eliminated redily by addition of mcorbic acid. Consequently, 0.2 ml. of a Table 111. Comparison of Two Dye 2.5% methanolic solution of ascorbic Methods for Determination of Thorium acid was invariably used for the preparain Manganese Nodules tion of the measuring solutions. Thorium, P.P.M. All the interfering and noninterferManganese Soloing ions (Table 11) can be quantitatively Nodule chromate separated by anion exchange (4, 7 ) , Fraction” Fast Thoronol Red SO that thorium can be determined in (2) samples of greatly varying composi17813 12.5 12.8 tion. 44.5 45.0 17823 17850 12.0 12.0 Calibration Curves. IN10 ML. of 17824 86.3 86.0 MEASURINQ SOLUTION. The solutions 63.9 64.2 17836 contained 0 to 250 yg. of thorium dis17821 73.5 74 .O solved in 1 ml. of IN hydrochloric acid, 0 The chemical and mineralogical com0.2 ml. of the methanol-ascorbic acid position of these samples has been desolution, and 1 ml. of 0.25% dyestuff scribed (1). The geochemical significance of the data will be discussed further elsesolution. These solutions were made where. up to volume with methanol and measured against a reagent blank solution at 490 mp. Beer’s law holds from 0 to 200 pg. of thorium. IN6.2 ML. OF MEASTJRING SOLUTION. above 10 pg. has a value of 5=1.5% for 10 ml. and 3% for 5.2 ml. of measurThe solutions contained 0 to 150 pg. ing solution, respectively. At lower of thorium dissolved in 1 ml. of the thorium concentrations the error may methanol-hydrochloric acid mixture, increase up to *5 to 10%. 0.2 ml. of the ascorbic acid solution, Application. To test the applic1 ml. of 0.125’% dyestuff solution, and ability of the method, six composite 3 ml. of methanol. These solutions mineral samples (ma’rine manganese were measured against a simultaneously nodules) were analyzed. Thorium prepared reagent blank solution at 490 was separated from accompanying my. Beer’s law applies from 0 to 120 elements by the anion exchange pg. of thorium. methods long used in our laboratory Sensitivity and Accuracy. Two micrograms of thorium per 10 m1.for the assay of thorium in marine min1.0 pg. of thorium per 5.2 ml. of measur. erals (4, 5‘). In each sample the final determination of thorium was performed ing solution-can still be determined. The average deviation of absorbance spectrophotometrically with Thoronol over the whole concentration range and Solochromate Fast Red. The re-
sults of these analyses are shown in Teble 111, which shows that Solochromate Fast Red can be applied tu successfully as Thoronol. ACKNOWLEDGMENT
The authors express appreciation to G. Arrhenius, University of California Scripps Institution of Oceanography, La Jolla, Calif., for furnishing the samples analyzed, and Imperial Chemical Industries, Ltd., Hexagon House, Blackley, Manchester, England, for supplying the Solochromate Fast Red. LITERATURE CITED
(1) Arrhenius, G., “Pelagic Sediments.
The Sea,” Interscience, New York, in press. (2) Banks, C. V., Byrd, C. H., ANAL. CHEM.25, 416 (1953). (3 Job, P., Ann. chim. 109,113 (1928). (41 Korkisch, J., Antal, P., 2. anal.
Chem. 171,22 (1959). (5) Korkisch, J., Janauer, G. E., Anal. Chim. Acta, in press. ( 6 ) Korkisch, J., Janauer, G. E., Mikrochim. Acta (Wien), 1961, 537. (7) Korkisch, J., Tera, F., ANAL. CHEM. 33,1264 (1961). (8) Vosbukgh, W. C., Cooper, G. R., J . Am. Chem. SOC.63,437 (1941). (9) Yoe, J. H.,Jones, A. L., IND.ENQ. CHEW,ANAL. ED. 16, 111 (1944).
RECEIVED for review April 4 1961. Accepted July 28, 1961. Work sponsored by the International Atomic Energy Agency and the U. S. Atomic Energy Commission under Contract 67/US, and by the latter agency also under contract AT(l1-1)-34, Project 44.
