Iron(II1) forms an extractable chelate with both reagents and must be removed when present in excess of the tolerance limits. Calcium does not react with A‘-nitrosophenylhydroxylamine, but it does form a loose chelate with 2-thenoyltrifluoroacetone. A single backwash suffices to remove calcium from the organic phase; accordingly, a t least 10 mg. of calcium can be tolerated in the aqueous phase. At the 384-mp band head, copper, ceriuni(III), and yttrium coextract and possess oxide band systems in this region of the spectrum. A preliminary separation must be made i j hen interfering elements constitute the matrix of the sample. Large amounts of heavy metals are conveniently removed by electrolysis with a mercury cathode. From steels, iron(II1) chloride can be removed from solutions 5 to 7 M in hydrochloric acid by extraction with 4-methyl-2-pentanone (11). Small amounts of iron are conveniently removed by an extraction 11 ith S-nitrosophenylhydroxylamine from a 1 to 9 hydrochloric acid solution ( 9 ) . For magnesium-base alloys, aluminum was selectively extracted a t pH 2.5 to 4.5 as the -1’-nitrosophenylhydroxylamine chelate with 4methyl - 2 - pentanone (7). Nagnesium is not extracted and the amounts of the other minor constituents of the sample, some of which accompany the aluminum, do not exceed the tolerance limits.
Preliminary extractions a t pH 1 with a 0.5M solution of 2-thenoyltrifluoroacetone in 4-methyl-2-pentanone or chloroform will serve to remove milligram amounts of zirconium, titanium, thorium, uranium(VI), iron(III), cerium(IV), and copper without loss of aluminum. This separation is valuable when analyzing thorium slurries. Similarly, 10-mg. quantities of zinc, nickel, iron(III), and copper can be removed by adding a 5% solution of sodium diethyldithiocarbamate and extracting with chloroform. Of the anionic substances tested, only fluoride and phosphate interfere seriously, presumably by preventing the extraction of aluminum (Table 11). RESULTS
The validity of the procedure IS substantiated by the results shown in Table 111, which are in satisfactory agreement with the known values. Selective extraction with a chelating agent in 4-methyl-2-pentanone can be used to isolate aluminum from many elements. When interferences were not completely removed by this extraction procedure, an alternate separation procedure is provided or suggested. ACKNOWLEDGMENT
H. C. Eshelman is indebted to Southwestern Louisiana Institute for a summer sabbatical leave which made part
of this work possible during the summer of 1957 and to the University of Tennessee for generously offering its facilities and supplies. The authors also wish to acknowledge the assistance of H . P. House and M. A. Marler in the preparation of this manuscript. LITERATURE CITED
(1) Bode, H., Z. anal. Chem. 142, 414 f 1954). (2) Bryan, H. A., Dean, J. A., AXAL. CHEM.29, 1289 (1957). (3) Kashima, J., Matanuchi, M.,. Japan . Analyst 4, 420’( 1955)(.4 ,) Kellev. Rl. T.. Fisher. D. J.. Jones.’ H. C., ANAL.CHEW31, i78 (1959). (5) Mavrodineanu, R., Boiteux, H., \ - - - - ,
“L’Analyse Spectrale Quantitative par la Flamme,” p. 163. Masson et Cie, Paris, 1954.’ (6) Menis, O., Rains, T . C., Dean, J. A., AKAL.CHEM.31, 187 (1959). (7) Meunier, P., Compt. rend. 199, 1250
(1934). (8) Mitchell, R. L., Robertson, J. M., J . Soc. Chem. Ind. 38T, 269 (1936). (9) Morrison, G. H., Freiser, H., “Solvent
Extraction in Analvtical Chemistrv.” Wilev. Ken. York. 1857. (IO) Sirhgne, RI., ~lontgareuil,P. G. de, Chim.anal. 36, 115 (1954). (11) Specker, H., Doll, W.,Z. anal. “
I
Chem. 152, 178 (1956). f 12) Torok. (12) Torok, T.. T., Ibid.. Ibid., 119. 119, 120 f 1940). (13) Vallee; Vallee, B: B. L., bartholomay, Bartholomay, -4. A. F., ANAL.CHEW28, 1753 (1956).
