Separation of Beryllium from Biological Material T. Y. TORIBARA AND P. S. CHEN, JR. School of Medicine a n d Dentistry, University of Rochester, Rochester, S. Y . accomplished by removing all possible cations by electrodeposition, using a mercury cathode and then extracting beryllium acetylacetonate into benzene at a suitable pH. The beryllium is then back-extracted into hydrochloric acid. Aluminum accompanies the beryllium but need not be separated if the morin method is employed. Wet- and dry-ashing methods were studied. No losses by volatilization of beryllium compounds occurred during ashing by either method. The separation scheme described is very simple, more complete, and less time-consuming than any previously reported. By concentrating the beryllium, the scheme extends the usefulness of existing methods for determining the element.
The methods used for the quantitative determination of small quantities of beryllium are subject to interferences from other ions. The existing schemes for separating the beryllium are tedious and not entirely quantitative. Some losses of beryllium during ashing had been reported, and a thorough investigation of this important step was desirable. The radioisotope Be' was used for the studies, and by utilizing carrier-free isotope quantities (less than gram) undetectable by any chemical or spectrographic method were investigated. Quantities of this magnitude could be separated completely from urine, soft tissues, and even bone if the extraction time were suitably increased. The separation is
T N T H E analvsis of biological for toxicniaterials. the - specimens 1 LD,, (a statistical term denoting the dose which, on the average, causes 50% Inortality) is important in determining the semitivity required of analytical Procedures. Beryllium, administered intravenously, is very toxic; the LD,, is approvimately 0.36 mg. per kg. ( 8 ) . Thus, for distribution and excretion experimerits, not more than 0.2 mg, per kg. can be administered. B ~ vllium tends to accumulate in certain organs and in the bone ( 9 ) . The blood level and the urinary excretion fall rapidly after the injection of a soluble beryl]iunl compound, hlany tissues contain 0.1 microgram per gram or less, and the quantities used for study ai e limited by the sensitivities of the analytical methods. In most cases. the usefulness of any analytical method may be extended by schenle for the-beryllium fronl other substances, the beryllium, and removing interfering Substances. ik?the accuracy O f any determination is limited by the completeness of the separation, the scheme should separate completely and concentra-te quantities less than could be determined. In this \vOrk, the radioisotope Be7 was used for making quantitative measurements. As this isotope is formed from and decays to Li7, it may be obtained essentially carrier-free. little as microgram can be measured accurately. This made feasible the development of a separation scheme involving much lower concentrations of beryllium than those detectable bv cheniical or ." spectrographic methods. The procedure was designed to e]iminate time-consuming steps sacrificing of separation.
-
tion. The glass stirrer was constructed with the blades tilted in a direction h i t forced the liquid d o ~ n r a r d . The mercury cathode cell was a modification of the Melaven cell with a cross of 6.2 sq. T~ the top of the cell sealed a 19/38 standard-taper outer joint and the platinum anode Fvas sealed to the inner joint. Mechanical stirring was provided by using a fluorothene (trifluorochloroethylene polymer) rod drawn t o a screwshaped tip and inserted through the vent tube ~ sealed diagonally on the top of the cell and into the mercury iOlln,.
'UJ L A .
