to uranium(1V) without formation of uranium(V1) was not achieved; air oxidation, direct potentiometric titration with dichromate, and addition of chromium(II1) followed by potentiometric titration of the resulting chromium(11) all proved unsuccessful. Khen determinicg uranium in the presence of iron, therefore, the formation of uranium(II1) should be avoided by reduction with the less active metal, lead. The lead reductor is easily prepared, amalgamation is unnecessary ( 6 ) , and the complications caused by the evolution of hydrogen are not encountered (9).
LITERATURE CITED
(1) Birnbaum, Nathan, Edmonds, S.
M.,
IND.ENQ. CHEY.. ANAL.ED. 12. 155
(1940). (2) Blalock, T. J., U.S. Bur. Mines, Rept. Invest. 5687 (1960).
(3) Bricker, C. E., Sweetser, P. B., ANAL. CHEM.25, 764 (1953). (4) Cooke, W. D., Hazel, Fred, McNabb, W. M., Ibid., 22, 654 (1950). (5) Ewing, D. T., Eldridge, E. J., J. Am. Chem. SOC.44,1484 (1922). (6) Furman, N. H., Schoonover. I. C., I h d . , 53, 2561 (1931). (7) Koblic, O., Chem. Listy 19, l(1925). (8) Kolthoff, I. M., Sandell, E. B., “Textbook of Quantitative Inorganic Analysis,” p. 580, Macmillm, New York, 1952. (9) Xilkantan, P., Jayaraman, N., IND. EYG.CHEY.,ANAL.ED. 11, 339 (1939).
(10) Patterson, J. H., U. S. At. Energy Comm., ANL 5410 (1955). (11) Rodden, C. J., ed.-in-chief, “Analytical Chemistrv of the Manhattan Proi_.. ect,” Nationh Xuclear Energy SeriG, Division VIII, Vol. I, Chap. 1, McGraw-Hill, Xew York, 1950. (12) Scott. W. W.. “Standard Methods . of Chemical Andysis,” p. 467, Van Nostrand. New York. 1939. (13) Sill, C: W., Peterson, H. E., ANAL. CHEM.24, 1175 (1952). (14) Someya, Kinichi, 2. anorg. allgem. Chem. 152, 368 (1926). (15) Willard, H. H., Merritt, L. L., Jr., ~
Dean, J. .Ail “Instrumental Methods of Analysis, p. 419, Van Nostrand, Xew York, 1958. RECEIVED for review September 27, 1962. Accepted December 26, 1962.
A N e w Spectrophotometric Reaction of Beryllium M. CABRERA
A.
and T. S. WEST
Chemistry Department, The University of Birmingham, Birmingham 7 5, England
b A highly sensitive method i s described for the spectrophotometric determination o f beryllium in the range 0.01 to 7 p.p.m. The color reaction between the reagent Fast Sulphon Black F and beryllium i s specific a t pH 1 1 to 11.2 in the presence of EDTA and KCN among some 25 cations examined. Fluoride, citrate, tartrate, etc., d o not interfere and a 10-fold amount of phosphate can b e tolerated. The only cations which tend to interfere are chromium(ll1) and tin(ll), and these can be rendered harmless b y previous oxidation to their higher valency forms. The stability, sensitivity, and freedom from interference of the proposed method compare favorably with those of standard methods now in use.
