decreases with increase in ammonium citrate concentration. I n subsequent testy 10.0 ml. of 20y0 ammonium citrate solution were used. Addition of Indicator. Neutral red does not absorb light a t 595 mp, hence no effect on the absorbance could be observed using varying amounts of indicator. Two to four drops of 0.05y0 neutral red indicator were used in subsequent tests. Effect of pH. Different amounts of 10% sodium hydroxide solution were added after neutralization. Amounts between 0.5 and 1.5 ml. had no significant effect, but amounts under 0.5 or over 1.5 ml. of this reagent depress the color development of the complex: the addition of 5 ml. of 10% sodium hydroxide had such a depressing effect that full color development was not achieved before 15 minute9 . The color of the complex develops rapidly in the presence of 0.5 to 1.5 ml. of the reagent. Therefore, an e x e s s of 1 ml. of 10% SOdium hydroxide solution was added in subsequent tests, the p H being about 9.0; full color development is achieved within 3 minutes. KO significant variation in absorbance occurs when different amounts of sodium borate buffer solution are uqed. Tests were performed in the range of 2 to 15 ml. of this reagent, and the p H of the solutions ranged from 8.9 to 9.1. The amount of 5 ml. of the buffer solution was used in subsequent teqts. Biscyclohexanone Oxalyldihydrazone Reagent. KO effect in t h e absorbance was observed by using dif-
suitable for determining copper in the ferent amounts of this reagent. d range 0.003 to loyo. The method is 25-fold w,/w. (biscyolohexanone oxalylselective; interference of iron and dihydrazone-copper) excess is necessary titanium can be overcome by using a for full color development. An amount smaller aliquot of the sample solution. of 2 ml. of this reagent was used in most A single determination can be carried of the subsequent tests. The reagent is out within 30 to 40 minutes, while for stable over a period of at least three routine batch-analysis purposes 25 to 30 months. determinations can be performed in 8 Stability of Color. T h e color of t h e hours by one analyst. organo-copper complex is stable for a t least 5 hours; the value of absorbance decreasing only slightly after ACKNOWLEDGMENT this period. Satisfactory results were The author thanks R. K. Rush for still obtainable after a standing time of helpful assistance. 15 hours. Effect of Temperature. T o check t h e method under extreme conditions, LITERATURE CITED measurements of absorbance were (1) ASTlI Standards, Part 32, 1956, p. performed at temperatures ranging from 498. 5’ to 35’ C. No significant variation (2) Crawley, R. H. A., Anal. Chim. Acta on the absorbance was observed. 13. 373 (1955). Interference. =Iluniinum, arsenic, (3) Haywood, L. J. A., Sutcliffe, P., Analilst 81, 651 (1956). bismuth, calcium, cadmium, lead, (4) Nilsson, G., d c t a Chem. Scand. 4, 205 magneqium , molybdenum , phosphorous, (1950). antimony, silicon, tin, and zinc do not ( 5 ) Sandell, E. B., “Colorimetrir Deterinterfere. I n the range of up to 1 0 ~ o , mination of Traces of Metals.” 2nd ed.. 1-01. 111, p. 304, Interscience, ’New York the presence of chromium, nickel, and and London, 1950. manganese has no significant effect. (6) Somers, E., Garroway, J. L., Chem. The color of the copper-organo complex Ind. (London), 1957, 395. develops slowly if titanium is present (7) Wetlesen, G., Gran, G., Svensk Papperstid. 52, 212 (1952). above l % , while the presence of 10% of (8) Williams, T. R., Morgan, R. R. T., titanium completely inhibits color deChem. Ind. (London) 1954, p. 461. velopment. Iron above 1% causes a (9) Wood, I).F., Clark, R. T., Analyst 83, sharp decrease in absorbance, but this 509 (1958). can be overcome by taking a smaller R. K. ROHDE aliquot of the test solution. W.Brown & Sons (T‘ic.) Pty., Ltd. Nan-Ferrous 3letals Division CONCLUSIONS Brooklyn Works Melbourne, Australia The proposed method offers a rapid PERMISSION to publish this paper was and reliable procedure for a variety of given by the directors of W. Brown & Sons nonferrous metals and alloys and is Proprietary, Ltd.