The flasks used for ashing urine samples v, ere made from standard 500-ml. Kjeldahl flasks. h 24/40 outer joint was sealed 011 near the and an inner joint served the neck* PROCEDURES
a
Urine. Place 250 ml. of urine and 25 ml. of concentrated nitric
acid in a 500-ml. Kjeldahl flask with a T joint. A wire gauze bent around the flask with a lining of asbestos paper distributes the heat uniformly. ,4dd three glass beads and heat the flask to boiling with a Jleker burner. Add 250 ml. of urine dropwise from a dropping funnel as evaporation Proceeds. T o ~ a r dthe end of the evaporation, lower the heat as the sample starts to foam. When the foam becomes viscous and puffs of smoke appear, discontinue the heating, The reaction is self-sustaining and may be spectacular. The phenomena observed in the flask varied from a small amount of scintillation accompanied by the evolution of much volatile material to a strong blue continuous flame. The volatile material does not carry any beryllium with it. When the reaction has ceased and the flask has become cool, add 10 ml. of concentrated nitric acid and evaDorate almost to'drvness. Repeat if necessary to oxidize all thebrganic matter. Add 10 ml. of concentrated nitric and 5 ml. of concentrated sulfuric acid and heat gently until the cake disintegrates. Evaporate most of the nitric acid and add 20 ml. of distilled water. Heat until the solid cake disintegrates. The solution will be cloudy because of the presence of calcium sulfate. Transfer the contents of the flask t o a 50-ml. conical centrifuge tube. Wash down the Kjeldahl flask three times with 3-ml. portions of water, shaking the flask well for each washing. Add the washings to the centrifuge tube and spin the contents a t 1800 to 2000 r.p.m. for 10 minutes. Decant the supernatant liquid into the mercury cathode cell. Transfer the solid to a small Hirsch funnel with a Whatman KO,40 filter, using 2 to 3 ml. of water and catching the filtrate in a test tube. Add this to the mercury cathode cell and electrolyze a t 2 amperes for 30 minutes (0.33 ampere per sq. em. for the cell used). Transfer the solution to a 100-ml. beaker and wash the cell down with a small quantity of distilled water. The volume should be 40 to 45 ml. a t this point. Add a few drops of glacial acetic acid, then concentrated ammonia until the pH is between 4 and 5 (usually 4.5). Place in a 125-ml. separatory funnel, add 4 ml. of acetylacetone, and stir for 5 minutes. Add 20 ml. of benzene and stir for 1.5 minutes. Check the pH of the aqueous layer before discarding (if below 4, add ammonia t o raise the pH and repeat the acetylacetone step). Wash down the separatory funnel with about 20 ml. of distilled water (do not stir), and discard the water. Add 15 ml. of 5 hydrochloric acid and
blATERIALS AND EQUIP-WENT
Preparation of Samples. Samples for analysis were obtained from bone, urine, liver, kidney, and other soft tissues of rabbits which had been injected intravenously with the carrier-free isotope. In addition, known quantities of beryllium to which the radioisotope was added were mixed ivith bone ash followed bv heating in the muffle under conditions used for ashing bone. & the quantity of urine obtained from a rabbit was small, no problems were encountered in the recovery of the beryllium. As a more adequate test of the procedure, human urine was used and beryllium was added t o 500-ml. samples (about half the normal daily output). Reagents. Baker's analyzed acids and ammonium hydroxide were used without dilution. The 5 N hydrochloric acid for extraction was prepared by diluting 200 ml. of the concentrated acid to 500 ml. with distilled water. The acetylacetone and thiophenefree benzene were Eastman white label quality used without further purification. Apparatus. Extractions were carried out in 125-mI. separatory funnels using an electric motor-driven stirrer to provide the agita-
539
ANALYTICAL CHEMISTRY
540 stir lor 15 minutes. The beryllium is now entirely in the acid layer. Washing the acid solution with fresh benzene removes more acetylacetone. To remove all traces of acetylacetone, evaporate the acid solution to dryness in a platinum dish. With a Meker burner heat the dish just enough to oxidize the organic matter. Add 5 drops of Concentrated sulfuric acid and heat until most of the acid has been removed. Dilute with distilled water to desired volume. The beryllium may also be taken up in 0.5 ml. of concentrated hydrochloric acid instead of the sulfuric acid. Bone. Take 10 grams of bone ash (treated a t 600") and dissolve i t in 20 nil. of concentrated hydrochloric acid. Add 150 ml. of distilled water and 9 i d . of concentrated sulfuric acid. Cool and filter the calcium sulfate on a Biichner funnel with a Whatman S o . 41 filter paper. Wash the beaker out with two 10-ml. portions of distilled water and pass through the filter. Raise the pH of the filtrate to 5.8 to 6.0 with concentrated ammonia and collect the precipitate by filtration or centrifugation, discarding the filtrate. Dissolve the precipitate in hot, dilute hydrochloric acid (about 30 ml. of 2 N acid are required) and transfer the contents to a 100-ml. platinum dish. Add 5 ml. of concentrated sulfuric acid and evaporate to fumes of sulfuric acid. Heat strongly for several minutes, cool, and add 15 nil. of distilled water. Heat the dish on a hot plate for several minutes and transfer the contents to a 50-ml. centrifuge cup using about 10 ml. of water for rillsing out the dish. Spin at 1800 to 2000 r.p.m. for several minutes ailti pour the supernatant liquid into a mercury cathode cell. Transfer the solid to a small Hirsch funnel, using 2 to 3 ml. of distilled water as in the analysis of urine. The electrolysis and subsequent step' are the same as for urine samples.
