ANALYTICAL CHEMISTRY
1886 as the amounts of free bases (micrograms per gram of material, for sake, milliliters) (Table VI). The distributions of pyridoxal, pyridoxamine, and pyridoxine in the natural materials so far tested are similar to the results of Ribinowitz and Snell. Consequently, the method has been considered practicable, inasmuch as less reagents are required for basal medium than in the previous method. ACKNOWLEDGMENT
The author wishes to express his appreciation to Tadanobu Kishibe and Hiromichi Saito for the technical assistances, to Hiroshi Shimizu for helpful suggestions, and to Ryohei Takata for his encouragement.
LITERATURE CITED
(1) Atkin, L., Schults, A.
S.,Williams, W. L., and Frey, C. N., 1x11. ENG.CHEM.,ANAL.ED., 15,141 (1943). (2) Oda, R., Shimisu, H., and Nakayama, Y., Chem. High Polymers ( J a p a n ) ,5,21 (1948). (3) Rabinowitz, J. C., Nondy, K. I., and Snell, E. E., J . Bid. Chem., 175,147 (1948). (4) Rabinowitz, J. C., and Snell, E. E., ANAL.CHEM.,19,277 (1947). (5) Rabinowitz, J. C., and Snell, E. E., J . Bid. Chem., 176, 1167 (1948). Shimisu, H., and Shiba, H., J . Chem. SOC.( J a p a n ) ,72,442(1951). (7) Snell, E. E., J . Bid. Chem., 157,491 (1945). (8) Snell, E. E., and Rannefeld, 4.N., Ibid., 157, 475 (1945). f6)
RECEIVED for
reriew February 9, 1953.
Accepted July 30, 1953.
Quercetin as Colorimetric Reagent for Determination ot iirconium FRANK S. GRIMALDI, United States Geological Survey, Wushington, D . C., AND CHARLES E. WHITE, University of Murylund, College Park, Md.
Methods described in the literature for the determination of zirconium are generally designed for relatively large amounts of this element. A good procedure using colorimetric reagent for the determination of trace amounts is desirable. Quercetin has been found to yield a sensitive color reaction with zirconium suitable for the determination of from 0.1 to 507 of zirconium dioxide. The procedure developed involves the separation of zirconium from interfering elements by precipitation with p-dimethylaminoazophenylarsonic acid prior to its estimation with quercetin. The quercetin reaction is
A
LTHOCGH numerous excellent reagents and procedures are available for the determination of macro amounts of zirconium, the situation is far from satisfactory with respect to the determination of microgram amounts. Only a few reagents have been developed for trace analysis and the reactions are not altogether ideal from the standpoints of sensitivity and selectivity. Alizarin (or Alizarin Red S) (4-7, 9, I O , I S , 1 4 ) is probably the most important reagent for the colorimetric determination of zirconium, but the color reaction is not too sensitive. p-Dimethylaminoazophenylarsonic acid (8, 11, 12) is second in importance to dlizarin Red S. The procedures are indirect, light absorption measurements being made on the dye solution obtained by decomposing the zirconium azo-arsonate with ammonia. Stehney and Safranski ( 1 2 ) determined microgram amounts of zirconium in this manner. Flavonol, introduced by .%lford and coworkers ( I ) , is important in zirconium analysis by fluorescence. This study, made in part on behalf of the Atomic Energy Commission, was undertaken with two objectives in mind: First to find a colorimetric reagent sensitive to small concentrations of zirconium and second, to apply it to the determination of microgram amounts of zirconium in siliceous materials. Quercetin was selected from more than 100 compounds tested, because of its high sensitivity, a nearly colorless blank, stable color over a wide acidity range, and availability in a pure state. EXPERIMENTAL
Factors Affecting the Zirconium-Quercetin Color System. When quercetin is added to an acid solution of zirconium an intense yellow color is obtained. Various factors affecting the
carried out in 0.5N hydrochloric acid solution. Under the operating conditions it is indicated that quercetin forms a 2 to 1 complex with zirconium; however, a 2 to 1 and a 1 to 1 complex can coexist under special conditions. Approximatevalues for the equilibrium constants of the complexes are KI = 0.33 X 10-6 and Kz = 1.3 X lovg. Seven Bureau of Standards samples of glass sands and refractories were analyzed with excellent results. The method described should find considerable application in the analysis of minerals and other materials for macro as well as micro amounts of zirconium.
