V O L U M E 23, NO. 2, F E B R U A R Y 1 9 5 1 Blendor with or without the aid of a small portion of n-hexane. The animal tissue was ground in a mortar, or tissue grinder. Each sample was then extracted for 1 hour with 250 ml. of n-hexane in a Soxhlet extractor. The extract was transferred to a beaker, covered with a ribbed watch glass, and evaporated just to dryness. While still warm, the residue was dissolved and quantitatively transferred to a Lewis-Benedict tube with a total volume of alcohol not exceeding 7.0 ml. This solution was used for analysis by the proposed method. If the colored solutions were turbid, they were centrifuged or filtered prior to the color estimation. It was found that n-hexane residue contained a small amount of color that interfered with the determination. Blanks were prepared for the lC!Oyo transmittancy setting b y , evaporating 250 ml. of n-hexane in a beaker, dissolving the residue in not more than 7 ml. of alcohol, and proceeding as directed for preparation of the calibration curve, This procedure eliminated the error caused by the solvent residue. Determination of Dilan in Animal Tissues Containing Fat. Animal tissue containing fat yielded a turbid solution that could not be clarified either by filtering or centrifuging. It w&s found that the solution could be clarified by adding 5 ml. of ether after the addition of the ferric chloride reagent, The solution was diluted to 25 ml. instead of 12.5 ml. with alcohol. A calibration curve was prepared for the determination of Dilan in animal tissues containing fat using the same modification, and blanks for the 100% transmittancy setting were likewise modified.
351
n-hexane in a separatory funnel. By this extraction procedure, recoveries of Dilan were obtained which were equal to those ohtained by the longer described procedure. Dilan added to animal tissue which was ground with anhydrous sodium sulfate to ensure dehydration of the tissue could not be recovered even on prolonged extraction with n-hexane. The following conclusions were drawn from a study of the results of analyses of several hundred samples of animal tissue: There is an average error of 4 8 micrograms for tissues from animals used as controls. This error probably is due to a combination of three factors: error in setting the instrument a t 100% transmittancy from day to day, error in reading the transmittancy from day to day, error in reading the transmittancy and calibration curve approaching 100% transmittancy, and difference in extracted color from different tissues and different amounts of the same type of tissue. The precision and accuracy of the method decrease rapidly as the Dilan content of the sample decreases below 50 micrograms. The authors consider a result less than 50 ;t: 10 micrograms as qualitative, and a result of 10 micrograms or less as zero. If 10 to 50 micrograms are found, a larger sample should be used or the result should be reported as less than 50 micrograms.
RESULTS
.4n alcoholic solution of Dilan of known concentration was evenly spaced by dropping on green beans and rabbit tissue. The beans and rabbit tissue were allowed to stand varying lengths of time from one hour t o one day, and were then analyzed for Dilan by the method given above. Typical data are presented in Tables I11 and IV. DISCUSSION
An alternative procedure for the recovery of Dilan froin green beans consisted of successively extracting (also called stripping) a weighed ~ainpleof the treated beans with three 100-ml. portions of
LITERATURE CITED
(1) Bose, K. P., Analyst, 56, 504-7 (1931). (2) Desvergues, L., Ann. chim. anal. chim.a p p l . , 13, 321-2 (1931). (3) Hass, H. B., and Riley, E. F., Chem. Revs., 32,395 (1943). (4) Konovalov, J., J . Russ. Phys. Chem. SOC.,27,453-5 (1895).
(5) Konovalov, M., Ber., 28, 1850-2'(1895). (6) Lowry, T. M., and hlagson, E. H., J . Chem. Soc., 98, 107-19 (1908). (7) Scott, E: W., and Treon, J. F., IND.ENG.CHEM.,ANAL.ED., 12, 189-90 (1940). RECEIVED -4ugust 19, 1950. Presented before the Division of Analytical SocxBrY, Cherniatry at the 118th Meeting of the . ~ M E R I C A S CAEMICAL Chicago, Ill.