Spectrophotometric Determination of Cobalt with Thioglycolic Acid V. D. ANAND,’ G. S. DESHMUKH, and C. M. PANDEY Chemical laboratories, Banaras Hindu University, Varanasi-5, India
b The yellow-red color of cobalt(l1) with thioglycolic acid (sodium salt) having maximum absorbance at 3 5 8 mp has been employed as the basis for a spectrophotometric method for the quantitative determination of cobalt. The system was found to obey Beer’s law between the concentration limits of 1.0 to 10.0 X 10-6 gram of cobalt(l1) and to remain stable for over 4 8 hours at room temperature. The effects of pH, reagent concentration, time of heating, and aging were studied. Interference by heavy metals such a5 copper, nickel, iron, chromium, molybdenum, uranium, vanadium, etc. was prevented by extracting cobalt from the solutions
as the dithizonate. Most of the common anions had no effect. The procedure has been applied to the determination of cobalt in steels and alloys and cobalt determined in National Bureau of Standards samples 153a, 167, 437, and 440 of cobalt alloys, and tool steels. The method is convenient, sensitive, reproducible, and accurate.
T
~n first use of thioglycolic acid, variously described in the literature as mercaptoacetic acid, thioethanolic acid, and thiolactic acid (WI), in quantitative analysis was reported by Mayr and Gebauer (IS).
A number of metals, including iron, cobalt, nickel, lead, bismuth, mercury(I), uranium (U02+2), silver, and gold produce more or less stable colors with thioglycolic acid. The deep blue to purple color due to iron in ammoniacal medium has found extensive application in iron determination (1, 4, 6, 9, 11). Those due to cobalt (yellowred) and uranyl (orange) ions are very deep and stable (18). Although the deep color, comparable in intensity to the color of iron or uranium, given by the cobalt reaction with 1 Present address, Indian Institute of Technology, Kanpur, India.
VOL. 33, NO. 13, DECEMBER 1961
* 1933
Co mere then subjocted to color development, and determined from the calibration curve as usual. STANDARDIZATION OF CONDITIONS
Absorption Spectra. Small aliquots (up to 5 ml,) of cobalt solutions of varying concentration were taken in 10-ml. standard flasks and treated with 2 ml. of 1.OM thioglycolic acid and 2 ml. of 4% sodium hydroxide. The volume was made up to the mark and absorbance measured a t different wave lengths against a mixture of 2 ml. of 1.OM thioglycolic acid and 2 ml. of 4y0 sodium hydroxide, made up to 10 ml. (the blank). The cobalt-thioglycolic acid complex absorption spectra, recorded for different concentrations Qf cobalt (0.5 to 10.0 pg. per ml. of Co) all show a peak between 355 and 360 mp (Figure 1). Subsequent measurements were, therefore, all made at a wave length of 358 Figure I .
