November 15, 1941
ANALYTICAL EDITION
Buxton, O., IND. ENG.CHEM.,ANAL.ED., 11, 128 (1939). Carter, P., and Gillam, A. E., Biochem. J., 33, 1325 (1939). Fraps, G. S., and Kemmerer, A. R., J . Assoc. Official Agr. Chem., 22, 190 (1939). (5) Fraps, G. S., Kemmerer, A. R., and Greenberg, S. M., Ibid., 23, 422 (1940). (6) Fraps, G. S., Kemmerer, A. R., and Meinke, W. R’.,Ibid., 23, 417 (1940). (7) Fraps, G. S., Treichler, R., and Kemmerer, A. R., J . A g r . Research, 53, 713 (1936).
(8) (9) (10) (1 1)
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Karrer, P., and Ruegger, A., Helv. Chim. Acta, 23, 955 (1940). Kuhn, R., and Grundmann, C., Ber., 653, 1746 (1933).
Ibid., 673, 593 (1934). Zechmeister, L., “Carotenoide”, p. 136, Berlin, Julius Springer 1934. (12) Zechmeister, L., Congr. intern. tech. chim. ind. agr., Compt. rend. Ve congr., 1, 20-1 (1937). (13) Zechmeister, L., and Tuzson, P., Biochem. J.,32, 11 (1938). PRESENTED before the Division of .4gricultural and Food Chemistry at the IOlst Meeting of the American Chemical Society, St. Louis, Mo.
Fluorescent Tests for Beryllium and Thorium J
CHARLES E. WHITE AND C. S. LOWE’ University of Maryland, College Park, Md.
F
LUORESCENT tests for both beryllium and thorium with morin and cochineal have been described b y Goto ( I ) , b u t in neither case is the reaction specific, since these reagents produce a fluorescence with many other cations. Recently morin as a re+gent for beryllium has been thoroughly studied b y Sandell (2). The response of beryllium and thorium to a common reagent is also shown by 1,2,5,8-tetrahydroxyanthraquinone (quinalizarin) , which gives the well-known cornflower blue color with beryllium. Willard and W n t e r (3) have noted t h a t thorium also gives a characteristic color reaction with this material. I n a search for reagents to give specific fluorescent tests with the cations, the idea of testing the hydroxyanthraquinones for beryllium and thorium presented itself. Several of these were tried and i t was found that 1-amino-4-hydroxyanthraquinone gives a n intense fluorescence with beryllium in alkaline solution and with thorium in acid solution.
Characteristics of Reagent The reagent, l-amino-4-hydroxyanthraquinone,is a purplishred powder, insoluble in water but soluble in alcohol. Water solution of alkalies, acids of concentration greater than 0.5 N , and alcohol solutions of over 50 per cent dissolve the compound. The color in alcohol and acids is red and in bases is purple. The alcohol and acid solutions fluoresce red, but the alkaline solutions do not fluoresce. If an alcohol solution of the material is added to a slightly acid solution of almost any cation other than thorium, a curious mode of precipitation takes place. A sacklike membrane seems to form on the walls of the test tube. This gradually contracts and the film of the same shape as the tube becomes smaller and smaller until it forms a flocculent suspension on the surface of the solution. Th++++ is the only ion that will keep this high-colored reagent dispersed in dilute acid solution. Oxidizing agents destroy the reagent; however, it seems to be stable in the presence of air. No changes in alcohol solutions are noticed after a period of several months. For testing purposes an approximately 0.1 per cent solution was made by dissolving 0.1 gram of the reagent in 100 ml. of 95 per cent ethyl alcohol. It is sometimes necessary to warm the alcohol for about 15 minutes to effect complete solution. Apparatus The source of the ultraviolet r a i s used in these experiments was the 100-watt, type 4,red-purple bulb, mercury lamp of the General Electric Vapor Lamp Company, oHoboken, K. J., which gives radiations between 3100 and 4000 A. with a maximum at 3650 A. Observations were made in a partially darkened room and ordinary soft-glass test tubes were used as containers. Beryllium Test The test solutions used contained 0.1 gram of beryllium per liter. I n making the test 0.1 ml. of this was placed in a test tube 1 Present address, National rissociation of Dyers and Cleaners, Silver Spring, Md.
