Determination of Copper by Dithio-oxamide in Magnes.ium and Magnesium Alloys H. H. WILLARD, Cniversity of Michigan, A n n Arbor, MMich., AND ROBERT E. MOSHER
AWD
Wayne University, Detroit, Mich.
4 . J. BOYLE,
A rapid, accurate, and direct colorimetric procedure for the estimation of copper in refined magnesium and magnesium alloys is presented. The color reagent employed is rubeanic acid (dithio-oxamide) in combination with a buffer complex composed of acetate and malonic acid. No separation or concentration techniques are required.
T""
followed by just enough concentrated nitric acid to dissolve the metal. Boil vigorously for 5 minutes after solution is complete to remove the oxides of nitrogen, cool, and transfer to a 250-ml. volumetric flask. Dilute to the mark with distilled water. Pipet one 25-ml. aliquot into a 100-ml. beaker, and a similar aliquot into a 100-ml. volumetric flask. Add 3 drops of methyl orange t o the beaker and neutralize by dropwise addition of concentrated ammonium hydroxide until color changes. Add the same number of drops of Concentrated ammonium hydroxide to the aliquot in the 100-ml. volumetric flask. Add 5 ml. of a 20% solution of malonic acid followed by 25 ml. of buffer color reagent. Dilute to the mark with distilled water. Mix thoroughly after each addition listed above. Permit the sample to stand for 30 minutes, then compare in a suitable photoelectric colorimeter using a blue filter. Copper in Refined Magnesium. This procedure is identical with that for magnesium alloys, except that no malonic acid reagent is added and only 5 ml. of buffer color reagent are used. I t is advisable to permit a development time of 60 minutes for these very low concentrations of copper, before comparison with standards.
' initial study of rubeanic acid (dithio-oxamide) appears to have been made by Wohler ( 7 ) ) who observed that this compound precipitated copper, silver, mercury, and lead. Rubeanic acid was first reported as a reagent for the quantitative precipitation of copper by RAy and R$y ( 6 ) ,and was subsequently used for detecting copper by a spot test technique ( 3 ) . Later Allport and Skrimshire (1) employed rubeanic acid in the colorimetric estimation of copper in certain drug materials following an extraction proceduie. Willard and Diehl (6) state that rubeanic acid may be used as a color reagent for copper jn the presence of mahganese and zinc but not cobalt and nickel. Center and RlacIntosh ( 2 ) introduced the use of rubeanic acid for the determination of copper in potable water supplies. The selection of rubeanic acid as the reagent for the colorimetric estimation of copper in magnesium and magnesium alloys appears to offer several advantages. The method is rapid, accurate, and direct, and requires only a fraction of a gram to determine copper in refined and alloy magnesium.
RESULTS AND DISCUSSION
To reduce the error due to segregation common in light metal alloys a 2.0-gram sample weight is advocated initially, from which an aliquot containing 200 mg. of metal is finally taken for analysis. Nitric acid serves best as the solvent for the metal, as it is important that all copper be present as cupric ion. A Cenco photelometer equipped with 50-mm. cells was used to estimate copper in the normal range for magnesium alloys as listed by the American Society for Testing Materials. For the lower concentrations present in refined magnesium use was made of a Lumetron Model 402E employing 100-mm. comparison cells.
REAGENTS
Kitric acid, concentrated, C.P. Ammonium hydroxide, concentrated, C.P. Glacial acetic acid, C . P . Sodium acetate trihydrate, C.P. Rubeanic acid, Eastman Kodak Company. Malonic acid, Paragon Testing Laboratories. Cupric sulfate pentahydrate, C.P. Gum arabic. blethyl orange. Buffer Color Reagent. Keigh out 300 grams of sodium acetate into 1-liter beaker, and add 300 ml. of distilled water to dissolve the salt. Filter the solution with suction through a properly oreaared Gooch crucible. Add 280 ml. of glacial acetic acid to the-filtrate. Dissolve 0.200 gram of finely powdered gum arabic in 20 ml. of distilled water in a 50-ml. beaker. I n a sepal'ate 50-ml. beaker dissolve 0.100 gram of rubeanic acid in 20 ml. of alcohol. Both the gum arabic and the rubeanic acid may require slight heating. Add the gum arabic and rubeanic acid solutions to the acetic acid-acetate mixture, cool, and dilute to 1 liter with distilled water. Malonic Acid Solution. Dissolve 200 grams of malonic acid in 500 ml. of distilled water. Seutralize with concentrated ammonium hydroxide to a faint odor of ammonia, cool, and dilute to 1 liter with distilled water. Methyl Orange Solution. Dissolve 1.0 gram of the indicator in water and dilute to 1 liter with distilled water. Standard Copper Solution. Dissolve 393 mg. of cupric sulfate pentahydrate in 1 liter of distilled water. This solution represents approximately 0.1 mg. of copper per ml. Two 100-ml. portions of this solution are taken for standardization. Suitable dilutions of the standard copper solution are then used for the preparation of the standard curve.
