solved in the aqueous stream from the tributvl phosphate-kerosine extractant is normally less than 0.2 gram per liter; however, during certain types of process ups&, additional tributyl phosphate becomes entrained in the stream and a larger break in the polarogranl is obtained, Interferences due to fission products, such 3s molybdenum, may present a problem. These have not been investigated. Clear presentation of the polarographic data is a problem in the process plant. Engineers usually have no difficulty in interpreting the conventional uranium waves, as long as a predetermined manner of measurement is followed. However, nontechnical plant
operators often have difficulty in making such a measurement. A derivative presentation n hich would be a partial solution has been tested, but is not practical because of the break caused b y tributyl phosphate in the uranium wave. The removal of oscillations from the scan lyith a filter system mould be another aid, Nonever, the use of the primitive polarographic wave as now done has certain inherent advantages. Information other than the concentration of iron in the stream is readily detectable from the increase in the length of the drop oscillations, and a n increase in the size of the break in the wave suggests a n unusual amount of tributyl phosphate in the stream.
LITERATURE CITED
(1) Bertram, H. W., Lerner, XI. K., Petretic, G. J., Roszkowski, E. S., Rodden, C. J., AXAL. CHEW 30, 354 (1958). (2) Carson, W.N.! Jr., hfichelson, C. E., Koyama, K., Ibzd., 27, 472 (1955). (3) Len.is, J. A,, Overton, K. C., Analyst 79,293 (1954). (4) P F e , C. E., Ind. Eng. Chem. 48, No. 3, , / A (1956). (5) Wilson, L. D., Smith, R. J., AKAL. CHEM.25, 334 (1953). RECEIVEDfor review January 28, 1958. Accepted May 26, 1958. Division of Industrial and Engineering Chemistry, Symposium on Xuclear Technology in the Petroleum and Chemical Industries, 131st Meeting, ACS, hfiami, Fla., ilpril 1957.
Spectrophotometric Determination of Copper in Titanium and Titanium Alloys by Dithizone Extraction HOWARD W. PENDER Research and Development Department, Chase Brass and Copper Co., Inc., Waterbury, Conn.
,A rapid spectrophotometric method using a dithizone extraction for the determination of copper in titanium and its alloys is presented. The procedure involves no preliminary chemical separation and is adaptable in the range from 0,0001 to 1%. Variables in the procedure and the effect of possible interfering elements have been investigated. Accuracy and precision data from analysis of synthetic samples, and comparison of results on other available samples a r e presented.
T
determination of small amounts of copper in titanium and its alloys is a fairly recent problem. Electrodeposition has been suggested ( I ) , but a large sample is required, and preliminary separations must be made if the common alloying elements used with titanium are present. Nikula and Codell (3) have reported a polarographic procedure for the simultaneous determination of copper, nickel, and cobalt; hovw-er, the useful concentration range is from 0.2 to 57, for each component. Frank, Goulston, and Deacutis ( 2 ) have reported a spectrophotometric method in which a chloroform-alcohol extract of a copper-neocuproine complex is used for the determination of copper in titanium. Chromium interferes and must be removed. This involves repeated fuming with perchloric and sulfuric HE
acids, filtrations, and finally, a double extraction. Shortly before the Frank, Goulston, and Deacutis method was published, work on a dithizone extraction method of analysis was started in this laboratory for the purpose of establishing spectrographic standards. When a solution of dithizone in carbon tetrachloride is shaken with a n aqueous solution of a reacting heavy metal, an internal complex salt, dithizonate, is formed. This complex salt generally is soluble in the organic solvent, to which it imparts a violet. red, orange, or yellow color, depending upon the metal involved ( 5 ) . Although dithizone reacts with nearly a score of metals, the reaction can be made specific for certain metals b y adjusting the p H of the solution to be extracted. For example, copper may be extracted from a n aqueous solution containing a certain combination of metals with a dithizonecarbon tetrachloride solution, by adjusting the aqueous solution to p H 2 . The titanium samples used in this investigation, for comparison, were obtained from the Watertown Arsenal Laboratories, Watertown, Mass. They were prepared for cooperative analysis under the direction of the Panel on Methods of Analysis, Rletallurgical Advisory Committee on Titanium, and distributed by the Watertown Arsenal for reference purposes. These samples were not primary standards.
