V O L U M E 21, N O . 1 2 , D E C E M B E R 1 9 4 9
1521
Table 111. Standardization of Thiosulfate
perchloric acid only as the solvent. The addition of bromine water is unnecessary when perchloric acid is used.
Deviation from
SO.
1 2
3 4
5b 6b
7b 8b
Cll ?iarS?Oi cu Average Gram .MI. G./Z. R hletallic Copper" Dissolved in Perchloric Acid 0,1618 34.48 4.693 -0.002 0.1711 36.44 4.655 *0.000 0.1773 37.75 4.697 t0.002 0.1684 35.85 4.657 -c0.002 0.1732 36.90 4.694 -0.001 n.mo 34.69 4.695 f0.004 0.1725 36.81 4.697 f0.002 0.1675 36.65 4.698 +0.003 .4v.4 . 6 9 5 0.002
Resublimed Iodine Iodine Gram 0.4167 0.4194 0.3966 0,4054 0.4112
-0,005 4.690 4.688 f0.003 4.693 -0,002 4.694 -0.001 4 4.702 +0.007 Av. 4 . 6 9 5 0,004 a 4verane of three electrodeposition analyses 100.003% (see Table 11). b i 0 ml.-of Bi-2 water added after dissolving, 50 ml. of Hz0 added, boiled 10 minutes. 1
2 3
44.60 44.81 42.33 43.25 43.80
acid treatment and digesting for 1.5 hours. During this period the nitric and perchloric acids were driven off; thus the later portion of the digestion took place with boiling concentrated sulfuric acid. After cooling, water and bromine-water were added and the solution was boiled for 10 minutes and titrated (Table I). The average of four determinations varied only 2 parts in 4613 from the average of eight determinations using
APPLICATION OF iMETHOD TO PURE COPPER
The thiosulfate was standardized against metallic copper dissolved with perchloric acid and also resublimed iodine to show that the perchloric acid method gives stoichiometric results. The copper metal was analyzed for purity by electrodeposition (Table 11). I n the thiosulfate standardization process metallic copper was dissolved and titrated under the same conditions as the ore sample. The metal dissolves somewhat more slowly than copper ore. The data presented in Table I11 include four solutions that were treated with bromine water and four that were not. Unusually precise results were obtained. It is apparent that the copper is in the cupric state after the perchloric acid digestion, inasmuch as the bromine water treatment did not alter the results. The standardization of the thiosulfate solution was checked against iodine and the data given in Table 111show that both methods give the same results. LITERATURE CITED
(1) Ciowell, Hillis, Rittenberg, and Evenson, ISD. E s c . CHEM., ANAL.ED.,8, 9 (1936). (2) Crowell, Silver, and Spiker,Ibid., 10, 80 (1938). (3) Crowell and Spiker, Ibid., 12, 147 (1940). 60, 1349 (1938). (4) Foote, J . Am. Chem. SOC., (5) Foote and Vance, I b i d . , 57, 845 (1935); IND.EVG CHEM., ANAL.ED.,8, 119 (1936); 9,205 (1937). (6) hfott, Chemist-Analyst, 1912, Xo. 5.5-7. (7) Parks,IND.ENG.CHEM.,ANAL. ED.,3 , 7 7 (1931). (8) Smith and Getz, Ibid., 9, 378 (1937).
RECEIVED April27,1949.
Iron in Aluminum Alloys Colorimetric Determination Using 1,lO-Phenanthroline J. A. RYAN AND G. H. BOTHAM, The A.P.V. Company, Ltd., London, England A study of several factors influencing the determination of iron in aluminum alloys containing copper, nickel, and zinc by means of 1,lO-phenanthroline is presented. A precise and accurate method which avoids interference by the above elements is detailed.