Absorption spectra of cobalt-thioglycolic acid complex
thioglycolic acid has tong been known, no attempt seems to have been made, so far to utilize this observation in an application to tlw determination of cobalt. Many substitution compounds of thioglycolic acid have, however, found use in cobalt analysis. In this connection, mention may be made of amides (5, 7 , $8, 15), arylamides (6), and anilides (2, 16) of thioglycoiic acid. Compounds of thioglycolic acid with cobalt have been described by Rosenheim and Davidson (17). ilnother brief description in the literature is given by hleyers (14). Michaelis and Schubert (lo’) made a systematic study of the cobalt complexes with thioglycolic acid in the presence of peroxydisulfuric acid, and reported the formation of a basic compound having the composition [Co (S.CH&OOH) 2 1 2 0 3 5H20. The complex was stable t o H2S, KOH, and KsFe(CN)e. The reddish brown complex was reported to absorb towards the violet end of the spectrum. Schubert (.%lo), in a subsequent study essentially substantiated these findings. More recently a detailed study of a cobalt compound with thioglycolic acid has been made by Hart (8). The utilization of the strong colorforming reaction of cobalt with thioglycolic acid, was, therefore, considered as a suitable colorimetric procedure for cobalt. A detailed and systematic study of the reaction was made, to evolve a set of conditions under which the above color reaction could be used as a spectrophotometric method for the estimation of cobalt. The application Qf the procedure to the determination of cobalt in complex alloys, steels, and tool steels wm also undertaken and is reported. I
1934
c
ANALYTICAL CHEMISTRY
EXPERIMENTAL AND RESULTS
Apparatus. A Beckman Model DU quartz spectrophotometer was used for the absorbance measurements. The pH measurements were checked with a Beckman Zeromatic p H meter. Solutions. A standard 0.01M (approx.) solution of cobalt(I1) chloride prepared from British Drug Houses AnalaR grade salt, was standardized by the anthranilate procedure (24) and checked by the l-nitroso-2naphthol method (23). A stock solution of thioglycolic acid was prepared by dilution from redistilled Merck’s reagent grade acid and 21.75 ml. of the 80% acid when diluted to 250 ml. gave an approximately 1.OM solution. Merck’s extra pure dithieone used in these studies was first purified by the procedure given by Sandell (19). A 0.01% eolution (wJv.) in redistilled carbon tetrachloride was prepared from this recrystallized sample. The sodium hydroxide solution was approximately 4y0. Procedure. In a 50-ml. borosilicate glass beaker containing between 0.1 to 10.0 pg, per ml. of cobalt were added 2 ml. of 1.OM thioglycolic acid and enough 4% sodium hydroxide to adjust the pH to 5.2. About 4 to 5 ml. of water was now added t o the beaker and the solution heated on a boiling water bath for 20 minutes, cooled, and made up to 10 ml. in a standard flask. The absorbance of the yellow-red complex was read a t 358 mp, against a water blank and the amount of cobalt present was read from the calibration curve. In the presence of interfering ions, dithizone extraction in a basic citrate buffer according to a modified procedure of Marston and Dewey ( I d ) was employed to remove the interferences. Aliquots of the extracted cobalt solutions, containing up to 10 pg. per ml. of
DP*
Beer’s Law. To determine if the colored system, cobalt-thioglycolic acid complex, obeys Beer’s law, colors were developed with the reagent for sets of different concentration of cobalt. The plot of concentration against absorbance was a straight line up to 10.0 pg. per ml. of Co. The limits of cobalt concentration for which reasonably accurate absorbance measurements could be made were determined to lie between 0.25 and 10.0 pg. per ml. of Co. Outside this range the color intensity was either too high or too low to be accurately measured. Effect of pH. For studying the effect of p H on the color reaction, several solutions containing identical quantities of cobalt (5 pg. per ml.) and the reagent were prepared as described above. Different amounts of sodium hydroside were, however, added so that the final pH values ranged from 3.6 to 9.9. The colored complex was heated in a 50-ml. beaker on a boiling water bath for 20 minutes. About 5 ml. of water was added to each set, to avoid the drying of the solution during heating, After cooling and checking the pH (no change being observed), the solution was made up to 10 ml. in a standard flask. A plot of absorbance (measured a t 358 mp) os. pH is given in Figure 2. The maximum color intensity was observed between pH 4.8 and 5.25 and a pH of 5.2 was, therefore, maintained in subsequent work. Effect of Other Variables. REAGENT. Keeping cobalt concentration, pH, and other factors constant, color development was done with varying concentrations of thioglycolic acid, to study the effect of reagent concentration. The optimum amount of
C O B A L T CONCENTRATIW CONSTANT
WOCLYCOLLIC ACID VARIED SODIUM HYDROXlDL 4% SOLUTION ( T O MAKE UP ApR OF 5.2)
TOTALVOLUME IOml. CELL PATHIcm.WAVE LENQTH 358mP
SOLUTION (5p.p.m.) i mi. THIWLYCOLLIC AGIO (lM),Zm(. SODIUM HYDROXIDE 4 X SOLUTION (USED FOR PH VARIATION) T O T A L VOLUME, 10hL CELL PATH,lCTII.
