(3) Zbid., 32, 544 (1960). ( 4 ) Collins, P. F., Kamienski, C.
W.,
Esmay, D. L., Ellestad, R. B., Ibid., 33, 468 (1961). ( 5 ) Eberly, K. C., J . Org. Chem. 26, 1309 (1961). 16) 36, 854 , , Everson. W. L., ANAL. CHEM. (1964). ( 7 ) Feldman, C. F., Perry, E., J . Polymer Sci. 46, 217 (1960).(8) Gilman, H., Haubein, A. H., J . Am. Chem. SOC.66, 1515 (1944). (9) Gilman, H., Langham, W., Moore, F. W., Ibid., 62, 2327 (1940).
(10) Gilman, H., Van Ess, P. R., Zbid., 5 5 , 1258 (1933). (11) Glusker. D. L.. Stiles. E.. Yonkoski. B,, 3. Polyker Sd.49, 297 (1961). (12) Kamienski, C. W., Esmay, D. L., J . Org. Chem. 25, 115 (1960). (13) Kohn, E., Schuurmans, H. J. L., Cavender, J. Y.,Mendelson, R. A., J . Polymer Sci. 58, 681 (1962). (14) Kuntz, I., Gerber, A., Zbid. 42, 299 (1960). (15) Natta, G., Porri, L., Carbonaro, A., Greco, A., Makromol. Chemie 71, 207 (1964). (16) Pro, M. J., Martin, W. L., Etienne, ~
A. D., U . S. A t . Energy Comm. TID 13828 (1961). (17) Wilzbach, K. E., Kaplan, L., Brown, W. G., Science 118, 522 (1953). (18) Wilzbach, K. E., Van Dyken, A. R., Kaplan, L., ANAL. CHEM. 26, 880 (1954).
RECEIVED for review September 14, 1964. Accepted Sovember 16, 1964. Presented in part before the Division of Analytical Chemistry, 147th Meeting, ACS, April 1964. The authors thank The General Tire & Rubber Co. for permission. to publish this work.
Separation and Determination of Rhenium by Anion Excha nge Using the FIuo ride-C hIo rid e System SlLVE KALLMANN and HANS K. OBERTHIN ledoux & Co., leaneck,
N. 1.
b Rhenium is retained by Dowex-1, when various combinations of solutions of HCI, HF, NH4F, and N H L l are passed through the resin b e d to remove constituents of steels, high temperature alloys, refractory metals and alloys, also minerals and ores. The subsequent elution of rhenium with perchloric acid allows the gravimetric determination of rhenium as the metal, as the tetraphenylarsonium perrhenate, or the photometric determination using the thiocyanate complex.
N
o
SPECIFIC chemical reactions of rhenium are known. I n most instances, it is therefore necessary to carry out preliminary chemical separations before the final determination of rhenium can be achieved. Rhenium can be separated from a number of elements by distillation from a solution containing hydrochloric or hydrobromic acid and a high boiling acid such as sulfuric, perchloric, or phosphoric ( 8 ) . Steam distillation from a sulfuric acid medium (7) a t 270' C. is less effective. Rhenium usually occurs in molybdenum-rich materials, therefore some molybdenum carry-over must be anticipated in the above distillation procedures (12). Other selective reactions involve the precipitation of rhenium as the heptasulfide, Re&, as nitron perrhenate ( S ) , and as tetraphenylarsonium perrhenate (17 ) . Molybdenum interferes with the determination of small amounts of rhenium by the thiocyanate procedure and also forms a n insoluble sulfide in rather strong acid media. Several ion euchange procedures have been proposed to achieve the separation of rhenium from molybdenum (and technetium). The difference in the distribu-
280
e
ANALYTICAL CHEMISTRY
tion coefficients of Re(VII), Mo(VI), and Tc(VI1) in a l;HaCSS medium is large enough to allow a sharp separation based on the early elution of the rhenium (1, 5 ) . If a 10% sodium hydroxide solution of perrhenate and molybdate is passed through Dowex-1 , molybdenum is recovered in the eluate, while rhenium is retained by the resin and is then recovered by elution with 7 to 8 M hydrochloric acid ( 2 ) . A potassium oxalate medium has also been recommended for the separation of molybdenum from rhenium. Rhenium is retained and subsequently is eluted with dilute perchloric acid (11). The phosphate medium has also been investigated (13)*
I n analyzing various iron, nickel, cobalt, tungsten, and tantalum-base alloys containing rhenium by the now widely accepted anion exchange techniques involving the HCl-HF medium (4, 9, fO),no rhenium appeared in any of the fractions. Additional tests indicated that the following eluents used in successive steps did not remove rhenium from the column: 4y0 HF (elutes iron, nickel, cobalt, copper, and manganese); 10% HF-50T0 HCl (elutes tungsten, titanium and zirconium) ; 25YG HC1-20y0 HF (elutes niolybdenum); 4y0 HF-14yG wt./v. NH4C1 (elutes niobium); and 470 HF-14% NH4C1 neutralized with ",OH to pH 5.5 (elutes tantalum). In addition, when mineral, slag, or ore samples containing rhenium were fused in sodium peroxide, and the melt was leached in water, then acidified with sulfuric acid and adjusted with H F and/or HCI to provide any of the media previously mentioned, rhenium remained on the column, while all other constituents of the sample were removed in successive steps.