I
N THE course of investigating the
complex formation between copper (11) ions and the bishydroxybisazo dyestuff Fast Sulphon Black F ((3.1. KO.26990) (2)
N
we have found that not only is the reaction very sensitive for the spectrophotometric determination of copper (11), but one of the very few cationic interferences is a positive one due to beryllium (1). Since this reaction was consistently observed and could not be
removed by the addition of fluoride to bleach the beryllium complex, we decided to investigate it further, in view of the limited number of satisfactory spectrophotometric methods available for beryllium. EXPERIMENTAL
Reagents. Fast Sulphon Black F, 1.55 grams of reagent in 1 liter of water. This solution diluted 10-fold provides the 2 x 10-4Llfreagent solution. Beryllium sulfate, 10-4M, prepared from a standardized 1Ow2Msolution of BeS04.4Hz0 containing 1.772 grams of solid per liter of slightly acidified water. Potassium cyanide, 10-zX, 0.65 gram of KCN per liter of HzO. EDTA (disodium salt), lO-ZW, 3.72 grams of disodium (ethylenedinitrilo) tetraacetate dihydrate per liter of HzO. Concentrated ammonia. sDecific zravity 0.88. pH 11 to 11.2 Buffer. Mix equal Darts of 10-lX NaOH and a solution which is 10-lM with respect t o both glycine and sodium chloride. Apparatus. Unicam SP.600 spectrophotometer with 4-cm. cuvettes. Procedure. CALIBRATION.I n t o 100-ml. standard flasks pipet 0 to 8 ml. of 10-4M beryllium sulfate solution plus 3 ml. of 10-*M KCN, 2 ml. of 10-2M EDTA, and 10 ml. of Fast Sulphon Black F reagent, followed by either buffer solution (5 to 10 ml. a s required) or 0.5 t o 1 ml. of NH3-i.e., sufficient t o obtain p H 11 to 11.2 as measured by a p H meter. Allow the color to develop for a minimum of 1.5 hours (preferably 3 hours if the p H 11to 11.2 buffer isused), dilute to volume, then measure the absorbance of the solution containing no v
beryllium against the test solution containing Be in 4-em. cuvettes a t 630 mP * The amount of cyanide may be increased as required and EDTA may also be added in amounts necessary to pvercome interference from foreign ions. With larger amounts of these masking agents, due heed must be paid to their influence on the p H of the solution. 1 ml. of lO-4-U Be + 2 solution = 0.902 pg. of Be+2 Determination. Proceed as above using near-neutral test solution, but add KCN and E D T A in larger amounts if necessary, with similar modification of the calibration procedure. NATURE OF COLOR REACTION
The color developed is similar to that with copper(II), suggesting, as would be expected for a small cation such as Be+2,that the color formation is due to configurational effects on the organic molecule rather than on the cation. The absorption curve of the reagent is shown in Figure 1, along with that of the same amount of reagent in the presence of 0.5 and 1 mole ratios of Be+2. It will be seen that the absorption band due to the beryllium complex a t pH 11 is of somewhat low intensity relative to the reagent band a t 600 or 450 mp. The complex is a 1 to 1 rather than 1 to 2 complex of beryllium with the reagent; further addition of beryllium produced only a slight change, presumably due to a mms-action effect. Subsequently, the application of a Job’s method of continuous variations revealed that this was true and a 1 to 1 complex is formed. VOL. 35, NO. 3, MARCH 1963
31 1
\\\ \ 500
400
600
700
ml.L
Figure 1. Absorption spectra of Fast Sulphon Black F and its beryllium complex A. 6. C.
Reagent alone Reagent 0.5 mole proportion of BeSO, Reagent 1 mole proportion of BeSO4
++
The optimum pH is 11 to 11.2 in an ammonia medium. Figure 2 shows the effect on the color system of varying the pH. The curve represents the difference in absorbance between the blank and the beryllium complex a t each pH. The optimum color is developed a t pH 11.4, but since it decreases sharply beyond pH 11.5 it was adjudged that the best range is from pH 11 to 11.2. At pH 11.2 the color system has developed fully after 1.5 hours and is stable afterwards for more than 24 hours, during which time it shows no observable diminution. In the experiments described below a standing time of 3 hours was observed as a matter of convenience. Because of the relatively low intensity of the absorption band due to the metal complex relative to reagent background, it was decided to make analytical measurements a t 630 mp. Since the reagent has the higher absorbance a t this wavelength, calibration curves and all other analytical measurements are made by setting the beryllium complex test solution on zero absorbance and measuring the reagent absorption against it. In this way, a good straightline plot was obtained for Beer's law from 0 to 7.2 pg. of beryllium. The beryllium solution used was 1 X 10-4M and the solutions were diluted to 100 ml. before extinction measurements were made. If it is assumed that the smallest sample to be taken is 1 ml. and allowance is made for the volume of reagent solutions, etc., to be used, the concentration range is from 0.01 to 7.0 p.p.m. with the absorbances in the corresponding range from 0.05 to 0.435 a t 630 mp with 4-cm. cuvettes. On the basis of experiments performed, the effective molar absorptivity is 6 = 13,700 and hence the sensitivity index based on the formation of a complex [CsoH,",O& Be]-3, such that log Zo/Z = 0.001 is 0.007 pg. of Be per sq. cm. These data are calculated on measure312
ANALYTICAL CHEMISTRY
ments carried out a t 620 mp following the decrease in the absorption due to free reagent, rather than direct formation of the low intensity complex. Study of Interference. Previous experience with the colorimetric reactions of this reagent shows that apart from beryllium all the other metals which form colored complexes with Fast Sulphon Black F also form Cu, strong cyanide complexes-e.g., Nil Mn, and Co. Accordingly, the method was developed by forming the beryllium complex in an ammonia medium in the presence of an excess of cyanide ion to minimize interference from these reactions. Under these conditions no interference was observed from 10-fold (molar) amounts of Cu, Xi, Co, Zn, Hg, Ag, Cd, Pb, As, IT,Mol Sn(IV), V(V), AI, hfg, or Fe(II1). The shade of the color in the presence of iron(II1) was visibly slightly different from the standard, but the correct absorption a t 630 mp was observed, nevertheless, in several experiments with this metal a t IO-fold concentrations. Slightly high results were obtained in the presence of IO-fold (mole) amounts of Cs,
Table I. Analysis of Unknown Solutions by Recommended Procedure Concn. of foreign ions, Beryllium, fig. Pg.