Table I shows the results for copper in the presence oi the elements common to magnesium alloys. .4s will be noted, the concentrations of these elements are maximum or in excess of that normally encountered. The standard copper curve may be prepared with the addition of purified magnesium nitrate or distilled magnesium. Results are the same within the limits of experimental error, however, using only standard copper solution.
Table I.
Determination of Copper by Rubeanic Acid
( I n mlutions containing magnesium, aluminum, zinc, manganese, iron, cadmiurn, and nickel) Cu Found 11 Present hlg. A1 Zn M n Fe Cd Ni A B hv. Mg. Ify. M g . Mg. 3 f g . Mg. M g . M g . Mg. Ma. Mg. 16 0,0409 0,0404 0.0407 0.0408 200 200 .. . . 0.181 0.178 0.180 0.184 . . . 0.0405 0.0410 0.0408 0,0408 200 20 0.184 0.184 0.184 200 0.184 20 0,0404 0,0403 0.0405 . . i6 0.0408 200 0.181 . . 0.184 0.183 .. 16 ... 0.184 200 . . . 0,0414 0.0412 0.0413 .. .. ... 0.0408 200 .. ,.. . . . 0.188 0.174 0.183 200 0.184 . . 0.0409 0.0404 0.0407 0.02 . . 0.0408 200 .. 0.02 . . . . 0,178 0.181 0,180 200 0.184 . . . 10 , . . 0.0410 0.0412 0.0411 0.0408 200 . . 10 . . . 0.181 0.178 0,180 0.184 200 .. 0.0408 200 . . . . . 0 . 0 2 0.0411 0,0407 0.0408 200 .. . . . . . 0 . 0 2 0.178 0.178 0.178 0.184 16 0.02 10 0.02 0.0408 0.0407 0.0408 0,0408 200 0.181 0.181 20 16 0.02 10 0.02 0.181 200 0.184
c
PROCEDURE
ib
Copper in Magnesium Alloys. Weigh a 2.0-gram sample of alloy into a 400-ml. beaker, and add 50 ml. of distilled water 598
V O L U M E 21, NO. 5, M A Y 1 9 4 9
599
. ...___~
Iron interferes in this method if present in the ferrous state Table TI.
Influence of Certain Cations on Color Intensity of Copper Rubeana te ( I n gresenre of Al, Bi. and Th) RIalonic
c il
A1
MQ.
MQ.
o to!
0.102 0.102 0.102 0.102 0.102 0.102 0.102 0.102 0.102 0.102 0.102 0.102 0,102 0.102 0.102
..
Bi
Th
MQ.
MQ.
.. t
..
.. ..
.o
1 .0
10 10 10 10
..
Acid Gram
l’.b 10
10 10 10
.. 10
to
10 10
1.0
.. ..
1. 0 1.0
f.0 1.0
Trnnsrnittanrr
% 24.5 24.5
19 9 19.6 23.0 24.6 19.6 19.8 18.8 22.6 21.4 20.6 24.3 23.7 20.6 20.3
.\lthough aluminum does not produce a color reaction with rubeanic acid, it decidedly affects the color intensity of copper rubeanate. Attempts at complexing aluminum with fluoride, tartrate, and citrate \yere without success. Results for copper in these circumstances were a l ~ a y high. s Malonic acid, however, served to eliminate this error in the presence of as much as 100 mg. of aluminum per aliquot. Employment of a boric acidboras-citrate buffer complex (pH 7 ) appeared to eliminate the aluminum error, but precision and color quality were unacceptable. The manner of niixing color reagent with standard copper solutions caused significant deviation in duplicate standards. Certain other multivalent cations shown in Table IT, although failing to produce a color reaction with rubeanic acid, influence the colloidal properties of copper rubeanate. Thorium and bismuth decrease color intensity. In the absence of malonic acid, copper standards show R lower color intensity.