Determination of Sulfur in Inorganic Sulfides Using O x y g e n Flask Com bustion SIR: We wish to report a method for the decomposition of several inorganic sulfides. The procedure developed is simple and the equipment required is inexpensive. The method should be especially quitahle for laboratories doing an occaqional sulfide analysis and should also prove valuable for routine analysis where combustion equipment is not available. The results obtained with several inorganic sulfides are reported in thic: paper. I n the procedure developed, the sulfide sample is mixed with a combustion mixture and is burned in an atmosphere of oxygen in a closed flask. The SOz and SOa formed during the combustion are absorbed in dilute hydrogen peroxide to form sulfuric acid. The apalysis of the sulfate is completed by either the usual gravimetric method or the volumetric method developed by Fritz and Yamamura ( 2 ) . The latter
method was found to be especially well suited t o the procedure described and was, therefore, used for most of the analyses. EXPERIMENTAL
Apparatus. T h e combustion apparatus used was similar to the usual commercial oxygen flasks except t h a t t h e sample holder consisted of a tapered spiral of 18 gauge Chromel A wire and t h e stopper was neoprene. T h e combustion flasks consisted of one- or two-liter filtering flasks without tubulation. T h e Chromel A spiral holder seemed to provide better combustions than platinum gauze holders and was also much more durable under the vigorous combustion conditions used. Since the feasibility of uqing neoprene stoppers in this apparatus was uncertain, blanks were run. From the results obtained it did not appear that these stoppers should be a
source of trouble for the samples being determined. Reagents. Standard Barium Perchlorate solution, 0.01OO.V. Dissolve 4.0 grams of Ba(C104)g.3H20 (G. F. Smith) in 400 ml. of distilled water and dilute to 2 liters with reagent grade methanol. Adjust the p H to 3.5 with perchloric acid and standardize with standard 0.00500.V sulfuric acid solution. Pipet 10.00-ml. aliquots of the standard sulfuric acid solution into 125-m1. Erlenmeyer flasks and dilute with 40 ml. of methanol. Add two drops of Thorin indicator and titrate while conqtantly stirring the solution with a magnetic stirrer. The color change is from yellow to pink. Thorin Solution, 0.2070. Dissolve 0.2000 grams of Thorin, 1,-(0-ilrsonophenylazo) - 2 - Naphthol - 3,6 - disulfonic acid disodium salt (Eastman S o . 6748) in distilled water and dilute to 100 ml. in a volumetric flask. “Starch Combustion Xixture.” ?\fix VOL. 38, NO. 7, JUNE 1966
913
Effect of Combustion Mixtures on the Determination of Sulfur in Inorganic Sulfides
Table 1.
Sulfur found, %
Mean 32.5
+
3 2 . 7 , 3 2 . 5 , 3 2 . 7 , 32.7, 3 2 . 4 3 2 . 3 , 3 2 . 3 , 3 2 . 4 , 32.7 3 2 . 3 , 3 2 . 6 , 3 2 . 0 , 32.6 3 2 , 4 , 3 2 . 8 , 3 3 . 0 , 32.5
+
21.3, 21.1, 22.9, 20.7 30.7, 30.4 30.0, 30.0 3 0 . 2 , 2 9 . 8 , 3 1 . 5 , 31.7
21.5 30.6 30.0 30.8
2 7 . 1 , 28.5 3 0 . 6 , 3 1 . 2 , 3 0 . 6 , 30.5 3 1 . 5 , 30.2
27.8
20.8, 20.8 22.2, 22.5, 22.3, 22.2 22.4, 22.3
20.8 22.3
1 1 . 2 , 11.5 1 1 . 8 , 13.0, 1 2 . 8 , 11.5 12.6
11.4 12.3
Sample“ Zinc sulfide Starch Starch magnesium Starch combustion mixture Copper(I1) sulfide Starch Starch (large excess) Starch magnesium Starch combustion mixture Iron(I1) sulfide Starch Starch combustion mixture Cadmium sulfide Starch Starch combustion mixture Mercury(I1) sulfide Starch Starch combustion mixture
32.4 32.7
30.8
RESULTS A N D DISCUSSION
Weights of samples, starch, magnesium and “combustion mixture” were about 25 mg. except where otherwise noted. Q
Table II. Effect of Starch Content on the Determination of Sulfur in Zinc and Copper(l1) Sulfides
Sample Zinc sulfide 1 2 3 4
Wt. sample, mg.