RECEIVEDfor reviev April 14, 1958. Accepted September 22, 1958. Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Pittsburgh, Pa., March 1958.
Extraction a nd FIa me Spectrophotometric Determination of Lanthanum OSCAR MENIS and T. C. RAINS Analytical Chemistry Division, Oak Ridge National laboratory, Oak Ridge, Tenn.
JOHN A. DEAN Department of Chemistry, University of Tennessee, Knoxville, Tenn.
b
Microgram quantities of lanthanum are selectively extracted by a 0.1M solution of 2-thenoyltrifluoroacetone in 4-methyl-2-pentanone from a 1M acetate solution buffered a t pH 5; lanthanum is then determined by a flame photometer. O f 18 elements tested, only titanium and aluminum interfere when they are present in greater amounts than the lanthanum; fluoride and phosphate interfere by preventing the extraction of lanthanum. When thorium, uranium, copper, and iron are major components of the sample, they are extracted with 2-thenoyltrifluoroacetone a t p H 1.5 before extraction of lanthanum. The lanthanum
emission emanates from a series of oxide bands; those a t 4 4 2 , 560, and 743 mp were investigated. The band a t 743 mp is the most suitable for the determination of lanthanum in the presence of interfering elements and when a red-sensitive photomultiplier tube is incorporated in the flame photometer. The emission intensity of lanthanum from the ketone solution is 1 00-fold greater than the emissivity from aqueous solutions. The sensitivity is 0.05 y of lanthanum per ml. per scale division 1).
(70
A
was required whereby minute amounts of lanthanum
hIETHoD
could be determined directly and precisely in thorium and uranium compounds destined for use in breedertype homogeneous reactors. Of the methods considered, flame photometry offers a number of advantages. Colorimetric methods lacked sufficient sensitivity (8). Serious difficulties or limitations are often encountered in the application of spectrographic methods associated with the interpretation of complex spectra. By contrast, the emission spectrum of lanthanum in an oxygen-fuel flame is relatively simple. The energy of dissociation of lanthanum oxide in the normal state is approximately 9 e.v. (6); accordingly, the flame VOL. 31, NO. 2, FEBRUARY 1 9 5 9
187
I'I
I 'I
I
1
zt I
145
165 185 2 0 5
145
165
185 2 0 5
145
r
165 185 205
ACETYLENE, f t 3 h i '
Figure 1. Emission of lanthanum oxide band at 791 mp for various flow ratios of fuel and oxygen
spectrum of lanthanum consists of a series of oxide bands that are degraded toward the longer wave lengths in the regions of 437 to 445, 538 to 568, 587 to 598, 701 to 772, and 791 to 860 mb (9, 10).
Ishida (4, in his study of the flame spectrum by means of a spectrograph and a filter photometer, limited his investigations to the red and yellow regions of the spectrum for the determination of lanthanum in monazite and lanthanite sands and in glass. de Albinati (1) used the oxide band a t 442 mp for the determination of lanthanum in uranium after removal of the uranium by extraction with ether from a nitrate solution. Ishida and de Albinati reported that a great number of elements interfered; however, they did not thoroughly investigate methods to circumvent these interferences. Initially a study was made of the characteristics of the several oxide bands of lanthanum when an aqueous or alcoholic solution was aspirated into an oxyhydrogen or an oxyacetylene flame. I n those media many interferences from other elements were encountered and the method was insufficiently sensitive (7). I n the present study, lanthanum was selectively extracted with 2 thenoyltrifluoroacetone in 4-methyl-2-pentanone from an acetate solution buffered a t pH 5. The sensitivity of the flame photometric method was enhanced approximately 100-fold when lanthanum was aspirated into the flame from the ketone solution instead of from an aqueous medium.
