its high copper (72.147,) and low cobalt (0.136%) content. Claassen and Daamen (3) reported recovering about 10% of the cobalt when 100 mg. of copper were present in the sample analyzed, using largely increased amounts of 2-nitroso-1-naphthol. I n initial attempts to analyze this alloy, no preliminary separation of copper was made, since it was believed that the isotope dilution method would give satisfactory results under these conditions. However, in addition to competing successfully for the complexing agent, copper formed a complex which could not be completely removed by the acid and base extractions and which absorbed slightly a t 535 mp, causing high results to be obtained for cobalt. Extensive modification of the acid and base extraction steps, such as increasing acid concentration stepwise up to 12M HC1, increasing base concentration up to saturated KOH or 28% NH40H, increasing the number of acid and base extractions, increasing the time of extractions, and increasing the volumes of acid or base used, failed t o remove the source of interference. This approach vias abandoned and an attempt was made to find a complexing agent that could be used to remove most of the copper in an extraction separation. Dithizone appeared to be ideally suited for this purpose (4, since it was a very high extraction constant for copper and
a low constant for cobalt in mild acid solutions, using chloroform as the extractant. For the 25-ml. aliquot of the aqueous sample solution taken for extraction, two preliminary 5-minute extractions, each using 50 ml. of a 0.7% (weight/ volume) solution of dithizone in chloroform, followed by two 1-minute extractions, each with 25 ml. of chloroform, were sufficient to reduce copper to a level where it no longer interfered. The separation was not specific, since in each case approximately 0.3% of the cobalt was removed by the first dithizone extraction and approximately 10% of that remaining was removed by the second. Because of this, the addition of the dithizone extraction t o the method of analysis used by Claassen and Daamen would not give accurate results. However, the use of the dithizone extraction with the isotope dilution principle proved to be ideal. RESULTS
The results obtained in four determinations with the copper-nickel-zinc alloy are shown in Table 11. The National Bureau of Standards certificate of analyses for this alloy lists a cobalt content of 0.136y0 (an average of nine values ranging from 0.13 to 0.147%). On the basis of this average value, the relative error of the mean of the values
obtained by the present method is
0.7%. Results of four determinations using the ingot iron sample are also shown in Table 11. The National Bureau of Standards provisional certificate of analysis for this iron sample lists a cobalt content of 0.006%. The results of the present method are in complete agreement, ACKNOWLEDGMENT
The authors are grateful to the United States Air Force for making it possible for one of them (W.D.R.) to undertake this study a t The Ohio State University. LITERATURE CITED
(1) Am. Soc. Testing Materials, Philadelphia, “ASTM Methods for Chemical
Analysis of Metals,” p. 120, 1950.
( 2 ) Ibid., pp. 239-40; (3) Claassen. A,. Daamen,’ rl., Anal. Chim. . Acta 12, 547 (1555).
(4) Sandell, E. B., “Colorimetric Determination of Traces of Metals,” 3rd ed., pp. 135-76, Interscience, S e w York, 1959. (5) Schwarzenbach, G;, “Complexometric Titrations,” pp. 18-9, Interscience, Kew York, 1957. (6) Sporek, K. F., ANAL.CHEJI.33, 754 (1561). RECEIVED for review March 2, 1961. Accepted November 6, 1961. Taken in part from the M.S.thesis of William D. Ralph, Jr., The Ohio State University, 1960.
Spectrophotometric Determination of Ruthenium with 2-Nitroso-1-naphthol D. L. MANNING
and OSCAR MENISI
Analytical Chemistry Division, Oak Ridge Nafional Laboratory, Oak Ridge, Jenn.
b A sensitive spectrophotometric method for the determination of ruthenium is based on the color reaction of ruthenium with 2-nitroso- 1 -naphthol in 3M hydrochloric acid saturated with sulfur dioxide. The colored species exhibits maximum absorbance a t 600 mp. Simple salts of ruthenium such as ruthenium chloride can b e determined in the presence of uranium without a prior separation. Beer’s law is obeyed over the concentration range, 1 to 10 pg. Ru per ml. The relative standard deviation is about 5%. The molar absorptivity of the colored species is approximately 6500.