zirconium-quercetin color system were studied to establish optimum working conditions. Preliminary experiments indicated that a certain amount of alcohol was necessary to prevent the precipitation of quercetin and this variable was included in the study. I n the experiments, all the solutions were made to a total volume of 25 ml. The order of addition of the reagents was always the same. The zirconium solution was added first, acid second, alcohol third, and an alcoholic solution of quercetin last. Absorbancies were determined with a Beckman spectfophotometer, Model DE, uEing 1-cm. cells and distilled water-as reference solution. The slit width was 0.05 mm. except for the spectral transmittancy data below 420 mp where 0.1 mm. was used. Unless otherwise indicated all solutions were 0.5B in hydrochloric acid and contained 3 mg. of quercetin and 8 ml. of alcohol. Spectral transmittancy data for the reagent blank and 307 of zirconium dioxide are given in Figure 1 . The optimum wave length was taken as 440 mp because at this wave length the absorption given by the blank is small and that by zirconium still large. In the work that follows, all absorbancies were measured at 440 mp. Figure 2 illustrates the effect of alcohol concentration on the absorbancy of 54.47 of zirconium dioxide. A precipitate of quercetin was obtained almost immediately from solutions containing less than 6 ml. of alcohol; with 6 ml. of alcohol some quercetin precipitated after 10 hours. It is desirable to keep the alcohol concentration to a minimum because of the smaller solubility of salts in alcoholic media. For this reason 8 ml. of alcohol in 25 ml. of solution was taken as optimum.
V O L U M E 25, NO. 12, D E C E M B E R 1953
1887
The effect on acid concentration on the absorbancy given by
54.47 of zirconium dioxide is illustrated in Figure 3. The absorbancy is almost independent of acid concentration in the region from 0.1 to 1X. The reagent blank increases sharply in absorbancy for acid concentrations above I N and reaches a value of more than 0.2 absorbancy unit a t 3 N . On the basis of the foregoing the optimum acidity was taken as 0 . 5 N . The reaction can also be carried out in nitric or perchloric acid solution, as comparable data are obtained. Hydrochloric acid is
70
60
50
d
40
30
20 IO
400
450
500
550
600
6%
700
750
WAVE LENGTH rnp
Figure 1. Spectral Transmittancy Curve
varying the quercetin concentration in each series. The absorbancies shown are corrected for the absorbancies of blanks containing the same amounts of quercetin. The optimum concentration of quercetin was taken as 3 mg. of quercetin for 25 ml. of solution. I n Figure 5 the quercetin concentration was kept fixed a t two levels (150 and 300y of quercetin) and the zirconium concentration was varied. D a t a for the working curve are given in Figure 6. These data were obtained using the optimum conditions previously established. The solutions viere 0.5N in hydrochloric acid and contained 8 ml. of alcohol and 3 mg. of quercetin in a total volume of 25 ml. A straight-line relationship between absorbancy and micrograms of zirconium dioxide is shown up to 607 of zirconium dioxide. Solutions containing from 60 to 150y of zirconium dioxide deviate slightly from the Beer-Lambert-Bouguer law but their absorbancies are reproducible. The region from 0 to 10y of zirconium dioxide was examined in detail for any deviation from the straight-line relationship, but none was found. The solutions, containing as much as 150y of zirconium dioxide, were allowed to stand for 24 hours, after which time the absorbancies were redetermined. The maximum change in absorbancy was found to be 0.003. The spectrophotometric sensitivity of the zirconium-quercetin color reaction is 0 . 0 0 4 ~ zirconium dioxide per square centimeter. Theoretical Analysis of the Zirconium-Quercetin Reaction. The relationship between absorbancy and mole ratio of quercetin to zirconium, curves (1) and ( 2 ) , Figure 4, is linear up to a mole ratio of 1 to 1. ;Zt ratios where the molar concentration of the quercetin is greater than that of the zirconium the absorbancy increases in a nonlinear fashion with increase in quercetin (zirconium concentration fixed) and reaches a nearly constant value for very high mole ratios. Various hypotheses were tested as possible explanations for the
::rr REAGENT BLANK
01
Figure 3.