COULT
I 1
2
Figure 2.
3
4
5
CO, p g . / k I L
8
9
1
0
1
1
solutions were made up to 10 nil. after cooling and the absorbance values measured as usual. The results are shown in Figure 4. A time interval of 20 minutes on the boiling water bath was enough t o get a constant color intensity. Stability of Colored Complex. T o determine the effect of aging on the intensity of the color once developed, the colored complex was prepared according to the optimum conditions and absorbance determined after various time intervals over a long period (4 days). The yellow-red comples of cobalt with thioglycolic acid was very stable and no fading of color or increase in intensity was observed even after 48 hours or more.
?I 1.0 1.5 2.0 2.5 3 . 0 3 5 4.0 4 5 eQNCL THIQGLYCOLLIC AClD(m1.)
0
Figure 3. Effect of thioglycolic acid concentration on cobalt complex
Calibration Curve. Varying amounts of cobalt solution (0.5 t o 5.0 ml.) containing 20 pg. per ml. of' Co, so as to give 1 to 10 fig. per ml. of Co after dilution, were taken in a 50-ml. borosilicate glass beaker and the color was developed in each case under the optimum Conditions defined above. Absorbance values for each set were recorded at 358 nip against the blank and plotted against parts per million of Co to get the calibration curve.
Error,
Found
74
0.4 0.6
0,398
-0.59
0 . GO4 0,800
+9. GG
0.8
1.205 1.600
+0.42
5.0 6.0
2.000 2.982 4.025 5 050 6.025 7,050 8,000 8.878 9,898
... -0.60 +9 .G2 3-1.00 +9. 33
7.5 8.0 9 .0 15.0
7
Determination of Cobalt in Known Solutions
Taken
1.2 1.6 2.0 3.5 4.9
PH
Variation of absorbance with pH
reazent for 10 ml. of the final solution was found to be 2 ml. of 1.031 acid. Excess of acid caused a decrease in color intensity (Figure 3). TIME. To study the effect of aging, 1 nil. of cobalt solution containing 50 pg. of Co was taken in a 50-ml. beaker and the color developed as usual. The solutioa was made up to 10 ml. and placed in the sample cell. Absorbance values recorded frequently at 358 mp against a blank had not become constant even after 5 hours. TEMPERATURE. To find the optimum temperature of heating, different sets of similarly developed colored compleses were immersed for 10 minutes in water baths maintained a t 40", 50", 60°, TO",SO", and 90' 6 ,and a t boiling temperature. After cooling, each set mas made up to 10 mi. and the absorbance measured against a blank. The results are shown in Figure 4. At the lower temperatures, up to 50°, the change is very rapid. Beyond this stage it falls off and attains a practically steady rate at the temperature of boiling water. Different similar sets of the reaction mixture were heated for varying time intervals on a boiling weter bath. The
Table 1.
6
, . .
+O.TI -0.28 -1.02
TEMPERATURE
Figure 4.
('c)
Effect of temterature and time of heatin
csba it-thisg c ycoiic acid
complex Left, Temperature Right, Time of heoting
VOL. 33, NO. 1 3 , DECEMBER 1961
m
11935
Table II.
Determination of Cobalt in NBS Samples
Per Cent Cobalt5 Average value found 5 8.448 5 42.810 5 2.898 5 11.800 ~
Sample 153a, Co-W-Mo steel 167, Heat-resisting alloy 437,Spectrographic tool steel 440, Spectrographic tool steel 5 Five determinations.