Table I .
SIlrCI (1 grtiii!]
SaiHPO, ( 1 g r a m KnC1 (1 gram) 5 .v €IC1
Table 11.
Recovery,
%
Treatment Evaporated to dryness with infrared
102
20
Ignited a t 750' for 17 hours
102
20
Ignited a t 750' for 17 hours after driving o f f NHrCI careiully Evaporated to drynesswith infrnred
20
20 20 Carrier-iree
Ignited a t 750' for 17 hours Ignited a t 7.50' for 17 hours Evaporated u-ith infrared l a m p and ignited a t 500' for 1 hour
99.2 99.7 98.4 103 100.3
5O-IMl. Urine Samples Dry Ashed in Platinum Dishes B e Added,
Temperature, 500
a
a
C.
Method of Solution Concentrated HzSO, heated strongly
4
Average Recovery.
I
%
03
95
500
Concentrated I l C l
4 03
96
750"
HF a n d HiSO, evaporated
4 03
92
750a
H F and HzSO, evaporated
8.06
102
t o fumes of sulfuric
STUDIES ON ASHING PROCEDURE
In all cases the ashing of specimens was the most time-consuming step. Cholak and Hubbard ( 8 ) reported that the direct ashing of urine at temperatures as low as 500" C. resulted in significant loses of beryllium. In their worst case, an ignition in a platinum dish, recovery of only 12.5% was reported. Such losses were not observed when a standard beryllium solution was prepared by dissolving pure beryllium metal in hydrochloric acid according to the method of Underwood and lieuman (IO). In standardizing the solution by evaporation and ignition to the oxide, exactly the same results were obtained whether sulfuric acid were added or not. As these standardizations were made using macro quantities (100 mg.), micro quantities were investigated. Microgram quantities of beryllium to which the radioisotope had been added were mixed with 1-gram quantities of the main salt constituents of urine. These solutions were evaporated to dryness under an infrared lamp and then placed in a muffle furnace a t 750" C. The samples were dissolved by evaporating with hydrofluoric acid to fumes of sulfuric acid and then diluting with distilled water. Measurement of the activities using a dipping tube counter ggwe the results shown in Table I. I n another experiment, samples pr;pared in the same ivay were heated for Periodic measurements showed no loss longer periods a t 750 of beryllium activity over an 8-day period. Samples of urine were ignited under the conditions used by Cholak and Hubbard and at a higher temperature, a j t h the results shown in Table 11.
.
Recovery of Added Beryllium (Be') Be Carrier Added, y 20
Salt HCI (1 nil.)
trouble was encountered in obtaining complete recoveries of as little as 10-lo gram of beryllium (0.1 millicurie of carrier-free isotope).
to fumes of sulfuric
Samples could not be extracted with acetylacetone.