Analytical Use of the Formation of the Beryllium-Fluoride Complex FRITZ FEIGL A S D A. SCHAEFFER Laboratorio da Produqcio Mineral, Ministerio da .4gricultura, and Laboratorio Quimico da Escola Tecnica do Exercito, Ministerio da Guerra, Rio de Janeiro, Brazil
Beryllium ions have such a great tendency to form stable complex BeFd-- ions that beryllium nitrate solutions are able to dissolve insoluble fluorides and to demask reaction systems which are masked by fluoride. Beryllium silicates and metallic beryllium are transformed into potassium fluoberyllate by fusing or sintering with potassium hydrogen fluoride. These effects permit essential simplifications in gravimetric analysis of fluorspar and cryolite, and detection of phosphate, molybdate, tungstate, iron, and titanium in presence of an excess of fluoride and of beryllium in minerals, ores, and alloys.
I
T HAS been reported ( 7 ) that fluorspar suspended in dilute
acids is completely dissolved upon addition of complex formers of fluorine: aluminum, iron, zirconium, and beryllium ions, as aell as boric acid. When beryllium nitrate or chloride is used, the calcium can be precipitated as oxalate, after solution in acid and buffering. New experiments have shown that calciuni fluoride, produced by precipitation, is completely dissolved, and finely powdered fluorspar is almost completely solubilized even in the absence of acids, merely by heating with concentrated solutions of beryllium nitrate. Obviously this is due to the elimination of fluorine ions from the solution equilibrium of cal-
cium fluoride (Equation l ) through formation of complex fluoberyllate (BeF*--) ions according to Equation 2. CaF2(.,l,d, +Ca'+
+ 2F-
+ B e + + --+ BeFa-2CaFz + Be+' +BeFd-- + 2Ca++
(1) (2 1
4F-
(1)
+:@I
Similar displacenient of equilibria is produced by aluminum, iron, and zirconium ions, due to the formation of complex AlFB---, FeF6- --, and ZrFs-- ions. Boric acid eliminates fluorine ions by formation of BF4- ions (2, 11). I n addition t o calcium fluoride,
ANALYTICAL CHEMISTRY
35 2 the insoluble fluorides of thorium, cerium, lanthanum, lead, and magnesium are dissolved by beryllium nitrate in esccss. Therefore these fluorides cannot be precipitated from heryllium-containing alkali fluoride solutions. Because t,he small concentration of fluorine ions in water suspensions of acid-resistant, fluorides is sufficient, to produce fluoherJ-llate ions, the same is to bc espected from the small fluorine ion concent,ration in w t e r solutions of compounds in which fluorine, owing t o comples or principal valence binding, is part of a stable anion. This really is true, and means that thv following gross reactions are v d i d :
+ +
2AIFs--3Be" --+3BeFd-Mo02F4-- R e A T 2H20 +Moo4--
+
+ 2A1++' (3) + BeF4-- + 4H+ (4)
-4ccording t o Equations 3 and 4, reactions of aluniiiiuni and molybdate ions, which arc masked in the presence of fluoride ions, occur immediately after addition of a sufficient amount of beryllium ions ( 6 ) . The same deniasking take8 pl:iccl in the solution of other eompounds of the above type. The solubilization of insoluble fluorides and the demasking in solutions of fluorincvontaining principal and coniples compounds by bwyllium salts arc due t o the great stability of fluoberyllate ions. It is t,herefore rimarkable that the color lake react,ion of beryllium with quinalizarin descrilxd by Fischer (9) occurs a l ~ o in solution of potamiiuin fluoberyllate. All other metals, box-evcr, which form color lakes with quinalizarin, are masked when present in the form of normal or comples fluorides. Fischer has used the sintering of beryllium-containing silicates with sodium silicofluoride, thus tran~formingmetals into fluorides and coniplex fluorides, in order t o determine beryllium colorimetrically through the quinalizarin rcact'ion. The format,ion of potassium fluoberyllate can also be obtained by sintering with potassium hydrofluoride, permitting thus, in combination with the quinalizarin reaction, a wisitive and specific test for beryllium in minerals, ores, and alloys. I n the folloTving, the analytical UPC of the formation of the ber~-llium-fluoridecomples is described. GRAVIMETRIC DETERMINATION O F CALCIUM IN FLUORSPAR
The analytical lit'erature does not show whether the abovementioned solubilization of calcium fluoride by berylliuni nitrate has been considered in the annlysis of fluorspar. Since 1941, in the Laboratories of Mineral Production of the Xinistry of -4griculture, Rio de Janeiro, all fluorspar analyses have h e m csccuted in the following m a n n c ~ :