T
HE colorimetric determination of iron in aluminum alloys is
usually carried out by employing the thiocyanate reaction. Recently, however, two methods have been published (2, 6 ) , based upon the color reaction of ferrous iron with 1,lO-phpnanthroline. Such a method has been in use in this laboratory for some time. Although l,l0-phenanthroline has greater sensitivity and greater stability of color than thiocyanate (7), and it follows Beer's law more accurately, the reagent is expensive and its use renders analysis considerably slower than the thiocyanate method in some cases. For routine use the 1,lO-phenanthroline method has proved inferior in the authors' hands to the thiocyanate method, but it may be used to advantage when a check on the latter is desirable, or in special cases such as the estimation of iron in pure aluminum. PRELIMINARY ATTACK ON ALLOY
To incorporate the use of l,l0-phenanthroline for the determination of iron in a concise scheme of analysis, the method of attack upon the alloy must produce a final solution which has the maximum freedom from elements known to interfere in the 1,10phenanthroline reaction and a t the same time contains as many of
the other elements to be determined as possible. The concentration of elements present in commonly occurring aluminum alloys likely to interfere has been determined by Fortune and Mellon ( 4 ) . Alkaline Digestion to Remove Aluminum, Silicon, and Zinc. Although this method succeeds in removing silicon and zinc, it is nevertheless very unsatisfactory. Variable proportions of iron dissolve in the caustic alkali; this is particularly marked for aluminum alloys containing high proportions of silicon, doubtless because of the high concentration of alkali needed in such cases. Thus, one alloy of 0.41% iron and 11.570silicon content gave only 0.02, 0.03, 0.06, 0.03, and 0.05% iron after digestion in sodium hydroxide. The hydrazine hydrate method of Bartram and Kent (3) was tried, but not only was appreciable iron dissolved by the strong caustic solution but it was extremely difficult to obtain complete recovery of manganese. The solubility of these elements in sodium hydroxide has been noted (1). Solution in 1 to 1Hydrochloric Acid. This method was used by Pepi (6),who claims that hydrochloric aaid attack prevents the solution of copper, bismuth, and silicon, the elements he had found to interfere with the iron determination. Such a method of attack has several disadvantages. It precludes the possibility of determining manganese and copper in a composite scheme, and it
ANALYTICAL CHEMISTRY
1522 introduces all the zinc present in the sample into the solution. Furthermore, the authors are unable to agree with Pepi that no cspper is taken into solution. When this method of attack was used, large and variable amounts of copper were found in the acid solution-in one case as much as 16 p.p.m. of copper in the solution in which the iron color was to be developed. Digestion with Mixed Acids. Digestion of the alloy in a mixture of sulfuric, nitric, and hydrochloric acids completely decomposes the alloys and on fuming produces final solutions that are free from silicon and chloride. All the zinc is taken into solution, but the effect of zinc can be successfully overcome. It was feared that this method would lead to production of final solutions having an erratic pH, but experience showed that solutions were produoed lying well within the prescribed p H limits given below. The procedure adopted to bring an alloy into solution is given under the heading Complete Method. The instrument used throughout this work was Hilger’s Spekker absorptiometer.
Table 111. Effect of Nickel Concentration on Rate of Fading Tinie Min 15
45 180
15 hor1r
Fe and Ni Concentrations i n Color Solution, P.P.M. 1 2 3 4 5 6 F e 1.13 F e 2.13 F e 3.13 Fa 4.13 F e 5.13 F e 6.13 Ni 10.20 Ni 10.20 Xi 10.20 Ni 10.20 S i 10.20 Xi 10.20 100 100 100 100 100 100 100 100 100 94 97 97 91 87 93 91 95 87 40 35 36 41 37 40 g H = 2.95. Temp. = 16’ C.
Table IV. Effect of pH and Temperature on Rate of Fading Solution
pH
1
2.15 2.90
Temp., C. 15 81 15 31
’
3 78 79 97 90
7 94 61 98 83
Time, Minutrs 15 25 96 100 55 30 100 100 73 49
30 96
I00 47
45 90
96
40
FACTORS INFLUENCING THE DETERMINATION
Choice of Filter. In view of the finding of Fortune and Mellon ( 4 ) that the nickel ion produces a change in hue of the iron1,lO-phenanthroline complex, the filter chosen for use in this determination was the Ilford green (604), for which the maximum absorption is a t 520 mp. Effect of pH. Pepi (6) has stated that in the analysis of aluminum alloys the pH of the color solution need not be regulated too closely, but color development is slow below p H 2 and reduction slow above pH 3. I t seemed necessary, therefore, to explore the influence of pH on color development. For this purpose astandard alloy was digested and a stock solution obtained. Details of the standard alloy, stock solution, and color solution are given in Table I. Five-milliliter aliquots were taken from the stock solution, a t which point it is 1 N in acid, reducing agent was added, and the solutions were buffered t o various pH’s by the addition of varying quantities of sodium acetate solution. The volumes were made up to 90 ml. with distilled water, 5 ml. of 1,lO-phenanthroline solution (0.2%) were added, and the volumes were adjusted to 100 ml. with distilled water. All pH measurements were made by the glass electrode. Table I1 records the percentage iron recovered a t stated intervals of time and the influence of pH upon recovery, a t 18°C.
