Information (Developmental Type)” (June 15, 1956). (4) Fisher, D. J., Oak Ridge National Laboratory Master Analytical Manual, TID-7015 (Section l), Method Nos. 1 003051 and 9 003051 (6-15-56), Office of Technical Services, De t of Commerce, Washington 25, D. (5) Fisher, D. J., Specification S o . SI162 18-12-57). available from Instrument’Department, Instrumentation and Controls Division, Oak Ridge National
8..
Laboratory, Oak Ridge, Tennessee. (6) Fisher, D. J., Laing, W. R., Ibid., Method Nos. 1 003050 and 9 003050, pp. 1-22 (Aug. 14, 1953). (7) King, W. H., Jr., Priestley, W.,Jr., Am. SOC.Testing Materials, Spec. Tech. P u b l . 116, 97 (1951). (8) Lewin, S. Z., ANAL. CHEM.30, 17A (July 1958). (9) Margoshes, M., Vallee, B. L., “Flame Photometry and Spectrometr . Principles and .4pplications,” in d l . I11 of
“Methods of Biochemical Analysis ” Glick, D., ed., Interscience, New Yo&, 1956. (10) Meloche, V. W.. ANAL. CHEX 28, . 1844 (1956): (11) Menis, O., Rains, T. C., Dean, J. A., Ibid., 31, 187 (1959). (12) Whisman, M., Eccleston, B. H., Ibid., 27, 1861 (1955). RECEIVED for review February 15, 1958. Accepted August 28, 1958.
Extraction and Flame Spectrophotometric Determination of Aluminum H. C. ESHELMAN’ and JOHN A. DEAN Department o f Chemistry, University of Tennessee, Knoxville, lenn. OSCAR MENIS and T. C. RAINS Analytical Chemistry Division, Oak Ridge National laboratory, Oak Ridge, lenn.
b Aluminum can b e selectively extracted from an acetate-buffered solution adjusted to p H 5.5 to 6.0 with a 0.1 M solution of 2-thenoyltrifluoroacetone in 4-methyl-2-pentanone; or from an acetate-buffered solution adjusted between p H 2.5 and 4.5, and containing N-nitrosophenylhydroxylamine (cupferron), with 4-methyl-2-pentanone. The organic phase is aspirated directly into an oxyacetylene or an oxyhydrogen flame and the emissivity of aluminum is measured a t either the atomic line a t 396.2 rnp or the sharp oxide band head a t 484 mp. When a 4-methyl-2-pentanone rather than an aqueous solution of aluminum is aspirated into the flame, the emissivity is increased 100-fold. At a slit width of 0.030 mm. the sensitivity is 0.5 y of aluminum per ml. per scale T). The calibration curve division is linear from 5 to 40 y of aluminum per ml. Tolerance limits for a wide diversity of ions have been determined. When necessary, preliminary separation methods have been devised to remove interfering elements.
(70
A
flame spectrophotometric method has been developed that is sufficiently sensitive to determine aluminum in low concentrations in a variety of materials. Except for a brief reference to the emission of aluminum in an oxycyanogen flame ( I S ) , only indirect methods (S, 8, 10, 12) for the determination of aluminum have been reported, based on the depressant DIRECT
1 Present address, Chemistry Department, Southwest Louisiana Institute, Lafayette, La.
effect of aluminum upon the flame emission of calcium. All other ions that might depress the calcium emission must be absent, as well as any ions that might enhance or otherwise affect this emission. Direct flame photometric methods for aluminum in aqueous solutions lack sufficient sensitivity and selectivity. However, when a 4-methyl-2-pentanone rather than an aqueous solution of aluminum is aspirated into the flame, the emissivity is increased approximately 100-fold and the interference of large numbers of elements is obviated. Sufficient sensitivity and freedom from spectral interference can be attained by use of either the atomic line a t 396.2 mp or the oxide band head a t 484 mp for making the emissivity measurement. The sensitivity is 0.5 y of aluminum per ml. per scale division (% T scale) EXPERIMENTAL WORK
Apparatus. The flame spectrophotometers used have been described
(2,C).