... ... ...
~i'('i35) Mn (275) Zr (455) Cu (320)
Supplied
Found
2.07 4.32 3.60 4.48 8.37 3.42 4.32 1.04 2.17
2.07 4.41 .. -~ 3.59 4.50 8.30 3.24 4.28 1.13 2.16
Ba, and Sr, but the effect was barely perceptible and may have been due to a beryllium impurity in the salts used. Low recoveries were obtained when Cr(III), Zr, and Ti were present, probably due to coprecipitation of Be(OH), with the basic compounds of these metals precipitated a t p H 11. However, i t was observed that 10-mole amounts of Cr(V1) do not interfere with the procedure a t 630 mp and consequently interference due to Cr(II1) may be circumvented by previous oxidation in an acid medium to the higher valency. Subsequently it was found that an excess of EDTA completely prevents the interference of zirconium and reduces that of titanium to negligible proportions. EDTA was also effective in removing the strong positive interference due to Mn(I1) which had not been eliminated by an excess of cyanide ion. Tin(I1) produced a red-colored compound, as did other reducing agents such as sulfide, ascorbic acid, and hy-
I
/ pH
lo
I2
Figure 2. Variations of absorption of beryllium complex against PH
droxylamine. However, since there is no interference from Sn(IV), SO4-*,etc., preoxidation of the solution may be used as in the case of Cr(II1) to prevent interference from these ions. Of the few anions examined, it was found that very large excesses of cyanide and EDTA were without effect on the color due to beryllium. Tenfold amounts of tartrate, citrate, and fluoride were without effect, and similar amounts of phosphate yielded results that were just perceptibly low. The analysis of a series of "unknown" sample solutions is shown in Table I. DISCUSSION
The Fast Sulphon Black F reagent for beryllium used in the presence of EDTA and/or cyanide ion is specific among the 25 cations examined by us. The only ions which still interfere-viz. Cr(III), Sn(II), and reducing agents-can be rendered innocuous by preoxidation. The tolerance for fluoride ion is remarkable and good tolerance also exists toward phosphate. The presence of much larger amounts of phosphate ion could be tolerated by inclusion of similar amounts of phosphate in the solution used for calibration. In this survey the interference of foreign ions was studied a t the 10-fold (mole ratio) level, but there would appear to be no difficulty in applying the method to much larger amounts of other ions, which form colorless complexes with EDTA or cyanide, such as Zn, Al, Pb, Cd, Cu, Zr, Ti, etc., provided sufficient EDTA or cyanide is added and that account is taken of the selfbuffering effects of large amounts of these masking agents. In the case of titanium, peroxide addition might also be necessary, and with colored ions such as Fe(III), Co(II), and Cr(V1) increase of their concentration might produce measurable absorption a t 630 mp, but incorporation of similar amounts in the solutions used for calibration should circumvent any difficulty, since none of these ions interacts with the reagent.