At pH values below 2.4 and above 3.5, color development was slow. Above pH 3.8 aluminum hydroxide tends to precipitate from the solution. For complete color development the optimum pH therefore lies between 2.9 and 3.5, and a reading can be taken a f b r 10 minutes’ standing. Slow color development can be corrected by the addition of uneconomical amounts of 1,lO-phenanthroliie. AE a solution of hydroxylamine hydrochloride deteriorates on standing, it must be freshly made up or its acidity adjusted before me.
Composition of Stock Solution of Alloy
Table I. Element % in alloy Mg./hter i n atock soh. P.p.m. in color solution, 5-ml. aliquot
Table 11. PH 2.10 2.40 2.66 2.88 3.10 3.52 3.86
Cu 3.20
Fe 0.80
Ni 0.22
Zn 0.16
,.
80
22
16
4
1.1
0.8
M g - M n Ti Si 0.05 0 . 3 8 0 . 0 2 4.85
..
5
38
2
0.25
1.9
0.1
Effect of pH on Rate of Color Development 5 Min. 50 64 96 97 98 98
88
10 Min. 61
89 98 100 100 100
aa
15 Min. 72 94 100 100 100 100 90
30 hfin. 83 100
100 100 100
100 92
Effect of Temperature. Experiments carried out a t pH 2.15 showed that increase of temperature has little effect upon color development in this particular case, and is unable to accelerate the complete formation of the complex a t p H well below the optimum Effect of Nickel. During the work the present authors observed repeatedly that solutions containing a high nickel content faded in color upon standing. This phenomenon is illustrated by data obtained from a Light Metal Founders’ Association standard Y alloy having the following composition: copper 4.25, nickel 2.04, manganese table color
100 100 100 100 100 100 100 100 100 100 100 100 100 100 100
100 100 100 100 100 100 100 100 100 100 100
100 100 100 100 100 100 100 100 100 100 100
100
ion
100 100 100
97 100 100
98 100 100 98 100 100 98 100 100 96 100 100 93 100 100
98 100 100 96 100 100 96 98 100 93 100 100 90 100 100
95 97 100 94 98 100 93
95 100 89 96
100 83 96 loo
72 83 100 73 82 100 70 83
100 48 73 io0 41 76 100
Pyrex beaker. Boil t o complete solution, and then take down to fuming. Fume gently for 5 minutes, cool, wash down the sides of the beaker, and dilute t o about 60 ml. with distilled water. Boil until salts are dissolved, and filter off the bulk of the insoluble material using suction. Wash the filter with hot water and pass hydrogen sulfide through the filtrate €or 5 minutes. Filter off copper sulfide on a Whatman Yo. 31 paper, and wash well with hydrogen sulfide water slightly acidified with sulfuric acid. Reserve the residue for copper determination. Boil the filtrate down t'o about 80 ml., cool, make up to 100 nil. in a graduated flask, and mix well. Pipet a 5-ml. aliquot into a 100-ml. graduated flask, and add 5-ml. aliquots of hydroxvlamine hydrochloride (20 grams per liter) and sodium acetate (84 grams of anhydrous salt per liter). Make u p t o 80 ml. with distilled water and either ( i r 1 add sufficient l,l0-phenanthroline (0.2%) to satisfy the antivipated requirements of iron and zinc-i.e., ([Fe]) X 9.6 X 1.5) ([Zn] X 2.0)-and read at the end of 10 minutes at, 18" C., or ( b ) add sufficient reagent, to satisfy the requirements of iron, nickel, and zinc-Le., ([Fe] X 9.6 X 1.5) ([Znl X 2.0) 4- ([Nil X 9.2). I n this case a reading cttn be taken at anv t,ime after 10 minutes' standing at any room tc.niperature up t o 31 C.