Procedure. From 0.1 to 0.2 gram of the finely powdered material is treated with 0.1 -V acetic acid for 30 minutes upon a water bath, and then filtered. The amount of calcium in the filtrate, determined by precipitation as calcium oxalate, indicates the "acid-soluble" calcium. The residue together with the filter paper is dried and calcined and then quantitatively transferred to a beaker where it is treated with 5 to 10 ml. of 2 S hydrochloric acid, 50 ml. of water, and 1 to 2 grams of beryllium nitrate. After heating for abbut 10 minutes any residue is filtered, dried, and calcined (insoluble residue). The filtrate from this residue contains, besides berylliuni fluoride and an excess of beryllium nitrate, the whole calcium formally bound with fluoride. This solution is treated with :tmmonia until a small amount of precipitate remains j then the precipitate is dissolved by dropwise addition of hot dilute acetic acid and calcium oxalate is precipitated and determined in the usual way. The amount of fluoride corresponding to this calcium value indicates the fluorine content of the material under examination. Instead of determining calcium by weighing the oxalate or by titrating the calcium-bound osalic acid xvith permanganate, the following can be recommentled: The precipitated calcium osalate is filtered after standing overnight and washed with dilute ammonium oxalate solution. After drying and calcination t o calcium oxide, the latter-which always contains calcium carbonate-is dissolved in a given amount of 0.1 -V hydrochloric acid, and the excess acid is backtitrated with 0.1 N sodium hydroxide, using methyl orange as iiidicator. This procedure has the advantage that the precipi-
tated calcium oxalate does not require washing with water, with its attendant small but inevitable losses. Any ammonium oxalate retained by calcium osalate is completely eliminated by calcination. Adsorbed beryllium salt is harmless, because beryllium oxide formed by glowing is not attacked by diluted acids. Iu order t o illustrate t,his procedure, calcium determinations were carried out with pure natural fluorspar crystals; in amounts of 0.1 t o 0.2 gram the product was dissolved in acid beryllium nitrate solution without leaving a visible residue. Ca, R 51.23 51.11 51.06 51.54 51.41 4 v . 51.27 Theoretical 5 1 . 3 3
Fluorspar, G . 0.1068 0.0941 0.1048 0.1007 0,0994
Ca, G. 0,0547 0.0481 0,0535 0,0519 0.0511
F Calcd., R 48.57 48.45 48.41 48.87 48.74 48.61 48.67
GRAVIVETRIC DETERhIJNATION O F ALUhIIKA IN CRYOLITE
The hitherto used procedure for gravimetric determination of alumina in cryolite ( Na3AIFs) consists in fuming the material with concentrated sulfuric acid, dissolving the residue in water, and precipitat,ing alumina by a known procedure. The following method of destroying the complex alumina fluoride and precipitating aluminum oxine according to Berg ( I ) is much simpler.
Procedure. From 0.1 t o 0.2 gram of the fine powdered mineral is warmed 5 minutes with 5 t o 10 ml. of 2 S hydrochloric acid, 50 ml. of water, and 0.5 to 1.0 gram of beryllium nitrate. Any residue is considered as gaiigue and eliminated by filtration. To the warm filtrate ammonia is added until a small precipitate remains, which is dissolved hy drop\vise addition of 2 N acetic acid. S o w 10 to 20 ml. of 2 S ammonium acetate are added, followed by a 4% solution of osine (8-quinolinol) in acetic acid, until no precipitation occurs, and heated to boiling. The aluminum oxine precipitate is filtered, aft,er standing an hour, through a filt,ering rrucible, washed with water, drirti at 110" to 120" C., and weighed. The results ohtained by the analysis of pure cryolite from Greenland were: Al, Yo 12 84 12 85 12 72 12 84 12 82 .i\., 12.81 Theoretical 19.83
.4I Oxinate, G. 0 2746 0 2733 0 1664 0 2379 0 2070
Cryolite, G. 0 1255 0 1248 0 0768 0 1088 0 0947
F Calcd.,
Yo
54 27 54 32 53 77 54 27 54 1'3
54.16 34.30
When an iron-containing cryolite is analyzed, ferric oxine together with aluminum osine is precipitated, as shown by a greenish color of bhe precipitate instead of a yellow one. I n this case t,he iron can be colorimetrically determined in a separate sample with thiocyanate after demasking with heryllium nitrate. DETECTION OF PHOSPHATE IN PRESEYCE O F LARGE AMOUNTS OF ALKALI FLUORIDE
Huchcrcr and Meier (5)as well as Xeuhaus ( I O ) have reported that the presence of fluorine ions prevents the complete precipitation of (NH4)3PO4.12M0O3.This interference is due t o the formation of fluomolybdate ions, whereby a precipitation of phosphate ions by molybdate ions occurs only when all fluoride is transferred in fluomolybdate ions (Mo02F4--). This must be kept in mind when phosphate is t o be det,ected in the presence of fluoride by the molybdate reaction. The following data were obtained by heating ( a t 80" C.) the test solution with 5 ml. of ammonium molybdate solution ( 5 grams of salt in 100 i d . of water poured into 35 nil. of nitric acid, d, 1.2).