-
188
ANALYTICAL CHEMISTRY
1
' i
I
\
I
I
I
I
425 to 450
550 to 575 710 to 830
EXPERIMENTAL W O R K
Apparatus. The flame spectrophotometers employed in this investigation have been described (8, 6). Reagents. 4-Methyl-2-pentanone (hexone). practical grade. 2 - Thenoyltrifluoroacetone (TTA), 0.1M. Dissolve 5.5 grams of the technical grade reagent in 4-methyl-2pentanone, then dilute to 250 ml. with additional solvent. Store in a cool place away from light. Lanthanum, standard solution, 100 y per ml. Dissolve 0.117 gram of lanthanum oxide, dried a t 110' C., in 5 ml. of 70% perchloric acid. Evaporate the solution to approximately 1 ml., then dilute to 1 liter with deionized water. Instrument Settings. The instrument settings, for both the ORNL and the Beckman Model DU flame spectrophotometers, are as follows:
Sensitivity control, 70adjust Selector switch, position Phototube resistor, megohms, Blue-sensitive Red-sensitive Phototube, volts per dynode Blue-sensi tive Red-sensitive (Farnsworth 16PMl) Acetylene, cu. feet per hour Hydrogen, cu. feet per hour Oxygen, cu. feet per hour Slit, nun. 400 to 600 mp 700 to 900 mp
/ , I
I , $ .
I
I
I
I
I
I
RCh 1P28 0 05 RCA 1P28 0 05 Beckman 156 0 3 Slit Width. The selection of the proper slit width is dependent on the particular wave length region a t which measurements are made, on the light-dispersing device (whether prism or grating), and on the photosensitive detector incorporated in the instrument. I n the region of 743 and 791 mp, the flame background is relatively weak compared to the emissivity of lanthanum; therefore, large slit vidths can be utilized successfully. I n fact, when the Beckman instrument is used in this region, large slit widths are required in order to achieve the desired sensitivity. Whenever spectral interferences are encountered in the red region of the spectrum, it is impractical to use wide slit widths. I n this situation the ORNL grating instrument, equipped with a red-sensitive multiplier phototube, can be applied with more success
25
25 25
Beckman
ORSL
70 0.1
High High
22 10,000
5
5
6O(RCA 1P28)
75(RCA 6217)
6.6
10.8
... 1.6 ...
0,050 0.30
80
...
7.6
0.25 0.50
sample cup or pour the entire contents of the funnel into a small beaker. Aspirate the organic phase (upper layer) into the flame and measure the emission intensity of the selected oxide band and the appropriate flame background : Oxide Band Peak,
Background, M/J
hfP 437 442 560 743 791
-
3-
\;I
i c
\\
.. .....
,...
..__
AAbE
-EL$%,
mi
Figure 3. Flame spectra of lanthanum oxide in hexone solutions of TTA measured on ORNL flame spectrophotometer
T a v e Length Region, M p 440 to 450 540 to 570 730 t o 820
La,
Phototube
y/M.
Slit, hlm.
2n_ -
20 5
than the Beckman instrument, a prism type. At shorter wave lengths the flame background is pronounced; consequently, narrow slit widths, ranging from 0.04 to 0.06 mm., are necessary to maintain the ratio of signal to background at a maximum. I n this case, the Beckman Model D U flame spectrophotometer may be used to advantage. Flow Rate of F u e l and Oxygen. I n determining the optimum flow rate of oxygen and of fuel, the flow of oxygen was maintained at a constant rate (usually the flow provided by employing the pressure suggested by the manufacturer of the integral-aspirator burner), while the flow rate of acetylene (or hydrogen) was varied and the emissivity of lanthanum in the concentration range of 5 to 25 y per ml. was measured a t 437, 560, and 791 mp. These measurements were repeated for different, fixed flow rates of oxygen. The optimum flow rate was selected on the basis of maximum sensitivity and linearity of the calibration curve. K i t h this criterion, a flow rate of 1.65 cubic feet per hour for acetylene and 7.6 cubic feet per hour for hydrogen was chosen. Partial data are given in Figure 1. To establish the optimum flow rate of oxygen, the flow of fuel was set a t its previously determined optimum value while the rate of flow of the oxygen was varied. The maximum emissivity of lanthanum was attained with
a flow rate of 6.6 cubic feet of oxygen per hour with acetylene as fuel, and a flow rate of 10.8 cubic feet per hour with hydrogen. At higher flow rates the flame tends to be extinguished when the aspirator is withdrawn from the organic solvent. Calibration Curve. Transfer 0.5-, 1-, 2-, and 3-ml. aliquots of the standard solution of lanthanum t o 50-ml. beakers. Add 10 ml. of 1M ammonium acetate solution and adjust the pH to 5.0. Transfer the solution to a 60-ml. separatory funnel. Add exactly 10.0 ml. of the 0.1M solution of 2-thenoyltrifluoroacetone. Shake for 1 minute. After the phases have separated, transfer the organic layer to the
Table 1.