APPARATUS AND REAGENTS
Transmittance measurements were made in matched 5-cm. Corex cells with a Beckman Rlodel B spectrophotometer. A Burrell wrist-action shaker was used for all extractions. Hydrion short range p H paper (1.4 to 2.8 and 6.0 to 8.0) was used for p H measurements. Dithizone (diphenylthiocarbazone) was obtained from the Eastman Kodak Co. and used as a n 8 mg. per liter solution in C.P. carbon tetrachloride. This solution was prepared weekly and stored under refrigeration. Standard Copper Solution. A0.1000gram portion of 99.99% vacuum-melted, vacuum-cast copper w3s dissolved in nitric acid (1 to 1) and diluted with water to 1 liter (1ml. = 100 of copper). Then 10 ml. of this solution !vas diluted to 1 liter and used as the standard copper solution (1 ml. = 1 y of copper). Standard Titanium Solution. A 1.0000-gram portion of crystal bar titanium (copper-free) w3s dissolved in sulfuric acid (1 to 1) and oxidized Kith hydrogen peroxide (30%). The excess peroxide was destroyed b y boiling and the s-olunie made u p to 100 ml. n ith n-ater. Citric Acid Solution. A 50% (weight per volume) solution of citric acid was used. Hydroxylamine Hydrochloride Solution. A 20% (weight per volume) solution of hydroxylamine hydrochloride was prepared daily. Distilled water. Double - distilled water Tvas used throughout the investigation. All reagents were of C.P. quality VOL. 30, N O . 12, DECEMBER 1958
1915
PROCEDURE
Dissolve a sample of suitable size, normally 0.5 to 1.0 gram, in 30 to 50 ml. of sulfuric acid (1 to 1) in a 250ml. beaker. When dissolution is complete, oxidize the solution b y dropmise addition of hydrogen peroxide (30%). Boil off the excess hydrogen peroxide. Cool slightly, R-ash down the sides of the beaker, and reboil for 5 to 10 minutes. Cool to room temperature. Transfer the solution to a volumetric flask of suitable size (determined by the approximate copper content), cool, di-
'O;C 90
'1 '
'
'
YFigure 1. Transmittance curves for dithizone and copper dithizonate
Table 1. Recovery of Copper from Solutions of Varying pH
pH
cu
Cu Added,
Recovered,
Error,
y
Y
Y
1.6
5.0
1.8
5.0
2.0
5.0
2.3
5.0
6.8
5.0
5.10 4.90 4.80 4.95 5 00 5.00 4.95 4.90 4.90 4.90
$0.10 -0.10 -0.20 -0.05 0.0 0.0 -0.05 -0.10 -0.10 -0.10
of
Sohtion
,
I
-I 20-
10
WAVL L E W T H , MILLIYICROHS
Table 11. Recovery of Copper from Titanium Base Solutions Containing Other Metallic Ions
Copper Recovered,
Error,
-/
Y
Cu and 10.0 mg. other metals added
5.00
Cr _.
