Flame Spectrophotometric Determination of Gallium in Copper-Gallium Alloys VlLLlERS W. MELOCHE and BENNY L. BECK Department of Chemistry, University of Wisconsin, Madison 6, w i s .
The determination of gallium in copper-gallium alloys in two concentration ranges is described. Because copper enhances the emission at the 417.2-mp gallium line, copper was added to the standard gallium solutions. One series of experiments allowed the determination of gallium in the range from 0 to 1%gallium to within O.Ol%, with an average absolute deviation of 0.003%; the other series allowed determination in the range from 0 to 10% gallium to within 0.1% with an average absolute deviation of 0.1%. The effects of iron, aluminum, thallium, indium, and zinc upon the emission of gallium solutions at this wave length were also studied.
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N T H E study of copper-gallium alloys, it was necessary to have a convenient and rather versatile method for the determination of gallium. The usual gravimetric method, in n-hich the hydroxide is ignited to the oxide and weighed, did not satisfy these conditions. Indium has been determined by flame spectrophotometry (4); therefore, the application of thie method to the determination of gallium was examined. The spectrum of gallium has two usable lines: one a t 417.2 mp and the other a t 403.3 mp. The response a t both wave lengths was examined. Although 417.2 mp is a reversal line, it v-as used in preference to the 403.3-mp line because of its greater intensity. The working curves and results presented below show t h a t this is justifiable. Although the alloys contained only copper and gallium, the effects of other elements likely to be present a i t h gallium \%-ere also examined (3).
for 10 minutes before any samples were run. The oxygen pressure, the hydrogen pressure and flow, and the wave length dial r1ei-e adjusted to give maximum sensitivity for gallium a t 417.2 mp. Working curves were prepared in the three concentration ranges of 0 to 10 p.p.m., 0 to 100 p.p.m., and 0 to 1000 p.p.m. of gallium, using slit widths of 0.1, 0.04, and 0.01 mm., respectively. I n preparing the working curves, the slit width was fixed a t the values noted, and the sensitivity Lyas adjusted so that each concentration range represented about 100 units on the transmission scale. Before any readings xere taken, the bucking circuit was adjusted so that 0.0 p.p.m. of gallium represented about 3 units on the transmission scale. With this arrangement, it was aln-aye possible to check for drift in the instrument. The selector switch was in the 0.1 position a t all times. The curve for 0 t o 1000 p.p.m. of gallium exhibited the most deviation from linearity, and is shox-n in Figure 1. The curve for the concentration range from 0 t o 100 p.p.m. was more linear, and the curve for 0 to 10 p.p.m. was linear. I n any case, the results for a given range were reproducible within experimental error. Alloy Analysis. A 0.1-gram sample is convenient for analysis. The sample is dissolved in a minimum amount of nitric acid, and diluted to 100 ml. or 1 liter as noted belon-, depending upon thr amount of gallium in the alloy.
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APPARATUS AKD MATERI4LS
The instrument used vias a modified Beckman Model DU flame spectrophotometer rn ith a hlodel 4300 photomultiplier attachment and a hIodel 4020 hydrogen burner. Rlodifications included a fine adjustment for the dark current control, a “bucking” circuit to balance the potential developed by the flame background, and an added 66-megohm load resistor. This load resistor was used only with gallium solutions in the 0- to 10-p.p.m. range. A stock solution was prepared for each of the following elements: gallium, indium, thallium, iron, aluminum, zinc, and copper. The concentration of each of the solutions n-as 1000 p.p.m. with the exception of the copper, which was 4000 p.p.m. Solutions of gallium, indium, iron, and zinc were prepared by dissolving 1.000 gram of each metal in a minimum amount of hydrochloric acid and diluting to 1 liter n-ith distilled water. For the copper solution, 4.000 grams of copper were dissolved in a minimum amount of nitric acid and diluted to 1 liter. Solutions of aluminum and thallium m-ere prepared by dissolving 8.952 grams of aluminum(II1) chloride hexahydrate and 1.303 grams of thallium(1) nitrate in distilled rrater and diluting each solution to 1 liter. All chemicals used were either of reagent grade or s h o r n to be satisfactory through spectrographic analysis. Gallium was obtained from Fisher Scientific Co., Pittsburgh, Pa. PROCEDURE