Modification for Separation of Carrier-Free Be7 from Bone. After removal of calcium sulfate following the first addition of sulfuric acid, evaporate the filtrate in a platinum dish down to the niisture of sulfuric and phosphoric acids. Heat strongly for several minutes, cool, add 15 nil. of distilled LTater, and transfer the contents to a centrifuge tube. Spin the contents and electrolyze as above. Much longer stirring n-ith acetylacetone is necessary, as shown in Table 111,-1. Soft Tissues. The wet-ashing procedure is similar to that used by others ( 2 , 4 ) . Take the Lvhole liver or kidneys or desired amount of other soft tissue and cut into small pieces. Place in a Iijeldahl flask of appropriate size with 100 to 150 ml. of concentrated nitric and 5 ml. of concentrated sulfuric acids and heat gentlv until the foaming has ceased. Boil dotvn and add nitric acid b t i l almost all the organic matter has been oxidized. Toward the end (Then the solution is a clear brown) add a few milliliters of perchloric acid and heat until the solution is colorless. Dilute with 15 ml. of distilled water and transfer to a 50-ml. centrifuge tube. S in at 1800 to 2000 r.p.m. for 10 minutes and follow the procelure outlined for electrolysis and extraction. No
This treatment removed all the beryllium from the platinum, but the element could not be absorbed on a cation exchange column nor extracted into solvent Kith acetplacetone. dfter evaporating the solution to dryness and heating the salts strongly with concentrated sulfuric acid for several minutes, it was possible to absorb the beryllium from solution with a cation exchange resin and to extract it with acetylacetone. Xot only was there no loss of beryllium in the dry ashing of urine, but it was impossible to lose any beryllium by heating in a muffle furnace a t 750" any mixture obtained by the evaporation, of an aqueous solution. It is believed that losses reported previously were caused by conversion of the beryllium to a relatively insoluble oxide .i\-ithresultant iow recoveries. For urine, the wet-ashing technique using nitric acid only was found to be the most rapid. This process is actually a semidry one because the evaporation is continued until a self-sustaining ignition of the organic matter starts. The small amount of organic matter in urine forms a scnni on the surface in the later stages of the concentration. The beryllium remains with the cake of inorganic salts, none of which is lost, although much volatile matter may be evolved in the ignition. After the reaction has subsided, evaporations with additional portions of nitric acid are made as many times as necessary to destroy all the organic matter. Perchloric acid should not be used because of the large quantities of potassium salts in urine. A 500ml. sample of urine may be evaporated and completely ashed in 1.5 hours by this procedure. Soft tissues were most conveniently wet-ashed using nitric acid and finishing with the addition of a small quantity of perchloric acid. For bone a dry-ashing technique was the most rapid, because a fat-extracting step could be omitted. -4temperature of 600" was found to be satisfactory. SEPARATION SCHEME
Cations are removed by electrodeposition using a mercury cathode, followed by the extraction of beryllium acetylacetonate into benzene a t a suitable pH. The beryllium is then back-extracted into hydrochloric acid. This separates the beryllium from all metallic ions commonly found in biological material ex-
541
V O L U M E 2 4 , NO. 3, M A R C H 1 9 5 2 cept aluminum. However, in the morin method of analysis conditions may be chosen so that aluminum does not interfere, and quantities of the order of 0.001 p.p.m. can be detected ( 7 ) . Traces of acetylacetone which are carried into the hydrochloric acid interfere with the fluorescence (6). These are most conveniently removed by evaporation to dryness followed by gentle ignition. The mercury cathode 3s coninionly eniploped for the removal of many ions (11). Flagg ( 3 ) studied the separation of beryllium in niilligrani quantities by extracting with an acetylacetone solution in benzene and recommended extraction from an aqueous phase having a pH between 3 and 4. Separation from calcium n-as complete (oxalate test), but iron and aluminum were carried