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
tion Curve. The reagent may be recovered in a pure state from the first XaOH wash-liquor by precipitation with 0.3M HCl as described under reagent purification. Transfer the organic layer to a graduated flask, and, if necessary, dilute with amyl acetate. Dry with anhydrous sodium sulfate and filter. Measure the absorbance of the solution a t 362 mp in an appropriate size of cell us. a blank. Size of sample solution aliquot, final amyl acetate volume, and size of cell should be selected as: Amyl Solution acetate Cobalt aliquot, volume, percentage ml. ml. 0.25 to 0 04 to 0.006 to 0.001 t o
0 6 0 3
0.06 0 008
100 50 50 25
5 5 10
25
cell size, cm. 1 1
2 2
B
F WAVELENGTH
Figure 1 . Table I. Tests of Cobalt Solutions for Interference from Iron, Chromium, Copper, and Nickel
Cobalt present, pg.
0 0 0 0 0
10 10 10
10 10
100
100 100 100 100 100 100 100 100 100
Element and amt. added 40 mg. Cr 40 mg. Ni 40 mg. Cu 40 mg. Fe 40 mg. Fe 35 mg. Xi 40 mg. Xi 20mg. Cu 30mg. Cu 40 mg. Cu 40mg. Cr 40 mg. Xi 40mg. Cu 40 mg. Fe 40 mg. Fe 40 mg. Ni 20 mg. Cu 30 mg. Cu 40 mg. Cu 40 mg. Cu
Cobalt error, rg. -0.1 0
-0.1 +3.2 + 0 . 5. 0
+0.2 -0.6 -0.6 -0.6 $0.4 -3.3 -7.8 -6.4 05 $0.4 +0.9 +0.9
-4.7 $0.4
Solvent and reference solutions in all spectra were amyl acetate (1 -cm. cells)
reagent added, ml. 10
Absorbance Curves. Absorption spectra for the cobalt 2-nitroso-lnaphthol complex and its relationship to the reagent and the blank are shown in Figure 1. The cobalt and blank spectra are those which result from a reagent addition of 10 ml. of 2.5% solution and a final amyl acetate volume of 50 ml. A test of Beer's law showed linearity of the absorbance curve between 0 and 70 pg. of cobalt at 362 mp and 0 and 100 pg. a t 530 mp. The color intensity is stable for a t least 12 hours. The calculated molar absorptivity of the cobalt complex is 3.6 X lo4 a t 362 mp and 1.4 X lo4 a t 530 mp. The calibration results show standard deviations of 0.6 pg. at 362 mp and 1.4 pg. at 530 mp. Effect of Other Elements. Nickel, chromium, iron, and copper are the only elements, other than cobalt, usually found in iron and steel which
10 _.
10 10
10 10
10
10 10 15 15 15 15
20
Determination of Cobalt in Standard Analyzed Samples of Iron and Steel and Nickel Base Alloys
Recommended cobalt Sampleasb content and range, 7, 0.008 (0.007 and 0.008) NBS 55a open-hearth iron NBS 115a 16Ni-6Cu-2Cr cast iron 0.08 0.30 (0.29-0.32) NBS 126a 36Ni steel 0 . 07lC NBS 160 19Cr-9Xi-3310 steel 0.67 (0,64-0.69) BCS 220 7W-5Cr-4hIo steel 0.021 (0.020-0.023) BCS 273 mild steel BCS 275 mild steel 0.059 (0.055-0.062) 0.076 (0.073-0.078) NBS 162a 64Ni-31Cu (monel type) NBS 169 77ITi-20Cr-lSi 0.19 (0.18-0.21) a NBS National Bureau of Standards. b BCS British Chemical Standards. c Revised figure (Private communication from NBS).
916
*
ANALYTICAL CHEMISTRY
640
Spectra of cobalt complex and associated blank
RESULTS A N D DISCUSSION
10 10 10 10 10 10
600
(mp)
A = 1.24 pg. of cobalt/ml. 6 = 1.0 pg. of purified reagent/ml. C = blank
Volume
of 2.570
a Sufficient fluoride added to decolorize buffered solution.