I n 10 ml.
I ~
[
PzOr, -Mg 2 2 2
+ +
+
NaF, G. 0.0 0.08 1.0
2
+
1.2
2
+
1.5
Strong precipitation Slow and incom lete precipitation ~ q ~ o \ rcolor on feating, nearly colorless on cooling; no precipitation Slqw yellow color on heating, colorless on cooling y o color, no precipitation
V O L U M E 2 3 , NO. 2, F E B R U A R Y 1 9 5 1 The above data show the danger that considerable amounts of phosphate may escape the sensitive molybdate test in a 1% sodium fluoride solution containing 0.02% phosphorus pentoxide. This danger is particularly great when smaller amounts of phosphate are to be detected in more concentrated alkali fluoride solutions. The masking action of fluoride, interfering Lvith the phosphate test, can be eliminated by later addition of befyllium nitrate. Instead of using the nitric acid molybdate solution, a beryllium-containing molybdate solution can be used. The latter is especially indicated when phosphates are to be identified by the molybdate reaction through a spot test on filter papw (6). DETECTION O F MOLYBDATE AND TUNGSTATE IN PRESENCE OF ALKALI FLUORIDE
The masking of reactions of molybdate and tungstate ions by fluorides ( 4 ) has probably found little consideration, because, in analyzing fluorine-containing material, all fluorine can generally be eliminated as hydrogen fluoride by fuming with concentrated sulfuric acid. This troublesome procedure where tungsten trioxide (and in part also molybdenum trioxide) remain together with insoluble sulfates and must be separated from the latter can be replaced by the simple demasking of fluorized molybdenic and tungstic acid. If, therefore, alkali molybdate and tungstate are to be detected in the presence of much alkali fluoride, an appropriate reagent for molybdate (or tungstate) is to be added to the test solution, followed by beryllium nitrate (solid or in concentrated solution). Different tests for molybdate and tungstate in fluorine-containing solutions were checked in this way. The limit of identification was found t o be about one half that in fluorine-free solutions. DETECTION OF BERYLLIU&l IN MINERALS, ORES, AND ALLOYS
The specific colorimetric determination of beryllium described by Fischer (9) is based on the formation of sodium fluoberyllate :tnd its reaction with alkaline quinalizarin solution, whereby the blue quinalizarin lake is formed. The formation of this lake and its stability toward hypobromite can be used for exact detection of beryllium in minerals, ores, and alloys. Silicatic or intermetallic bound beryllium can easily be transformed into potassium fluo1wrvll:itr by heating with potassium hydrogen bifluoride:
+
+
+
BeSiOs 6HF +BeFz 3HlO SiFp 2HF +BeFz Hz” Beo BeF2 2KF +KzBeFl
+
+
+
b::\periments have shown that the products of fusing and sinterof potassium hydrogen fluoride with magnesium, calcium, fcrrir, aluminum, titanium, and zirconium oxides do not react with srnnioniacal quinalizarin solution (50 mg. of quinalizarin in 100 nil. of 10% ammonia solution) It seems therefore that the follo\\ ing test is specific. Procedure. A few milligrams of the material t o be tested [powder or shavings) mixed with a threefold amount of potassium hydrogen fluoride are fused and sintered in a platinum spoon for 3 to 4 minutes. After cooling, the mass is treated with 2 ml. of cold water. After 5 minutes it is filtered or centrifuged. One drop of the clear supernatant liquid is placed on a spot plate and a drop of quinalizarin solution is added. I n the neighboring depression of the spot plate a blank test is carried out with a drop of water. If beryllium is present, a blue color or blue precipitate, according to the amount of beryllium, is visible, whereas the ammoniacal quinalizarin solution remains unaltered-Le., violet. If saturated bromine water is added dropwise, only the blank test is decolorized.