Certified value 8.46 42.90 2.90 11.80
Determination of Cobalt. The method developed above was tested for accuracy and precision by determining the cobalt content in solutions of known concentration. The results are given in Table I. EFFECT
OF DIVERSE IONS
Anions. The thioglycolic acid procedure for spectrophotometric determination of cobalt was remarkably free of interference from common anions, many of which must be entirely absent in most other colorimetric procedures for cobalt. Chloride, bromide, iodide, nitrate, carbonate, hydrogen carbonate, hydrogen sulfite, sulfate, citrate, tartrate, acetate, fluoride, and phosphate in concentrations up to 20 mg. in 10 ml. of final solution had no effect on the intensity of the color. Up to 7 mg. of cyanide was tolerated under similar conditions. The tolerance limit for oxalate, however, was only 1 mg. Cations. The effects of iron, nickel, copper, manganese, vanadium, chromium, uranium, molybdenum, and tungsten, which commonly interfere in colorimetric procedures for cobalt, were critically examined. Iron for which thioglycolic acid is a well known colorimetric reagent, produced a purple-red. It interfered even in trace quantities. Nickel also produced a purplish color but of low intensity. The nickel color could be sequestered by potassium. cyanide, but a large excess of cyanide itself interfered. Copper gave a heavy yellow precipitate, which dissolved on heating, giving an orange solution. Addition of potassium cyanide prevented the reaction. Silver aIso formed a yellow precipitate, soluble in excess alkali. The reaction was masked by potassium cyanide. Chromium, as chromate, produced a bright green; manganese, a dirty yellow colloidal solution, which gave an amber color on shaking. Vanadium produced a bluish green; tellurium, deep orange; thallium, a dark yellow solution; palladium, yellow; while lead gave a yellowish white precipitate. Sodium, nium, tungsten, thocium, barium, stronzinc, zirconium, aluminum,beryllium, and selenium did not
Average Deviation 0.046
0.088 0.030 0.040
cause any interference in the thioglycolic acid procedure for cobalt. Recourse was taken to the dithizone procedure of Marston and Dewey (12) to remove the interference by the heavy metal ions. The effect of 10 mg, each of these ions per 0.1 mg. of cobalt was studied by extracting the cobalt as the dithizonate from the citrate buffered solutions. The modified extraction procedure finally adopted for this purpose was as follows: To a 10-ml. solution of cobalt (containing about 1 mg. of Go) in the presence of the interfering ions; individually, in combination, or all together was added 5 ml. of 10% sodium citrate and ammonia, in small portions, until the pH was 9.0. A 0.01% solution of pure dithizone in carbon tetrachloride (5 ml.) was now added to the cobalt solution containing the interfering ions, taken in a 100-ml. separating funnel. After thorough shaking for 2 minutes the organic layer was carefully removed. The procedure was repeated until the organic layer did not turn red even after shaking for 1 minute. The extracted cobalt dithizonate was washed with 10 ml. of pure deionized water and evaporated in a silica dish over a water bath. The sides of the dish were rinsed with carbon tetrachloride, to bring all the residue in the center and after careful evaporation of the small amount of carbon tetrachloride, the dish was heated to redness to destroy all organic matter. After cooling, the revidue was treated with 1ml. of concentrated hydrochloric acid and 1 ml. of stron nitric acid was added, distributing t f e acid mixture with a glass rod to mix thoroughly, rinsing the rod with a few drops of strong hydrochloric acid. The dish was heated to dryness and the residue brought into solution with 1 ml. of strong hydrochloric acid and diluted to 100 ml. Aliquots from this solution were used for absorbance measurements. DETERMlNATlQN OF COBALT IN STEELS AND ALLOYS
The procedure evolved above was tested on synthetic mixtures of cobalt and interfering ions; and finally applied to the determination of cobalt in some standard NBS (National Bureau of Standards) samples of cobalt containing alloys and steels. Portions of different NB8 samples, containing 10 to 30 mg, of cobalt were