Effect of Alcohol Concentration
preferable to perchloric acid because of the greater stability of zirconium in hydrochloric acid solution ( 3 ) . For example, it was found that standard perchloric acid solutions of zirconium lose strength rapidly if the acid concentration is below 20% by volume. Kitric acid is inferior to hydrochloric acid because of its tendency to oxidize quercetin. At elevated temperatures this effect is serious for solutions of greater acidity than 0 . 5 N . The sensitivity of the zirconium-quercetin color reaction is greatly diminished in sulfuric acid medium, probably because of the complexing action of sulfate with zirconium. The data in Figure 4 were obtained by keeping the zirconium concentration fixed at two levels (20 and 54.47 of zirconium dioxide) and
03
04
OS
06
07
08
09
IO
NORMALITY OF HCI SOLUTION
ML. ALCOHOL
Figure 2.
02
Effect of Acidity
07 0 6
>
y 3 2
2
O 5 0 4
O3 02 01
10
20 -.
10
MOLE RATIO OF OUERCETIN TO ZIRCONIUM
Figure 4.
Effect of Quercetin Concentration with Zircnnium Concentration Fixed
1888
ANALYTICAL CHEMISTRY and a t constant hydrochloric acid concentration (ZrOCIQ)(QH) = (ZrOQd
07
06
0
OS 04
54
2
03 0 2 01
Figure 5.
0 7 0 6
OS 0 4
03
02
It is possible, from the spectrophotometric data given, to test the hypothesis by calculating k for the various test solutions in which the two complexes coexist and noting if these values are reasonably constant. For these calculations the absorbancy indexes of the pure 1 to 1 and 2 to 1 complexes are required. The absorbancy index of the 1 to 1 complex may be calculated from the absorbancies obtained on extrapolation of the curves, Figure 5, to zero 10 IS 20 mole ratio. -4reasonably close average value of the absorbancy index of the 2 to 1 complex MOLE RATIO OF QUERCETIN TO ZIRCONIUM may be calculated from the absorbancies a t Effect of Zirconium Concentration with Quercetin mole ratio 40 to 1, Figure 4. The calculations Concentration Fixed for k are simplified if it is assumed that in solutions where both complexes coexist the concentration of uncombined zirconium is negligible and that no complexes of zirconium other than the quercetin complexes are formed. The values of k were found t o be reasonably constant and lend weight to the foregoing interpretation. Approximate values of the equilibrium constants for the 2 to 1 and 1 to 1 complexes were determined, K I = 0.33 X 10-6 and Kz = 1.3 X 10-9. The method of Bent and French ( 2 ) is especially applicable to the determination of formulas of dissociable complexes. Thia method indicated that in the dilute region only the 1 to 1 complex is formed. It was possible to isolate this complex and chemical analysis indicated the probable formula to be:
OH
01 I
20
IO
30
40
l
I
l
SO
70
60
Y Z r 0,
Figure 6.