Table II.
500
400
340
Cobalt found, yo 0.005,O.006,O.006 0.079,O.080,O. 082
0.292,O.299,O. 300 0.073,0,074,0.074 0.658,O.666,O. 666 0.020,0.020,0.021 0.057,O.057,0.058 0.075,O.075,O.076 0.183,O. 183,O. 183
form complexes with 2-nitroso-1-naphtho1 in the p H range of 5 to 6 ( 7 ) . Their complexes are destroyed by hydrochloric acid but the cobalt complex is unaffected. T o remove gross amounts of iron in this way would require, however, large amounts of reagent which would have to be extracted subsequently. Rooney avoided these difficulties by a preliminary separation of iron (and copper) with cupferron (6, 7 ) . A simpler method is addition of ammonium fluoride to the buffered solution. This avoids the additional requirement of the destruction of the excess cupferron. Trivalent chromium precipitates when the sodium acetate buffer solution is added to the sample aliquot. It is said not to interfere ( 7 ) . However, cobalt mas occluded when appreciable amounts of chromium(II1) precipitated rapidly, the rate of precipitation being proportional to chromium(II1) and dissolved silica concentrations. The occlusion was reduced to a negligible amount by delaying the precipitation of chromium until cobalt had reacted with the 2-nitroso-1-naphthol. This was achieved by dehydrating silica, with perchloric acid, and diluting the aliquot to 50 ml. before adding sodium acetate. The extraction of cobalt into the amyl acetate layer, with only small amounts of the complexes of the other elements, was ensured by the addition of 20 ml. of 12111 hydrochloric acid to the sample solution after the formation of the 2nitroso-1-naphthol complexes ( 7 ) . The interfering complexes were removed by the washing procedure, leaving only the cobalt complex dissolved in the amyl acetate. The amounts of reagent re-
quired for different amounts of nickel, copper, and chromium in the presence and absence of cobalt (to a maximum of 100 p g . ) are shown in Table I. These results were obtained by following the extraction technique detailed in Procedure, the exceptions being that the iron interference was tested with and without fluoride present and the others were tested with a standard addition of 5 ml. of fluoride. The resistance of the iron complex to complete decomposition (following two acid washes as in Procedure) and the removal of iron interference with ammonium fluoride is also indicated. The introduction of a second alkali wash removes the free naphthol which is liberated when the last traces of inter-
fering complexes are decomposed by the final acid treatment. This reduces the blank value, particularly at 362 mp. The results given in Table I, size of reagent blank, and the sensitivity of the reagent to cobalt, taken together, enabled the construction of the table given in the Procedure which relates cell size, sample aliquot, and amyl acetate volume to the expected cobalt content. The method can be applied to alloys of nickel and copper by suitable selection of aliquot and reagent volumes (see Tables I and 11). LITERATURE CITED
(I) American Society for Testing Na-
terials, "ASTM Methods of Chemical
Analysis of Metals," pp. 54-5, Philadelphia, Pa., 1964. (2) Boyland, E., Analyst 71, 230 (1946). ( 3 ) British Standard 1121, Part 42, 1961. (4) Claassen, A,, Daamen, A., Anal. Chim. Acta 12, 547 (1955). (5) . , Cozan. E.. AXAL. CHEM. 32. 973 (1960). ' ' (6) Rooney, R. C., rMeta2lurgia 58, 205 il9)nS). (7j-zm:, 6 2 , 175 (1960).
XAWJEL NEEDLEMAN
Department of Supply Defence Standards Laboratories Australian Defence Scientific Service hlaribyrnong, Victoria, Australia The author thanks the Chief Scientist, Autralian Defence Scientific Service, Department of Supply, Melbourne, Victoria, Australia, for permission to publish this paper.