The radiation for a given concentration of gallium was about twice as intense a t 417.2 mp as it was a t 403.3 mp. Because fewer elements seemed to interfere a t the former wave length ( I ) , it was used throughout this study. General. The instrument was allowed a warm-up period of about 1 hour, and the oxyhydrogen burner Tyas allom-ed to burn
u 600 800 1000 PPM. GALLIUM
Figure 1. Relative intensity vs. concentration of gallium at 417.2 mp
0 TO 1Sc RASGE. If a 0.1-gram sample is dissolved and diluted to 100 ml., the total concentration is 1000 p.p.m. of alloy. If lY0 galliumis piesent, then the solution contains 10 p.p,m. of gallium. By using the 0 to 10 p,p.m, range on the flame spectrophotometer, each intensity unit corresponds to 0.1 p.p.m. or 0.017, gallium in the alloy. I n such a system, the copper concentration varies betn-een 990 and 1000 p,p.m.: therefore, 995 p.p.m. of copper m-ere added t o the standard gallium solutions. 0 TO 10% RASGE. If a 0.1-gram sample is dissolved and diluted to 1 liter, the total concentration is 100 p.p.m. of alloy. If 10% gallium is present, the solution again contains 10 p.p,m. of gallium. Through the same reasoning as above, each intensity unit equals 0.1 p.p.m. or 0.1% gallium in the alloy. Because the copper concentration varies from 90 to 100 p.p.m., 95 p.p.m. of copper were added to all gallium standard solutions.
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V O L U M E 2 8 , NO. 1 2 , D E C E M B E R 1 9 5 6
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Table I. Apparent Gallium Due to Various Concentrations of Pure Copper Solutions at Various Slit Widths (Wave length = 417.2 mp) cu Concn., P.P.h l .
0.02
0.04
100 250 500 750 1000 2000 3000 4000
0.0 1.1 1.3 2.6 2.9 4.8 8.8 12.1
0.0 1.3 1.8 2.9 3.5 7.5 11.2 15.0
Slit Width, Mm. 0.06 0.08 0.10 Bpparent Gallium, P.P.M. 0.8 1.7 2.9 4.0 5.2 10.4 15.3 19.8
0.9 2.0 3.8 5.3 7.0 14.3 21.4 28.5
1.0 2.6 4.7 6.8 9.2 18.6 27.6 36.4
0.12
0.14
1.1 2.4 5 0 7.0 9.5 19.2 29.1 38.3
1.3 2.8 5.6 8.1 11.2 22.3 33.4 44.0
INTERFEREYCE STUDIES
Copper. Since the copper concentration was relatively high in the copper-gallium alloys, it was decided to first examine the effect of copper on the gallium radiation at 417.2 mp. For thi: work, the slit was set a t 0.04 mm. and the gallium concentration of 0 to 100 p.p.m. was used. Two series of solutions were prepared by proper dilution of the stock solutions. The first series contained five solutions of 10 p.p.m. of gallium with 10, 50, 100, 250, and 500 p.p.ni., respectively, of copper. A second series was identical except that it contained 50 p.p.m. of gallium. As the concentration of copper increased, the intensity of radiation increased, giving a high apparent concentration of gallium. The apparent concentration of gallium in parts per million was determined by transferring the intensity reading obtained to parts per million of gallium via the working curve prepared for the 0 to 100 p.p.m. range. I n the presence of 500 p,p,m. of copper, the apparent gallium concentration was about 2 units higher than that actually present. Inspection of the copper spectrum available in this laboratory showed continuous radiation at 417.2 mg, and further examination of data showed the copper interference to be additive. Therefore, a second set of experiments was performed. Eight solutions were prepared containing 100, 250, 500, 750, 1000, 2000, 3000, and 4000 p.p.m. of copper, respectively. These were examined in the gallium range from 0 to 100 p.p.m. a t vaiious slit widths a t 417.2 mp. The summary in Table I shoir s clearly that the copper interference increases with increasing concentration and slit nidth. Thus, it would be desirable to nork a t small slit widths. The effects were also examined a t 403.3 mp, and found to be more