1809
V O L U M E 23, NO. 1 2 , D E C E M B E R 1 9 5 1 directed in the preceding method., will not vary b j more t h a n 1 0 . 2 unit among differrnt analysts 0.107 water solution of eriochromeEriochromecyanin R. cyanin R (Harleco-color index S o . 722) was used in this ~ r o r k without any attempt a t purification. Solutions prepared and stored in broJvn bottles gave very consistent values over a period of 0 months without any signs of deterioration. Even though straight-line calibration curves are not obtained, t h e curves have yielded satisfactory valucs over a period of a year without making any changes. The greatest handicap in the use of eriochromecyanin R is the dark color of t h e dye itself in t h e absence of aluminum A purer form of the dye (9) might give less color in the absence of aluminum and more nearly approach a straight-line calibration curve This K-as not investigated since t h e proposed method proved t o be very simple t o perform and was found t o be quite satisfactor? foi the Pmall amounts of aluminum being determined. CONCLUSION
A rapid and accurate mrtthod has been developed for t h e determination of small amounts of aluminum in zinc and steel using eriochromecyanin R. The technique of the method is simple enough for routine ube and the method is reproducible enough for research investigation. Elements normally present in zinc do not interfere m d intr,rfrlring elements normally prrwnt in
carbon steel are removed by the use of isopropyl ether followed by cupferron. ACKNOWLEDGiMENT
The permission of the Armco Steel Corp. t o present this information is gratefully acknoJv1edged by the authors. LITERATURE CITED
(1) Alten, F.,Weiland, H., and Knippenberg, E., Z. anul. Chem., 96, 91 (1934). (2) Eegriwe, E., Ibid., 76, 438-43 (1929). 13) Klinaer. P.. Koch, W., and Blaschczyk, G., Tech. Mitt. K r u p p Forschungsber., 3, 255 (1940). (4) Lundell, G. E. F., and Knowles, H. B., I d .
[email protected]., 18, 60 (1926). ( 5 ) Rauch, A., 2. anal. Chem., 124, 17 (1942). (6) Sandell, E. B., “Colorimetric Determination of Traces of hfetals,” p. 116-25, New York, Interscience Publishers, Inc., 1944. (7) Schemer, J. A., and Mogerman, hl. D., Bur. Standards J . Research, 21, 105 (1938). (8) Seuthe, A., Stahl u. Eisen, 64, 493 (1944); Brutcher Translation S o . 1739. (9) Thrun, 1%‘. E., ANAL.CHEM.,20, 1117 (1948). (10) Welcher, Frank J., “Organic Analytical Reagents,” Vol. 4, pp. 3 6 5 9 , New York, D. Van Nostrand Co., 1948. (11) Yoe, G. H., and Hill, 11.C., J . Am. Chcm. SOC.,49,2396 (1927) RECEIVEDMarch 30, 1961.
Presented a t t h e Pittsburgh Conference on Analytical Chemistry a n d Applied Spectroscopy, March 7, 1951.
Colorimetric Determination of Boron in Aluminum with 1,l-Dianthrimide D W 4 I S E 4. BREWSTEK Kaiser ..iluminic in c i n d Chemical Corp., Spokane, Wash. The determination of boron in aluminum is important in the evaluation of aluminum conductor materials and experimental wrought aluminum alloys. .i colorimetric procedure was developed that utilizes 1,l-dianthrimide as the color-forming reagent. Accuracy and precision w-ere found to be excellent when tested on several representative aluminum alloys. Results conipared falorably with values obtained by the mannite titration procedure and quantitative spectrographic anal>-sis. The method provides a simple, rapid, and accurate procedure
T
HE determination of t~oronin :iluniinum is iniportaiit in the evaluation of aluininuni conductor materials and experimental n-rought aluminum alloys. I n the only method generally recommended for determining boron in aluminum, boric acid is titrated with sodium hydroxide in the prePence of mannitol ( 9 ) . This procedure requires preliminary separation of the boron rither by distillation as methyl borate or by precipitation of most of the aluminum with carbon dioxide folloived by a final titration of the mannitol-boric acid complex with sodium hydroxide. The method is cumbersome in manipulation and time-consuming, and for the determination of small amounts of boron the accuracy is questionable. The procedure is not ad:~ptnhlefor large numbers of routine determinations. I n principle, a method that involves lengt,hy separation techniques is generally not as reliable and exact as a direct selective procedure. A colorimetric determination would appear to be advantageous.
that may be used to advantage for the routine determination of boron in aluminum. It may be applied to various aluminum materials without danger of interferences from major alloying elements. This method offers a distinct advantage over the usual mannite titration procedure, inasmuch as low amounts of boron may be determined. Boron present in amounts from 0,010 to 0.2207‘ has been successfully determined and this range may be extended in either direction by controlling the aliquot that i s taken for analysis.