435 445 558 735 775
To obtain the net emissivity, subtract the reading due to the flame background from the total emission reading of the lanthanum oxide band. The calibration curve is linear from 5 to 25 y of lanthanum per ml. at all wave lengths: however, a t higher concentrations of lanthanum, the curve bends toward the concentration axis. Procedure for Monazite Sand. Dissolre a 5-gram sample in 60 mi. of 70% perchloric acid in accordance rrith well established procedures (3. l a ) . Dilute the solution to 250 ml. and transfer a 1-ml. aliquot, equivalent to 20 mg. of sample, to a 125-ml. separatory funnel. Add 20 ml. of a 570 (w./v.) solution of ammonium molybdate and remove phosphate as the yellow molybdophosphoric acid by extraction with 50 ml. of n-butyl alcohol. Allow the phases to separate. Remove the original layer and wash it once with 20 ml. of an aqueous 0.1M solution of perchloric acid. Combine the aqueous phases; discard the alcohol layer. Transfer the aqueous phase to a 400-ml. beaker and dilute the solution to approximately 200 ml. Add 10 ml. of 70% perchloric acid and cool the solution in an ice bath. Precipitate the excess molybdate ion by the addition of 20 ml. of a 2% (w./v.) solution of a-benzoinoxime in ethyl alcohol. Allow the precipitate to age 10 to 15 minutes in the ice bath and then filter the solution through a Whatman No. 42 filter paper. Wash the precipitate with 150 ml. of an ice-cold solution, freshly prepared by adding 10 ml. of a 2% solution of a-benzoinoxime in alcohol and 5 ml. of 70% perchloric acid to 135 ml. of water. Collect the washings with the original filtrate. Add 5 ml. of concentrated nitric acid
Relative Sensitivity of Flame Emission Peaks of Lanthanum Oxide in W a t e and Hexone (Standard solutions, 5 to 50 y of lanthanum per ml.)
Wave Length, hfr 437 442 541 543 560-563 590-593 740-743 791-794
Effective Band Width, Mfl Beckman ORNL 1 .o
1.5
Water Beckman ORNL 0.7 0.7 1.4 1.4 0.6 0.8
1.4 1.6 16.2 18.6
Relative Sensitivity,
y/Ml. /Scale Division
3.3
... ...
1.1 0.7 ...
...
0.7
...
0.5 0.5
Hexone Beckman ORXL 0.06 ... 0.06 0.18
0.18 0.06 0.08 0.11 0.09
0.04 ...
...
0.03
0:005 0.005
VOL. 31, NO. 2, FEBRUARY 1959
189
and evaporate the filtrate and washings to incipient dryness. Dissolve the salts in distilled water and transfer to a 50-ml. volumetric flask. Dilute to the mark and mix thoroughly. Transfer aliquots containing from 100 to 300 y of lanthanum to 50-ml. beakers. Pro-
Table II.