pronounced. Because gallium could be determined accurately in the 0 to 10 p.p.m. range, and because a t low gallium concentration the absolute amount of copper present would be smaller, it was decided to use this range for the determination, and to add copper to the standard solutions. Other Metals. I n addition to the effect of copper on the gallium radiation a t 417.2 mK, the effects of iron, aluminum, zinc, indium, and thallium were also studied. The same two series of solutions were prepared for each metal as for the preliminary copper interference study-Le., five solutions containing 10 p.p.m. of gallium and 10, 50, 100, 250, and 500 p.p.m., respectively, of each metal and a similar set of five solutions containing 50 p.p.m. of gallium. Of the five metals studied, iron showed the most interference. This is not surprising, as there is much iron radiation in this portion of the spectrum. -4linear relationship was noted above 50 p.p.m. of iron betneen the concentration of iron present and the apparent concentration of gallium. The apparent concentration of gallium had risen to 24 and 65 p.p.m. in the 10- and 50-p.p.m. gallium series, respectively, in the presence of 500 p.p.m. of iron. Thallium exhibited no effect. Zinc decreased the intensity slightly. Aluminum and indium increased the intensity, giving an apparent part per million gallium reading one
to two units higher than that actually present in the gallium solution in the presence of 500 p.p.m. of these two elements. Variation of the acid strength of hydrochloric and nitric acids up to 0.5N showed no effect. The acid strength of all solution3 was less than this value. RESULTS
Solutions were prepared and tested in the 0 to 1% and in the 0 to 10% gallium range. Working curves ?\ere first prepared with 2, 4, 6, 8, and 10 p.p.m. of gallium containing the concentrations of copper given above. All solutions contained 0.04% Sterox SE (Monsanto Chemical Co.) which Boycks (2) found eliminated drift of spectrophotometer readings due to formation of small air bubbles in the capillary. Readings had to be made only to the nearest unit on the transmission scale of the instrument to obtain the results (Table 11), and these readings could be reproduced with no deviation.
Table 11. Application of 3Iethod to Gallium-CopperAllo) s Solution
P.P.M. in Solution Ga
Cu
% in Alloy Ga
Cu
Ohsd. Ga,
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Absolute Error
0 t o 1% Range
A B
C
D E
F
G
H
J
999.5 998.8 997.3 996.1 994.7 993.2 992.0 991.0 gsn.5
0.5 1.2 2.7 3.9 5.3 6 8 8.0 8.9 9.5
99.6 98.7 97.4 96.0 94.B 93.1 91.9 91.0 90.3
0,4 1.3 2.6 4.0 5.4 6.9 8.1 9.0 9.7
99.95 99.88 99.73 99.61 99.47 99.32 99.20 99.10 99.05
0.05 0.12 0.27 0.39 0.53 0.68 0.80 0.89 0.95
0.05 0.12 0.28 0.39 0.53 0.07 0.81 0.89 0.95
0.00 0.00
+O.Ol 0.00 0.00 -0.01 +0.01 0.00 0.00
0 t o 10% Range
K
L
.I1 A-
P
w
S
T
99.6 98.7 97.4 96.0 94.6 93.1 91.9 9i.n 90.3
0.4 1.3 2.6 4.0 5.4 0 9 8.1 9.0 9.7
0 1 2 4 5 6 8 8 9
5 4 7 0 4 8 0 9 6
+o +o +o
1
1 1 0 0 0.0 -0.1 -0 1 -0.1 -0.1
I n the 0 to 1% range, the addition of 995 p.p.m. of copper to the standard gallium solutions gave excellent results with a masimum absolute error of only 0.01%. The trend of slight error observed in the 0 to 10% range can easily be explained. In solutions of low gallium concentration, the copper concentration was above the 95 p.p.m. in the standard solutions, giving a positive error, while in the high gallium concentrations, the copper conc6ntration was below 95 p.p.m., giving a negative error. This effect was not noted in the 0 to 1% range because the percentage copper variation was smaller. Severtheless, a maximum absolute error of only 0.1% was obtained. ACKNOWLEDGJIENT
The work described n-as supported in part by the Research Committee from funds supplied by the Ksconsin Alumni Research Foundation. LITERATURE CITED
(1) Beckman Instruments Inc., South Pasadena, Calif., Reprint R-56.
(2) Boycks, E. C., Ph.D. thesis, University of Wisconsin, 1955. (3) Hampel, C. A , ed., “Rare Metals Handbook,” p. 147, Reinhold. Kew York. 1954. (4) Ileloche, V. W., Ramsay, J. B.. l l a c k , D. J., Philip, T. V., A s ~ L . CHEX 26, 1387 ( 1 9 5 4 j . RECEIVED for review Kovernber 10, 1955.
Accepted August 11, 1956.