+
+
ACCURACY OF ~
I METHOD E
te the accuracy and reproducibility of the method, standard alloys n-rre analyzetl by two unskilled assistants who had no previous experience rvit,hthe method. Assistant 1 was given a sample of D T D 421, which h ~ been d standmliaed by t \ V < J independent analysts, and assistant 2 w a s given a Light &Metal Founders' Sssociation standard Y alloj-. Each assistant ?:wried out siy determinations: LtTD 424 Analysis
Fe, 7c
Firm .I Firm B
0.80 0.80
.4v. 0.801 a = 1 0 003
Y L.11.F.A. 0.225
* 0.01
Alloy .Analysis
Assistant 2
0.224 0.228 0.231 0.228 0.225 0.323 Av. 0.226 i = 1o.on3
In both cases all the results fall within a range about the average of less than 28, so the precision is high. Compared with independent analyses which are assumed to he true figures, the results obtained show the accurac'y of the method is also high. CONCLUSIOYS
If certain requirements are fulfilled, 1,lo-phenanthroline is a satisfactory reagent for the determination of iron in aluminum alloys. The optimum pH range is 2.9 to 3.5. At pH less than 2.9, color development 1s slow and increase of temperature to 31 C. causes no deceleration. A large excess of 1,lO-phenanthroline corrects this slow development. For stable color development sufficient reagent must be added to allow for the formation of both nickel and iron complexes. Providing pH and temperature are correct, only sufficient 1,lQphenanthroline need be added to satisfy the requirements of iron if a reading is taken a t the end of 10 minutes and not later. The effect of zinc can be overcome by adding an additional amount of reagent equivalent to 2 0 times the zinc concentration a t 18" C., or 1.5 times a t 31 'C. The order of addition of reagents has n o significant effect ACKNO WLEDGMEhT
The authors gratefully acknowledge the helpful criticism and encouragement of Richard Seligman and G. .4. Dummett during the
1524
ANALYTICAL CHEMISTRY
course of this work. They are also grateful to the directors of The A.P.V. Company, Ltd., for permission to publish. LITERATURE CITED
(1) Aluminum c0. of *irnerica,~~Chernical ~ ~of A ~~ ~ ~ l 1441. (2) A l ; i & n Research Institute, Chicago, Ill., “Analytical Methods for Aluminum Alloys,” 1948.
~
(3) Bertram, J. H., and Kent, P. J. C . , Meletallurgia, 1946, 179-81. (4) Fortune, W. B., with Mellon, 34. G., I N D . ENG. Cmiv., ASAL. ED..10. 60-4 (1938). (5) Goodman, K ’ . , - ~ ~ A L . ’ C H E19, M 141-2 ., (1947). (6) Pepi, M. S.,I IND. ANAL.ED.,18, 111-12 (1946). ~ ~~ , ~ * i ESG.CHEM., ~ (7) Woods, J. T., with Mellon, M. G., Ibid., 13, 551-4 (1941). RECEIVED December 27, 1918.
Spectrophotometric Determination of Sulfaquinoxaline Its Application to Poultry Feeds and Feed Premixes JAMES P. DUX AND CHARLES ROSENBLURI, Merck & Co., Znc., Rahway, N . J . The suitability of the Bratton-Marshall color reaction as the basis for a spectrophotometric assay of sulfaquinoxaline was investigated using iV-(1naphthyl)-ethylenediamine dihydrochloride as the coupling agent. Because a nonlinear relationship between concentration and color intensity obtains in the adopted procedure, extinction coefficients were determined at several concentrations. The effects of acidity and salt concentrations on the color
S
ULFBQUISOXALINE (15) (2-sulfanilamidoquinoxaline) has been found (2, 5, 5, fa) to be an effective chemotherapeutic agent, for the prevention and control of certain poultry diseases. Being a sulfonamide in which sulfanilic acid is condensed with 2-aminoquinoxaline, it shoa s the typical color reaction that is the basis of the assay method proposed- by Marshall (1, 8-11) and colleagues for sulfanilamide and related compounds. The color is generated by diazotization of the free arylamino group and coupling with a suitable agent. Of the large number of coupling agents examined (I), N-(1-naphthyl)-ethylenediamine dihydrochloride was cited by Bratton and Marshall as the most satisfactory. The present authors have studied this reaction spectrophotometrically in the ca8e of sulfaquinoxaline and find that, despite the many factors that influence the color intensity, it may be made the basis of an analytical method. The resulting colored compound has the same yisible absorption spectrum as the azo dye obtained from sulfanilamide ( I ) , exhibiting a characteristic band a t 545 mp. The method was tested with a number of sulfaquinoxaline samples of known purity and was applied to mixtures with inorganic diluents. An extension to mixtures of sulfaquinoxaline with an organic diluent, such as poultry feed, which requires extraction of the sulfonamide is also described. SPECTROPHOTOMETRIC STUDY
Reagents. The following aqueous reagents were employed in this investigation: 0.02 N and 0.50 AT solutions of hydrochloric acid, 0.5 N solution of sodium hydroxide, 0.1% solution of sodium nitrite, 0.5% solution of ammonium sulfamate (La Motte ‘‘purestandardized”), 0.1% solution of N-(1-naphthyl)-ethylenediamine dihydrochloride (Eastman Kodak), and sodium chloride. Unless otherwise stated, Merck reagent grade chemicals were employed. The coupling agent was stored in a dark-colored glass bottle to avoid photodeterioration. Fresh sodium nitrite solution waa pre wed daily. The concentrabion of the 0.50 N acid had to be regukted fairly accurately because p H control was necessary for reproducible color production.