a
ceed as described for the calibration curve. Procedure for Didymium Oxide. Dissolve a 1-gram sample of didymium oxide by boiling it with 15 ml. of 70% perchloric acid. Cool and transfer the solution t o a 100-ml. volu-
Effect of Extraneous Substances on Determination of Lanthanum (Lanthanum present', 20 y per ml.) Interference Lanthanum, yo Concn., Element 743 mp 560 mp 442 mp Y /ml. Aluminum 20 100 93 99 91 50 96 99 87 100 92 94 74 500 61 60 2500 31 25 18 Barium 20 100 100 100 93 100 98 98 91 94 500 98 96 97 99 2500 Calcium 20 100 250 98 ... 100 107 100 112 100 500 ... Cerium 20 104 104 99 100 102 102 99 104 104 500 100 Chromium 100 100 105 102 103 500 100 98 2500 106 102 100 Copper 20 100 98 96 100 100 100 87 74 103 500 99 Iron 20 99 97 99 100 134 100 99 500 100 99 175 Lithium 20 98 84 98 100 97 99 94 500 82 98 99 94 2500 92 78 Magnesium 20 106 99 98 100 100 100 97 102 100 500 95 Neodymium 20 100 105 99 100 100 98 90 500 97 84 88 Potassium 20 96 100 94 100 96 96 100 500 97 96 96 Praseodymium 20 96 100 98 100 122 102 95 500 Rubidium 20 110 100 100 100 117 106 110 500 114 100 100 Sodium 20 93 104 98 100 96 100 98 500 93 100 98 Thorium 20 100 100 98 100 95 98 98 500 100 102 96 100 102 60 2500 Titanium 20a 100 96 89 76 100 81 70 60 500 59 48 Uranium 20 100 100 98 100 100 99 98 500 100 95 98 Zirconium 20 100 85 94 79 100 100 94 73 64 64 500Q Precipitation occurred on adjusting solution to pH 5.
190
ANALYTICAL CHEMISTRY
metric flask. Dilute t o the mark. Transfer aliquots of this solution which contain from 100 to 300 y of lanthanum to 50-ml. beakers and proceed as for the calibration curve. RESULTS A N D DISCUSSION
Flame Spectrum of Lanthanum. The prominent bands in the lanthanum oxide spectrum are shown in Figures 2 and 3, and were obtained with the Beckman Model D U and the ORNL Grating instruments, respectively. Although prominent, the lanthanum oxide band at 590 mp was omitted from this study because of its proximity to the strong sodium line at 589 m p . The relative sensitivity of each of the lanthanum oxide bands in water and in 4-methyl-2-pentanone is given in Table I. With the ORSL instrument equipped n ith a red-sensitive multiplier phototube, the more intense flame emissivity is associated with those bands whose heads are a t i 4 3 and 791 mp. With a flame spectrophotometer equipped only with a bluesensitive multiplier phototube, the pair of band peaks that occur a t 437 and 442 mp and the closely spaced doublet a t 560 and 563 nip prove more useful. The background radiation in the vicinity of the various band groupings differs considerably. I n the region of 743 and 791 mp, the background is weak and essentially continuous for both hydrogen and acetylene flames. By contrast, the background due to the flame in the regions of the other oxide bands is mcst pronounced and includes several peaks. A prominent band due to C H radicals from the organic solvent occurs at 431.7 m p ; less intense bands due to Cz molecules are found a t the following wave lengths: 436.5, 437.1, 438.3, 516.5, and 563.5 mp. Extraction of Lanthanum. The acetate ion concentration in the aqueous phase has a marked effect on the degree of extraction of lanthanum into a 0.1M solution of P-thenoyltrifluoroacetone in 4-methyl-2-pentanone (Figure 4). As the acetate ion concentration increases, the p H a t which complete extraction of lanthanum can be achieved is higher. Advantage can be taken of this effect when large quantities of thorium or uranium are present. These elements can be quantitatively extracted from a 1M solution of acetate adjusted to p H 1.5, whereas, at this pH, no lanthanum is extracted. Above p H 2, lanthanum is extractable; however, it can be completely extracted from a 1M acetate solution only a t p H 5. A prior extraction at pH 1.5 is recommended when thorium, uranium, copper, and iron are present in large amounts. These elements also react with the chelating agent, and if a prior separation
Table 111. Effect of Anionic Substances on Determination of Lanthanum
(Lanthanum present, 20
Figure 4. Effect of acetate ion concentration on extraction of lanthanum into 0.1 M TTA in hexone
Concn., ?/Ml.