The above observations naturally offer the pleasant prospects of a separation of rhenium from virtually any combination of elements encountered in metallurgical analysis. EXPERIMENTAL
Apparatus. Polystyrene columns, 1 inch inside diameter containing 10 inches of 100- to 200-mesh Dowex-1 resin, 8 to 10% divinylbenzene crosslinkage (10). Reagents. Various HC1-HF solutions (see Table I ) ; 10% (vol./vol.) perchloric acid; 1% (wt./vol.) tetraphenylarsonium chloride; 20% (wt./ vol.) sodium thiocyanate solution; 0.5Oj, (wt./vol.) stannous chloride solution. Dissolve 5 grams of SnClz. 2 H 2 0 in 50 ml. of hot HCl and dilute to 250 ml. with water. Procedure. SOLUTION O F THE
SAM-
Tungsten, molybdenum, titanium, zirconium, niobium, and/or tantalum base alloys. Dissolve 0.5 to 3 grams of sample in a covered beaker of platinum, polyethylene, or Teflon in 15 to 75 ml. of warm hydrofluoric acid with the occasional addition of a minimum amount of nitric acid. Do not heat longer than absolutely necessary. Iron, Nickel, and/or Cobalt Base Alloys. Dissolve 0.5 to 3 grams of sample without heating in a covered polyethylene or Teflon beaker in 25 to 50 ml. of hydrochloric and 2 to 10 ml. of nitric acid. After the reaction ceases, add 10 ml. of hydrofluoric acid and 0.5 ml. of phosphoric acid and evaporate to dryness on a steam bath. Add 5 ml. of HC1 and 5 ml. of H F and repeat the evaporation. Minerals, Ores, and Concentrates. Fuse 0.5 to 5 grams of sample in an iron, nickel, or zirconium crucible in an appropriate amount of sodium peroxide. Leach the cold melt in a polyethylene beaker in a minimum PLE.
amount of water and remove the crucible after thorough rinsing. Add to the solution slowly 9.11 sulfuric acid until just acid to litmus paper, then add an appropriate amount of HF and HCl for the subsequent anion exchange separation of rhenium from other constituents of the sample as detailed below. ANIONEXCHANGE SEPARATION.The choice of a specific HF-HCl medium depends on , t h e weight and composition of the sample and on whether rhenium is the only element to be det,erniined (See Discussion Section). I n the following example it is assumed that the sample contains more than 1 gram of iron, chromium, nickel, cobalt, aluminum, manganese, and/or copper and not more than 1 gram of combined titanium, zirconium, tungsten, molybdenum, niobium, and/'or tantalum. I t is further assumed that a t least one of the six elements (Ti, Zr, W, 110, Nb, and T a ) will be determined too. Transfer a 1 J l hydrofluoric acid solution of the sample onto the resin bed. Filter, if necessary and remove Fe, Co, Ni, Cr, Cu, Al, and/or M n with 400 ml. of the same eluent. [The addition of 1% (vol.:vol.) of HC1 to the above eluent increases the solubility of chromic fluoride and aids the removal of the chromium.] Elute titanium, zirconium, andlor t,ungsten with 450 nil. of 50:10:40 HC1: HF : HzO solution. Elute molybdenum with 350 ml. of 25: 10:65 HC1: H F : H 2 0 solution, elute niobium with 350 ml. of 4y0 HF-14yo "&I, and tantalum with 350 nil. of the same HFNHaCl medium after neutralization wit'h ammonia to p H 5.5. The 5 eluates obtained above can be used for the determination of the various elements involved in the chromatographic separation by standard