ANALYTICAL CHEMISTRY
1520
ment was 99% or better. For coefficients of the order 0.107, the agreement was a t least 90%. The same satisfactory agreement was obtained for pattern coefficients of n-hexadecane. Pattern coefficients can also be determined directly with the data reduction system by setting the highest deflection in a given galvanometer trace into the Teleducer as 999 and then confining all subsequent peak height measurements to that particular galvanometer trace. The agreement of the pattern coefficients obtained in this way with those calculated from the manual measurements was poor. As might be expected, the greatcst deviations occurred in the case of low peak heights, which under normal conditions would be measured on a more sensitive galvanometer trace.
Table I.
Hydrocarbon Type Noncycloalkane Nonocycloalkane Dicycloalkane Monoaromatics CS
c7
0.5 0.0 0.0 0.0
CS CQ C1a a
Gasoline Analyses
85"-114° C. Fraction Manual DRSa, method, vol. % vol. % 70.2 70.4 28.6 28.4 0.0 0.0 1.3 1.3 0.8 0.8
114°-1560 C. Fraction Manual1-01. DRS, % method. vol. % 55.9 42.6 0.0 1.6
0.2 0.3 1.0
0.5 0.0 0.0 0.0
0.0
0.0
Table 11.
CONCLUSIOhS
The suggested system for reduction of mass spectrometric data has several noteworthy advantages over the manual method. It is considerably faster, with no loss of accuracy. It has almost eliminated operator fatigue, and has eliminated transfer of data from the chart to calculation forms. I t s relative ease tends to encourage development of new high molecular weight methods by permitting reduction of spectra in a quantity that would be impracticable by the manual method. The system is remarkably trouble-free and requires only an hour for the training of an operator.
0
0 2
0 1 0 0
2 2 0 0
Data reduction system.
Analyses of a 180" to 250" C. Fraction
REPEATABILITY
An idea of the repeatability with which one peak can be measured was obtained when three different operators measured the same peak using both methods of measurement. The galvanometer zero was redetermined before each measurement. Because of the subjectivity inherent in repeated measurements of the same peak by the manual method, only one manual measurement was made by each operator. The repeatability obtained with the data reduction system was as good as that given by the manual procedure.
5.5 9
42 (3 0 0 1 6
Hydrocarbon Type Noncyoloalkanes Noncondensed cycloalkanes Condensed cycloalkanes Monoaromatics Diaromatics Data reduction system.
DRSa, Vol. %
Manual Method, VOI. %
ACKNOWLEDGMENT
The authors wish to acknowledge the material assistance of W. 0. Lease, who installed the equipment and made many modifications, and of H. W. Schutz and H. M. Hicks, who made the measurements. LITER4TURE CITED
(1) Clerc, R. J . , Hood, A., O'Neal, AI. J., Jr., d s . 4 ~ .C H m f . 27, 568 (1955). (2) Hochgesang, F., Socony->lobi1 Research and Development Department, Paulsboro, N. J., ASTAI E-14 meeting, San Francisco, Calif., 1955. (3) O'Neal, 11.J.,Jr., Wier, T. P., Jr., - 4 ~ 4CHEM. ~ . 23,530 (1951). RECEIVEDfor review M a y 3, 1956. 84, Shell Development Co.
Accepted June 28, 1956.
Publication
Spectrophotometric Determination of Aluminum in Ferrous and Nonferrous Alloys Application of 8-Hydroxyquinaldine ROBERT J. HYNEK and LEWIS J. WRANGELL Research Laboratories, Allis-Chalmers Manufacturing Co., Milwaukee
The new analytical reagent, 8-hydroxyquinaldine, does not react with aluminum but does react with many elements that ordinarily interfere in the determination of aluminum. This property is used in a widely applicable method for the elimination of some interferences prior to the spectrophotometric determination of aluminum-8-hydroxyquinolinate in chloroform at 389 mp, A mercury cathode partially removes metallic ions. Interferences are ultimately eliminated by adjustment of the pH to 9.2, and use of 8-hydroxyquinaldine, chloroform, and hydrogen peroxide. For certain alloys, it is not necessary to use the mercury cathode. Gross separations of interferences can be accomplished by the direct application of S-hydroxyquinaldine and chloroform to the dissolved sample. The method has been applied to a wide variety of standard and commercial alloys containing up to 10% aluminum.
P
1, Wir.