( 4 ) . Solution of the sample in nitric acid precludes this possibility. The yellow color of ferric citrate is also a source of error. As malonic acid both decolorizes and complexes ferric iron, this factor is conveniently eliminated. The presence of ammonium phosphate, sulfate, perchlorate, and chloride in 1-gram quantities had no effect on the results. The full development of the olive green copper rubeanate is complete within 30 minutes in the range common to magnesium alloys. For refined magnesium in which copper concentrations are extremely low it is advisable t o permit a 60-minute development period before comparison. When the log of the transmittance was plotted against amounts of copper froin 0.010 to 0.002 mg., a straight line was obtained, showing that the results are equally good for these very small amounts of copper. In samples requiring malonic acid (alloys), retardation of color development orcurs if this substance is present in concentrations fully developed colors are stable for ieveral evceeding I %. hours. The application of this method to feiioua and other nontexrous alloys as 4 ell as biological inaterials is being inve5tigated. LlTERATURE CITED
(1) Allport, N. L., arid Skrimshire, G. H., Quart. J . Pharm. Pharmacol., 5, 481 (1932). ( 2 ) Center, J. E., and MacIntoah, R.M.,IND. ESG. CHEM.,Aiv.4~. ED.,17, 239 (1945). (3) Feigl, F., and Kapulitzas, €1. J., Mikrochemie, 8, 239 (1940). (4) Nilsson, G., Analyst, 64, 501 (1939). ( 5 ) RLy, P., and M y , R. M.,Quart. J . Indian Chem. SOC.,3, 118
(1926).
(8) Willard, H. H., and Diehl, H., “Advanced Quantitative -4nalysis,” New York, D. Van Nostrand Co., 1943. (7) Wohler, F., P o g g e n d o r f ’ s A n n d e n , 3, 178 (1825). R E C E I V E .July D 8, 1948.
Metallic Contaminants in Fluid Cracking Catalyst Determination by Emission Spectrograph E. L . GUNN, Humble Oil & ReJining Company, Baytown, Tex. 4 method has been developed for the routine analysis of fluid cracking catalSst for trace metal contaminants bj means of the emission spectrograph, employing the internal standard technique with direct current arc excitation. As applied to typical plant samples, the precision of the method in the respective concentration ranges involved is expressed by a standard deviation of approximatell 8% for iron, 16% for sodium and calcium, 12% for nickel, and 5 % for chromium and vanadium. Results obtained by the spectrographic method are in fair agreement with those obtained by chemical methods. The influence on the method of changes in the alumina content of the catalyst is discussed.
I
X FLUID catalytic cracking operations, quantitative analyses of the catalyst are usually desired a t periodic intervals as an aid in controlling operations and in interpreting results. The analyses required usually are not for the major components, alumina and silica, but for trace contaminants which can accumulate on the catalyst either through metal erosion in the system 01 the deposition of inorganic components imparted to the catalyst from the feed stocks during cracking operations. The tedious and time-consuming nature of chemical methods of analysis makes such methods practically prohibitive for routine control use. The emission spectrograph has been used in this laboratory for the routine determination of catalyst contaminants for about 3 years, and it has pioved capable of providing results of adequate precision and accuracy R hich compare favorably
with those obtainable by the more difficult chemical niet,hods. Furthermore, only 2 to 2.5 hours are required for the complete spectrographic analysis of a catalyst sample for iron, nickel, chromium, vanadium, sodium, and calcium contaminants. Spectrographic methods have been applied (3, 6, 6) to the analysis of various minerals and ores. A method has been described ( 1 ) for the analysis of silica-alumina catalyst for contaminants in which lines of silicon and aluminum are used for reference; empirical factors are introduced to compensate for the differences of film emulsion response of the separate spectral regions of the film. The method of catalyst analysis emplo.yed in this laboratory differs from that described ( 1 ) in several significant respects: (1) the present method uses added internal standards as references against the sought elements; (2) the ex-