Spectrophotometric Deter rnina tio n of Cyclohex a none Oxime in Sulfuric Acid Solution of Epsilon-Caprolactam SIR: RIost of the current industrial processes for the production of t-caprolactam involve the 13eckmann rcarrangement of cyclohexanone oxime in concentrated sulfuric acid. This reaction proceeds nearly quantitatively and a very small amount of the oxime remains unchanged in the Ueckrnann rearrangement solution. .A number of methods for the quantitative determination of the olime have been reported-e.g., the gravimetric determination of the oxime by 2,4-dinitrophenylhydrazine (4, the spectrophotometric determination of 1chloro-1-nitrosocyclohexane(9) or formhydroxaniate (3) derived from oxime, and polarography ( I O ) , However, these methods have many limitations, e-pecially for the determination of trace amounts of the o\;ime. The present paper report- a novel method for the determination of trace amounts of the oxime in wlfuric acid wlution of t-caprolactam. It is ha-ed on the analysis of an azo dye compo-cd of sulfanilamide 1-naphthyl)-ethylenediamine, a and -Y-( proccdure firqt uied hy Shinn (8) in the determination of nitrous acid. Also included 1- a quantitative modification of Feigl's spot test ( 2 ) ,in which an azo dye composed of sulfanilic acid and 1-naphthylamine, the Griess-Ilosvay reagent (5, 6 ) , is ana1yzc.d. .A comparison betneen Shinn'q reagent and the Griess-Ilosvay reagent is described. EXPERIMENTAL
Apparatus. hbsorbance measurements were made with a Hitachi EPU-2 spectrophotometer in a 1.000cm. quartz cell. p H determinations were made with a Hitachi-Horiba AI-3 type p H meter with a glass electrode.
Reagents. *A 0.2% sulfonamide solution was prepared by dissolving 0.2 gram of sulfanilamide in about 70 nil. of distilled water on a water b a t h a t 50" C., followed b y dilution t o 100 ml. with distilled water. A 0.1% N-(1-naphthyl)-ethylenediamine dihydrochloride solution was stored in a red bottle. Iodine-acetic acid solution was prepared by adding 1.3 grams of iodine to 100 ml. of glacial acetic acid; t h e supernatant liquid was used after undissolved iodine settled. Procedure. Ten grams of the Beckm a n n rearrangement solution [cyclohexanone oxime is usually rearranged with more t h a n 1.5 molar ratio of sulfuric acid at 110' t o 120' C. (4)] of cyclohexanone osime is weighed accurately and then brought t o a total volume of 250 nil. with distilled water. T h e diluted Beckmann rearrangement solution (26 ml.) is pipetted into a conical flask equipped with a condenser, and 1 N sulfuric acid is added t o make t h e solution contain approximately 1.72 grams total weight of sulfuric acid in order to obtain a suitable p H range in t h e color reac-
Then, 5.0 ml. of the iodine-acetic acid solution is added a t a temperature below 10' C., followed by the addition of 10 ml. of a 50% aqueous solution of sodium acetate. The solution is kept a t a temperature between 14' and 18' C., and excess iodine is decomposed by addition of O.1N sodium thiosulfate solution. Ten miililiters of the 0.1% S-(1-naphthyl)ethylenediamine dihydrochloride solution is added and diluted accurately to 250 nil. with distilled water. T h e absorbance is read a t 540 inp after 2 minutes. Equivalent amounts of the reagents are added t o distilled water in t h e reference cell. RESULTS AND DISCUSSION
Color Reaction. The color reaction involved may be indicated by the fo!!owing successive reactions : Cyclohexanone oxime is readily hydrolyzed in acidic media to cyclohexanone and hydroxylamine, which is oxidized quickly and quantitatively into nitrous acid by iodine in acetic acid solution. 0
NOH
",OH
+ 212 + HZO
tion. T h e solution is refluxed for 1 hour. After cooling, 5.0 ml. of t h e 0.2% sulfonamide solution is added.
-
HNO,
+ 4HI
(2)
When Reaction 2 is carried out in the presence of sulfonamide, the nitrous acid produced serves as a diazotization agent. 8
0
N m I
VOL. 38, NO. 7, JUNE 1966
917