Fe
Sn
v
5.00 4.98 4.99
0 co -0 ( 2 -0.01
5.20 5.00 5.00
+o. 20
4.97 5.00 1.99
-0.03 0.00 -0.01
4.98
-0.02
5.05
$0.05
5.01 4.99 5.00
+0.01 -0.01 0.00
3.75 4.85 4.50
-1.25 -0.15 -0.50
0.00 0.00
V (Hydroxylamine hydrochloride added) Pb
1916
0
5.10 5.00 4.95
+o. 10
4.98 4.99 4.97
-0.02 -0.01 -0.03
0.00 -0.05
ANALYTICAL CHEMISTRY
lute to the mark with Iyater, and mix thoroughly. Using a microburet, transfer the aroaer sized aliauot to a 125-ml. Squibb- 0; similar separatory funnel. Add 5 ml. of the citric acid solution and 5 ml. of the hvdroxylamine hvdrochloride solution. "Adjist the solhion t o PH 2 with ammonium hydroxide or sulfuric acid. Cool to room temperature, if necessary. Add 25 ml. of dithizone solution, stopper the separatory funnel, and shake on the mechanical shaker for 10 minutes a t maximum sneed. When the carbon tetrachloride and aqueous layers have separated, draw oft the carbon tetrachloride layer, containing the coppper dithizonate (redviolet color), into a 25-nil. volumetric flask and make up to volume ryith dithizone solution. Let stand in the dark for 15 minutes. Transfer a aortion of the solution to a 5-cm. cell Ad measure the transmittance n i t h the spectrophotometer a t a wave length of 520 mp. Carry a reagent blank through the entire procedure and use to establish a 100% transmittance setting on the spectrophotometer. Read the number of micrograms of copper present in the aliquot from a calibration curve and calculate the per cent of copper in the sample. The calibration curve is constructed as folloirs: Pipet 10-ml. portions of the standard titanium solution into five 125-ml. separatory funnels. From a microburet, add 1, 3, 5 , 7, and 9 ml., respectively, of the standard copper solution to the separatory funnels. Add 5 ml. of the citric acid solution (507,), 5 ml. of the hydroxylamine hydrochloride solution (20G70), and continue as before. On semilog graph
paper, plot the per cent transmittance us. the micrograms of copper present. EXPERIMENTAL STUDY
According to Sandell ( 6 ) . a wave length of {lo 111~is preferred for the transmittance measurement of copper &hizonate, l ~ and paige ~ (4) ~ report, in their iIlvestigation of a method for copper in biological material, that a wave length of 520 WJ is most dependable. A transmittance curve was run on a synthetic sample containing 5 y of copper and compared with one which contained no copper (Figure 1). It was determined by these curres that a wave length of 530 mp gave the greatest copper dithizonate absorbance; however, at 515 mp the least dithizone interference Tvas noted. Therefore, by compromise, and in agreement n ith Morrison and Paige, a wave length of 520 mp appeared to be most reliable. I n considering the p H of the solution to be extracted, Sandell (5) holds that the solution be made 0.05 to 0.1N in hydrochloric or sulfuric acid bcfore extraction. Morrison and Paige (4) report that experimental data indicate a p H of 2 must be approximated for consistent recovery of copper. The work performed in regard to the p H of the solution substantiated the findings of Morrison and Paige (4). If a pH of 2 is approximated, the error in recovery of copper will be negligible (Table I). Extensive study was done on the
~
recovery of copper in the extraction step. It mas found that 10 ml. of a n 8 nig. per liter dithizone solution was insufficient to extract the most concentrated standard of 9 y of copper. The volunie of dithizone mas then raised in increments of 5 ml. until a volume of 25 nil. was reached. This excess was necessary to ensure complete extraction. Shaking of the separatory funnels containing the sample solution was also n rritical factor. Periods of shaking from 2 to 15 minutes were tried. A 10-minute shaking period was needed to ensure complete extraction; however, as it n a s practically impossible to shake each sample by hand for 10 minutes and reproduce the exact conditions, the Burrell wrist-action shaker was successfully tried and adopted. -4 15minute period, following the extraction step, was found ncccssary for complete color development. Color stability was approximately 1 hour. One, two, and even three separate extractions were tried on synthetic samples containing titanium. Results indicated that 100% of the copper was recovered with one extraction, and a second or third extraction was unnecessaiy. With one extraction, 25 ml. of a n 8 mg. per liter dithizone solution, and a 10-minute shaking period it was possible to extract all the copper from synthetic samples containing titanium with good reproducibility. Once these conditions were established, different concentrations of dithizone were tried to see what effect this had on the recovery of copper. Solutions of 6 and 10 mg. per liter of dithizone wore tried and the results compared n-ith those using 8 mg. per liter of dithizone. There were no apparent differences. Copper calibration curves both with and without titanium prwent indicated that one curve was superimposed upon the other and that both obeyed Beer’s law, INTERFERENCE STUDY
Synthetic samples were prepared containing known amounts of standard titanium, copper, and other metals whose effects as interfering substances were to be studied. Nine metallic ions were tested for interference with the synthetic samples made up to contain 10% of each ion (Table 11). All nine metallic ions tested, with the exception of vanadium, showed negligible or no interference. Vanadium tended to oxidize the dithizone solution and thus gave l o ~ vrecoveries. The addition of 5 nil. of hydroxylamine hydrochloride
Table Ill.