and 1 ml. of 2.5 IV sodium hydroxide was added. This was diluted to 10 ml. and 0.5 ml. of 0.1 per cent alcohol solution of l-amino-4hydroxyanthraquinone v a s added. This solution under the ultraviolet lamp gave a red fluorescence extending from about 6300 to 6800 A. In visible light the beryllium solution had the same purple color as an alkaline solution of the reagent. The test is excellent to the extent of one part of beryllium in 108 parts of water and can be observed in a dilution of 1 in 4 X lo7parts. One or 2 nil. of solution can be easily observed, but it is better to use over 5 if that quantity is available. At this concentration the test is much more definite than the familiar one with quinalizarin. If such a quantity of beryllium salt is used that the hydroxide does not dissolve in 1 ml. of 2.5 N sodium hydroxide, a 10 per cent solution of sodium potassium tartrate is added drop by drop until the precipitate dissolves. An excess of sodium hydroxide must be avoided, since over 0.3 N alkali causes an appreciable diminution in the fluorescence. Mixtures containing beryllium were run through the usual procedure of analysis and the beryllium was easily detected in the presence of the aluminum by dissolving the hydroxide precipitate in sodium hydroxide and adding the reagent.
INTERFERIXQ IONS.Reasonable quantities of cations and anions, except lithium, have no effect on this test. It requires 20 grams of sodium chloride in 100 ml. of solution to destroy the fluorescence, Lithium in concentrations of 0.007 gram per 10 ml. or greater gives a fluorescence like that of beryllium. This similarity in action of lithium and beryllium was also noted b y Sandell ( 2 ) when using morin as a reagent. Colored ions such as Cr+++ in small quantities cause no difficulty, but a deep green solution will mask the fluorescent color. The other cations which remain unprecipitated in 0.2 A’ alkali seem to have no effect. Calcium ions in saturated calcium hydroxide produce a faint fluorescence, but the amount remaining after addition of 0.2 N sodium hydroxide has no effect. Small amounts of iron causing a brownish color need not be precipitated but may be rendered noninterfering by the addition of tartrate. The cations listed below under thorium were examined in this test. The common anions, such a s chloride, nitrate, sulfate, horate, and fluoride, have no effect. Ions which precipitate beryllium in alkaline solution, such as phosphate, arsenate, molybdate, tungstate, and uranate, may be nullified b y having tartrate present. Tartrate decreases slightly the intensit? of the beryllium fluorescence, but this is not serious unless exceedingly large concentrations of tartrate are used with small concentrations of beryllium. It requires 0.5 gram of sodium potassium tartrate tetrahydrate to destroy the fluorescence of 1 microgram of beryllium. Chromate oxidizes the reagent and destroys the test. If ammonium ions are present in the solution, care must be taken to make the solution decidedly
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INDUSTRIAL AND ENGINEERING CHEMISTRY
alkaline, since these ions will neutralize an equal quantity of sodium hydroxide.
Thorium Test Thorium salts in weakly acid solutions with l-amino-4hydroxyanthraquinone produce a purple colloid which gives a red fluorescence of the same wave-length range as that given by the beryllium in alkaline solution. With this reagent thorium gives a fluorescence only in acid solution and beryllium only in alkaline solution. The thorium solution to be tested must be adjusted to a pH of about 2 without too large a quantity of salt present. This is best accomplished by using thymol blue as an indicator and adding acid or alkali until the yellow point representing a pH of 1.75 is reached. Neutralizing to the phenolphthalein end point precipitates the thorium, which is rather difficult to redissolve. In addition, the quantity of salt produced in this operation is likely to precipitate the thorium colloid formed. It is important not to have the solution too acid, since the reagent itself dissolves to a sufficient extent in 0.5 N acid to give an intense fluorescence. The purple color of the thorium complex in visible light is given in the acid solution by no other element except zirconium, and it is only to distinguish this that the fluorescence need be used. The test is not apparent for less than 40 micrograms of thorium in a dilution of 1 to 125,000. Thorium nitrate or chloride forms the most convenient test solution, which is made t o contain 1 gram of thorium ion per liter. The acidity of this concentration is satisfactory for the test without further adjustment. One milliliter of this solution is mixed with 10 ml. of water and 0.5 ml. of 0.1 per cent 1-amino-4-hydroxy anthraquinone is added. The mixture is examined either directly or under the ultraviolet lamp. In testing for thorium from highly acidic mixtures such as are obtained from the separation of monazite sand, it is necessary to precipitate the thorium as a hydroxide, iodate, or oxalate, filter, and redissolve in concentrated hydrochloric acid or aqua regia. The latter is used in the case of the iodate and oxalate and hydrochloric acid is added to this until all the nitrate is removed. The material is then evaporated just to dryness to remove the excess hydrochloric acid, and the cryqtals are dissolved in water and adjusted to the proper pH with thymol blue.