R
one of the most abundant elements formed during nuclear fission, is of interest in the homogeneous reactor program because of its 94
UTHENIUM,
ANALYTICAL CHEMISTRY
effect upon the stability of solutions of uranyl sulfate and upon the corrosion rate of austenitic steel systems. Numerous chromogenic reagents for the spectrophotometric determination of ruthenium are recorded in the literature (f-3, 6-7). Color reactions with ruthenium are frequently carried out in weakly acidic solutions a t a controlled pH, after the ruthenium has been separated from other substances by a distillation process. Jacobs and Yoe (S), however, introduced another reagent that can be used in a strong mineral acid solution without a close control of p H after distillation. A new chromogenic reagent, 2-nitrosoI-naphthol, is proposed for the colorimetric determination of ruthenium. The feasibility of utilizing various naphthols for the colorimetric determination of ruthenium was reported by Ryan
(5), but no experimental details were presented. I n this laboratory, ruthenium, in a medium of hydrochloric acid saturated with sulfur dioxide, reacts with 2-nitroso-1-naphthol to form a blue complex which exhibits maximum absorbance a t 600 mp. This reagent and that proposed by Jacobs and Yoe can be utilized in a strong mineral acid solution without close pH control. Ruthenium can also be determined without prior separation in the presence of milligram amounts of uranium and microgram quantities of the corrosion products of steel such as iron, nickel, and chromium when 2-nitroso-1-naphthol is used as the chromogenic reagent. 1 Present address, Nuclear Materials and Equipment Corp., A4pollo,Pa.
\
I I
e,*-'/.'
I
10-
Ru, y/ml
'\
I 0.5
0,2-C 300
'\-
I
400
500
600
700
800
900
IYAVELE'YGTH ( m ' p i
Figure 1. Absorption spectra of ruthenium-2-nitroso-1 -naphthol complex and 2-nitroso-1 -naphthol reagent Ru 14 pg./ml. Cell path 1 cm. Ruthenium-2-nitroso-1 -naphthol complex 2-Nitroso- 1 -naphthol
+''0. O oo
____
I n the present investigation, optimum conditions were established for the deterniinntion of microgram quantities of ruthenium and ruthenium-nitroso salts in solutions of uranyl sulfate. I n the case of ruthenium-nitroso complexes, however, a separation of the ruthenium is necessary before developing the color with 2-nitroso-1-naphthol. Ruthenium, whether present as the metal, oxide, hydrate, or other ruthenium compound, is separated through the application of a fusion pyrolysis technique developed by Powell and hlenis ( 4 ) , utilizing sodium bisniuthate (NaBiOs) as a flux. REAGENTS AND APPARATUS
Standard ruthenium solution, 100 pg. of Ru per ml. Prepare from reagent grade RuC13 according to the procedure of Banks and O'Laughlin ( I ) . 2-Nitroso-1-naphthol solution, 0.3%. Dissolve 300 mg. of the recrystallized salt in 100 nil. of ethyl alcohol. Hydrochloric acid, 3 M , saturated with SO2. Bubble SO2 through 100 ml. of 3M HCl for about 10 minutes. Sulfur dioxide, compressed cylinder, lecture bottle size. Spectrophotometer, Beckman Model
DU.
RECOMMENDED PROCEDURE
Ruthenium. Transfer a n aliquot of the sample solution which contains from 50 to 400 pg. of ruthenium and not more than 50 mg. of uranium to a 50-ml. volumetric flask. Add 25 ml. of the 3114 HC1-S02 reagent and 5 ml. of 0.37, 2-nitroso-1-naphthol. Heat the sample in a boiling mater bath for approximately 20 minutes. Remove the flask and cool by immersing under a
i
HYDROCHLORIC 2 ACID, 3 c?