into the organic phase with the beryllium. Seuman and Kosel ( 6 ) estracted Be7to which a small amount of carrier had been added a t a pH of 4.5 with a benzene solution of acetylacetone. Bolomey and Broido ( 1 ) used a similar procedure in the preparation of carrier-frre Be7. % . pH between 4 and 5 resulted in the most rapid estraction of microgram quantities, In some cases, the removal of calcium was essential to prevent precipitation of phosphates as the pH was raiscti lor t,he extraction with acetylacetone. Copreeipitation of a large part of the bei.yllium was not prevented by the presence of a coniplesing agmt such as acetylacetone. hlost. of the calcium was removed as the sulfate from a strongly acidic solution with no loss of beryllium. Ronc was a special problem in this reapevt, arid the trea.t,ment of large qua.ntities of urine also required c.al(,iumremoval. Soft tisbues which leave little inorganic materi:tl on ashing presented 110 problcnia in the separation of berylliuni. In the case of bone, advantage was tnlicn of the tendency of beryllium to accompany other precipitates at elevated pH's, and a collecting step ivas introduced as a means of concentrating the beryllium as well as separating it from the bulk of the phosphate. Following the removal of the bulk of the calcium as the sulfate from a strongly acid solution, the addition of concentrated ammonia to a p H of 6 caused precipitation of calcium phosphate, which collected the beryllium almost quantitatively. This precipitate was dissolved with hydrochloric acid and evaporated to fumes of sulfuric acid followed hy several minutes of strong heating, to ensure complete solution of the beryllium (dry-ashing bone a t elevated temperatures converts the beryllium to an inaoluble form). The use of a collecting step limits the amount of beryllium which may be separated quantitatively. \Then 10 grams of bone ash containing approximately 0.1 microgram per gram of ash were run through the separation scheme, the results shown in Table 111, B, v a s obtained. \!-hen this sainc pi.ocedure \$-asapplied to samples containing carrier-free ber,ylliuni, or less than 0.01 microgram per gram of ash, erratic recoveries mere obtained with a maxinium' of 70%, -4atep\\-isc inr-wtigat,ion showed that these
Table 111.
Recover?-of Berylliuni from 10 Grams of Bone Ash Sample
1.
2. 3. 4.
IllinUtes Stirred with Awtslucetone
7%
Extracted
il. Omitting Collerting Step for Carrier-Free Be' 1st extraction 2nd a n d 3rd extractions l i t extraction 2nd extraction 30 23
y
1 s t extraction
2nd extraction
40 30
1st extraction 2nd extraction
90 43
'
97
82.3
1 3 . 1 ) 95.4
B. Csing Coilecting Step with Carrier Added One extraction onlv on 4 samples, each bon96,5, 94.9 taining 1.3 y beryllium 93.4, 95.1
losscs o c . c ~ u ~ , ~inw lthe collecting step. When the concentration was effectrd by evaporating the solution after calcium removal, carrier-lree beryllium was recovered quantitatively (Table 111,A). However, much longer time of stirring with acet'ylacetone was necessary because none of the phosphate present in the bone ash had b e c ~separat,ed. For larger quantities of beryllium even longer periods of stirring with acetylacetone were necessary. I n XQ-niI. urine samples, most of the calcium was removed as the sulfate by the addition of sulfuric acid following the ashing with nitric acid. Perchloric acid could not be used because the relatively insoluble potassium perchlorate did not dissolve in the volume used in the extraction, and appreciable quantities of beryllium were retained by the solid. As no collecting step was used in the procedure for urine, less than gram of the carrier-free isotope was completely recovered (Table IV). JVhole rabbit livers and kidneys were ashed and carried through the separation scheme; carrier-free beryllium isotope was completely recovered with a single estraction.
Table I \
.
Recoieries of Beryllium from 500 RII. of ITrine
H c i 1 llirini .\dded
Recovpri-,
/
9i
1.3
101.: 99.3 99.6 100.5 (80.0 + 20.5; 98.5 97.5 101.7 182.8 f 18.9)
1.3 1.3
I. 3 a 1.3 1.3
I , 3h Carrwr-free YB.6 Carrier-free 100.3 a Req1,irerl two cxtractIons, pII.of atjiiroiis phase after first extraction >I-&* 3.0. b Reqiiired two extractions, p H of aqueoua phnse after first extraction w a s 3.3.