RIOR to the application of 8-hydroxyquinaldine to the determination of aluminum. the Allis-Chalmers Research Laboratories has used three methods of analysis, all of which have disadvantages. The first method is a colorimetric procedure for a variety of ferrous and nonferrous alloys. After an initial separation of interferences by sodium hydroxide, the aluminum is precipitated as aluminum phosphate. The blue phosphomolybdate complex is developed from the phosphorus contained in the precipitate, and the light absorption is measured in a filter photometer. The aluminum equivalent of the complex is obtained from a calibration curve. This method is limited in precision, and it is difficult to eliminate interferences completely. Furthermore, if the aluminum content is less than 0.0107; in steel and iron, a lengthy ether extraction is necessary to remove iron from the larger samples required to provide sufficient aluminum for a satisfactory determination. The second method, used for ferrous alloys, involves a partial separation of iron from alumin\im I)>- the use of sodium bicarbon-
V O L U M E 28, NO. 10, O C T O B E R 1 9 5 6 ate, the complete removal of iron and some other interferences
xvith sodium hydroxide, precipitation of t,he aluminum wit,h 8-hydroxyquinoline (8-quinolinol), and titration with bromatebromide and thiosulfate solutions. Although accurate, this method is cumbersome and slow (requires 2 to 3 hours). The third method is generally applied to nonferrous alloys, particularly those that contain more than 1% of aluminum. Hydrogen sulfide is used to separate major interferences from aluminum prior to precipitation of aluminurn S-hydroxyquinolinate. The final determination is made t,itrimetrically. Precision and accuracy are good, but 3 to 4 hours are required for the analysis. The disadvantages of these methods prompted a study of other analytical techniques. For the removal of interferences, mercury cathode electrolysis is particularly effective. Base met:& are deposited in sulfuric or perchloric media. HoTI-ever, perchloric acid is preferred because it smoothly expels the volatile acids that are used for rapid sample dissolution; only slight fuming occurs during electrolysis; and perchloric acid solutions are more readily adjusted by ammonium hydroxide t o t,he pH value required for extraction of interferences. For the measurement of aluminum, attention was given t o colorimetric reagents. The organic reagent Ferron, n-hich permits the tleterminatiori of aluminum in the presence of iron ($), is very sensitive t o small amounts of aluminum. Hoxvever, many elements interfere, and extreme precautions (precipitations anti extractions) must be taken to avoid errors ( 5 ) . .I well known reagent for the determination of aluminum in the presence of small amounts of those elements not completely removed by the mercury cathode is the Aluminon reagent, ammonium aurin tricarboxylate. However, this laboratory has had very little siicress with .Uuminon because a variety of difficultly controllablr factors influence the color development (6). Certain colorimetric methods (3, 7 , 10) utilize S-hydroxyquinoline. These methods depend upon a chloroform extraction of aluminum &h3.droxyquinolinate from aqueous solution and a spectrophotometric analysis of the extract. This reagent appeared to be the most promising, except for its reactivity with many other elements. .I similar reagent, 8-hydroxyquinaldine (2-methyl-8-hydroxyquinoline), \vas observed by Merritt and Walker (8) to react with many of the elements (iron, chromium, nickel, manganese, copper, vanadium, titanium, molybdenum, tungsten, zinc, lead, and magnesium) commonly found in ferrous and nonferrous alloys. However, it, differed from 8-hydroxyquinoline in that it did not react with aluminum. This fact suggested to the authors of this paper that 8-hydroxyquinaldine could be used to eliminate interferences prior to the colorimetric determination of aluminiini with 8-hydroxyquinoline. It was therefore proposed that a new method of analysis consist of the following principal parts: 1. Separation of large amounts of base metals and other significant interferences from aluminum by mercury cathode electrolysis. 2. Use of 8-hydroxyquinaldine to remove all traces of inlerferences not removed completely by the mercury cathode. 3. Spectrophotometric determination of aluminum 8-hydroxyqriinolinate in chloroform. APPARATUS
Mercury Cathode. The mercury cathode consists, in part, of the heat exchanger, platinum electrodes, split plastic cell cover?, and borosilicate glass cell (35-ml. mercury capacity), as manufactured by the Eberbach Corp., Ann Arbor, hlich. ( 1 ) . A cylindrical Alnico KO. 3 magnet, 4 em. in depth and 6 cm in diameter, provides the magnetic field. The cathode cell rests on this magnet, n-hich is embedded in a Yo. 15 rubber stopper -2 single-phase, unfiltered, full-wave, 60-cycle selenium rectifier with a 28-volt and 30-ampere capacity is the power source for the csathode. Copper wire (14-gage) conducts the current t o the cathode.