4
(SATURATED WITH S02)
Figure 2. The effect of the concentration o f hydrochloric acid on the absorbance of the ruthenium-2nitroso-1 -naphthol complex
stream of running water. Add 10 ml. of ethanol and dilute to volume with the HC1-SO2 reagent. llIeasure the absorbance us. a reagent blank a t 600 mp. Determine the ruthenium concentration by referring the measured absorbance to a previously prepared calibration curve. EXPERIMENTAL
Absorbance Spectra and Adherence to Beer's Law. The absorption spectrum of the ruthenium-2-nitroso-lnaphthol complex measured us. a reagent blank is shown in Figure 1. The complex exhibits maximum absorbance a t 600 nip. At this wavelength, Beer's law is obeyed over the concentration range, 1to 10 pg. Ru per ml. as demonstrated in TableI. Over this range, the relative standard deviation is about 4%. The molar absorbancy index is approximately 6500 for measurements made a t 600 mp. The color is stable for about 1 hour and fades approximately 20y0 over a period of 24 hours. Efforts to determine the mole ratio of the complex were not successful because the reagent is slowly decomposed in the HC1-SO, solution which is required to keep the ruthenium in the reduced form. Effect of HC1. The effect of the concentration of hydrochloric acid on the color reaction between ruthenium and 2-nitroso-1-naphthol is illustrated in Figure 2. The molarity of the hydrochloric acid was varied from one t o four. The absorbance of the complex is a maximum in 1 M acid, b u t decreases somewhat as the concentration of HCl is increased to 2M; from 2 to 4,
the absorbance of tlie complex is not significantly affected by small variations in the acid concentration. For subsequent work, an acid concentration of 3M was selected because this concentration is about the midpoint of the range over which the formation of the colored species is least affected by small changes in the HCl concentration. Effect of the Concentration of 2Nitroso-1-naphthol and Uranium. I n the absence of uranium, as noted in Table 11, the absorbance of the complex changes only 3% when the reagent concentration is varied approximately threefold. As long as a n excess of the chromogenic reagent is present, the concentration, therefore, is not a critical factor.
Table I. Calibration Data for the Determination of Ruthenium with 2-Nitroso-1 -naphthol 2-Sitroso-1-naphthol, O.3yO 5 ml. HCl (satd. with SO*) 35 50 ml. Volume 1 cni. Cell path
Ruthenium,a pg.
Absorbance, 4
600
0.802
Factor, pg./A
747
Average 712 Relative standard deviation, yo 4 RuC&
VOL. 34, NO. 1, JANUARY 1962
95
Table II. The Effect of Uranium on the Absorbance of the Ruihenium-2Nitroso-1 -naphthol Complex in the Presence of Increasing Concentrations of Reagent
Ruthenium 400 pg. 50 ml. Volume 2-Nitroso-1-naphthol, 0.3 % Uranium.O 3 ml. 5 ml. 10 ml. Mg. ilbsorbance Ruthenium Complex None 0.610 0.596 0.590 0.585 0.590 0.600 50 100 0.532 0.555 0.545 200 0.520 0.535 0.500 0.495 0.465 250 0.455 5 AS UOzSOd.
In the presence of uranium, there is a general decrease in the absorbance of the colored species as the amount of uranium is increased above the total of 50 mg. The effect from uranium is not altered even with a threefold increase in the concentration of the 2nitroso-1-naphthol reagent. With the maximum concentration of uranium tested, 250 mg., the relative decrease in absorbance is approximately 25%.
Therefore, for the determination of ruthenium in the presence of known, larger quantities of uranium, calibration data can be established (Table 111). As noted in Tables I and 111, the precision of the method is essentially the same whether uranium is present or absent. The essential requirement is that the concentration of uranium in the samples and standards be approximately the same. As evident from Table 11, microgram quantities of uranium will not interfere.