Alloy
No. WA-5
WA-7
Analysis of Watertown Arsenal Titanium Samples
Type of
Alloy 10.57, Cr 4.570 Fe 2% Cr 2.77, Fe 2 . 1 % Rfo 0.170 2.37, Sn 0.15% Fe
% Watertown Arsenala
Dit hizon e extraction
0,0094, 0.0092, 0.0092
0.0094, 0.0092, 0,0094
0.017, 0.017, 0.016
0.016, 0.014, 0.016
0.131, 0.133, 0.136
0.132, 0.132, 0.13-1
n-
WA-44
Results of neocuproine method. Table IV.
Sample W A-5
Test of Validity of Analysis of Watertown Arsenal Titanium Samples by Standard Addition
Copper, Y Added Present ... 4.7 1.0 3.0 4.0
WA-7
WA-44
5.7 7.7 8.7 ‘29
... 1.0 1.5 2.0
6.6 7.6 8.1 8.6
solution established a reducing medium that prevented oxidation of the dithizone solution b y the vanadium. The addition of hydroxylamine hydrochloride was incorporated into the procedure t o cope with amounts of vanadium up to 10%; for concentrations over lo%, additional hydroxylamine hydrochloride may be required. RESULTS
The results obtained on the Watertown Arsenal titanium samples are shown in Table 111. Because of the lack of primary standard titanium samples, i t appeared that the only other procedure for proving the validity of the method was that of standard addition. Known amounts of copper were added to aliquots of the Watertown Arsenal samples t h a t had been previously analyzed and the total copper content was determined according to this method (Table IV). The method of standard addition reveals the accuracy and precision of the method to be within 1 to 2%. Results obtained by the dithizone extraction method on W a t e r t o m Arsenal titanium samples compare favorably with those obtained by the Watertown Arsenal Laboratory.
Transmittance,
70
39.0 31.5 22.0 17.5 47.0 39.0 25.5 20.5 27.0 21.5 19.5 17.5
Copper Found,
Error,
Y
%
4.7 5.8 7.6 8.7 3.8 4.7 6.8 7.9 6.6 7.7 8.2 8.7
0.0 +1.8 -1.3 0.0 0.0 -2.0 0.0 +1.3 0.0 +1.3 +1.2 +1.2
CONCLUSIONS
The procedure presented affords a rapid, quantitative. spectrophotometric method whereby copper in titanium and its alloys may be determined in the range from 0,0001 to 1% without preliminary chemical separation. ACKNOWLEDGMENT
The author wishes to acknodedge the constructive criticism and suggestions of J. J. Aldrich and the assistance of E. G. Grenier, both of this laboratory, and to thank Chase Brass and Copper Co., Inc., for permission to publish this work. LITERATURE CITED
(1) Armour Research Foundation,. Chicago, Ill., “Proceedings of Symposium on .4nalysis of Metallography of Titanium,” p. 10, June 1951. (2) Frank, A. J., Goulston, A. B., Deacutis, A. -4,, A s a ~ CHEJI. . 29, 750 (1957). (3) Mikula, J. J., Codell, l f . , Ibid., 27, 729 (1955). (4) Morrison, S. L., Paige, H. I,,, ISD. CHEM.,ANAL. ED.18, 211 (1946). (5) Sandell, E. B., “Colorimetric Determination of Traces of Metals,” p. 88, Interscience, Xex York, 1950. (6) Zbid., pp. 301-3.
RECEITEDfor review December 10, 1957. Accepted July 9, 1958.
VOL. 30, NO. 12, DECEMBER 1958
1917