Like all other spectrophotometric methods for beryllium, this new procedure is not as sensitive as that based on the fluorescence of the morin complex. The latter has been said to lack precision (9) and to be susceptible to the effects of varying the concentration of indifferent electrolytes (6), but more recent work (6, 7) has apparently eliminated these troubles. The method based on Fast Sulphon Black F is, when used in the presence of EDTA and cyanide ion, more selective than previously described methods (6, 8) based on sulfosalicylic acid (ultraviolet method; Ce, Zr, Cu, Fe, NOS-, PO,-* interfere), quinizarin-2-sulfonic acid (Zn, Ca, Cu, Mn, Al, F-, NOS- interfere) p-nitrophenylazo-orcinol (E = 2000, Mg, Zn, Cu interfere), quinalizarin (Fe, Ti, Zr, Co, Ni, etc., interfere), and 8hydroxyquinaldine (most heavy metals interfere). It compares most closely perhaps with the acetylacetone method, which is dependent, however, on an extraction and ultraviolet measurement. Although the molar absorptivity for this last method (E = 31,600) (3) is twice that of the Fast Sulphon Black F method, citrate, acetate, ammonia, and moderate amounts of aluminum interfere. The stability of the Fast Sulphon Black F reagent and its beryllium complex is excellent and considerably better than that of some of the above reagents. Many of the lake-formation methods (Aluminon, Eriochrome Cyanin, etc.) require the presence of gelatin for stabilization and are subject to a wide
range of interferences, though many of them could probably be made much more selective in the presence of cyanide or EDTA. CONCLUSIONS
The proposed method for beryllium offers the advantages of high selectivity and good sensitivity without necessitating the use of extraction, ultraviolet equipment, or a fluorometer. The calibration curve is very reproducible and all the solutions are stable. The pH range requires careful control and consequently the ammonia medium used in these experiments may be profitably replaced with a pH 11 to 11.2 buffer to allow more latitude in experimental manipulation. A buffer based on sodium hydroxide and glycine proved to be entirely satisfactory for work in pure beryllium solution and could presumably be used in the presence of a large number of other ions. A piperidinebased buffer similar to that used by Sill and his coworkers (6, ‘7) in their improved morin procedure would probably be yet more satisfactory and the EDTA and KCN could be incorporated in it in a similar manner. Color development with the glycine buffer was slower than in an ammonia medium and slightly lower absorbances were obtained than when NHa was used, but the system was well established within the recommended 3-hour period. Elwell and Scholes (4) have observed that the time of color development may
be greatly reduced by heating the solution after addition of the reagents. ACKNOWLEDGMENT
We are grateful to the Spanish High Council for Scientific Research for the provision of a research grant to one of us (A.M.C.), and to F. Burriel Marti for granting leave of absence from the University of Madrid to allow the scholarship to be taken up. We also acknowledge our debt to R. Belcher for helpful discussions and thank W. T. Elwell and I. R. Scholes of I.C.I. (Metals Division), Ltd., for independently verifying the recommended procedure. LITERATURE CITED
(1) Belcher, R., Cabrers, A. M., W a t , T. S., Anales Real. SOC. Espaii. Pis. y Qubm., in press. (2) Belcher, R.,Close, R. A., West, T. S., Chem. and Ind. (London)1957, 1647.
(3) Charlot, G.,“Dosages ColorimBtriques des Elements Min&aux,” 2nd ed., p. 168, Masson et Cie., Paris, 1961. (4) . . Elwell, W. T., Scholes, I. R., private communication.’ (5) Sandell, E. B.,NColcrimetric Methods for the Determination of Traces of Metals,” pp. 304-24, Interscience, New York, 1959. (6) Sill, C. W., Willis, c. P., ANAL. CHEM.31,598 (1959). (7)Sill, C. W., Willis, C. P., Flygare, J. K., Ibid., 33,1671 (1961). (8) Snell, F. D., Snell, C. T., Snell, C. A., “Colorimetric Methods of Analyais,” Vol. I I A , pp. 188-200, Van Nostrand, New York, 1959. RECEIVED for review September 21, 1962. Accepted December 10,1962.
Characterization of Granular Solids by Quantitative Attrition DAVID E. KRAMM and IRVING C. STONE Washington Research Center, W. R. Grace & Co., Clarksville, Md.
b A new method for the characterization of granular solids has been developed. The method involves quantitative attrition and the usefulness is illustrated by some studies with silicaalumina catalysts.
A
SOLID composed of fine particles bonded together to form a cohesive intact body may be called a granular solid. If such a solid is of uniform composition, possessing uniform strength, then repeated physical impacts will gradually break away surface particles, decreasing the mass of the intact solid. This process, termed attrition, has been studied for granular solids.
Granular solids can be formed from free flowing loose powders by compaction or pelleting. Such diverse materials as a graphite electrde, a cube of sugar, or an aspirin tablet are examples of granular solids. Technologies such as powder metallurgy obviously depend on granular solids. Many workers have studied the physical properties of granular solids. In particular, physical strength has often been important. The methods used to measure physical strength have been largely empirical. For example, Sheinhartz and McCullough (3) determined a friability index by tumbling granular solids and then doing a sieve analysis. Other empirical methods fre-
quently employed have measured crushing strength (2) or resistance to highvelocity air jets (1). In our work with silica-alumina catalysts we have developed a fundamental method for studying granular solids. Specifically, a quantitative attrition method for characterizing granular solids has been developed. EXPERIMENTAL
Equipment. A Model 3A Wig-L Bug, manufactured by the Crescent Dental Co., was used in this work. The Wig-L-Bug was equipped with a small metal sample chamber 1 inch long and 0.5 inch in diameter. A Veeder-Root clutch speed counter, VOL. 35, NO. 3, MARCH 1963
313
