table 1.
1
4.26, 3.98
4.14, 4.16
2
Silicate
8 . 0 4 , 8.22
7.87, 7.91
3
Silicate
6.18, 6 . 2 4
6.18, 6.19
4
Silicate
3.59, 3.63
3.63, 3.67
5
Silicate
1 . 1 6 , 1.18
1.19, 1.27
6
Copper ore gangue
6.40
6.49, 6.49
Lead base alloy Wrought aluminum Zinc base alloy
0 . 2 1 , 0.22 3.97, 3 . 9 9
0,28, Average 3.99, Average
1 . 0 1 , 1.04
1 . 0 1 , Average
Zn, AI
No. 85b No. 94b
Major
-
Trace
- 2'%.
* Minor - 0.1-2y0.
634
of Methods
Majora Al, hlg, Si, Fe, Ca Si, Al, hlg, Fe, Ca Al, Mg, Si, Ca Al, Si, Mg, Ca Si, Ca, Al, Mg, Fe Pb, S, Te, Se, Au, Ag, Bi Pb, Sb, Sn Al, Mg
NBS No. 53d
ANALYTICAL CHEMISTRY
en Method
cu, % Control analysis
Constituent Silicate
Ore
a
Analysis of Ores and Alloys-Comparison
now made up to volume and shaken well. If a precipitate had formed, it wa9 filtered through a Whatman ?io. 42 paper into a vial. The vial n-as stoppered until measurement. If the absorbance readings of these solutions were too high, 10 ml. of the filtered solution was transferred into a 100-ml. volumetric flask, 4 ml. of en reagent solution mas added, the solution was made up to volume, and the absorbance was measured at 540 nip. Analysis of Ores and Alloys. Samples of 1 t o 5 grams each of the ores (ground t o pass a 200-mesh sieve) and powdered alloys listed in Table I were digested in covered beakers with a mixture of 25 ml. of water, 25 ml. of concentrated hydrochloric acid, and 25 ml. of concentrated nitric acid for 1 hour at steam temperature. After this period, the solution was evaporated t o dryness. Five milliliters of concentrated nitric acid and 50 ml. of water were added to the residue; the mixture was heated to boiling and filtered through No. 42 Whatman filt'er paper into a 250-ml. volumetric flask. The residue, where applicable, was washed with hot water containing a few After drops of concentrated "Os. cooling to room temperature, the solution was made up to volume with water. -4 50-ml. aliquot of the copper containing solution was placed in a 100-ml. volumetric flask. -4 10% sodium hydroxide solution was added dropwise with shaking until a slight turbidity was noted which a-as redissolved with a few drops of nitric acid. Five milliliters of en reagent solution was added, and the flask \vas stoppered and shaken well. Indicator paper was used to assure a p H >8. The volumetric flask was filled to the mark with water and shaken well. A portion of this solution was filtered through Whatman No. 42 filter paper
Constituents Minor6 Mn, Ka, Ti, Zn )In, Na, Zn, Ti Fe, Mn, Zn, Ti, Na, Ag Fe, Mn, Pb, Zn, Na, Ti, Ag Sb, Pb, Mn, Ti Bi, As, Ni (trace)" Mn. Fe. Cr. Si. Ni. Zn. Ti, ~ b Ga, , 1 7 as traces; M Fe, hfn, Pb, Ni, Sn, Ed as tracesC
and collected in 2-oz. vials. The vials were stoppered and kept for measurement. The 1-em. cells were filled directly from the vials. Readings lvere made a t 540 mp. The insoluble residue from the acid digestion was dried, and a 10-mg. sample was mixed with 10 mg. of a graphitegermanium dioxide matrix. The sample was burned in a 12 amp. d.c. arc on an Ebert Spectrograph. Emission spectra were recorded on a Kodak SA-1 emulsion. The analytical wavelength for copper was 3247.5 A. The copper content of the residues, as estimated by visual comparison of the sample spectra with standard calibration spectra, ranged from 0.0005 to 0.002%. The residues n-ere therefore considered copper free. The control analyses of the ores listed in Table I involved sodium peroxide fusion of the ores (Parr-Bomb method), dissolution of the residues in nitric acid containing a small amount of concentrated sulfuric acid, and heating to boiling. After cooling to room tem-
perature, the solution was diluted and filtered to remove SiO,. Hydrogen peroxide was added, and copper was deposited electrolytically in a conventional manner. Comparison of the results obtained by the ethylenediamine method with the control analyses showed that the ethylenediamine method gave reliable results with ore and alloy samples containing from 0.2 to 8% copper, in the presence of a variety of metals. ACKNOWLEDGMENT
The authors thank L. B. Dworsky and W. F. Herd for accumulating much of the experimental data, and J. F. Capodanno, Central Research Department, for supplying the control analyses listed in Table V. LITERATURE CITED (1). “Beilstein’s Handbuch
der Organischen Chemie,” Band 4 pp. 230, 4-1 pp. 398 4-11 pp. 676, Verlag von Julius bpringer, Berlin, 4. Auflage (1922, 1929, 1942).