353 sium hydrogen fluoride under the given conditions the fluorization occurs on the surface of the products examined, but because of the sensitive quinalizarin reaction the amount of potassium fluoberyllate formed is always sufficient t o secure the specific detection of beryllium, wen when present in small quantities. DETECTION OF SMALL A.MOUNTS OF IRON OR TITANIUM IN PRESENCE O F FLUORINE
Because of the decrease of ferric ion concentration when FeFB--- ions are formed, detection of iron by the thiocyanatr test fails in the presence of an excess of fluorine. The same is true of the delicate iron test with oxine in acetic acid solution. Therefore, when traces of iron are to be detected in alkali fluoride, iron(II1) should be reduced with hydrogen sulfide to iron(I1) and the latter detected through the color reaction with 1,l’-bipyridine (8). The deniasking of FeFc--- by beryllium chloride or berylliuni sulfate permits identification of iron in fluorides, which might be the basis for a colorimetric determination. Procedure. One drop of the test solution is mixed on a spot plate with some crystals of potassium thiocyanate, followed by addition of one drop of hydrochloric acid. If, after beryllium chloride or beryllium sulfate is added, a red or pink color is developed, iron is present. In this way 2.5 micrograms of iron were detectable hi presence of 25 mg. of ammonium fluoride. Instead of the thiocyanate test, the more sensitive oxine test (green coloring or dark green precipitate) can be used. In this case a neutral test solution must be acidified with acetic acid, or an acetic acid solution buffered with alkali acetate, before an acetic acid solution of oxine is added. Analogous to the behavior with iron, titanium ions are masked in the presence of an excess of fluorine, owing t o the formation of TiFs-- ions. Thus the well-known reaction for titanium in acid solution with hydrogen peroxide (formation of titanium peroxo compounds) is masked in the presence of fluorine. Here also by demasking through beryllium nitrate, titanium ions are produced, which form with hydrogen peroxide the yellow TiO*X,-ions (X = univalent acid radical). In the form of a spot test, the peroxide reaction for titanium has ft limit of identification of 2 micrograms of titanium in one drop (0.05 ml.). The authors found that twice this amount can be detected in a saturated solution of alkali fluorides, when dernasking with beryllium nitrate is used. This corresponds in the case of ammonium fluoride t o a ratio of 1 part of titanium to 6100 parts of ammonium fluoridc. ACKNOWLEDGMENT
iiig
In this nay, several beryllium-containing minerals were examined, among others a product of the following composition: 1 % BeO, 25% A41203, 24% CaO, 3% MgO, 5% PzO6, 6% Fe203, 1% Mnz03, 7% SO2. The test was always confirmative; the same was true when examining beryllium-containing alloys. By the above procedure not all beryllium (together with the other metals) is transformed into fluoride. By sintering with potas-
The authors wish to thank I,. BItumfeld for carrying out many tests for detection of beryllium in minerals, ores, and alloys. LITERATURE ClTED
Bel g, Richard, “Die analytische Verwendung von o-Oxychinclin, Oxin, und seiner Derivate.” p . 47, Stuttgart, Ferdinand Enke, 1938. Borkovskii, A. A . , and Porfir’ev, N. A., Zavodskayn Lab., 3, 1089 (1934). Bucherer, Th., and Weier, F., 2. anal. C’hem., 104, 26 (1936). Feigl, F., A n a l . Chim. A c t a , 2, 397 (1945). Feigl, F., “Chemistry of Specific, Selective, and Sensitive Reactions.” Cham IV. New York. Academic Press. 1949. Feigl, F., “Qualitative Analysis by Spot Tests,’’3rd ed., p. 250, New York, Elsevier, 1946. Feigl, F., 2. angem. Chern., 42, 212 (1929); “Chemistry of Specific, Selective, and Sensitive Reactions,” p. 109, New York, Academic Press, 1949. Feigl, F., and Hamburg, H., 2. anal. Chem., 86, 7 (1932). Fischer, H., Ibid., 73, 54 (1928); “Beryllium, Its Production and Application,” pp. 26, 47, S e w York, Chemical Catalog Co., 1932.
Neuhaus, F. W., 2. anal. Chem., 104, 416 (1936). Schrenk, W. T., and Ode, W.H., IND.ENQ.CHEX.,.XN.IL. ED.,1, 201 (1929). RECEIVED May 3, 1950