Several colorimetric methods for boron in agricultural products have appeared in t h e literature and some of the most promising , \vxe investigated. The employment of curcumin (j)carmine S o . 40 1 . E ’ . (4),and quinalizarin ( I ) a s color-forming reagents were not adaptable t o this problem because of relative insensitivity, interference of aluminum, and interference due t o ahsorption by excess reagent. The reagent most suited for the author’s purpose and the one chosen for the described method was 1,l-dianthrimide (1,l’dianthraquinoylamine), which has been reported by Ellis, Zook, and Baudisch (3). The purpose of the present work was t o develop a colorimetric method for the determination of boron in aluminum alloys based upon the color change (greenish yellow t o blue) of 1,I-dianthrimide in concentrated sulfuric acid medium. REAGENTS AND APPARATUS
Standard boron solution, 0.5715 gram of C.P. orthoboric acid diluted t o 1000 ml. This gives a concentration of 100 micrograms of boron per nil.
1810
ANALYTICAL CHEMISTRY
1,l-Dianthrimide, A stock solution of the dye is prepared by dissolving 400 mg. in 100 ml. of concentrated sulfuric acid. The working solution is prepared by diluting 5 ml. of the stock solution to 200 ml. with concentrated sulfuric acid. While the stock 1,l-dianthrimide solution is stable for several months if stored in the refrigerator, best results are obtained when this solution is not over 2 or 3 weeks old. This compound may be purchased from the Dajac Laboratories, 3430 West Henderson St., Chicago 18, Ill. Calcium hydroxide c.P., saturated lime water. Triacid mixture, 750 ml. of water, 250 ml. of sulfuric acid, 300 ml. of hydrochloric acid, and 300 ml. of nitric acid. Borodicate glass beakers, volumetric flasks, and pipets. Model DU Beckman spectrophotometer equipped with 1-em. cells.
amounts of boron preadded and those found, along with the per cent recovery, are tabulated in Table I. The average recovery was 104.3%. The concentrations of the alloying elements normally found in aluminum alloys had no apparent effect on boron recovery and could, therefore, be disregarded as a source of interference. The amount of boron found was either the same or slightly greater than the amount added. This would indicate that boron is not lost as volatile compounds such as boron hydride or boric acid during initial solution of the sample. Colorimetric boron values obtained on several aluminum alloys as compared t o mannite titration ( 2 )values are listed in Table 11. The greatest difference between the two methods was 0.01% and the average difference was 0.0065%.
PROCEDURE
Tenth-gram samples are weighed into 100-ml. beakers and 5 ml. of saturated lime suspension are added. After solution of the material in 5 ml. of the triacid mixture, the solutions are transferred to 100-ml. volumetric flasks and diluted to volume with distilled water. Two-milliliter aliquots are taken from the 100-ml. volume and pipetted into 100-ml. beakers. F3r samples that are lower than 0.01% boron, a larger aliquot may he taken. Two milliliters of concentrated sulfuric acid are added and the solutions are heated to fumes, care being taken that solids do not separate out. j.0
Table I.
Recovery of Boron Added to Aluminum Alloys Principal Slloying Constituent
TYP? of Aluminum
Boron Added
Boron Found
25 3s
14s 14s 24s 525 52s 72s 75s Av. recovery
Commercially pure Mn CU cu C u a n d hIg M g hIg Zn Zn and J f g
Recovery
M Q.
MQ.
%
0,050
0,052
104
0.050 0.010 0.100 0.050 0.100 0.150 0.050 0.050
0.050 0.010 0,100 0,056 0.104 0.158 0.053 0.054
100 100
100
112 104 105 106 10s 104.3
0.8
Table 11.