accurately weighed and dissolved in a minimum amount (10 to 20 ml.) of 2:1 mixture of concentrated hydrochloric acid (dl.10) and fuming nitric acid. (In case of the alloy, the sample was first boiled with 20 ml. of concentrated hydrochloric acid and fuming nitric acid added drop by drop till the whole of it was dissolved.) The solution was evaporated to dryness, the sides of the beaker washed with 5 ml. of hydrochloric acid and the residue brought into solution by gentle warming and the addition of a few drops more of the acid, if required. Another evaporation of the solution assured complete removal of the last traces of nitric acid. The residue was brought into solution with the least quantity of hydrochloric acid, diluted with ca. 50 ml. of distilled water, boiled for a few minutes, cooled, and filtered directly into a 250-ml. standard flask. The insoluble residue (silica and tungstic acid) was first washed with a 2% hydrochloric acid solution, then with distilled water and the solution made up to the mark. Small aliquots were taken for dithizone extraction of cobalt (vide supra). The extracted solutions of cobalt after being freed from organic matter were made up to 25 ml.; small portions (2 to 5 ml.) were used for color development with thioglycolic acid as usual and the absorbance measured a t 358 mp. The results are recorded in Table 11. DISCUSSION
The chemical reaction between cobalt and thioglycolic acid in the presence of potassium hydroxide may be presented by the equation (16) COClz HSCHzCOOH KOH Ha0 0 -P [CO(SCH~COO)KH]~O
+
+
+
+
Since like cysteine, thioglycolic acid also has in addition to the -SH group, some other group (-COOH) capable of either direct salt formation or complex formation, the whole molecule would give an inner complex of the type proposed by Ley (10). The formation of the deep yellowish red compound of cobalt and thioglycolic acid needs oxygen. This fact is in clear agreement with the observation (see Experimental) that the maximum color intensity is reached after a long time under ordinary conditions and the equilibrium is attained more quickly on heating on a boiling water bath for 20 minutes. Once developed, however, the colored complex showed high stability; no change in intensity was observed for up to 4 days. The continuous increase in intensity even after 300 minutes of eging also shows the slow aerial oxidation of the complex-which was found in experimental trial to become faster on shaking or stirring. The colored complex of cobalt with thioglycolic acid was found to give a band of maximum absorption at 358 rnb (see Figure I) and the concentration 08. absorbance plot gave a straight
b e between wide limits of cobalt concentration. Variation of p H had a marked effect on the color intensity of the system. A large excess of the reagent, leading to higher acidity, was found to lower the depth of color in itself but even if a higher pH was maintained, a large excess of the reagent was not tolerated. The optimum pH was between 4.8 to 5.25 (see Figure 2) and in the range of determinable cobalt (0.25 to 10 fig. of Co per ml.) 2 ml. of 1.OM thioglycolic acid was safely tolerated. The procedure was free of interference from most common anions in large concentrations. Most cations too were found to have no color reaction with the reagent, but iron, nickel, copper, manganese, chromium, vanadium, uranium, molybdenum, and tungsten, the usual interfering ions in colorimetric procedures for cobalt, caused serious positive or negative interference in the present procedure. All of these could, however, be easily eliminated by dithizone extraction of cobalt in basic citrate medium. The present method gave easily reproducible and accurate results in actual determinations of cobalt in solutions of known concentration. In its application to the determination of cobalt content of NBS samples of alloys and steels, the data obtained compare favorably with the specified certificate values. The thioglycolic acid procedure for
the determination of cobalt may, therefore, be claimed to be a simple, accurate, and dependable method of wide applicability for the determination of cobalt content of pure compounds, alloys, and steels. The technique evolved should ala0 find ready application to the determination of cobalt in soils, biological materials (such as animal tissue), ores, and other cobaltbearing samples. ACKNOWLEDGMENT
Sincere thanks of the authors are due to S. S. Joshi for keen interest and to R. H. Sahasrabudhe for permitting the use of the instruments. The award of a senior scholarship to V.D.A. by the Ministry of Scientific Research and Cultural Affairs is also acknowledged. LITERATURE CITED
(1) Allport, N. L., “Colorimetric Analysis,” p. 55,Chapman and Hall, London, 1947. (2) Bersin, T.,E. anal. Chem. 85, 428 (1931). (3) Buscarons, F.,Artigas, J., Anales real. soc. espafi. fh.y quim. (Madrid) 48B, 140 (1952); C.A. 46, 10044 (1952). Ibid., 49B, 375 (1953): C.A. 48, 2524 (1964). ’ (4)Chirnside, R. C., J . SOC.Glass Tech. 22 41-T(1938). (5)khirnside, R. C., Pritchard, C. F., Ibid., 23,26-T(1939). ( 6 ) Escudero-Tineo, R. E., Anales fac. farm. y bioquim., Univ. nucl. mayor
pect ro photo metric Determina ti o n ,I 0-phenanthroli
Sun Marcos ( f i m )3, 489 (1952); C.A. 48,5735 (1954).