Working Curve
nature of the curves plotted from these data. The only consistently logical explanation is based on the hypothesis that two zirconium-quercetin complexes coexist in the test solutions. The zirconium forms only the 1 to 1 complex in dilute solutions of quercetin. This complex is largely dissociated ( C Y being constant in the straight line portion of the curves), and as the quercetin concentration is increased (zirconium concentration fixed) a greater fraction of the zirconium forms the 1 t o 1 complex. As the quercetin concentration is increased still further a point is reached where nearly all the zirconium is in the form of 1 t o 1 complex and the 2 to 1 complex makes its appearance. The relative amount of the 2 to 1 complex increases as more quercetin is added until all the zirconium is present in the form of the 2 to 1 complex. At this point the absorbancy of the solution should remain constant. The equilibria involved are
ZrOCIQ
+ H + = ZrO++ + QH + C1+ 2H+ = ZrO++ + 2QH
ZrOQn and
For both complexes coexisting in equilibrium
(1) *
(2)
Reactions of Quercetin with Other Elements. h'early all of the elements were tested t o determine their behavior with quercetin under the optimum conditions used for the zirconiumquercetin reaction. Each element was tested in the absence of zirconium and a t two levels of zirconium (5 and 25y of zirconium dioxide) from a total volume of 25 ml. The absorption given by colored ions in 0.5N hydrochloric acid was also determined. A density difference of 0.003 unit (equivalent to 0.37 of zirconium dioxide) was taken as the cutoff for reporting interference. Elements not discussed were not tested. The following cations do not interfere in the maximum amounts taken (expressed as oxides) : 0.5 gram: Na, K, and NH, 0.1 gram: R h , Cs, Mg, Ca, Ba, Sr, Zn, Cd, Hg++, Ag, Pb, TI+, Mn++, and A s + + + 0.05 gram: La and Y 0.004 gram: E u , Yb, Gd, and D y Acetate (0.5 gram) and bromide (0.2 gram) ions do not interfere. Some elements interfere by decreasing the color intensity given by zirconium. These elements probably consume reagent or their anions react with zirconium. Some elements interfere because of the natural color of their ions in hydrochloric acid solution. Some elements produce unstable colors with quercetin! whereas other elements react to increase the color intensity of the solution. The maximum amount of each element that can be tolerated and the nature of the interference are given in Table I. Serious interference is given by the following ions: oxalate, fluoride, phos-
V O L U M E 25, NO. 1 2 , D E C E M B E R 1 9 5 3 Table I . JZaximum Permissible Amounts of Various Anions and Cations in the Colorimetric Determination of Zirconium with Quercetin (.imounts calculated as oxides unless otheruise mdlcated) Maximum Amt. hIaximurn Amt. a t 25, ZrO? Nature of a t 5 7 ZrOt Level Level Interference Compound 10 mg. acid 1 mg. arid S e g . , quenches Citric acid 10 mg. acid 1 mg. acid Neg. Tartaric acid 6 4 7 Pi05 S e g . (NH~ZHPOI >loo-/ PZOS ~y F Seg. NaF 10y E 13 mg. $ 0 3 3 . 5 ing, SO$ Neg. KazSOr 16 nig. Neg. LiCl > 50 mg. 0 . 2 5 mg. 0 . 2 5 mg, Pos., colored ion HAuCln 3 mg. Unstable soln. 5 mg. CUCl? 3 rng. PO?. 3 mg. Be(Noaj9 2 5 mg n Illy. Seg. Ce(S0da in 111~. Pos. 10 m g . Sni(N0da 10 Ill... 1'0s.. colored ion 10 mg. Pr(N0ala 2.; m g . 1'0s. 25 m g . N d ( N 0 s )3 Sc(NOl,r 20r 1'0s. 20Y 8 mg. 8 n i q . Pos. HaBO3 0 . 6 mg. 0 . 6 ing. Pas, AlCli 15, 1 iy Pos. G a ( N O 28 7 mg. 7 nlg. Pos. In(iY0a)r 150, 1.5 0 y Unstablz Poln. HgNOs 15 y Pos , TiCIz(0Ac)z ';yi3y 0 7.5; Pos . HfOClz io-, Pas. Th(X0i)r 401 7: y 7: y Pos. GeClr 0.4y 0 i y POS. SnClr 2oo.i Lnstable s o h . NHiTOa 200Y 5 mg. .I nig. Pos. BiCls X0.f Pos.. colored ion CrClr 2507 iy C1.?03 Pos. KzCrzOT I y CrzC3 O.2r Pos. ( N H d d o;Ou 0.2y 0 .3 y Pos. NazKO, 0 . 