procedures. ELUTIONOF RHENIUM.After the removal of the other elements, elute the rhenium by passing 400 ml. of 10% perchloric acid through the column. The eluate can be used either for the gravimetric or spectrophotometric determination of the rhenium. GRAVIMETRICDETF:RSIINATIONOF RHENIUM (Re>lO ing.). Determination as the Metal. Dissolve 5 grams of boric acid in t'he eluate, add 350 ml. of concentrated hydrochloric acid, then pass a rapid stream of HzS through the solution for about one hour. Allow to stand for a t least' 2 hours, filter the Re& precipitate through a tared gooch crucible containing an asbestos ])ad, police the beaker, and wash the cruciblc 15 times with 5.11 hydrochloric acid saturated wit'h H2S. Place the crucible inside a Rose crucible and replace the air with hydrogen. Heat the crucible first a t a low temperature (200" to 250" C.), then increase the heat gradually to between 950" and 1000" C., always maintaining a stream of hydrogen. Hold at this temperat,ure for about 25 minutes. Allow to cool, first in hydrogen, finally in argon. When cold, weigh as rhenium metal. Determination as Tetraphenylarsonium I'errhenate. Filter the Re& precipitate through a filter paper and wash
Table I.
Eluent NO. 1 2
3 4 5 6
Eluents Used for Separation of Rhenium from Other Metals
Composition of eluent 4'A HF-1% HC1 50y6 HC1-1070 HF 25Yc HC1-20c/L H F
4c/, HF-14% NHaCl 4% NH4F-14% "4Cl 10% " 2 1 0 4
Elements eluted Elements retained Fe, Xi, Co, Cr, Mn, Cu, A1 Ti, Zr, W, RTo, Kb, Ta, Re All elements above, plus Ti, Mo, Kb, Ta, Re 7r -.,
..
u'
All elements above, plus Mo. Nb, Ta, Re All elements above, plus N b Ta, Re All elements above, plus Ta Re
Re
a t least 20 times with 5Jl HCl, saturated with H2S, to remove every trace Table II. Volatility of Rhenium of perchloric acid. K a s h the precipitate Evaporation of 50 ml. of aqua regia back into the original beaker with solution to dryness, followed by a second water. Pour 25 ml. of 5% ( ~ o l / v o l . ) evaporation with intermittent addition of of sodium hydroxide containing 1 ml. 10 ml. of H F of 30y0 hydrogen peroxide through the HZO4 paper receiving the solution in the Re, mg. added, Other original beaker. Warm until a clear Taken Found. ml. addition solution is obtained. Filter through the original paper and wash with hot 50.0 46.2 ... 100.0 95.3 ... water. A\dd to the filtrate dropwise 100.0 99 0 0 5 hydrochloric acid until the solution is 100 0 99 8 0 5 just acid, then render it slightly 100 0 100 3 0 5 '/2 gram ammoniacal. Evaporate the solution of Ni, to 60 ml., add 1 ml. of ammonia, 3 '/2 gram grams of sodium chloride and a slight of c o excess of a 1% (wt./vol.) solution of a Rhenium determined as metal after tetraphenylarsonium chloride. Conprecipitation as sulfide. tinue as directed by Reference 17. SPECTROPHOTOMLTRIC DF~TERMIKATION (Re 10 mg.) or in form of a perrhenate solution. The data clearly indicate that the method is specific and useful for the determination of micro and macro amounts of rhenium in ores, concentrates, metals, and alloys. LITERATURE CITED
(1) Atteberry, R. W., Boyd, G. E., J . Am. Chem. SOC.72, 4805 (1950). (2) Fkcher, S. A., hfeloche, V. W., ANAL. CHEM.24, 1100 (1952). (3) Geilman, W., Voigt, A., 2. Anorg. Chem. 193, 311 (1930).