1521 Beckman spectrophotometer Model DU, with 1-cm. borosilicate glass absorption cells is used. T h e p H meter is Beckman, Model H2. REAGENTS AND SOLUTIONS
DISSOLVING ACID. Mix equal volumes of hydrochloric. acid, nitric acid, and water. PERCHLORIC ACID, 70%. TARTARIC ACIDSOLUTION.Dissolve 125 grams of tartaric x i d in approximately 150 ml. of w t e r >and dilute t o 250 ml. AMM~\IONIUM ACETATESOLCTIOS. Dissolve 125 grams of animonium acetate in approximately 150 ml. of water, and dilute t o 250 ml. A 4 M ~ O HYDROXIDE, ~ ~ ~ ~ f 15s. 8-HYDROXYQCIXALDINE SOLUTIOS. Dissolve 12.5 grams of 8hydroxyquinaldine in 25 ml. of glacial acetic acid with gentle heating; add 200 ml. of water, filter, and dilute t o 500 ml. (The 8-hydroxyquinaldine used for most of the work in this investigation was obtained from the Hach Chemical Co., Ames, Iowa. Quantities have h e n obtained also from the hldrich Chemical Co., Milwaukee, Wis.) 8-HYDROXYQUINOLISC SOI.TTIO.V. Dissolve 12.5 grams of 8hydroxyquinoline in 25 ml. of glacial acetic acid with gcmtle heating; add 200 ml. of watcr, filter, arid dilute to 500 ml. HYDROGEN PEROXIDE, 30%. CHLOROFORM, Mallinckrodt, Baker's analyzed, or Merck. SODICMSULFATE? anhydrous, granular, Mallinckrodt, IYY E STI GATION
Precipitation of Diverse Ions by 8-Hydroxyquinaldine. Initial experiments with 8-hydroxyquinaldine were conducted to determine whether iron could be quantitatively separated from solution by precipitation and filtration techniques. It was found that 10- or 100-mg. quantities of iron could be precipitated from an ammonium acetate-ammonium hydroxide buffered solution a t p H 9. The recovery at the 100-nig. concentration was not complete, however, because some of the organic precipitate volatilized during ignition to ferric oxide. Under conditions similar to those involved in the precipitation of iron, 50-mg. quantities of nickel, lead, and zinc were precipitated quantitatively. At pH 5) 100 mg. of copper were precipitated very satisfactorily. (.kt higher pH values, copper 8hydroxyquinaldinate dissolved.) The salmon-colored chelate filtered very rapidly and washed easily. The precipitate was ignited to cupric oxide and gave no evidence of volatility. The recovery (99.8 mg.) was quantitative within the limits of experimental error. The apparent success of the precipitations led to the conclusion that 8-hydroxyquinaldine could be used to remove interferences prior to the precipitation of aluminuni with 8-hydroxyqiiinoline. At p H 9, a solution which contained 100 mg. of iron and 9.87 nig. of aluminum was treated with 8-hydroxyquinaldine. The iron 8-hydroxyquinaldinate was removed by filtration and the aluminum in the filtrate n-as precipitated by 8-hydroxyquinoline. h bromometric titration of the aluminum 8-hydroxyquinolinate s h o m d a recovery of 9.58 nig. oE aluminum, approximately 07% of the amount added. The next experiment utilized the mercury cathode for a partial scparation of 1 gram of iron from 0.87 mg. of aluminum. The undeposited iron (estimated to be approximately 25 mg. ) was precipitated a t pH 9 v-ith 8-hydroxyquinaldine and removed by filtration. The aluminum in the filtrate mas precipitated by 8-hydroxyquinoline. A bromometric titration indicated that !B.8yoof the aluminum had been recovered. During subsequent precipitation experiments it was observed that small quantities of iron 8-hydroxyquinaldinate had passed through the filter paper. The use of tight filter paper and large quantities of filter pulp eventually provided fairly satisfactory separations, but upon refiltration of apparently clear filtrates, trace amounts of precipitate were recovered. Subsequent precipitations of iron required increased amounts of 8-hydroxyquinaldine. As many as four additions of reagent,
ANALYTICAL CHEMISTRY
1522 and a corresponding number of filtrations were necessary to effect a satisfactory separation. Reagent coprecipitation effects were observed also, as indicated by clumps of iron &hydroxyquinaldinate which adhered strongly to the stirring rod and to the bottom and sides of the beaker. Extraction of Diverse 8-Hydroxyquinaldinates. I n an effort to avoid the effects of the undesirable reactions and reagent characteristics encountered in precipitation separations, solvent extraction techniques were investigated.
A quantity (10 mg.) of dissolved iron was treated a t pH 9 with 10 ml. of S-hydroxyquinaldine solution, and the precipitate was removed by filtration through a No. 42 Whatman paper. The a parently clear filtrate was transferred to a 250-ml. separatory i n n e l and 10 ml. of chloroform were added. After the mixture had been shaken for 10 to 15 seconds and allowed to stand for a few minutes, traces of greenish black iron 8-hydroxyquinaldinate were visible in the chloroform phase. Upon eubsequent extraction, the chloroform phase became colorless.
It was concluded that small amounts of iron could be eliminated very rapidly from a solution by extraction techniques. To determine whether 8-hydroxyquinaldine and chloroform could adequately extract elements other than iron, the extraction reactions of 21 additional elements were studied a t pH 9.2 after it was determined that a pH in excess of 8 was required for the quantitative extraction of manganese and titanium %hydroxyquinaldmates. A t a p H of 9 or above, molybdenum, tungsten, chromium, and vanadium, although not extracted by &hydroxyquinaldine and chloroform, do not interfere during the extraction of aluminum 8-hydroxyquinolinate ( 4 ) . No further adjustment of pH is necessary for the extraction of aluminum 8-hydroxyquinolinate [extraction range, pH 4.9 to 9.4 (IO)]. The pH of 9.2 was first observed as a result of using perchloric acid during mercury cathode analysis. It was determined later that a solution is buffered well a t pH 9.2 by the use of 5 ml. of perchloric acid, 1 gram of tartaric acid, 1 gram of ammonium acetate, and 12 ml. of ammonium hydroxide in a 125- to 150-ml. volume. The color of the various metal 8-hydroxyquinaldinates and the aluminum recovery from solutions of those metals are shown in Table I. Table I.