Wt. starch, mg.
Sulfur found,
24.5 24.4 25.4 24.8
26 110 212 415
32.7 28.1 18.5 2.9
35.6
503
30.4
yo
Copper(I1) sulfide
6
Table 111.
together, without grinding, 43 grams of granular tin, 43 grams of powdered iron, 14 grams of thermite and 100 grams of starch. Procedure. Weigh 25 mg. of the Dowdered sulfide s a m d e into a filter paper sample cup. The combustion mixture is weighed or measured approximately into this cup with the sulfide sample. After mixing, the sides of the sample cup are tightly folded over the contents and the resulting disk is wrapped in a piece of flag-shaped filter paper. The filter paper and contents are then placed in the combustion holder. The combustion flask is prepared b y adding 5 ml. of 30’% hydrogen peroxide to 45 ml. of distilled water contained in the flask. The flask is flushed with oxygen and the sample is burned in the usual manner. After absorption of the SO2 and SO3 is complete, the contents of
Summary of Results for the Determination of Sulfur in Inorganic Sulfides
Sample Zinc sulfide
Sulfur found, 70Peroxide Flask method method 32.4 (7) 32.5 (9)*
Difference
+0.1 0.0 3 2 . 4 (4)b 32.7 (4)c +0.3 Copper(I1) sulfide 3 0 . 4 (8) 3 0 . 0 (2)b -0.4 30.8 (4)c +0.4 30.6 (2jd +0.2 Iron(I1) sulfide 31.1 (4) 30.8 (6jc -0.3 Cadmium sulfide 22.4 (8) 22.3 (6)” -0.1 Mercury( 11) 13.6 (4) 12.3 ( 5 ) c -1.3 Numbers in parentheses indicate the number of determinations. a Starch sample.
+ + +
+ +
Starch magnesium sample. c Starch combustion mixture + sample. d Large excess of starch sample. b
914
0
ANALYTICAL CHEMISTRY
the flask are quantitatively transferred to a beaker and boiled to reduce the volume to about 25 ml. This solution is then passed through a cation exchange column (Dowex 50, H + form) which drains into a 100.0-ml. volumetric flask. The column is flushed with small portions of distilled water until the flask is filled to the mark. The sulfate is determined by a titration procedure based on the method developed by Fritz and Yamamura (2). A 10.00-ml. aliquot of the solution is pipetted into a 125-m1. Erlenmeyer flask and diluted with 40 ml. of methanol. Two drops of Thorin indicator are added and the sulfate titration with Ba(CIOJz is carried out as previously described under “standardization of Ba(C104)* solution.”