c.,
(7) Gupta H. M. L.,
SOgmi, No ANAL.&EM. 31,9>8(1959). 18) Hart. 6. S.. Dtseert. Ab&. 13, 651 . ,(1953): (9) Koenig, R. A.,Johnson, C . R., J . Bid. C h . 142,233 (1942). (10)Ley, H.,Z. Ekktrochem. Soc. 10, 954 (1904). (11) Lyons, E.,J. A*. Chem. Soc. 49, 1916 (1927). (12) Marston, H. R., Dewe D. W., Azlstralian J . Exvtl. Biol. A d d . Sei. 18, 343 (1940). (13) Mayr, C.,Gebauer, A,, 2.anal. Chem. 113,189 (1938). (14’1Mevers. C. N.. J. Lab. Clin. Med. ‘ 6,359“192p ‘ (15) Mic aelis, L., Schubert, M. P., J . A m .Chem. Boc. 52,4418 (1930). (16) Misra, R. N., GuhwSircar, 5. S., J . Indian Chem. SOC.32,127 (1955). (17)Rosenheim, A., Davidson, J., 2. anorg. Chem. 41,231 (1904). (18) Sandell, E.B., “Colormetric Determination of Traces of Metals,” p. 543, Int,er!rRaience. __- ..-.. New York. 1959. (19)Ibid., p. i70. (20) Schubert,M. P., J. Am. Chem. Soc. 54,4077 (1932). (21) Snell, F. D.,Snell, C. T.! “Colorimetric Methods of Analysis,’ p. 319, Van Nostrand, New York, 1954. (22) Ubeda, F. B., Capitan, F. Analee real. SOC. espaii. fis. y quim. (Madrid) 46B, 453 (1950); C.A. 45, 5073 (1951). (23) Vogel, A. I., “A Text Book of Quantitative Inorganic Analysis,” p. 461,Longmans London J953. (24) Wenger, .PI E.,.&merman, c., Corbaz, A,, Mikrochzm. Acta 2, 314 (1938). (25) West, P. W.,Duff, M. A,, Anal. Chim. Acta 15,271(1956). RECEIVZD for review November 30, 1960. Accepted June 5, 1961.
6
races o
n
Application to Vanadium, Chromium, Titanium, Niobium, Tantalum, Uranium, Tun sten Metals, Alloys, and Compounds A. R. GAHLER, R. M. HAMNER, and
R. C.
SHUBERT
Research and Development Analytical laboratory, Technology Department, Union Carbide Metals Co., Division of Union Carbide Corp., Niagara Falls, N. Y.
b A rapid, accurate, spectrophotometric method for the determination of iron is described. It is particularly applicable for the determination of iron in high-purity vanadium, chromium, titanium, niobium, tantalum, and tungsten metals; aluminum-vanadium alloy; titanium-aluminum-vanadium alloy; uranium monocarbide; and compounds of these metals. The method is applicable over a wide concentration range-0.0001 to about 2%. Accuracy and precision data are pre-
sented for iron at various concentration levels in different materials. A determination can be made within ‘ / z hour after dissolution of the sample; therefore, it can be applied to control analyses.
accurate, sensitive, and rapid method has been needed for the determination of iron in the range of 0,0001 to 20/, in high-purity metals, alloys, oxides, carbides, metal halides, N
and other inorganic materials. The difficulty experienced in obtaining accurate results with existing procedures, particularly for iron in high-purity vanadium metal and alloys containing Vanadium, indicated that an improved method was needed. A method of wide applicability wets sought because of the general interest in small amounts of iron in various materials. A preliminary survey of published methods indicated that the spectrophotometric method for the determinaVOL 33, NO. 13, OECEMBER 1941
*
1937