Table 111. Calibration Data for the Determination of Ruthenium in the Presence of Uranium
Uranium Volume Cell path Ruthenium, Absorbance, pg. 100
200 300
400 500
ACKNOWLEDGMENT
The authors thank F. E. Jenkins for investigating the color reaction of ruthenium with 2-nitroso-1-naphthol and H. P. House for aid in the preparation of this manuscript. LITERATURE CITED
(1) Banks, C. V., O’Laughlin, J. TV., AXAL.CHEM.29, 1412 (1957). 121 \ , Beamish. F. E.. McBrvde. W. A. E.. Anal. Chim. Acta’9, 349 11953). (3) Jacobs, W.D., Yoe, J. H., Talanta 2, 270 (1949). (4) Menis, O., Powell, R. H., ANAL. CHEM.34, 167 (1962). (5) Ryan, D. E., Analyst 79, 707.( 1954). (6) Sandell, E. D., “Colorimetric Metal
A 0.125 0.255 0.401 0.525 0.652
200 mg. 50 nil. 1 em. Factor, pg./A’ 800
785
750 763 800
Average 780 Relative Standard Deviation, yo 3 Analysis,” 3rd ed., Vol. 3, p. 778ff, Interscience, New York, 1959. (7) Snell, F. D., Snell, C. .T., “Colorimetric Methods of Analysis,” Vol. IIA, p. 443ff, Van Nostrand, New York, 1959. RECEIVEDfor review June 6, 1960. Resubmitted June 19, 1961. Accepted October 19, 1961. Work carried out under Contract No. TV-7405-eng-26 a t Oak Ridge Kational Laboratory, operated by Union Carbide Nuclear Co., a Division of Union Carbide Corp.,for the Atomic Energy Commission.
Determination of Sodium in Silicate Minerals and Rocks by Neutron Activation Analysis GERALD L. SCHROEDER’ and JOHN W. WINCHESTER Department o f Geology and Geophysics, Massachusetts Institute of Technology, Cambridge
b A procedure is described for the determination of sodium in natural silicate minerals by pile neutron activation and counting the induced y radiation in the irradiated specimen without chemical processing. An integral scintillation counter set to accept all y-rays with energies above 2.6 m.e.v. is used for radioactivity measurement. Precision and absolute accuracy of the method are of the order of 1 to 270, and interference by trace elements is virtually negligible. Results are presented for the analysis of the standard granite G - 1, diabase W - 1, argillaceous limestone NBS l a , and flint clay NBS 97.
T
HE determination of the alkalies in naturally occurring silicate minerals is difficult where high accuracy is desired. Fairbairn ( 2 ) and, more recently, Ahrens (1) have shown that the determination of N’a and K by conventional chemical methods often leads t o
96
0
ANALYTICAL CHEMISTRY
large errors. Analyses of the standard granite G-1 and standard diabase W-1, distributed to approximately 30 laboratories, were compared, and the standard deviations of sodium contents for each laboratory reporting were 5.270 for G-1 and 9.3% for W-1. The potassium contents showed standard deviations of single values reported of 6.8% for G-1 and 23Y0 for W-l. These errors are too large for most geochemical purposes. In this work, a procedure for the determination of sodium in a wide range of naturally occurring silicate minerals is reported which requires no chemical processing and is shown to be accurate, even where the sodium content is very low. It is based on pile neutron activation and selective counting of high energy y-rays of iYa24. A similar procedure for determination of potassium was reported earlier (9). Minerals composed of the elements 0, Si, Al, Na, K, Mg, Ca, and Fe, when irradiated with thermal neutrons, give
39, Mass.
rise to radioisotopes in proportion to the amount of each element present. A short irradiation followed by a 1- to 2day “cooling” time leaves 14.97-hour Na24 and 12.46-hour K42as the principal radioactive species for common rock minerals. Shorter-lived nuclides from 0, Si, Al, Mg, and Ca decay t o low levels, and little radioactivity is induced in Fe. NaZ4decays by emitting 1.394-m.e.v. p , 1.368-m.e.v. y, and 2.754-m.e.v. y, each in 100% of the decays (8). In the K42 decay, particles emitted are 3.55-m.e.v. fi in 82% of the decays and 1.99-m.e.v. p and 1.53m.e.v. y, each in 18% of the decays (8). The high energy y of S a z 4 may be counted selectively without interference from K42 or trace elements by using a scintillation counter and integral discriminator set to exclude y-rays of energy E y < 2.6 m.e.v. 1 Present address, Department of Physics, Massachusetts Institute of Technology, Cambridge 39, Mass.