Reagents. 4-Methyl-2-pentanone, practical grade. Bluminum, standard solution, 100 y per ml. Dissolve 0.100 gram of pure aluminum mire (Fisher, Certified ACS grade) in hydrochloric acid, then dilute to 1 liter with demineralized water, ’Y-Nitrosophenylhydroxylamine(cupferron), 0.1M. Dissolve 1.6 grams of reagent in 100 ml. of water. If the aqueous solution is strongly colored, make it slightly ammoniacal and purify the solution by equilibrating it with 100 ml. of 4-methyl-2-pentanone for 15 minutes. Allow the phases to separate and remove the aqueous layer containing the S-nitrosophenylhydroxylamine. Store the reagent in a dark place.
ZThenoyltriBuoroacetone (TTA), 0.1M. Dissolve 5.5 grams of the technical grade reagent in 4methyl-2-pentanone, then dilute to 250 ml. with additional solvent. Store the solution in cool place away from light. Instrumental Settings. The instrument settings for the ORNL and Beckman Model DU flame spectrophotometers are as follows: Beckman ORNL Sensitivity control, yo adjust 50 High Selector switch, position 0.1 High Phototube resistor, megohms Blue-eensitive, RC.4 1P28 22 5 Phototube, volts per dynode 60 75 0.030 0.25 Slit. mm. Spectral slit width, mp At 396 mp 0.6 1.6 At 484 mp 1.2 1.6 Slit Width. \i7Tith the Beckman Model D U flame spectrophotometer, the slit width used was 0.030 mm.; this corresponds t o a spectral slit width of 0.6 mp a t 396.2 mp. The atomic lines of aluminum a t 394.4 and 396.2 mp are incompletely resolved from each other a t slit widths exceeding 0.050 mm. A similar range of slit widths is recommended for the oxide band a t 484 mp. F u e l and Oxygen Flow Rates. Optimum flow rates of oxygen and acetylene are different when a combustible solvent is aspirated. Also, a larger volume of organic solvent is aspirated per minute (2.0 ml.) as compared with an aqueous solution (1.0 ml.). Figure 1 shows a plot of the emission intensity of aluminum as chart divisions above the flame background us. the acetylene pressure for various oxygen pressures; Figure 3 shows the flow rates which corVOL. 31, NO. 2, FEBRUARY 1959
* 183
O2 P R E S S U R E
re
re
1 I
001 I
‘
2
1
3
1
4
1
1
’
I
‘
1
1
’
5 6 7 8 9 1 0 1 1 ~ 2 1 3 P R E S S U R E OF C2H2, p.81.
Figure 1. Intensity of aluminum and aluminum oxide emission as function of acetylene pressure at various oxygen pressures respond to the range of pressures investigated. TVith increased consumption of acetylene, an increase in emission intensity occurs, By contrast, variation in the oxygen flow rate exerted only a slight effect on the emission intensity (Figure 2). On Figure 2 the region to the left of the dashed line denotes the region of oxygen and acetylene pressures in which the flame becomes unsteady and flame background corrections become uncertain. The ratio of flow rates of oxygen to acetylene is important. At high ratios the aspirated solvent becomes the major source of fuel and the flame is extinguished when solvent aspiration is discontinued. At low ratios insufficient oxygen is provided for complete combustion of the acetylene and the solvent, and an unsteady flame background results. In Figure 3 a plot of these variables for the 396.2-mp line of aluminum is shown. Except for a displacement in the steep segment of the curve to the right, a similar plot is obtained for the oxide band a t 484 mp. The region of oxygenacetylene ratios between 5.5 and 9.5 looks flat and is independent of the actual value of the ratio, but emissivity is low and the flame invariably blows out when the aspirator is withdrawn from the solvent. For oxygen-acetylene ratios less than 2.2, the flame is unsteady; for ratios exceeding 2.7, the emission intensity is diminished with a resulting loss in sensitivity. Khen the oxide band is used, the oxygen-acetylene ratio should be maintained between 2.7 and 3.2. Similar plots obtained using an oxyhydrogen flame indicate that the optimum ratio of flow rates is unity for the oxide band. As the oxygen flow rate is more or less fixed by the orifice characteristics of a particular burner, the operator should adjust the acetylene flow rate until the ratio of the flow rates of oxygen to acetylene (or hydrogen) falls within the recommended limits. Calibration Curve. Transfer 1-, 2-, 3-, 4-, and 5-ml. aliquots of the standard aluminum solution t o 50-ml. beakers. Add 10 ml. of 1M ammo184
ANALYTICAL CHEMISTRY