Other investigators ( ' I , 3, 6 ) shook a solution of acetylacetone in benzene with the aqueous phase containing the beryllium. In this nork stirring the aqueous p h a v \vith undiluted acetylacetone hastcned the formation of lieryllium iwetylacetonate by maintaining a mesimum concentration of the acetylnwtone in thc aqueous 1)h:i.se. The benzrne wis :ttlthd later to transfer the berylliuiii complex t o the organic: phase. I t was iriiportant to niaint,ain the p1-I kietxwen 4 antl 5 to obtain complete extraction in the timr, specified (Table IT-). Because this pH is in the region \\.here phosphate does not buffer well, a few drops of g1ari:tl acetic acid were added to maintain the proper pH. \Vhere pH control was inadequate, the p1-I was readjusted betiyeen 4 and 5 for i: second extraction, antl the beryllium \\-as thrn found to be complrtc,ly transfered to the organic phase. nIscu s SION
The scheme of separation was designed to be used with the morin method of analysis, in n-hich aluminum does not interfere. If it is necessary to remove the aluminum, the aqueous phase may be estracted v4th a solution of 8-quinolinol in chloroform ( e ) ,which removes the aluminum as the oxinate and leaves the beryllium behind. The ashing studies showed that it was impossible to lose beryllium by volatilization from the evaporation of an aqueous solution followed by heating to 750". Thus, the berj.llium may be obtained in as small a quantity of solution as desired by evaporation of the final hydrochloric acid solution. In agreement with the work of Bolomey and Broido ( I ) , it was found that some losses occurred in the evaporation of a benzene solution of extremely small quantities of beryllium acetylacetonate. Dry-ashing a t temperatures above 500 converts the beryllium to a relatively insoluble oxide which requires boiling with concentrated sulfuric acid for conversion to a soluble form. The extractions were made by stirring the two phasrs toget,her rather than shaking by hand, and much better reproducibility
ANALYTICAL CHEMISTRY
542
was obtained. The extraction procedure for concentrating the beryllium is quantitative for the smallest measurable amount (less than 10-10 gram), whereas the use of a collecting precipitate for such quantities gave between 50 and 70y0 recoveries. Klemperer and Martin ( 4 )have developed a scheme which utilizes two collecting steps, and they report an average of 80% recovery. Cholak and Hubbard ( 2 ) added calcium phosphate as a collecting agent, but their data do not indicate whether the variations in the determinations are to be attributed to spectrographic variations or to separation procedures. The spectrographic analysis of the final hydrochloric acid solution showed only aluminum present in addition to the beryllium. In agreement xith Flagg’s results ( S ) , no calcium was found spectrographically. I t is believed that the separation scheme described is very simple, more complete, and less time-consuming than any previously reported.
for much assistance with the count’ingequipment and L. T. Steadman for spectrographic analyses.
ACKNOW’LEDGRZENT
RECEIVED for review June 10, 1961. Accepted December 11, 1951. Presented before t h e Division of Analytical Chemistry a t the 119th Meeting of t h e AMERICAK CHEMICAL SOCIETY, Boston, Mass.
The authors wish to thank J. F. Bonner, Jr., and R. E. Nosteen
LITERATURE CITED
(1) Bolomey, R. A , , and Broido, A , Atomic Energy Cornmission, Rept. ORNL 196 (December 1948). (2) Cholak, J., and Hubbard, D. M., ASAL. CHEX,20,73 (1948).
(3) Flagg, J. F., unpublished work. (4) Klemperer, F. W., and Martin, A. P., ANAL. CHEM.,22, 828 (1950). ( 5 ) Laitinen, H. A,, and Kivalo, P., personal communication. (6) Nouman, T. F., and Kosel, G., dtomic Energy Commission, R e p t . UR-35 (June 1948). (7) Sandell, E. B., IND.EKG.CHEM., AXAL.ED.,12, 674 (1940). (8) Scott, J. K., “Pneumoconiosis,” edited by A. J. Norwald, p. 369, New York, P. B. Hoeber, Inc., 1950. (9) Scott, J. K., Neuman, W.F., and Allen, R., J . B i d . Chem., 182, 291 (1950). (10) Underwood, 8. L., and Neuman, IT. F., ANAL.CHEM., 21, 1348 (1949). (11) Willard, H. H., and Diehl, H., ”-idvanced Quantitative Analysis,” p . 58, Kew York, D. Van Nostrand Co., 1943.