Recovery of Aluminum at pH 9.2
(After removal of diverse ions with 8-hydroxyquinaldine and chloroform) Aluminum, 1 0 3 Ion" 8-Hydroxyquinaldinate in CHCL Present Recovered 100 90 Orange-yellow, translucent Ti + 4 141 100 Maroon Ce+++ 104 100 Yellow-green Zn 98 100 Mahogany, translucent + 100 100 Green-yellow 101 100 Pb++ Yellow-green 100 100 Yellow, pale Sn +4 104 100 Yellow, pale Sb+++ 121 100 Brown-ruddy Mn+7 99 100 Yellow. translucent Mn++++ 101 100 Green, 'translucent Cd++ 101 100 Mahogany + 99 100 Green-black 101 100 Green-black Fe+++ 0 1 mg. each except for P b (0.5 mg.); Ni, Zn. and Co (0.1 mg.).
i: $+
g,U+
Solutions of the metals were bufiered a t pH 9.2 and 3 to 5 ml. of the 8-hydroxyquinaldine solution and 5 ml. of chloroform were added. The solutions were shaken vigorously in 250-ml. separatory funnels for 10 to 15 seconds, and allowed to stand until the chloroform and aqueous phases had settled sufficiently to permit separation. This process was repeated until the characteristic chelate color for the particular metal ion was no longer visible in the chloroform phase. To ensure removal of all traces of the metallic ion chelate and excess 8-hydroxyquinaldine, two additional extractions with 5d. portions of chloroform were made. Four to five extractions with the 8-hydroxyquinaldine solution and chloroform remove all the metals shown (except titanium
and cerium) a t the specified concentrations. Onemilligram quantities of titanium require five or six extractions in addition to those normally required for other metah. Unlike other chelates, most of the titanium 8-hydroxyquinaldmate is removed in the form of amorphous aggregates which settle out on top of the chloroform layer, and when drawn off with the chloroform layer, are accompanied by small portions of the aqueous phase. The additional extractions and the loss of the aqueous phase probably account for the low aluminum recovery shown for the titanium solution in Table I. Cerium reacted d t h &hydroxyquinaldine to form a marooncolored chelate, but could not be removed completely by the use of 8-hydroxyquinaldine. Thus, the cerium which remained waa co-extracted as an 8-hydroxyquinolinate together with aluminum 8-hydroxyquinolinate, thereby causing an interference (Table I). The removal of zinc, cobalt, nickel, and lead appeared to be more efficient a t pH 6 to 7 , but small amounts of these ions can be removed a t pH 9.2. Tin and antimony, which precipitate during the dissolution and dehydration of a sample, produced only faintly colored extracts. However, only tin has been encountered in an amount sufficient to precipitate. The precipitate can be largely decomposed by electrolysis, and any undecomposed precipitate can be removed by filtration, as indicated in Procedure I. Manganese introduced as the permanganate ion resulted in the iormation of a slightly soluble substance which interfered (Table I), but this interference may be avoided entirely by reduction to the manganous ion, the chelate of which is extracted easily. Just enough ferrous iron is added to discharge the pink color. (The addition of ferrous iron is necessary only when iron is absent after electrolysis.) Cadmium, copper, and iron are extracted very quickly. As much as 25 mg. of iron was separated from microgram amounts of aluminum, although excessive amounts of 8-hydroxyquinaldine and chloroform were required. A more convenient separation was obtained for 10 mg. of iron. Two to three extractions with 10 ml. of the 8-hydroxyquinaldine solution and 30 ml. of chloroform were sufficient to remove the iron. The extraction was finished with 5-ml. quantities of both reagents. (The extraction of iron in this way led to the development of Procedure 11, which permits the determination of aluminum without the aid of the mercury cathode.) One milligram of tantalum and 0.25 mg. of magnesium did not react with 8-hydroxy quinaldine and 8-hydroxyquinoline (Table 11). However, 3-, 27-, and 150-7 errors were experienced when 0.5, 1.0, and 2.0 mg. of magnesium were present during the extraction of aluminum. The small error a t the 0.5-mg. concentration would assume significance only if a very large aliquot factor were involved in a determination. Chromium, molybdenum, tungsten, vanadium, niobium, thorium, uranium, and zirconium could not be extracted from solution with 8-hydroxyquinaldine and chloroform. (Chromium, introduced as dichromate, and vanadium reacted in the aqueous phase to