nium acetate solution and adjust the p H between 2.5 and 4.5. Transfer the solution to a 60-ml. separatory funnel. Add 5 ml. of 0.1M N-nitrosophenylhydroxylamine and a known volume of 4-methyl-2-pentanone. A minimum volume of 3 ml. of 4methyl-2-pentanone is needed for convenient manipulation. Shake for 2 minutes. Modify the procedure when using 2-thenoyltrifluoroacetone as follows: Adjust the pH of the ammonium acetate solution between 5.5 and 6.0. Transfer the solution to a 60-ml. separatory funnel. Add a known volume of 0.1M solution of 2-thenoyltrifluoroacetone in 4-methyl-2-pentanone. Shake for 5 minutes. Allow the phases to separate and discard the aqueous layer. When large amounts of alkali and alkaline earth elements are present in the original aqueous phase, backwash the organic layer with 30 ml. of 0.1M nitric acid. Appropriate standard solutions must be prepared, as slightly larger emission readings are obtained when working Kith 2-thenoyltrifluoroacetone as the chelating agent. Decant the organic phase into the sample cup or pour the entire content of the funnel into an individual 30-ml. beaker. As the organic phase is lighter than the aqueous phase, the organic layer can be aspirated from the beaker directly into the flame without a phase separation. Aspirate the organic phase into the flame. Measure the emission intensity of the atomic line or the oxide band head and the appropriate flame background a t the following wave lengths: Emission Line or Band, Mp 396.2 484
Background,
m
395 482
To obtain the net emission intensity, subtract the flame background measurement from the total emission intensity of the aluminum line or the aluminum oxide band. At 484 and 396.2 mp the calibration curve is linear from 5 to 40 y of aluminum per ml., but shows a gradual concavity toward the concentration axis a t higher concentrations of aluminum. Effect of Aqueous-Organic Volume Table 1. Effect of Aqueous-Organic Volume Ratio on Recovery of Aluminum (Original volume of organic phase, 5 ml.) Volume Recovery of Aluminum, 7 0 Ratio. Aaueous Aaueous Aqueous’ to phase not phase Organic preprePhase equilibrated equilibrated
a
1 100 100 5 101 104 10 1125 102 25 1505 102 50 150 ... 100 No phase separation Only 4.5 ml. of organic Dhase re-
covered: b Onlv 3.5 ml. of organic ohase recovered:
2 01 6
1 1 I 1 7 S 9 IO /I OXYGEN PRESSURE, p s i
I
12
Figure 2. Intensity of aluminum oxide emission as function of oxygen pressure at various acetylene pressures Aluminum, 40 y per ml.; slit, 0.030 mm.
Ratios. The effect of the aqueousorganic volume ratio on the percentage of aluminum recovered ITas investigated. To varying quantities of 1/11 acetate solutions adjusted to pH 6.0, 100 y of aluminum was added. Prior to the addition of aluminum, one series of the acetate solutions was equilibrated for 5 minutes m-ith a 0.1111 solution of 2-thenoyltrifluoroacetone in 4-methyl-2-pentanone; a second series Kas not pre-equilibrated, Each series of solutions was then equilibrated for 5 minutes with 5.0 ml. of the 0.1-Ifsolution of 2-thenoyltrifluoroacetone, after which the “apparent” concentration of aluminum in the organic phase was determined. The results are given in Table I. The acetate buffer solution apparently dissolves a small amount of 4-methyl-2pentanone and, if not pre-equilibrated with the solvent prior to the extraction step, the volume of the organic phase recovered is less than the original volume pipetted into the separatory funnel. Consequently, although the amount of aluminum extracted is unaffected, the smaller volume of organic phase recovered results in an apparent increase in the concentration of aluminum in the organic phase. When the aqueousorganic volume ratio exceeds 5, preequilibration of the acetate buffer is necessary. If this is done, the volume ratio can be extended to a t least 25. Similar results were obtained using lV-nitrosophenylhydroxylamine as chelating agent. PROCEDURES
Magnesium-Base Alloys. Dissolve the sample in the minimum amount of I N sulfuric acid. Transfer the solution to a volumetric flask and dilute to the mark. Transfer an aliquot that contains between 100 to 500 y of aluminum to a small beaker and adjust the pH between 2.5 and 4.5 with 1M ammonium acetate. Transfer this solution to an extraction funnel, then rinse the beaker with several portions of water. Adjust the volume to approximately 30 ml. and add 3 ml. of a 0.1M solution of N-nitrosophenylhydroxylamine (7). Add a known volume
I
c
I
I
,
I
1
I
I
I