5 ~ 61. Pos.. unstable soln. FeCls 6-r 507 ,507 Pos.. unstable soln. Fe(SHI)2(SO,)z n1g. Pos., colored ion 5 mg. coc12 5 nig. I J nig. 1Pos., IP NaI 3 m y . As& Neg. KazHAsOr 30 mg. SeO? Neg. HzSeOz >"Q.Z g. SeOt 10 mg. TeOz 10 me. TrO. Pos. HzTeOg 8 mg. 8 ing. ' Pos.. colored ion XiCh 3 mg. 3 mg. POS. qoz ( S O : )1 40 1 1 ~ ~ . ?ieg. .. haz9iOa ShClr 31 Pos. 37 iYhzOa in HzSOr 1i Po-. 1Y TazOa in HtSOd 2y Pos. 2Y 607 Pd 60y Pd Pos., colored ion HzPdCh lOOy R h l O O y RII Pos., colored ion HiRhClj 4 y RII 4y R ~ I Pos., colored ion HzRuCla 300r T't Pos., colored ion 5OOy Pt HzPtCle
phate, scaudium, gallium, mercurous mercury, titanium, hafnium, thorium, germanium, tin, vanadium, chromium, molybdenum, tungsten, iron, antimony, niobium, tantalum, and the platinum metals tested. hlthough the interfering elements are many, only scandium, titanium, hafnium, thorium, iron, and possibly antimonj-, niobium, and tantalum would interfere after a potassium hydroxide .weparation of zirconium under oxidizing conditions. Some additional observations are to be noted. Tungsten, antimon) . niobium, and tantalum form precipitates with quercetin. Xs quercetin does not precipitate titanium and zirconium, it may prove valuable for the separation of niobium and tantalum from titanium and zirconium. The sensitive color reaction given by tin with quercetin is being investigated for the colorimetric determination of tin. Quercetin may also prove useful as a colorimetric reagent for fluorine (by quenching of the zirconium-quercetin color), and for hafnium, molybdenum, antimony, and hevavalent chromium. PROCEDURE
In the determination of zirconium by mearis of quercetin provisions must be made for the removal of interfering ions, especially iron and titanium, which are common constituents in most naturally occurring materials. Precipitation of zirconium by means of either propylarsonic acid or mandelic acid would be an effective means of accomplishing this, but no carrier for zirconium could be found that would be precipitated by these reagents. At this point it seemed that the best approach was to find a zirconium reagent that would quantitatively precipitate microgram amounts (57 of zirconium dioxide) of this element without carrier and that would a t the same time separate zirconium from interfering element.. The reagent p-dimethylaniinoazophenylarsonic acid
1889 offered a means of accomplishing this if it were possible to prevent the precipitation of titanium with hydrogen peroxide. Preliminary experiments indicated that hydrogen peroxide could not be used because of its rapid and complete oxidation of the azoarsonic acid. Attempts to prevent the precipitation of titanium with the azoarsono dve bv emdovine media of hiKh acidity were not completely successful. At the same time it was observed that the titanium formed no precipitate when the solutions were hot, a precipitate being obtained only during the cooling process. Experiments indicated that only a few micrograms of titanium were coprecipitated with zirconium if the zirconium precipitate was 85) hydrochloric acid solution and the solution formed in (15 was filtered hot (70" to 90' C.). I n this manner microgram amounts of zirconium could be separated from at least 10 mg. of titanium dioxide (see Table 11). The maximum amount of titanium dioxide coprecipitated was 257 when 5007 of zirconium dioxide were used. Because only a few micrograms of zirconium dioxide may be determined with quercetin, even