Std. dev. (flask method) 0.18 0.29 0.28 0.94 0.49 0.12
An objective of this research was to find a combustion mixture which could be used with different inorganic sulfides to give quantitative yields of sulfur (as SO1 and SOs) on combustion in an oxygen atmosphere. Results of experiments for determining sulfur in zinc sulfide, copper(I1) sulfide, iron(I1) sulfide, cadmiun sulfide, and mercury(I1) sulfide with various comhstion mixtures are reported in Table I. Some interesting results obtained by varying the starch content with zinc sulfide and copper(I1) sulfide are shown in Table 11. These results were rather surprising and no explanation can be given for the opposite trends observed with increasing starch content. The large amount of starch necessary to give satisfactory results with copper(I1) sulfide was very difficult to handle and is, therefore, not practical for analytical use. Some mixtures that were tried were magnesium powder and starch; aluminum powder and starch; magnesium, aluminum and starch; thermite; and a mixture of iron powder, granular tin, thermite, and starch. This latter mixture was based on one developed by Cardano and Fantini (1) for the determination of carbon and sulfur in steel and cast iron. This mixture provided the most complete burning of any of those tried. However, in most cases additional starch was added to produce a smoother less vigorous combustion. It can be seen from Table I t h a t similar results were obtained with zinc sulfide regardless of which combustion mixture was used. However, in the case of iron(I1) sulfide, the “starch combustion mixture” was the only mixture found to be suitable. It can be seen from the data in Table I and Table I11 that satisfactory results were obtained with all of the sulfides tested except for the mercury(I1) sulfide which gave consistently low results. The results obtained by the oxygen flask method are compared with those
obtained by the peroxide fusion method in Table 111. Since t h e per cent sulfur in most commercially available sulfides is not reported, the results obtained by the peroxide fusion method are here assumed to represent the theoretical per cent sulfur values. ;\lthough the oxygen flask conib u 4 o n s were generally vigorous, no darigerous situations resulted. However, these combustions were carried out behind a safety shield and the operator \\ore safety glasses. The authors believe that the method described in this paper offers a simple, accurate and relatively rapid procedure for the determination of sulfur in many
inorganic sulfides. Extensions of this technique to the determination of sulfur in other inorganic compounds, to sulfide ores, and to other types of inorganic substances should also be feasible. ACKNOWLEDGMENT
T h e authors thank IVilliam A. Sedlacek, George 0. Moses, and Franklin G. Doolittle for carrying out portions of the experiniental work on this project. LITERATURE CITED
(1J Cardano,
llenato, Fantini, Kicola,
t o “ T E R N ” Societa per I’industria e l’elettricita, Ital. Patent 460,119 (Oct. 19, 1950); C. A . 4 6 , 4 9 5 8 ~(1952).
S.,Yamamura, Stanley S., ANAL.CHEM.27, 1461 (1955). (3) Heinrich, B. J., Grimes, -M. D., Puckett, J. E. “Treatise on Analytical Chemistry,’’ Part 11, Sec. A, Tol. 7, I. XI, Kolthoff and P. J. Elving, ed., Interscience, New York, 1961. (4) Kodama, K., “Methods of Quantitative Inorganic Analysis,” Chap. 58, Interscience, New York, 1963. ( 5 ) MacUonald, A. 11. G., Analyst 86, 3 (1961). ARNOLDR. JOHNSON, JR.~ GARYB. MCT’ICKER Department of Chemistry University of Wyoming Laramie, Wyo. ( 2 ) Fritz, James
Present address: Department of Chemistry, Minot State College, Minot, N. D. 58701.
Spectrophotometric Determination of Cobalt in Iron and Steel with 2-Nitroso-1-Naphthol SIR: The method developed by Rooney (6, 7 ) , Claassen and Ilaaman (4),and Boyland ( 2 ) ,for the detennination of cobalt in iron and steel using 2nitroso-1-naphthol, is simpler and quicker than the American and 13ritish standard methods (1, 3 ) . JIoreover, it is not subject to the losses that can occur with the latter a t the zinc oxide separation stage. It also overcomes difficulties noted by Cogan ( 5 ) . However, measuiement of absorbance is not made a t the most sensitive wavelength, 362 nip, because of high and erratic blank5 in this region. Instead, another wavelength, 530 mp, is used a t which there is less than half the sensitivity, but where blanks have less effect. This deficiency is removed in the method described, and a cupferron separation with subsequent destruction of excess cupferrori (7) is eliminated. The method is applicable to a wide variety of irons and steels in the range 0.001 to 0.6% cobalt and, with suitable selection of sample aliquots, to nickelbase alloys. EXPERIMENTAL