Determination of Boron in Aluminum Pig
Sample
0 6
hfannite Method
1,l-Dianthrimide hZethod
%
%
0.022
0.018
0.045
0,055
0,220
0.220
1
0.4
n nan
Difference
-n nn4
=k0.0065
Av. difference
0
4
2
3
4
5
6
7
8
Figure 1. Optical Density us. Boron Concentration Beckman spectrophotometer, 620
mp
The samples are allowed to cool for a few minutes and then placed in an oven operating a t 90" C. Five milliliters of freshly prepared 1,l-dianthrimide reagent are added and the samples are heated for 3 hours to obtain maximum color development. The temperature of the oven should be carefully controlled, as at 80" C. about 5 hours are required for maximum color development and if the temperature exceeds 90' C., destruction of the color is likelv to occur. After cooling, the solutions are transferred to 10-ml. volumetric flasks and diluted xith concentrated sulfuric acid. A calibration curve is prepared from synthetically prepared samples containing 0.1000 gram of boron-free aluminum and known quantities of boron. Convenient concentrations of boron in the standards were found to be: 50,100,150,200,250,300,350, and 400 micrograms per original 100-ml. dilution. .A blank is prepared from boron-free aluminum. The standard samples along with the blank are carried through the entire procedure simultaneously with the unknowns. h typical calibration curve is shown in Figure 1. The optical density of the standards and samples is determined with the Beckman spectrophotometer, using the blank as a reference solution. Maximum absorption is a t 620 mu. A slit opening of 0.08 mm. is employed.
Comparative data obtained by the described colorimetric method and a spectrographic procedure employing -4RL equipment are presented in Table 111. I n this case, the greatest difference between procedures was 0.005% and the average difference was 0.0016%. An idea of the precision of the method may be formulated from the examination of the data presented in Table IV. Four aluminum pig samples were analyzed for boron, the determinations being made in quadruplicate. The average deviation from the
Table 111. Sample
Spectrographic hlethod
1,l-Dianthrimide Jf et hod
%
%
0.026
0,024 0.035 0,040 0,054 0.059 0.060 0.095 0,008 0,025
1
2 3
0.040 0,038 0.050 0,058 0.060 0.095 0 007 0.025
4
6 7 8 9 Sv. difference
Table JF'.
RESULTS AND DISCUSSION Sample No.
The recoverv of boron added to a series of six wrought aluminum alloys was tested. Known quantities of the standard boric acid solution were added to 0.1-gram samples of the alloys and the boron was determined by the described method. Each alloy was assayed for boron before the boric acid solution was added and this value was subtracted from the final results. The
Determination of Boron in Aluminum Pig Difference
70 -0.002 -0.005 +a. 002 f0.004 +0.001 0 000 0.000 +o ,001 0.000 f0.0016
Precision of JIethod
No. of Determinations
Average Boron Found
4 4
0.057 0.025
Range, % Minimum Maximum
% 1
2 3 4 Total av. deviation
4 4
hverage Deliation from Mean
70
0.021
0.056 0,027 0.021
0.099
0,095
0.059 0.030 0.023 0.103
fO.OO1O +0.0010 zkO.0007
rtO.0040 rt0.0016
1811
V O L U M E 2 3 , NO. 1 2 , D E C E M B E R 1 9 5 1 mean values ranged from iz0.0007 t o *0.0040%. Results may be duplicated on the same sample with an average precision of about zkO.0016%. Some of the observations of others (5’) regarding the nature of the reagent have been confirmed. Thus a t 90” C. maximum color developed after 3 hours, while a t 80” C. a t least 5 hours were required. The colored complex is stable for a t least several hours. The e~clusionof moisture from the reaction medium is necessary. Although this situation is not ideal, it did not present any serious difficulties. The reagent is both selective and sensitive t o boron and a maximum concentration of 10 micrograms of boron per 10 ml. should not be exceeded in the solution used for final photometric measurement. The normal time required t o complete a determination is approximately 4 to 5 hours. CONCLUSIONS
1,l-Dianthrim:de may be used as a colorimetric reagent for the determination of boron in aluminum alloys. The average recovery of added boron from representative wrought aluminum alloys v a s 104yob. This indicates that the
method may be applied t o various aluminum materials without danger of interferences from major alloying elements. Boron was not lost by volatilization during initial solution of the sample. The colorimetric procedure gives results that compare favorably with the mannite titration method ( 2 ) and quantitative spectrographic techniques a s applied in this laboratory. The average difference in values for boron determined by the mannite and colorimetric methods is zk0.0065% for aluminum alloys containing from 0.0220 t o 0.2200~0boron. This difference is dewhen the colorimetric method is compared creased t o =t0.0016~0 to results obtained by spectrographic analysis. Results may be duplicated on the same sample with a precision of about +0.0016 %. LITERATURE CITED
(1) Berger, K. C., and Truog, E., IND.EKG.CHEM.,ANAL. ED.,11,
540-5 (1939); Soil Sci., 57, 25-31 (1914). (2) Churchill, H. V., “Chemical Analysis of riluminum.” 3rd ed., p. 30, Pittsburgh, Pa., Aluminum Co. of America, 1950. (3) Ellis, G. H., Zook, E. G., and Baudisch, O., ANAL.CHEM.,21, 1345-8 (1949). Hatcher, J. T., and Kilcox. L. V.. I t i d . , 22, 567-9 (1950). ( 5 ) Naftel, J. A., IND.EKG.CHEXI..- 4 h - a ~ ED.. . 11, 407-9 (1939). (4)
RECEIVEDd p r i l 16, 1951.