l
a
4 4.0
F M A l N L Y SOLVENT BURNING
4
I
9.0
mmT
i 4
"I
5
00
I
/ O 20
I
30
OXYGEN
40
50
- ACETYLENE
60
7.0
8.0
90
100
F L O W RATE RATIO
Figure 3. Intensity of aluminum emission at 396.2 m p as function of ratio of flow rates of oxygen to acetylene Acetylene. 1 to 10 p.5.i.; 0 . 8 8 to 3 . 6 5 cu. ft. per hour Oxygen. 8 . 0 to 1 3 P A . ; 7 . 1 0 to 9 . 2 5 cu. ft. per hour
0.0
of 4-methyl-2-pentanone and shake until any precipitate which may form in the aqueous phase has disappeared ; then shake for an additional 2 minutes. Allow the phases t o separate and proceed as described for the calibration curve. Zinc-Base Alloys. Dissolve the sample in the minimum amount of 1S nitric or sulfuric acid. Transfer the solution t o a volumetric flask and dilute to the mark with water. Transfer an aliquot containing between 100 and 500 y of aluminum to a small beaker and adjust the p H between 6.0 and 6.5 with a 2M solution of ammonium acetate. Transfer the contents of the beaker to a 60-ml. separatory funnel. Add a sufficient volume of sodium diethyldithiocarbamate solution t o react with all of the zinc and manganese in the aliquot ( 1 ) ; 1 ml. of a 5% solution of the reagent is required for each 13 mg. of zinc or manganese. Add 20 ml. of chloroform and shake for 2 minutes. After the phases have separated, draw off the organic layer and discard it. Equilibrate the aqueous phase with successive, fresh, 10-ml. portions of chloroform until the organic phase is no longer colored, indicating that zinc removal is complete. Four 10-ml. portions are usually sufficient. Transfer the aqueous phase to a small beaker and carefully adjust the p H between 5.8 and 6.0 with a 1 M acetic acid solution. Return the contents of the beaker to a clean 60-ml. separatory funnel. Add a known volume of O.1M 2-thenoyltrifluoroacetone in 4-methyl2-pentanone and shake for 5 minutes. After the phases have separated, draw off the aqueous phase and discard it. Equilibrate the organic phase with 30 ml. of a 0.1M nitric acid solution, then proceed as for the calibration curve. Steels. To determine acid-soluble aluminum, weigh samples containing between 100 and 500 y of aluminum (or, for larger amounts of aluminum, a t least 0.1-gram samples) into a 150-ml. beaker and dissolve in the minimum amount of 5N perchloric acid. Remove any residue by filtration through a loose-textured paper. Wash the residue with hot, 1% 'perchloric acid. Transfer the filtrate to a mercury cathode elec-
WAVE LENGTH, m p
Figure 4.
Flame emission spectrum of aluminum
Aluminum present, 25 y per ml.;
trolysis cell and electrolyze until spot tests indicate that the total residual iron content is less than 1 mg. Evaporate the electrolyte to 20 ml. To the entire sample or to an aliquot that contains between 100 and 500 y of aluminum, add 10 ml. of 1M ammonium acetate solution and adjust the pH between 2.5 and 4.5 with 1 M aqueous ammonia. Transfer the solution to a 60-ml. separatory funnel. Add 5 ml. of a 0.1M solution of S-nitrosophenylhydroxylamine and a known volume of 4-methyl-2-pentanone. Shake for 2 minutes, then complete the analysis as described above. Bronzes. Weigh a sample containing 100 to 500 y of aluminum into a 150-ml. beaker and dissolve it in 10 ml. of 5 N hydrochloric acid and 5 ml. of 30% hydrogen peroxide. After dissolution, add 10 ml. of 5 9 perchloric acid and evaporate to copious fumes of perchloric acid. Allow to cool, then transfer to a mercury cathode electrolysis cell. Electrolyze and process the sample, or a suitable aliquot, in the same manner as for steels. Minerals. For siliceous minerals and glasses, weigh a sample containing 0.2 to 1.0 mg. of aluminum oxide into a platinum dish. Moisten with distilled water, and add 5 ml. of 48y0 hydrofluoric acid and 0.5 ml. of 36N sulfuric acid. Heat to fumes of sulfur trioxide. Cool, add 2 ml. of hydrofluoric acid, and evaporate to dryness. Ignite carefully until sulfur trioxide ceases to be evolved. Dissolve the residue in 1 to 9 hydrochloric acid and transfer the solution to a 60-ml. separatory funnel. Rinse the dish with l to 9 hydrochloric acid solution. Add 5 ml. of 0.1M N-nitrosophenylhydroxylamine and 25 ml. of 4-methyl-2-pentanone. Shake for 2 minutes to remove the heavy metals (9). After the phases have separated, draw off the aqueous phase into a 50-ml. beaker. Add 10 ml. of 1M ammonium acetate solution and adjust the p H between 2.5 and 4.5
slit, 0.030 mm.