Anion
so,-c1c104-
PO,--F-
is not made, larger amounts of 2thenoyltrifluoroacetone must be added in order to ensure the complete extraction of lanthanum at p H 5. However, concentrations of chelating agent in excess of 0.1M are to be avoided because unsteady flame conditions often are encountered. Interference Studies. T h e degree t o which other substances interfere n i t h lanthanum extraction a t a p H of 5 from a n aqueous solution 1M in acetate ion is given in Table 11. Barium, chroniium(T’I), lithium, magnesium, potassium, rubidium, and sodium are either not extracted or extracted only in negligible quantities (11). hiilligram quantities of thorium and uranium accompany the lanthanum in the extract; however, a t the concentrations studied, neither thorium nor uranium interfere with the determination of lanthanum in the organic phase. Interference by aluminum and titanium is noted a t all wave lengths, although only relatively high concentrations of these elements and zirconium interfere a t 743 nip. Many interferences are found a t 560 mp; a t this wave length, results are low if aluminum, copper, lithium, neodymium, titanium, or zirconium are present. Of the anionic substances that were tested, phosphate and fluoride interfere seriously by preventing the extraction of lanthanum (Table 111). Application. T h e validity of the proccdure was tested by determining the lanthanum content in the rare earth oxide fraction of a monazite sand from
South Africa and in a mixture of residual rare earth oxides designated “didymium oxide.” Both samples were obtained from the Lindsay Chemical Co. Their compositions were reported as follows: Rare Earth Oside Fraction of Monazite Sand
Didymium Oside
22 47 5 16 3.5 -3 -2 -1.5
44 1 9.5 32 5.5 -3 -3 -2
The value obtained for lanthanum oxide in the monazite sand vias 22.2%, rrhich is in essential agreement with the value furnished by Lindsay Chemical Co. For the didymium oxide, an average value of 46.6% lanthanum oxide was obtained, which is somewhat greater than the value reported by the supplier. For both determinations the relative standard deviation !vas approximately 3%. ACKNOWLEDGMENT
The authors acknowledge the assistance of H. P. House and M. A. hiarler in the preparation of this report. LITERATURE CITED (1) Albinati, J. F. de, Anales asoc. quim. arg. 43, 106 (1955). ( 2 ) Bryan, H. A, Dean, J. A,, ANAL. CHEM.29, 1289 (1957). (3) Hillebrand, W. E ., Lundell, G. E. F.,
y
per ml.) Lanthanum Eound, %I at 743 hfcc
960 9600 350 3500 1000 10000
100 Si
950 9500 19 190
83 0 10 0
97 97 99 93
Bright, H. .I.,Hoffman, J. I., “Applied Inorganic Analysis,” 2nd ed., pp. 54958, Wiley, New York, 1953. (4) Ishida, R., J . Chem. Soc. Japan, Pure Chem. Sect. 76, 60 (1955). (5) Kelley, &I. T., Fisher, D. J., Jones, H. C., ANAL.CHEM.31, 178 (1959). ( G ) Mavrodineanu,
R., Boiteu.;, H., “L’halyse Spectrale Quantitative par la Flamme.” u. 196. Masson e t Cie. Paris, 1954.’ ( 7 ) Menis, O., Rains, T. C., Dean, J. A,, A
Anal. C h i m Acta 19, 179 (1958). (8) Moeller, T., Record Chem. Prog. 14, 69 (1953). 19) Piccardi. G.. Gam. chim. ital. 63, 127 ‘ (1938). (10) Rodden, C. J., Plantinga, 0. S., I N D . EXG.CIIE?!I., ANAL. ED. 8, 232 (1936). (11) Suttle, J. F., U. S. Atomic Energy Comm. LAM-936 (AECD-2800)(1950). (12) Willard. H. H.. Gordon. I,.. .4XAL. ‘ CHEX.20,’1G5 (1948). I
,
RECEIVED for review February 15, 1958. Accepted September 22, 1958. Division of Analytical Chemistry, 132nd Meeting, A4CS,New York, N. T., September 1957.
Direct Photometric Determination of Aluminum in Iron Ores-Correction In the article on “Direct Photometric Determination of Aluminum in Iron Ores” [ANAL.CHEM.28, 1419 (1956)l the last line of the fourth paragraph in the second column should read: To 8 nil. of this solution add 10 ml. of hydrochloric acid and dilute to 1 liter. 1 nil. = 8 of A.1203. T i . T. HILL
VOL. 31, NO. 2, FEBRUARY 1959
191