Apparatus. Bausch and Lomb Spectronic 505 and Beckman DU spectrophotometers were used for absorbance measurements with 1- and 2-em. cells. Reagents. T h e size of t h e reagent blank is directly related t o t h e organic impurity content of t h e 2nitroso-1-naphthol and t o t h e amount of reagent required t o react with cobalt and other complex forming elements. Rooney (6, 7 ) found that 40 ml. of 1% reagent was the maximum amount he could add and still obtain an acceptable blank at 530 mp. I n experiments to obtain a reagent with a low blank at 362 mp, vacuum sublimation gave a highly satisfactory product, but the
process was too slow to be of practical use, Eventually the following method was developed. Di.solve 10 grams of 2nitroso-1-naphthol in 400 ml. of acetone, without heating, add 4 grams of activated charcoal, and shake the mixture for 15 minutes. Filter into a large separating funnel, add 500 ml. of redistilled amyl acetate, mix, add 200 ml. of 1J1 NaOH, and shake for 30 seconds. Run off and retain the aqueous layer. Repent the extraction twice more using 100 ml. of S a O H solution each time. Combine the aqueouc extracts and add to 2 liters of 0.3N HC1 with stirring. Filter off the bright yellow precipitate and dry under vacuum a t room temperature. Yield, about 8 grams. The reagent was used as a (2.5% w./v.) solution in acetone, prepared daily. 2.11 hydrated sodium acetate, 1-b1 ammonium fluoride, and 1J1 sodium hydroxide were prepared from analytical grade reagents. Standard Cobalt Solution. Dissolve 0.5 gram of high purity cobalt in a minimum amount of 12J1 HC1 and dilute to 1 liter. Dilute an aliquot of this solution to prepare a working solution containing 2.5 pg. of Co per ml. Preparation of Calibration Curve. Transfer portions (0, 2 , 5, 10, 15, 20, and 25 ml.) of the working solution to 100ml. separating funnels and add 1 nil. of 1231 HCI, 20 ml. of sodium acetate solution, and 1 ml. of 2-nitroso-1-naphtho1 solution. Shake the mixture after each addition and allow the reagent to react for about 2 minutes. Add 25 ml. of amyl acetate and shake for about 30 seconds. Run off and discard the aqueous layer. Wash the organic layer successively with 10-ml. portions of water, 12J1 HCl, water, XaOH solution, water, 1221 HC1, water, S a O H solution, and water (twice), shaking the mixture for about 15 seconds after each addition, and discarding each aqueous layer. If an emulsion forms a t any stage, add a few grams of KCl. shake until the emulsion clears, and continue the washing procedure.
Transfer the organic layer to a 50-ml. graduated flaTk and dilute to the mark with amyl acetate. Add anhydrous sodium sulfate, shake, and allow to stand for a few minutes. Filter through a medium speed filter paper and measure the absorbance of the solution us. the blank at 362 mp using 1-em. cells. Plot a calibration curve. Procedure. Transfer 0.5 gram of sample to a 150-ml. squat beaker, add 15 ml. of 1 2 M HC1, 5 ml. of 16J1 H S O , , and allow t o dissolve, with warming if necessary. Two ml. of 2631 HF should be added to the acid mixture to assist the decomposition of high silicon irons and to remove silica. When solution of the sample is complete, evaporate to small volume. For alloys high in chromium, add 5 ml. of 11J1 HCIOl to the solution of the sample and evaporate almost to dryness. Add 10 ml. of 12M HCl and warm to dissolve soluble salts and reduce chromium if present. Cool and dilute to 100 ml. in a graduated flask. Alloys containing tungsten bhould be decomposed with a mixture of 5 ml. of 18.11 HJSOI, 5 ml. of 16.11 HNOe, and 1 ml. of 88% phosphoric acid. When the sample has decomposed, add water and warm until solution is complete. Cool and dilute to 100 ml. in a graduated flask. Allow insoluble material to settle, and pipet a suitable aliquot into a 250ml. separating funnel. Add water to a total volume of 50 ml.; 25 ml. of sodium acetate solution; ammonium fluoride solution until the color caused by iron has disappeared; and 10 ml. of 2-nitroso1-naphthol solution. Shake after each addition and allow the final mixture t o stand for a minimum of 2 minutes. Add 20 ml. of 12M HCl and 25 ml. of amyl acetate, shaking the mixture after each addition (for about 30 seconds in the latter case). Run off and discard the aqueous layer. Wash the organic layer as described under Preparation of CalibraVOL. 38, NO. 7, JUNE 1966
915