this slight interference of titanium dioxide is removed by dilution. Other elements usually precipitated by the azoarsonic acid were found to be more soluble under these conditions. Of the elements that would interfere seriously in the determination of zirconium by means of quercetin only tungsten, tantalum, niobium, scandium. and thorium were precipitated by the azoarsonic acid in hot (15 85) hydrochloric acid solution. The amount of scandium precipitated is small and possibly 0.5 mg. of the oxide can be tolerated in the solution used for precipitating zirconium. The interference of thorium is negligible, as only 57 of thorium dioxide was precipitated when 10 mg. were tested. Yo precipitates were obtained for molybdenum, bismuth, beryllium, gallium, chromium( HI), uranium(VI), platinum, tin( 117)-50 mg. of each oxide tested; cerium (111),yttrium, praesodymium, gadolinium20 mg. of each oxide tested; 15 mg. of germanium dioxide; or 5 mg. of auric ovide. Vanadium and other strong oxidizing agents destroy the azoarsonic acid and should be absent. I
I
_
"
I
I
+
+
Table 11. Coprecipitation of Titanium Cornhination T!Oz TiOr, 11g. I i
10 10
0 2 0 03
ZrO?,
irg,
0 5 0.2: 0.13 0.10 0 03
0.05 0.02
Co precipitated, nIg. 0 025
n
n2n
0.050 0.015 0.015
S o t detected Not detected
The precipitation of zirconium in microgram amounts by p is seriously hindered by microgram amounts of fluoride ion. Fluoride should beavoided in the preparation of the solution for analysis because it cannot be completely removed even by prolonged fuming with perchloric acid, especially if aluminum is present. I t is possible, however, to separate fluorine when present in the original sample by fusing the sample with an alkaline flux and filtering the water leach. Small amounts of sulfate (70 mg. of SO$ maximum tested) do not interfere. Phosphate in amounts under 0.6 mg. of PpOa (maximum tested) was also without effect. The detailed procedure calls for the addition of ferric iron and potassium hydroxide to the leach of the carbonate melt prior to the filtration of the solution. This ensures that a carrier is present for small amounts of zirconium; the high alkalinity serves to destrov soluble complex carbonates of zirconium and allows most of the silica to remain in solution. The precipitate of zirconium with the pararsonic acid tends to leak through the filter unless a very tight filter, such as Whatman No. 12,and paper pulp are used in the filtration. The precipitate should be heated slowly (preferably in a small muffle furnace) and in the absrnre of drdftq to prevcnt dusting losses. The tempera-
dimethrlaminoazophenylarsonic acid
ANALYTICAL CHEMISTRY
1890 ture should not exceed 500" C. or the residue becomes difficult to dissolve in sulfuric acid. After solution in sulfuric acid, the excess sulfuric acid is removed because sulfate quenches the zirconium-quercetin color. Reagents and Apparatus. To prepare a standard stock solution of zirconium (1 ml. contains approximately 2 mg. of zir1) hydrochloric acid to 2.17 conium dioxide), add 100 ml. (1 grams of zirconyl nitrate dihydrate and boil gently until 75 ml. 1) remains. Make to 500 ml. in a volumetric flask with (1 hydrochloric acid. Standardize by taking 20-ml. portions and precipitating with redistilled ammonium hydroxide and igniting to oxide. Zirconium dioxide prepared from reagent grade zirconyl nitrate contained less than 0,3y0 hafnium dioxide by spectrographic tests. To prepare standard zirconium solution in ( 1 4) hydrochloric acid (1 ml. contains 107 of zirconium dioxide), take 5 ml. (or appropriate amount) of stock solution, add 395 ml. 1) hydrochloric acid, and make t o 1 liter with