produce a distinct yellow coloration, but the coloration remained in the aqueous phase throughout the extraction.) The interferences of these elements were eliminated by techniques discussed in the following sections. Elimination of Interferences at pH 9.2. The effect of pH upon the extraction of metal chelates of %hydroxyquinoline is known and has been used advantageously. Gentry and Sherrington ( 4 ) observed that chromium, molybdenum, tungsten, and vanadium did not produce colored extracts a t pH 9, and were able to determine aluminum in the presence of large amounts of molybdenum and tungsten. Talvitie (9) used pH control in the colorimetric determination of vanadium with 8-hydroxyquinoline in biological materials. The reactions of chromium, molybdenum, tungsten, and vanadium with 8-hydroxyquinoline were investigated subsequent to an extraction treatment with 8-hydroxyquinaldine and chloroform
V O L U M E 28, NO. 10, O C T O B E R 1 9 5 6 a t pH 9.2. Only vanadium and chromium (dichromate) reacted to any extent, but no significant interference occurred during the extraction of aluminum (Table 11). The reaction of vanadium and chromium with 8-hydroxyquinoline was similar to their reaction with 8-hydroxyquinaldine-a distinct yellow coloration was observed (in the aqueous phase) which was not extracted by the chloroform. The extraction of aluminum 8-hydroxyquinolinate a t pH 9.2 was affected seriously by niobium, thorium, uranium, zirconium, and cerium. The elimination of the interferences caused by these metals is discussed in the follov-ing section. Elimination of Interferences by Use of Hydrogen Peroxide. Hydrogen peroxide has been used to prevent interferences of certain metals during precipitation (6) or extraction (8, 7) of eluminum 8-hydroxyquinolinate. The addition of peroxide causes the formation of peroxy acid complexes which apparently inhibit the formation of the metal 8-hydroxyquinolinates. The complexing effect of hydrogen peroxide upon niobium, thorium, uranium, zirconium, cerium, titanium, tantalum, molybdenum, arid vanadium was studied a t pH 9.2. (Although the elimination of the interferences by titanium, tantalum, molybdenum, and vanadium had already been provided for, it was desired to determine the effect of hydrogen peroxide upon the extraction of these elements.) Five milliliters of 30y0 hydrogen peroxide vere added to solutions of these metals after reagent impurities had been removed by Shydroxyquinaldine and chloroform. (The customary complete extraction of titanium with 8-hydroxyquinaldine was not necessary when hydrogen peroxide was used. The peroxide, which was added after a portion of the titanium had been extracted, prevented further chelation of titanium by Shydroxyquinaldine. Consequently, it was necessary to extract only titanium 8-hydroxyquinaldinate formed prior to the addition of hydrogen peroxide.) The solutions were treated subwquently for aluminum, and of those metals which had interfeied previously (niobium, thorium, uranium, zirconium, and cerium), only the interference of zirconium was not eliminated (Table 111). However, zirconium can be separated from aluminum by cupferron ( 6 ) , preferably after a mercury cathode separation and before extraction of interferences with 8-hydroxyquinaldine.
Table 11.
Recovery of Aluminum at pH 9.2
(In presence of diverse ions not removed b y 8-hydroxyquinaldine and chloroform) Aluminum, IO*Iona Present Recovered T a +) 100 99 If&,+;' 100 100 Cr 100 98 Cr +e 100 102 M o +8 100 99 w +8 n n 106 107 100 400 100 206 u +e 0 144 Zr+4 100 150 a
1 mg. each except magnesium (0.25 mg.).
Table 111.
Effect of Hydrogen Peroxide upon Diverse Ions at pH 9.2 Ion0 Nb +o
T h +4
grT4 Ce +(
Ti +4 Ta M o +d
*
1 ' +6
1
mg. each.
Aluminum, 10-8 Present Recovered
1523
Cerium reacted with hydrogen peroxide to form a perosy complex more stable than the 8-hydroxyquinaldinate arid 8hydroxyquinolinate. The presence of the peroxy complex was indicated by a yellov color in the aqueous phase. However, unlike the peroxy complexes of other metals (titanium, niobium, etc.) the cerium peroxy complex was extracted by chloroform. Large, yellow bubbles in the chloroform phase were characteristic of this extraction. The extracted peroxy complex of cerium probably rould have interfered, but for an unusual adsorption reaction between the extracted complex and anhydrous sodium sulf:ite, xliich limited the interference of 1 mg. of cerium to l';;..
Table IV.