intensity w-ere also investigated, and optimum conditions for color formation recommended. The method was applied to sulfaquinoxaline samples of known purity, to certain of its salts, to mixtures with inorganic diluents, and to medicated poultry feeds and feed premixes. In the use of the feed mixtures, convenient sample sizes and dilution schedules are suggested for handling mixtures containing up to 15% of sulfaquinoxaline.
Procedure. The conditions for color formation were studied with a sulfaquinoxaline preparation, the purity of which was 99.8% as determined by solubility analysis (7, 14). Elementary analysis of this standard compound showed 56.29% carbon, 4.29% hydrogen, and 18.86% nitrogen compared to the calculated 55.96% carbon, 4.037, hydrogen, and 18.66% nitrogen; the meltingo oint, with decomposition, of the standard was 248.2-248.5 compared to a reported value (16)of 247-248” C. Extinction coefficients and the effect of factors that might influence the color formation were studied a t a series of sulfaquinoxaline concentrations ranging from 0.05 to 0.35 mg. per 50 ml. In a typical series of experiments, about 25 mg. were weighed (microbalance) into a 250-ml. volumetric flask containing 50 ml. of 0.5 N sodium hydroxide, and the resulting solution of the sodium salt of sulfaquinoxaline was diluted to volume. Appropriate portions of this stock preparation were diluted with water to yield solutions containing 0.5, 1.0, 1.5, 2.0, 2.5, and 3.5 mg. of sulfaquinoxaline per 50 ml., and 5-ml. aliquots of each were transferred to individual 50-ml. volumetric flasks for color formation. These aliquots, containing =0.05 to 0.35 me. of alkali and 0.05 to 0.35 mg. of sulfaquinoxaline, were just neutralized to phenolphthalein by addition of 0.02 N hydrochloric acid, after partial neutralization of the more alkaline solutions of a series with 0.5 A’ acid. Although the procedure finally adopted for routine analyses utilized less alkali, thereby obviating any need for this neutralization step, it was retained throughout the spectrophotometric investigation to permit proper acidity control a t the diazotization and coupling stages of the color development. To each of the neutral solutions were added in succession 5 ml. each of 0.50 N hydrochloric acid and 0.1% sodium nitrite solutions, After standing for 3 minutes, 5 ml. of 0.570 ammonium sulfamate solution were added. Finally, after an additional lapse of 2 minutes, 5 ml. of the 0.1% solution of coupling agent were added, and the flask contents were diluted to volume. The contents of the flasks were swirled to ensure mixing after each addition of reagent. The final pH of these diazotized and coupled sulfaquinoxaline solutions was 1.3 to 1.4. The red color developed rapidly to maximum intensity and could be measured 30 seconds after coupling. Except a t the highest concentrations involved, the color was stable for several hours. At the highest concentrations (0.25 to 0.35 mg. per 50 ml.) the color tended, to fade slowly owing to precipitation of the azo dye, a t a rate which the authors believe to be influenced by acidity. Under the conditions recommended herein, this effect amounted to 2 to 3%
8.