with aqueous l M ammonia. Transfer the solution to a 60-ml. separatory funnel. Add 5 ml. of a 0.1M solution of N-nitrosophenylhydroxylamine and a known volume of 4-methyl-2-pentanone. Shake for 2 minutes, then proceed as for the calibration curve. For other types of minerals, such as limestone, proceed with the ordinary scheme for the removal of silica. Recover any oxides occluded with the silica by the procedure described above. Process the filtrate from the silica dehydration, or a suitable aliquot, in the same manner as outlined for siliceou5 minerals. DISCUSSION
Flame Spectrum of Aluminum. Prominent band heads and atomic lines in the flame spectrum of aluminum are shown in Figure 4. The band head of the strongest oxide system appears a t 484 mp. It is degraded toward the red. Less intense band systems appear between 435 and 478 mp and also betweeen 510 and 518 mp. The energy of dissociation of aluminum oxide has not been established with certainty ( 5 ) , but its value is low enough that considerable dissociation into atomic aluminum is possible in an oxyacetylene flame. A pair of atomic lines is observed a t 394.4 and 396.2 mp. Their relative intensities are in the ratio of 1 to 2. The intensity of the stronger atomic emission line is equal to the intensity of the strongest oxide band head when an oxyacetylene flame is employed. The atomic lines are too weak to be useful when an oxyhydrogen flame is used as the source of excitation. The background radiation in the vicinity of the peak of the most intense oxide band was measured a t 482 mp. At this wave length the emissivity of the C) and aluminum oxide band systems with VOL. 31, NO. 2, FEBRUARY 1 9 5 9
185
,
Table
II.
Tolerance Limits for Diverse Ions (Aqueous phase contained 200 y of aluminum; 10 ml. of 4methyl-Zpentanone used
as extractant) Tolerance Limit, Mg., for Chelating Agent N-Nitroso2-ThenoylphenylDiverse trifluoro- hydroxylIon Present acetone amine Barium 10 50a Boron 2 25 Cadmium 1o a 5 Ca1cium 5Oa 504 Cerium( 111) 1 5 Chromium(II1) 0.2 10 Chromium(VI) Cobalt Copper Iron( 111) Lanthanum Lead ... 100 ~. Lithium 2 loa Magnesium 10 50a Manganese 0.5 50 Molybdenum 1 0.25 Nickel 0.2 5 Potassium 10 10 Sodium 5On 50a Strontium ... 50" Thorium 10 10 Titanium 4 1 Uranium 10 10 Vanadium ... 10 Yttrium ... 0.1 Zinc 10 10 Chloride 100 1005 Fluoride 0.2 0.2 Sitrate 50a 505 Perchlorate 1ooa 1000 Phosphate 0.2 0.2 Silicate ... 50a Sulfate 1005 1000 a Maximum quantity tested.
heads occurring beh-een 460 and 478 mp has diminished to negligible values. Correction for the background radiation in the vicinity of the atomic lines is made by measuring the minimum emission between the two atomic lines. Extraction of Aluminum. I n the determination of aluminum by flame spectrophotometry, the aluminum must be dissolved in a n organic solvent if adequate sensitivity is t o be achieved. Previous studies (2, 6) have shown that flame emissions are markedly enhanced when 4-methyl-2-pentanone solutions are aspirated. Furthermore, by utilizing solutions of chelating agents in 4-methyl-2-pentanone as the extractant, the aluminum can be isolated from many matrix elements by selective extraction (7, 9). Chelating agents
~~
2
3
4
5
6
7
PH
Figure 5. Extraction of aluminum with TTA as function o f pH and concentration o f acetate ion ~
~~
Table 111.