Analytical Error Associated with Use of Hydrogen Peroxide
Difference, 10-8 Aliquoted Found Gram Factor 100. oa 101.8 1 1.8 1 zoo. 05 200,5 0.5 250.0' 260.5 1 0.5 116.0b 10 0.5 116.5 112.2 4.2 10 116.0b 152.0 10.5 200 162.5C 152.8 9.7 200 162.5e 196.O d 6.5 200 189.5 2.0 196. O d 200 194.0 a Standard aluminum solution. b NBS 22C Bessemer steel (A1 = 0.116%). C NBS 116A ferrotitanium (ill = 3.26%). d NBS 94 zinc base alloy (A1 = 3.92%). Aluminum, 10-8
Error, 10-6
Gram 1.8 0.5
Error,
%
0.5
5.0 42.0
2100.0
1940.0 1300.0 'LOO. 0
n nni2 0.2100 0.1940 0.1300 0.0400
The use of hydrogen peroxide was incorporated into the annlytical procedure, but when actual samples were analyzed, erratic aluminum results were obtained. Although the errors were small when aluminum was extracted from standard solutions and from samples that contained relatively small amounts of aluminum, larger errors were observed for samples that contained relatively large amounts of aluminum (Table IV). Upon investigation it was noted that a Thitish film composed of a substance insoluble in both the aqueous and chloroform phases was formed during the extraction; excessive aqueous phase was unavoidably introduced into the extract flask; and aluminum 8-hydroxyquinolinate appeared to be extracted less rapidly than previously. Consequently, hydrogen peroxide is used only in the analysis of materials that contain less than 0.10% aluminum. Spectrophotometric Determination of Aluminum 8-Hydroxyquinolinate. The wave length of m a h u m absorption for aluminum 8-hydroxyquinoliiate has been reported to be 389 (io),390 (7), and 395 (4) mp. To determine the point of maximum absorption with the spectrophotometer used in this investigation, absorbance values were obtained at each wave length between 375 and 395 mp for two extracts which differed in aluminum content. The maximum was observed a t 389 mp. After preliminary extractions of 0 to 50 y of aluminum indicated that a Beer's law relationship existed between absorbance values and aluminum concentrations, several extractions were made t o study the curve characteristics over a range of 50 to 250 y . Constant errors, which can be caused by trace aluminum and contaminants in reagents, glassware, etc., and by variations in extraction techniques, were eliminated by the use of reference extracts prepared simultaneously during the extraction of the standard aluminum solutions. The method of least squares (II), used on the results from 29 extractions over the range of 50 to 250 y of aluminum, showed the absorbance-aluminum relationship to be represented by the formula: absorbance X 203.6 = micrograms of aluminum. PROCEDURE1
Mercury cathode, 8-hydroxyquinaldine, 8-hydroxyquinoline. Range, 0.000 t o 1 0 . O ~ aluminum. o
ANALYTICAL CHEMISTRY
1524
This proceduie is subject to interference from titanium, magnesium, niobium, thorium, uranium, zirconium, and cerium. However, a maximum of 1 mg. of titanium and 0.26 mg. of magnesium is permissible in the aliquot taken for the extraction. For aluminum below O . l O O ~ o ,hydrogen peroxide may be used to eliminate interferences caused by titanium, niobium, thorium. uranium, and cerium. X schematic diagram of the andytical procedure is shown iii Figure 1. €'re-extraction Analytical Conditions .\luminum Content,
70
0.000- 0 010
0.010- 0 100 0.100-10 .o
Sample Weight, Grams 2.0 1.0 0.5
.kcid,
111.
Electrolysis Time, RIin.
30 20 15
60 40 20
Dissolving
Current, .4mperea 20
1.5 15
Add 3 mi. (with a pipet) of the 8-hydroxyquinoline solution and 5 ml. of chloroform to the separatory funnel; shake vigorously for 16 to 20 seconds. While the extract ,settles, clean the tip of the separatory funnel thoroughly. Transfer the aluminum 8-hydroxyquinolinate extract t o a 50-ml. glass-stoppered borosilicate glass volumetric flask which contains approximately 1 gram of anhydrous sodium sulfate. Repeat the extraction and then extract residual aluminum 8-hydroxyquinolinate and excess 8-hydrosyqiiinoline from the aqueous phase with two 5-ml. additions of chloroform. Rinse the separatory funnel tip and the transfer funnel n-ith chloroform t o ensure the complete transfer of the extract to the flask. Dilute the extract to volume; stopper the flask 2nd shake it vigorously to mix the extract thoroughly and to permit the sodium sulfate to absorb all traces of moisture. Transfer a port,ion of the reference extract to nn absorption cell and a portion of t'he sample extract to a second cell, cover the cells, and place them in the spectrophotometer. Adjust the wave-length dial to 389 mp and the slit width dial t.0 0.56 mm. Determine the absorbance of the sample extract, correct for cell differences, and calculate the aluminum content of the sample from the following relationship:
A. Acid-Soluble Aluminum. Select the proper sample si7e from the table, weigh it, and transfer it to a 400-ml. borosilicate glass beaker. Add the prescribed amount of dissolving acid 1' x c x T' and heat gently to expedite dissolution, Add 10 ml. of per% nliiminiim = SXP chloric acid and a few silicon carbide boiling chips. Heat to heavy fumes of perchloric acid and continue to heat for 1 to 2 where A = net absorbance of estract minutes to ensure the complete expulsion of volatile acids and C = 203.6 X water. Cool. Rinse the cover glass and beaker with water: V = volume of electrolyzed and/or diluted sample, ml. swirl contents of beaker to dissolve soluble salts. (If objectionS = sample weight, grams able amounts of carbides, silica, and/or precipitated metallic P = aliquot taken, ml. acids other than metastannic acid are oresent. filter before electrolysis.) Transfer the sample to the cathode cell which contains 20 ml. of mercury; add water to adjust Cd C o C u Fc Mn Mo the volume to 100 ml. Insert the electrode and heat exchanger unit into the cell and electrolyze Ni P b S b Sn Z n C r Ti V W T o M q SI N b T h U Z r C e AI the sample for the required time with the proper current. Then reduce the current to less than MERCURY CATHODE ELECTROLYSIS 5 amperes and cool the sample to approximately 40" C. Drain the sample from the cell and simultaneously rinse all inner surfaces of the cathode with water t o ensure the complete ~PARTIALLY REMOVED 7 transfer of the sample. (If the presence of the I I permanganate ion is indicated by a pink color, , C d Co C u Fa Mn M o l add just enough ferrous iron to discharge the color.) ?b, s_",Z~-C~l Ti V W Ta Mg Si N b Th U Zr C c AI If the aluminum content of the electrolyzed Sam le is less than 250 y and it is not necessary EXTRACTION WITH 8-HYDROXYQUINALDINE AT pH 9.2 to fiyter the sam le t o remove suspended matter, collect the sampre in a 250-ml. separatory funnel. If the aluminum content is greater than 250 y, collect the sample in a volumetric flask and dilute to volume. If the diluted sample is not r DIS -C L F L EXTRACT AQUEOUS clear, filter a portion or let the solids settle t o provide sufficient clear solution for an aliquot. Transfer an aliquot (up to 250 y Mo p d Co Cu Fe Mn Ce: of aluminum) t o a 250-ml. separatory funnel. Dilute the sample or aliquot with water t o Pb S b S n Zn-ZiJ C r V W T a M q SI Nb T h U Z r C e AI -------approximately 100 ml. and add 2 ml. each of the tartaric acid and ammonium acetate E X T R A C T I O N W I T H 8-HYDF,OXYWINOLINE AT p H 9 . 2 solutions. Follow with 5 ml. of perchloric acid, except where the entire dissolved and electrolyzed sample has been taken for extraction. Add 12 ml. of ammonium hydroxide. (In another separatory funnel prepare a similar DISCARD - - - - - - - - - --- AQUEOUS EXTRACT solution of the reagents used for extraction. An extract must be obtained from this solution for use as a reference during the spectrophotometric determination.) Add 5 ml. of the 8-hydroxyquinaldine soluN b T h U Z r Ce A I tion and 5 ml. of chloroform; shake vigorously I T T T for 15 . t o 20 seconds to transfer interferences-i.e., 8-hydroxyquinaldinates of iron, W I L L NOT B E IN EXTRACT IF H202 IS ADDED JUST copper, manganese, etc.-from the aqueous YRGR_ IO-AEDLT ION- 0-F -8 - H LDKO x_V UQ- "']O_LINEL - - phase t o the chloroform phase, Let settle; shake the funnel briefly t o cause any floating chloroform t o join the extract a t the bottom. Drain and discard the extract. Continue the -C A-N-BE - -E L ' E E A I E D _BY-A-CXPEERR_OE E p A R ~ I ~ N I- - - J extraction with 8-hydroxyquinaldine and chloroW I L L BE ABSORBED BY ANHYDROUS Na2SO4 IF H 2 0 2 IS ADDED form until the chloroform phase is clear or a -PRIOR --TO- A -D E T L O N -0E 3 ~ H ~ D ~ O ~ x V _ a u _ l N _ O-~ I-~ E _E ,- very faint pale yellow. (For aluminum below O.lOO%, add 5 ml. of hydrogen peroxide a t AI this point.) Extract undetectable traces of interferences and excess 8-hpdroxyquinaldine Figure 1. Schematic diagram for determination of aluminum as in with two 5-ml. additions of chloroform. Procedure I
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V O L U M E 28, NO. 10, O C T O B E R 1956
1525
B. Acid-Insoluble Aluminum. IVeigh sufC.d b Cu Fc M n Ni Pb Sb Sn Zn Ti Mo C r V W To. Mg Si Zr AI ficient saniple to provide up to 250 y of acidinsoluble aluminum and transfer it to a 400-ml. borosilicate glass beaker. Add the prescribed EXTRACTION WITH 8-HYDWXYQUINALDINE AT pH 9 . 