Determination of Cobalt and Manganese
bv Photometric Methods J
LOLIS W-1LDBACER AND NELL 31. WARD, S t a t e University of Iowa, Iowa City, Iowa
C
OBALT can be determined in the presence of manganese when t h e latter is present up t o as high as 99.40 per cent, by means of the chloroform extract of the cobaltinitrosobeta-naphthol coinpound in the photelonieter, using a green filter. Manganese can lie determined by separation as the manganese ammoniuni phosphate n ith subsequent conversion to t h e manganese formaldoxime compound and then determilled in t h e photelometer 11-ithout a filter. The method is satisfactory even n hen t h e cobalt is present in amouiitq as high as 99.50 per cent in the origiiinl sample. In t h e course of otlici n ork, it became iniperatire to determine small amouriti of cobalt in the presence of large amounts of manganese, and iiix111 amouiitq of manganese in the presence of large aniounts of cobalt. S o n e of the methods :~vailahlein the literature zeemed satibfactory and hence the follon ing methods n erc lvorked out. The procedures and techniques are simple :inti preciqe
'r~41i1,l.;
I.
C'obalr
,.
100.O i l 3 7 , 50 23.08 13.04
D E T E R U I S A T I O X O F C:OU.ILT (0.30 M G . ) PRESESCE OF > l . I S G h S E S E
3langaiieie
Readings
r ic
.Wicroamperes 4 5 , on 4 5 . 0(! 45.00
S6.9(i
45.00
A fifi
-4 standard curve was established for cobalt, using a photoelectric photometer with samples varying from 0.01 t o 0.60 mg. of cobalt by the following procedure: Enough 5 N hydrochloric acid ~ - aadded > to 10 ml. of ammonium citrate reagent in a 260ml. flask to make it just acid, then the solution of the sample \vas introduced. Sfter heating just to boiling, 25 ml. of alphanitroso-beta-naphthol reagent were added, and the solution !vas allowed to stand for 2 hours ( 7 ) and then filtered. The filter paper and the precipitate were washed nith distilled water to free them as much as p ible from the color of the reagent and dried at 100" C. The ecipitate was extracted from the filter paper, using chloroforni in 10- to 15-ml, portioiis until they were ahsolutely colorless. The volume of the extract was made up to exactly 100 ml. with chloroform. The alpha-nitroso-betanaphthol reagent was prepared by boiling 1.0 gram of the compound with 200 ml. of water and 10 ml. of 5 S sodium hydroxide. filtering. and diluting to 2 liters. The ammonium citrate reagent contained 1000 prams of citric acid, 250 ml. of water, and 1000 i d . of :tmmonia solution (rp. gr. 0.90). A green filter i n s used in the photometer (Cenco-Sheard-Sanford photelometer). The sample containing the cobalt and manganese was treated as directed in the preceding paragraph and the standard curve 11-asused t o determine the amount of cobalt present. The results obtained are given in Table I. These datu showed t'hat t h e method \\-as precise Ivithin t h e range indicated and t h a t determinations were reproducible. According to t h e literature, diralent cobalt is oxidized t o trivalent by alpha-nitroso-beta-naphthol and precipitated :E cobaltinitroso-beta-naphthol(R), and the cobalt is separated from the manganese without the reagent affecting the niwiiganese ( 2 , 3 ) . It is a matter of small importance whether the precipitate carries do\\-n absorbed material, since it does not pi,oduce a colored compound d h the reagents used.
I S THE
Cobalt
Jf Q , 0.30 0.30 0.30
0.30 0.30
Cobalt
Manganese
The method described for the determination of cobalt is based upon t h e extraction of colialtinitroso-beta-naphthol with chloroform. It is particularly designed for samples having low cobalt and high manganese content.
The follon-iiig method for the deteriniliation of manganese, ivliich is particularly designed for samples having lo^ manganese and high cobalt content, is based upon the formation of a purple colored compound produced when t h e manganese and t h e formaldoxime reagent react in a n alkaline solution.
A standard curve for manganese \vas established with samples varying from 0.01 t,o 0.75 mg. of manganese. The sample vias placed in a 100-ml. volumetric flask, diluted to 50 to 60 ml., and made just neutral with 5 -\i ammonia solution. A 4 to 5-ml, excess of the ammonia solution was then added, and 1 to 2 ml. of formaldoxime reagent ( I ) , and sufficient water to make the final volume exactly 100 ml. The formaldoxime was prepared by dissolving 4 grams of hydroxylamine hydrochloride in 100 ml. of xvater and adding 4 to 5 ml. of 40 per cent, formaldehyde. S o filter was used in the photelometer. A series of curves was established in which the faint' yellow color produced by the cobalt was compensated for by adding to this standard known amounts of cobalt. This was necessary, since cobalt will precipitate with manganese in the procedure used in actual analysis.
TABLE
11.
A M O U S T S O F COBALT A S D ? u l A S G A S E s t : F O R LISHING CURVES 7
M Q
NQ.
Curve I1 Xg.