3-0 171
Sample Type
Analysis of Standard Samples Certified A1 Found, % AI Value, 70 AV. XBS Samples
agnesium alloy
2.98
94b Zinc alloy
4.07
102 Silica brick
1.03
la
Argillaceous limestone
2.20
106a Cr-Mo-A1 steel
1.08
125 Silicon steel
0.261
lOOa Manganese steel
0 ,040
2.89, 2.95, 2.95, 3.03, 2.88, 3.00, 2.87,3.04 4.16, 3.98, 4.05, 4.04, 4.07,4.02, 3.98 1.04, 1.05, 1.00, 0.98, 1.09, 1.09, 0.99, 0.96, 1.00, 0.95 2.09, 2.16, 2.25, 2.40, 2.47, 2.18, 2.26, 2.24, 2.06, 2.02, 2.08, 1.98, 2.44, 2.32, 2.20, 2.21 1.16, 1.05, 1.13, 1.18, 1.10,1.12 0.286, 0.283, 0.270, 0.289,0.270,0.276 0.046,0.046,0.040, 0.038, 0.039, 0.037, 0.037, 0.037
Std. dev.
2.95
0.07
4.04
0.06
1.02
0.05
2.26
0.12
1.12
0.05
0.279
0.008
0.040
0.004
Synthetic Thorium Slurry AI.
I
Present, Mg. per M1. Th, 50; U, 500; Fe, 200; Ni, 100; Cr, 100
186
ANALYTICAL CHEMISTRY
Y.
Der MI.
1
Present
Found
Av.
Std. dev.
50
50.0, 52.0, 50.0, 53.5, 51.5, 54.2, 52.5, 51.5, 54.2, 53.5
52.0
1.6
investigated were 2-thenoyltritluoroacetone and N - nitrosophenylhydroxylamine. The acetate ion concentration has a marked effect on the degree of extraction of aluminum with 2-thenoyltrifluoroacetone in 4-methyl-2-pentanone. I n 0.5 to 1.OM acetate solutions, the per cent of aluminum removed by a single extraction increases with pH, becoming quantitative a t pH 5.5 to 6.0, and then decreasing with a further increase in pH (Figure 5). A single 5-minute extraction suffices to remove as much as 600 y of aluminum. Concentrations of 2-thenoyltrifluoroacetone in excess of 0.1M are undesirable, as erratic flame conditions may be produced. To decrease further the source of erratic flames, the burner should be rinsed with acetone after a series of four to six samples has been aspirated. For many applications X-nitrosophenylhydroxylamine is the preferred chelating agent. Aluminum is extracted within a broad interval of pH, emulsion formation is never observed, and the extraction is rapid. A single extraction removes as much as 750 y of aluminum, the maximum amount tested. For an unknown reason the emissivity of standards and samples prepared by extraction with iY-nitrosophenylhydroxylamine was only 85% as intense as those prepared mith 2thenoyltrifluoroacetone as chelating agent. The latter reagent, however, is very expensive. Interferences. The effect of a large number of interferences on the emission intensity of aluminum is shon-n in Table 11. I n these studies solutions containing known amounts of aluminum and the various test ions were carried singly through the extraction procedure. KO attempt was made to determine the amount of each cation coextracting with the aluminum; the concentration listed for each ion (tolerance limit or maximum amount investigated) is the amount present in the aqueous phase before extraction and the amount which causes no change, within 2%, in the recovery of aluminum. When 2 - thenoyltrifluoroacetone is used as chelating agent, it is desirable to backwash the organic phase with a 0.1M solution of nitric acid. Large amounts of the alkali and alkaline earth elements accompany aluminum in the extraction, but these elements can be removed by a single backm-ash nithout any loss of aluminum. The tolerance levels of these and other elements which would otherwise offer serious interference can thus be extended. T h e n the atomic line at 396.2 mp is used, direct spectral interference is encountered only with calcium and iron,
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 1). scale division
(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