(4) Hague, J. L., Brown, E. D., Bright, H. A., J . Aratl. Bur. Std. 62, 11 (1959). (5) Hamaguchi, H., Kawabuchi, K., Kuroda, R., ANAL. CHEM. 36, 1654 (1964). (6) Hillebrand, W. F., Lundell, G. E. F., “Applied Inorganic Analysis,” Wiley, S . Y., 1953. (7) Hiskey, C. F., Meloche, V. W., IND. ENG.CHEM.,ANAL.ED. 12, 503 (1940). (8) Hoffman, J. L., Lundell, G. E. F., J . Res. A’at2. Bur. Std. 22, 465 (1939). (9) Kallmann, S., “Treatise on Analytical I. and P. J. Chemistry,” I. &Kolthoff Elving, eds., Part 11,Vol. 6, Interscience, N. Y., 1964. (10) Kallmann, S., Oberthin, H., Liu, R., ANAL.CHEM.34, 609 (1962). (11) Meloche, T’. W., Preuss, A. F., Ibid., 26, 1911 (1954). (12) Rulfs, C. L., “Treatise on Analytical Chemistry,” I. M. Kolthoff and P. J. Elving, eds., Part 11, Vo1. 7, Interscience, N. Y., 1961. (13) Ryabchikov, D. J., Bonsova, L. M., Zh. Anal. Khim. 13, 340 (1958). (14) Tombu, C., SociCt6 GCn6rale Lf6tallurgique de Hoboken, private communication, 1961. (15) Tribalat, S., Anal. Chim. Acta 3, 113 (1949). (16) Smith, W. T., Line, L. E., Bell, W. A., J . Am. Chem. SOC.74, 4964 (1952). (17) Willard, H. H., Smith, G. M., IND. ENG. CHEM., h A L . E D . 11, 305 (1939). RECEIVED for review September 8, 1964. Accepted November 20, 1964.
Propagation of Analytical Error in Normalized Data JOHN D. HINCHEN and W. E. KOERNER Organic Chemicals Division, Research Department, Monsanto Co., Si. louis, Mo.
b The effect of normalizing a group of analytical tests on a mixture of components depends on the amount of each component present, and the variability of the method of measuring each component. The standard method of normalizing (dividing each reported per cent by the sum of all reported per cents) can b e misleading. This technique is discussed under several conditions, and recommendations are made for use of an alternative technique, which depends on previous knowledge of the reproduci bility of the original measurements.
T
chemical composition of mixtures of several compounds may be analyzed in many ways. The components may be individually determined by independent chemical analyses or by instrumental techniques, such as gas chromatography and ultraviolet or infrared absorption. For example, a mixture of HC1, methanol, and water might be analyzed as follou-s: HE
HCI by titration hleOH by gas chromatography H20 by Karl Fischer method
The Karl Fischer result may be twice as precise as the GLC value, and the acid titration may be ten times as precise. I n such a system of analysis, the independent responses may be ‘‘normalized”-that is, adjusted so that their total reported percentages add up to 100%. This technique makes the individual reported percentages interdependent, and under certain conditions may influence both the accuracy and the precision of the results. I n general, in any closed system in which measurements are taken and then adjusted to fit the restriction Xi X Z . . . X, = K where the X’s are the observed values and K is a constant, the adjusted values and their errors are interdependent. Some aspects of this relationship are covered in this paper, Three general situations are covered. I n the first, the error is proportional to the amount of component present; in the second, it is independent of the amount present; and in the third, the individual observations were made using methods which vary widely in reproducibility. It is recommended that normalizing
+
be done in such a way that the amount of change in the percentage of a given component due to normalizing is proportional to the standard deviation of the measurement. I n the case where the standard deviations are proportional to the amount present, the results will be the same as when normalizing is done merely by dividing each reported proportion by the total. Where the standard deviation is independent of the amount present, the effect of normalizing will be considerably different. Where one (or more) readings are considerably more precise than the others, acceptable results may be obtained by taking this reading (or readings) as absolutely precise. When the ratio of standard deviations is in the order of 10 to 1, this method gives results practically undetectable from those obtained by normalizing in proportion to the standard deviation. Some potential applications of these thoughts include: gas chromatography analysis; infrared and ultraviolet analysis; complete chemical analysis of a sample; and material balance studies. In general, when normalizing techniques are used, the accuracy and pieelVOL. 37, N O . 2, FEBRUARY 1965
283