Spectrophotometric Determination of Zirconium E. W. KIEFER
AND D. F. BOLTZ W a y n e Unizlersity, Detroit, Mich.
The need for a method of determining small amounts of zirconium prompted this investigation, the ultimate qbjective being the development of a spectrophotometric method. I t was found that zirconium could be precipitated by the addition of a standard phosphate solution and that the concentration of the supernatant phosphate solution following centrifugation decreased in proportion to the amount of zirconium present. The phosphate was determined spectrophotometrically as the molybdiphosphoric acid complex. The concentration range is 1 to 80 p.p.m. of zirconium using 1-cm. cells. The recommended general procedure should be valuable to those concerned with the microdetermination of zirconium.
T
HE gravimetric determination of zirconium as zirconium phosphate is one of the most widely used macromethods for
determining zirconium (2, 3). The purpose of this investigation was to develop a spectrophotometric method applicable to the microdetermination of zirconium. The spectrophotometric method which Bras developed is based upon the addition of a standard phosphate solution to precipitate zirconium phosphate and the determination of the phosphate concentration of the supernatant solution. APPARATUS AND SOLUTIONS
The absorbancy measurements were made with a Beckman Model DU spectrophotometer and 0.998-em. Corex cells. The reference cell contained distilled water for all the measurements. Two zirconium solutions were used containing, respectively, 0.05 and 0.10 mg. of zirconium per ml. The solutions were prepared by dissolving the required amounts of zirconyl chloride octahydrate in distilled water and diluting to 1 liter. It is recommended that these solutions be standardized gravimetrically using cupferron, mandelic acid, or trimethyl phosphate as precipitant.
A phosphate solution was prepared by dissolving 0.5000 gram of potassium dihydrogen phosphate in distilled water and diluting to 1 liter. A 10% solution of sodium molybdate was prepared by dissolving 25 grams of sodium molybdate in distilled water, filtering, and diluting to 250 ml. A 10 N (approximate) sodium hydroxide solution was prepared fresh as needed by dissolving 40 grams of sodium hydroxide in 100 ml. of distilled water and filtering. The concentrated nitric acid used was Baker and Adamson’s c.P., which showed no evidence of decomposition. The 2.8 N nitric acid was prepared fresh as needed by adding 8.75 ml. of the concentrated acid t o distilled water and diluting to 50 ml. FUNDAMENTAL REACTIONS
The treatment of an acidic solution of zirconyl ions with an excess of a standard phosphate solution results in the precipitation of zirconium phosphate. After digestion, the precipitate is separated by centrifugation and an aliquot of the sdpernatant solution is used to determine the concentration of the excess phosphate ions. The addition of a molybdate solution to an acidic phosphate solution gives a yellow hue due t o the formation of molybdiphosphoric acid (1). The following general procedure was used in studying the effect of solution variables: An aliquot portion of the zirconium stock solutions containing the desired amount of zirconium in a final dilution of 25 ml. was pipetted into a 50-ml. Lusteroid centrifuge tube. Five milliliters of concentrated nitric acid were added to each tube and sufficient distilled water was added to each solution, with the aid of a buret, to make a final volume of 25 ml. Ten rmlliliters of the phosphate solution were next added, and the solutions were allowed to stand for a specified period of time. The resulting precipitate was centrifuged for 15 minutes. A 25-ml. aliquot of the supernatant solution was transferred to a 50-ml. volumetric flask and neutralized with 10 N sodium hydroxide to a phenolphthalein end point. Five milliliters of 2.8 N nitric acid were added to the solution, and the solution was diluted to the mark. Five mlliliters of the sodium molybdate reagent were added and absorbancy readings were made a t 380, 400, and 520 mG.