Fractionation of Lanthanum-Cerium(Ill) and Lanthanum-Praseodymium Mixtures By Precipitation f r o m Homogeneous Solution LOUIS GORDON AND R. A. BRANDT, Syracuse University, Syracuse, N . Y., LAURENCE L. QUILL AND MURRELL L. S..ILUTSICY’, Kedrie Chemical Laboratory, Michigan State College, East Lansing, JMich. A comparison is made of the efficiency of homogeneous and heterogeneous fractional precipitation methods using standard lanthanum and cerium mixtures. In the conventional method for the fractional p;ecipitation of rare earth oxalates, oxalic acid is added directly to a rare earth solution. Heterogeneous precipitations of this type are not so efficient as methods in which the precipitant is homogeneously produced within the solution. In
T
HE principle of precipitation from homogeneous solution
( 2 , 7 ) has been successfully employed in the fractional separation of pairs of similar chemical elements, such as zirconium and hafnium as phosphates ( 8 ) and praseodymium and lanthanum as carbonates ( 4 ) . This principle is utilized in this investigation for the fractional separation as oxalates ( 1 , 3, 9) of lanthanum and praseodymium and of lanthanum and cerium. A comparison is made of homogeneous and heterogeneous precipitation methods using lanthanum and cerium mixtures. Because the solubility differences of rare earth oxalates (6) are very slight, local interference is unavoidable and a poor separation is obtained when oxalate ion is added directly t o a rare earth solution. If the reagent is added internally by the hydrolysis of dimethyl oxalate, this interference is reduced and the separation per fractionation step is improved. The precipitation of rare earth oxalates (11 = rare earth) from a chloride 1 Present address, I\lound Laboratory, .\Tonsanto Chemical Co., Miamisburg, Ohio.
this investigation rare earth oxalates are precipitated from homogeneous solution by the addition of oxalate ions internally through the hydrolysis of dimethyl oxalate. For the experimental conditions described, 10 fractionation steps by the homogeneous method are equivalent to 17 steps by the heterogeneous method. The homogeneous method is more efficient as a greater yield of product of desired purity is obtained with fewer fractionation steps.
solution hy the hydroll-sis of dimethyl oxalate is shown by the following reaction: 211CI3
+ 3(CH,)sCiOi + 6HOH +
+
hf,(c,o,)3 6CHaOH
+ 6HC1
EXPERIMENTAL
Three procedures were used in this investigation: Procedure -4 for the lanthanum-praseodymium mixtures, and Procedures B and C for lanthanum-cerium mixtures. Dimethyl oxalate was used in Procedures A and B as a n internal precipitating reagent, whereas oxalic acid was added directll- in Procedure C. Procedure A. Five grams of a mixed oxide of lanthanum and praseodymium were converted to a chloride mixture and then dissolved in 600 ml. of 1 N hydrochloric acid. A solution containing 2.8 grams of dimethyl oxalate dissolved in 400 nil. of 1 N hydrochloric acid was added to this rare earth chloride solution a t a rate of 1 drop every 2 t o 3 seconds. The reaction mixture was stirred continuous1,y during the addition of t,he ester solution and for 1 hour afterwards. Under these conditions