0.0(I
0.00
0.10
I\lsnganere
(1.10
COBALT, MILLIGRAM
a
FI~;I-RE 1. STANDARDIZATIOS CT-RVEFOR COBALT
727
0.00
0,111
0.10 0.00 0.10 0.00 0 . l(1 0.00 0.30 Standard curve for manganese. 0 . 20 0.23
I
Curve Ia
Cobalt Curve 111
ESTAB-
Curve IV
Mg.
.\I Q
0 ,9 0 0 20 0.20 0 20 0.20
0.30 0.30 0.30 0.30 o ,30
Vol. 14, No. 9
INDUSTRIAL AND ENGINEERING CHEMISTRY
728
MANQANESE, MILLIGRAM
FIGURE 2. ST.4SDARDIZATIOS CURVE
FOR M A N G A S E S E
TABLE111. ESTABLISHMENT OF STAXDARD MANGANESE CURVESCOMPENSATED WITH COBALT
MANGANESE
Manganese
Microampere Readings 0.20 mg. Co
0.00 mg. Coo
0.10 mg. Co
99.50 80.67 67.67 62.00 58.00
99.00 80.50 67.25 62.00 57.25
Q
98.50 80.25 67.00 61.75
...
COBALT PRESENT
WITH
0.30 mg. Co
MU. 0.00 0.10 0.20 0.25 0.30
, MILLIGRAM
CURVESFOR MAXGANESE FIGURE 3. STANDARDIZATION
(No filter)
98.00 79.50 67.00 61.50 57.00
Standardization curve for manganese.
Table I1 suggests the combinations for samples for the series of curves. These known samples were treated according to the method given above, and the reference curves were obtained from the photelometer readings (Table 111). When a cobalt blue filter was used in the photelometer, a wider spread of curves was obtained (Figure 3). To a sample containing the manganese and cobalt in a volume not greater than 60 to 65 ml., 4 to 5 grams of solid ammonium chloride were added and sufficient water so that when about 25 ml. of ammonia solution (sp. gr. 0.90) were added, the final solution was highly ammoniacal and its volume approximately 90 ml. To the almost boiling solution, 10 ml. of saturated ammonium phosphate solution were added dropwise with constant whirling (6). The solution was then cooled and 10 ml. of 95 per cent ethyl alcohol were added. As soon as the precipitated manganese ammonium phosphate (6) was well crystallized, it was filtered and washed with portions of a wash solution made of 250 ml. of concentrated ammonia, 100 ml. of saturated solution of sodium phosphate, 100 ml. of ethyl alcohol, and 550 ml. of water. If the precipitate was definitely colored with the cobalt it was dissolved in 5 N hydrochloric acid and reprecipitated. The final precipitate was dissolved in 5 N hydrochloric acid, the paper washed with water, and the solution diluted to exactly 250 ml. A 25-ml. portion was transferred to a 100-ml. flask and treated with ammonia solution and formaldoxime reagent as directed in the preceding paragraph, and the photelometer readings were taken. The amount of cobalt present in a 25-ml. aliquot portion of the solution was determined by the chloroform extraction method previously described. The amount of manganese was determined by references to the proper curve. The results obtained, given in Table IV, showed t h a t the method was precise within the range indicated and t h a t the determination was reproducible. Cobalt precipitated with the manganese in all concentrations used. If t h e precipitate had a cobalt content greater
than the manganese content, it was simply dissolved and reprecipitated
(4).
Conclusions Cobalt can be determined in the presence of 99.40 per cent of manganese b y a simple and precise method. Manganese can be determined in the presence of 99.50 per cent of cobalt. Indications are that successful results could be obtained at still higher concentrations.
TABLE Iv. DETERXINATION O F MaNGANESE (0.25 MG.) I N PRESENCE OF COBALT
THE
(No filter)
co %
Mn
% 33.33 20.00
66.67 80.00 88,89 95.24 99,010 99.50n
11.11 4.76 0.99 0.50
Readings
Microamperes 62.00 62.00 62.00 62.00 61.75 62.00
a Samples were reprecipitated.
Literature Cited (1) Furman, N. H., “Scott’s Standard Methods of Chemical Analysis”, 5th ed., Vol. I, footnote 5, p. 560, New York, D. Van
Nostrand Co., 1939. (2) Kahare, E., Ann. chim. anal., 17, 175-8 (1935). (3) Kolthoff, I. M., and Sandell, E. B., “Textbook of Quantitative Inorganic Analysis”, p. 77, New York, Macmillan Co., 1937. (4) McAlpine, R. K., and Soule, B. A,, “Prescott and Johnson’s Qualitative Chemical Analysis”, p. 336, New York, D. Van
Nostrand Co., 1933. (5) Peachkova, V. M., and Ovsiannikova, Zavodskaya Lab., 6,800-3 (1937). (6) Willard, H. H., and Furman, N. H., “Elementary Quantitative Analysis”, 3rd ed., p. 331, New York, D. Van Nostrand Co., 1940. (7) Yoe, J. H., “Photometric Chemical Analysis”, Vol. I, p. 1173, New York, John Wiley & Sons Co., 1928. A CONDBNSATION of the dissertation submitted by Ne11 M. Ward t o the graduate faculty in partial fulfillment of the requirements for t h e Ph.D. degree.