INTERFERING IOKS.The only cations, other than thorium, found to give the slightest fluorescence under the above conditions were gallium and praseodymium, which give a weaker fluorescence of a little darker shade than that of thorium. If a trace of thorium is mixed with these elements, the intensity is much greater and there seems to be little chance of confusion. Both gallium and praseodymium produce red solutions in contrast to the purple of thorium and, on standing a few minutes, they form red curdy precipitates, whereas the thorium is permanently stable. It requires 1.5mg. of gallium and 10.0 mg. of praseodymium to produce the same fluorescence as 0.1 mg. of thorium. Zirconium and ferric ions do not cause a fluorescence but decrease the intensity of thorium. Oxidizing agents of the order of Ce++++, Ag+, Au+++, Hg+, and the ions of the platinum metals destroy the reagent. I n addition to those already indicated, solutions of the following cations were examined and found to have no effect: lithium, sodium, potassium, rubidium, cesium, copper, beryllium, magnesium, calcium, barium, strontium, zinc, cadmium, aluminum, lanthanum, cerous cerium, neodymium, a mixture of the rare earths as taken from monazite, indium, thallium, zirconium, hafnium, tin, lead, bismuth, antimony, chromium, manganese, cobalt, and nickel. The influence of some of the anions seems to be the effect of charged ions on a sensitive colloid, and in other cases precipitation of the thorium takes place. It required 4 grams of sodium chloride in 10 ml. of solution to destroy the colloid, and hence the fluorescence, gram of thorium. Phosphates, fluoproduced by 2 X rides, and sulfates present in quantities expressed in grams per liter half as large as the thorium destroy the fluorescence. Iodates, arsenates, oxalates, molybdates, tungstates, and uranates precipitate the thorium.
Vol. 13, No. 11
Results with Other Hydroxyanthraquinones K i t h 1,8-dihydroxyanthraquinoneJberyllium in alkaline solution gives a red fluorescence which is not so intense as that described above but can be used to detect beryllium in dilutions as low as 1 in lo6. The smallest quantity detected was 1X gram. The other ions soluble in sodium hydroxide do not interfere. Xeither beryllium nor thorium fluoresces in acid solution with this reagent. I n alkaline solution 1,5-dihydroxyanthraquinonegives a slight fluorescence with beryllium but is not of sufficient intensity to serve as a qualitative test. Seither beryllium nor thorium affects this reagent in acid solution. S o fluorescence is given by lJ2,5,8-tetrahydroxyanthraquinone with either beryllium or thorium. I n slightly acid solution this reagent with alumiFum gives a beautiful orangered fluorescence (6100 to 6500 A.) which is destroyed by the addition of thorium; 2 X 10-5 gram of thorium will destroy the fluorescence of 1 X l o + gram of aluminum in 10 ml. of gram of solution. The reagent is sensitive to only 1 X aluminum in 10 ml. and this is destroyed by many other ions and by addition of acid; hence i t cannot be considered a good test reagent for either aluminum or thorium. 4,&Diamino-1,5-dihydroxy-2-sulfonic acid anthraquinone does not fluoresce with either thorium or beryllium; l-amino5-hydroxyanthraquinone gives a slight fluorescevce with beryllium in alkaline solution but none with thorium in acid solution.
Summary The reagent 1-amino-4-hydroxyanthraquinone serves well for detecting beryllium in alkaline solutions and thorium in acid solution. I n the case of beryllium, the test is less sensitive but more specific than morin, and is much more definite than with quinalizarin. I n application to thorium the sensitivity is not so great as might be desired, but is sufficient for many practical purposes and provides a vivid color reaction for the identification of this element’. Several hydroxyanthraquinones were tested with these elements and the only other one found to present analytical possibilities was 1,8-dihydroxyanthraquinone. While all possibilities have not been tried, i t seems obvious that tests with metallic ions may assist in identifying the location of groups in the anthraquinones. Acknowledgment The authors wish to express their appreciation to W. Reeve and W. H. Power of the Organic Department of the university for preparing the 1-amino-4-hydroxyanthraquinone and to J. Lander for preparing the 1-amino-5-hydroxyanthraquinone.
Literature Cited (1) Goto, H., J . Chem. SOC.Japan, 59, 547 11938). (2) Sandell, E. B., IND. ENG.CHEW,A N ~ LED., . 12, 762 (1940). (3) Willard, H. H., and Winter, 0. B., Ibid., 5, 8 (1933). PRESENTED before t h e Division of Physical and Inorganic Chemistry, a t t h e 100th Meeting of t h e ilmerican Chemical Society, Detroit, M i c h .
CORRECTIOK.I n the article entitled “A Fluorescent Method ESG. CHEY.,Ax.4~.ED.,9, 430 (193 ’)I, we for Aluminum” [IKD. find it an improvement t o make up the Pontachrome Blue Black R in 95 per cent ethyl alcohol and to heat the test solution to about 80’ C. before adding this reagent. This gives a permanently stable reagent, and using the higher temperature gives an immediate result with low concentrations of aluminum which would require several hours to develop at room temperature. C. E. WHITE