(2) Bjerrum, J., Nielsen, E. J., Acta Chem. Scand. 2,297 (1948). (3) “1946 Book of ASTM Methods of Chem. Anal. of Metals,” pp. 323-5,
Am. SOC.for Testing Materials, Philadelphia, 1946. (4) Carlson, G. A., McReynolds, J. P., Verhoek. F. H.. J . Am. Chem. SOC.67. 1334 (1945). ‘ (5) Cotton, F. A., Harris, F. E., J. Phys. Chem. 59, 1203 (1955). (6) Heine, H., Bergwerksjreund 1 , 33 (1830). (7) Huttner, C., 2. anorg. Chem. 86, 361 (1914). (.8.) Job. P.. Ann. chim. (Paris) 9. 113 (1928). ’ (9) Laitinen, H. A., Onstott, E. I., Bailar, J. C., Jr., Swann, Sherlock, Jr., J . Am. Chem. SOC.71,1550 (1949). (lo) Mehlig, J. P., IND. ENG. CHEM., ANAL.ED. 13,533 (1941). (11) Milner, 0. I., Ibid., 18, 94 (1946). (12) Snell, F. D., Snell, C. T., Snell, C. A., “Colorimetric Methods of Analysis,” 3rd ed., Vol. 11, p. 78, Van Nostrand, New York, 1949; Vol. IIA, p. 46 (1959). (13) van Uitert, L. G., Fernelius, 1%‘. C., J . Am. Chem. SOC.76,375 (1954). (14) Yoe, J. H., Barbon, C. J., IND. ENG.CHEM.,ANAL.ED. 12, 456 (1940). RECEIVED for review October 31, 1961. Accepted February 23, 1962.
Use of Organic Solvents in Limited Area Flame Spectrometry BRUCE E. BUELL Union Oil Co. o f California, Union Research Center, Brea, Calif.
b The scope of flame spectrometry can b e extended and line-to-background ratios can b e increased by carefully selecting the area of the flame to b e viewed by the spectrometer when using organic solvents with an oxy-hydrogen flame. The distribution of emission and excitation potentials in organic solvents covers a wider range of heights in the flame than when using aqueous solutions; emission is also lower in the flame with organic solvents. In addition to flame characteristics, solvent qualities and enhancing factors are studied for various solvents. Some theoretical conclusions are given which indicate that chemiluminescence may b e a major factor in solvent enhancement. Data are given to show how the height of maximum emission for lead depends on the particular lead compound in the sample. The determination of nitrogen b y means of CN bandheads i s also discussed.
L
IMITED
area flame spectrometry
(LAFS) in a sense has been in use since the inception of flame spectrometry, because normal instrumentation
does not view the entire flame. For this investigation, LAFS refers to areas in the flame which are smaller than those used with normal instrumentation. Mavrodineanu (9) reviewed studies concerning differences between emission in the inner cone and outer mantle of flames. He also reviewed LAFS applied to certain interference studies in aqueous solutions. Knutson (8) used a narrow horizontal mask for magnesium determinations. Dubois and Barieau (4) used a similar mask with a Cary spectrophotometer to study emission of various elements dissolved in hydrocarbon solutions. Carnes (2) used a 6-mm. light pipe of aluminum or silvered glass in conjunction with a variable-height burner to study emissions which emanate from the vicinity of the reaction zone of oxy-acetylene flames employing organic aerosols. LAFS has also been applied to studies of combustion mechanisms and is thus by no means new. The purpose of this investigation was to explore further LAFS, particularly when atomizing organic solvents into an oxy-hydrogen flame. This area of research appeared promising because preliminary results revealed atomic emission for lines normally unobserved and
which emanate from lower arc’as of the flame. Because many of the samples in petroleum laboratories are organic, potential applications are numerous. Rather than report details concernine these numerous applications, this paper will concentrate on fundamental considerations such as differences in the dirtribution of emission in the oxy-hydrogen flame when atomizing aqueous solutions and organic solutions. INSTRUMENTATION
The Beckman Model DU spectrophotometer has been utilized to a certain extent for LAFS in this and other laboratories by adjusting the burner-housing mirror and by changing the flame height through adjustment of hydrogen flow. Its use for this purpose is limited and also complicated by the fact that a flame height of about 20 mm. is normally viewed both directly and, a t the same time, as an inverted and condensed flame image from the burnerhousing mirror. Recently Gilbert (6), during his study of chemiluminescence, and this laboratory have utilized the technique of viewing a flame area about 6 mm. high with the burner-housing mirror only. The current investigation employed this same technique in VOL. 34, NO. 6, M A Y 1962
635