distilled (1 water. Tests indicated t h a t zirconium solutions containing more than 2% by volume of hydrochloric acid are stable for a t least 6 months. p-Dimethylaminoazophenylarsonic acid solution [ 0.3% in (1 1) hydrochloric acid] was prepared in the following way: Powder the pararsonic acid in an agate mortar and dissolve 3 grams in hot (50" C . ) (1 1) hydrochloric acid and make to 1 liter with (1 1) hydrochloric acid. The alcoholic solution of quercetin (1 ml. contains 1.00 mg. ot quercetin) was made up in the following way: Dissolve 0.500 gram of quercetin in 300 ml of 95% alcohol, warming if necessary. hIake to 500 ml. with alcohol. The solution should be filtered if necessary. (The quercetin used was obtained from Delta Chemical Co., 23 West 60th St., New York, S. Y. Quercetin of suitable quality is also available from other sources including S. B. Penick Co., 50 Church St., New York, N. Y., and T. Schuchardt, Ltd., Leopoldstrasse 4, Munchen 23, Germany.) Potassium hydroxide solution was prepared by dissolving 100 grams of potassium hydroxide in 100 ml. of distilled water. To prepare ferric chloride solution (1 ml. contains 1 mg. ferric oxide), dissolve 0.1 gram pure iron wire in hvdrochloric acid, using a small amount of hydrogen peroxide to oxidize the iron. Evaporate the solution to dryness on the steam bath. 1) hydrochloric acid and 20 ml. of water, Add 1 ml. of (1 digest the solution, cool, and make to 100 ml. The carbonate-borate flux was made by mixing 3 parts of anhydrous potassium carbonate a i t h 1 part of borax. Redistilled hydrochloric acid was used for all work, including the preparations of reagents. Sulfuric acid was reagent grade. Beckman spectrophotometer, Model D E , was used.
+
+
+
+
+
+
+
.4dd 10 drops of sulfuric acid, cover the crucible, and heat 011 the hot plate for about half an hour to dissolve the zirconium residue. A small amount of silica usually follows zirconium up to this point, so that a complete solution of the residue may not result. However, the zirconium is dissolved by this treatment. Remove the cover and allow the sulfuric acid to evaporate on the hot plate until no more fumes of acid appear. Holding the crucible with platinum-tipped tongs, remove the last traces of sulfuric acid by gently heating below 500" C. over a low burner. Add 5.2 ml. of (1 4) hydrochloric acid by a pipet. Cover the crucible and warm the solution a few minutes to dissolve the zirconium. Rinse the cover with water, adding the washings t o the crucible. Transfer the solution to a 25-ml. volumetric flask. An aliquot of the solution should be taken here if the sample is known to contain more than 25 t o 507 zirconium dioxide. Additional acid will then be required to bring the acidity up to 0.5N hydrochloric acid used in the determination of zirconium with quercetin. Adjust the volume t o about 15 ml. Kith water. Cool. Add 5 ml. of alcohol and 3 ml. of quercetin using pipets. Mahe t h e solution to the mark, mix, and obtain the absorbancy of the solution in the spectrophotometer a t 440 mp using a slit width of 0.05 mm. Determine the amount of zirconium by reference to a standard curve. A blank should be run in the procedure. For example, ly zirconium dioxide was found in the combined residue of the filter paper and pulp used for the filtration of the azoarsono precipitate.
+
Test of the Procedure. The procedure was applied to the determination of zirconium in glass sands, clays, and refractories. Bureau of Standards standard samples were used. The results obtained for zirconium by the quercetin procedure are compared with certified analyses in Table 111. The agreement is satisfactory.