2 amount of dissolving acid and heat gently to expedite dissolution of the acid-soluble constituents. Add 10 ml. of perchloric acid and heat DISCARD to strong fumes to expel volatile acids and r----EXTRACT AQUEOUS water. (Samples larger than 2 grams require I L additional amounts of perchloric acid to permit Cd Co Cu Fa Mn Ni Pb Sb S n Zn T i Mo Cr V W To. Mg SI Zr AI complete expulsion of volatile acids and water without the formation of difficultly soluble salts.) Cool. Rinse cover glass and beaker with EXTRACTON WITH 8-HYDROXYQUINOLINE AT pH 9.2 water and dilute to a t least 100 ml. Filter the dissolved salts through an 11-em. No. 40 Whatman paper which has a small amount of paper pul in the point'. Wash the residue thoroughly w i t t w m n 1% sulfuric acid. Transfer the DISCARD - -AQUFOUS EXTPACT paper and residue to a platinum crucible and burn off the paper. Cool the crucible. Add 2 or 3 drops each of sulfuric and hydrofluoric acids. Heat the crucible gently to volatilize silicon tet,rafluoride, and then cautiously. expel . the acids with strong heat. -BE_ LLLMfiLTLD =Y_A-C_UP_FE_RR_ONS_EPEP_AR.AZO-N .Idd potassium pyrosulfate in an amount just sufficient to ensure the complete fusion of the residue. (Potassium perchlorate will preAI cipitate in the separatory funnel if more than 2 grams of potassium pyrosulfat,e are present Figure 2 Schematic diagram for determination of aluiriinum as in diuing the extraction.) Fuse the residue until Procedure I1 clenr. Cool, and add approximately 25 ml. of water. Heat on an asbestos-covered hot plate until the melt has dissolved. If the insoluble residue was primarily alumina and/or silica, glass and beaker with \\atel and swirl contents of beaker to transfer the dissolved melt directly to a 250-ml. separatory dissolve soluble salts. Transfer the dissolved sample to a 1000funnel for the extraction of interferences and aluminum. If ml. volumetric flask, dilute to the mark with distilled water, large amounts of iron ( > l o mg.) were observed in the residue, and mix. If the diluted sample is not clear, filter a portion or electrolyze the dissolved melt in the mercury cathode with a let the solids settle to provide a sufficient amount of clear solution current of 10 amperes for 10 minute's. from which an aliquot may be taken. It is necessary to determine the aluminum content or equivalent Transfer an aliquot containing 10 mg. or less of the dissolvcd of the potassium pyrosulfate. Add to a platinum crucible an sample, but not more than 250 y of aluminum, into a 250-ml amount of pyrosulfate ( 1 mg.) equal to that which was used for separatory funnel, and dilute v i t h water to approximately 100 the fusion of the insoluble residue. Fuse and then cool. Disml. Add 2 ml. each of the tartaric acid and ammonium solve in approximately 25 ml. of water on an asbestos-covered acetate solutions. Follow with 5 ml. of perchloric acid and 12 hot plate. Transfer to a 250-ml. separatory funnel. mi. of ammonium hydroxide. (In another separatory funnel Dilute each of the dissolved melts to approximately 100 inl. prepare a similar solution of the reagents used for the extraction. and continue the analysis as prescribed in the procedure for aeid.4n extract must be obtained from this solution for use as a refersoluble .aluminum from that point where the tartaric acid and ence during the absorbance measurements.) Add 10 ml. of the ammonium acetate solutions are added to the separatory funnel. 8-hydroxyquinaldine solution and 30 ml. of chloroform. Shake Calculate the insoluble nlumininn content of the sample in the vigorously for 15 to 20 seconds to transfer interferences-i.e., follon-ing nixriner : 8-hydroxyquinaldinates of iron, copper, manganese, etc.-from the aqueous phase to the chloroform phase. Let settle; shake the funnel briefly to cause any floating chloroform to join the 2 1 , q - d,,,= (2) extract a t the bottom. Drain and discard the extract. Continue the extraction with 8-hydroxyquinaldine and chloroform where A ( * ) = absorbance of insoluble residue extract until the chloroform phase is a very faint clear yellow. (Smaller &4cVj= absorbance of pyrosulfate extract quantities of reagents may be used to complete the extraction -4 (z) = net absorbance of insoluble residue extract when the interferences have been substantially removed ) Extract undetectable traces of interferences and excess %hydroxyquinaldine with two 5-ml additions of chloroform. Continue the analysis according to Procedure I A, from that point where 3 ml. of the 8-h\-droxyquinoline solution is added to the wparatory funnel. where C = 203.6 X S = sample weight, grams
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DISCUS SI O h PROCEDURE I1
8-Hydroxyquinaldine, 8-hydroxyquinoline. Range, 0.100 to 10.O~oaluminum. This procedure is subject to interference from titanium, magnesium, niobium, thorium, uranium, zirconium, and cerium. However, a maximum of 1 mg. of titanium and 0.25 mg. of magnesium is permissible in the aliquot taken for extraction. -4 schematic diagram of the analytical procedure is shown in Figure 2 . Dissolve 0.2 gram of the saniple in a 400-ml. borosilicate glass beaker with 15 ml. of the dissolving acid. Heat gent1 to expedite dissolution. Add 10 ml. of perchloric acid and a &w silicon carbide boiling chips. Heat to heavy fumes of perchloric acid and continue to heat for 1 to 2 minutes to ensure the complete expulsion of volatile acids and x a t w . Cool. Rinse the cover
Application of Proposed Methods. Procedure I (which utilizes the mercury cathode) has been applied to a wide variety of standards (Tables V,VI, and VII), It has been applied also to a copper-aluminum alloy (99.5 Cu-0.4 Al); SAE 65 bronze (89 Cu-11 Sn-