Table 111. Comparison of Results of Zirconium Analysis
+
Detailed Procedure. T e i g h 0.200 gram of sample, ground to an impalpable powder, into a platinum crucible. Burn off organic matter if present in the sample. Add 3 grams of the carbonate-borate flux and mix thoroughly. Cover the crucible and heat gently a t first and then fuse the sample a t high heat over a burner for 30 minutes. The fusion period can be greatly shortened for samples that are not refractory. Cool. Leach the melt with about 50 ml. of water. Remove crucible and the cover, scrubbing and rinsing them before setting them aside. The total volume a t this point should be about 70 ml. Add 10 ml. of potassium hydroxide solution, 5 ml. of ferric chloride solution, stir, and digest the solution on the steam bath for 30 minutes to an hour. Filter the solution on Khatman No. 40 paper and wash the precilnitate with 1% ' potassium hydroxide solution. Drain the pape; and stem of thefunnel thoroughly. Dissolve the precipitate with 10 ml. of hot (1 1) hydrochloric acid (use pipet), collecting the filtrate in a 100-ml. beaker. Wash the paper with water. Add 5 ml. of p-dimethylaminoazophenylarsonicacid solution, adjust the volume t o 50 ml. and digest the solution on the steam both for a t least an hour. Add a generous amount of paper pulp and filter the precipitate of zirconium while hot. I n order to prevent precipitation of titanium the solution must not be allowed to cool below 70" C. during the filtration. Wash the precipitate thoroughly with a hot wash solution of the dye (made by taking 10 ml. of the azo-arsonic acid solution, 70 ml. of concentrated hydrochloric acid, and diluting to 500 ml. with water). Transfer the paper and precipitate t o a platinum crucible and remove most of the water by drying in an oven. Then gently ignite the precipitate in a small muffle furnace a t 500" C., starting with a cold furnace.
+
Zirconium Dioxide, % ' Certified analysis (Quercetin) (av.) procedure 0.07 0.072 0.09 0.089 0.12 0.112 0.114 B.S. 81 0.031 0.033 0.029 0.0095 B.S. 91" 0.0100 0.0104 B.S. 97 0.245 0.25 B.S. 98 0.041 0.0409 This sample contained 5.72% F.
Bur. Standards Sample No. B.S. 76 B.S. 77 B.S. 78
5
LITERATURE CITED
(1) Alford, W. C., Shapiro, L., and White, C. E., ANAL.C m x , 23, 1149 (1951). (2) Bent, H. E., andFrench, C. L., J . Am.Chem. SOC., 63,568 (1941).
(3) Connick, R. E., and Reas, W.H., C. S. Atomic Energy Commission, AECD-2491, declassified (March 2, 1949). (4) DeBoer, J. H., Rec. traa. chim., 44, 1071 (1925). (5) Flagg, J. F., Liebhafsky, H. A., and Winslow, E. H., J . Am. Chem. SOC.,71, 3630 (1949). (6) Green, D. E., ANAL.CHEM.,20, 370 (1948). (7) Guenther, R., and Gale, R. H., U. S. Atomic Eneigy ('ommission, KAPL-305 (1950). (8) Hayes, W. G., and Jones, E. W,, IND. ENG.CHEM.,ANAL.ED., 13, 603 (1941). (9) Liebhafsky, H. A., and Winslow, E. H., J . Am. Chrm. Soc., 60, 1776 (1938). (10) Mayer, A,, and Bradshaw, G., Analyst, 77, 476 (1952). (11) Nazarenko, V. A,, Zhur. Priklad. Khim., 10, 1696 (1937). (12) Stehney, A. F., and Safranski, L. W.,U. S. Atomic Energy Commission. AECD-3097 (1951). (13) Tananev, N. A., and Khovyakova, R. F., ZhLr. Obshchd Khim., 21, 808 (1951). (14) Wengert, G. B., A N ~ LCHEM., . 24, 1449 (1952). RECEIVED for review July 7 , 1953. Accepted September 17, 1963. Publioetion authorized by the Director, U. S. Geological Survey. Presented before the Division of Analytical Chemistry a t the 124th Meeting of the AMERICAN CHEMICAL SOCIETY,Chicago, Ill. From a thesis submitted in partial fulfillment of the requirements for the degree of doctor of philosophy. University of Maryland, June 1953.
