Amperometric Determination of Zirconium with 1-Nitroso-2-naphthol RAY F. WILSON and THORNTON RHODES Texas Southern University, Houston 4, r e x .
An aliquot of the standard stock solution of zirconium, sufficient to give the final concentration desired, was placed in a 100-ml. volumetric flask. Then 4 ml. of 0.27, gelatin solution, 5 ml. of 2M acetate buffer, and 5 ml. of 25% potassium chloride (to maintain a high constant ionic strength during the titration) were added, and the solution was diluted to volume with distilled water. A 20-ml. aliquot of this solution was transferred to an H-type cell, and oxygen-free nitrogen (6) was passed through the solution for 15 minutes. All current measurements were taken at -0.4 volt and were corrected for dilution effects. This solution was titrated amperometrically with standard 1-nitroso-2-naph-
An amperometric method has been developed for the determination of zirconium, based on the interaction of this element with 1-nitroso-2-naphthol. This method can be used for the accurate determination of zirconium in the presence of small amounts of fluoride ion; however, large concentrations of fluoride ion interfere. The amperometric titration of zirconium in the presence of several other diverse ions indicated that only nickel interfered with the titration. The average relative analytical error of the method, corresponding to a tenfold change in concentration of zirconium, is 3~0.4%. The method is rapid and involves only a few operations.
A
LTHOUGH numerous precipitation reactions of zirconium have been reported ( I ) , it appears that only one of these
reactions has been utilized for the amperometric determination of zirconium. This is the titration of zirconium with cupferron (3) in sulfuric acid solution, which was found to be applicable for the determinatjion of this elenlent in fluoride solution. The analytical precision of the method was reported to be 0.4Oj, or better. Wilson and Lovelady (6) have studied the amperometric titration of iron(II1) with 1-nitroso-2-naphthol in acetic acid-sodium acetate buffer. Kolthoff and Langer (Z), while investigating the amperometric titration of cobalt with 1-nitroso-2-naphthol, observed from a few experiments that palladium and copper could also be titrated with the same reagent. Zirconium salts ( 5 ) react with 1-nitroso-2-naphthol solution to form a greenish yellow amorphous precipitate of the composition CloH60(NO)~Zr0. However, zirconium reacts with 1-nitroso-2-naphthol in acetate buffer to form a dark brown precipitate. Also, when the pH is less than 5, zirconium acetate solutions of high ionic strength show 0 0.2 0.4 0.6 0.8 1.1 no apparent tendency to form hydrous oxide of zirconium; this VOL. I-NITROSO-2-NAPHTHOL. ML. fact suggests that zirconium probably exists in solution as a Figure 1. Titration of 20 ml. of stable complex or colloid. 0.150 X M zirconium with The present investigation was undertaken to study ampero0.0930M 1-nitroso-2-naphthol metrically the zirconium-1-nitroso-2-naphthol reaction in acetate buffer, to develop a method for the rapid determination of m a l l amounts of zirconium, and to determine the effect of certain diverse ions on the titration. Table I. Amperometric Titration of Zirconium in Acetate Buffer at -0.4 Volt us. S.C.E. EXPERIiMEYTAL
Reagents and Solutions. A weighed amount of C.P. zirconyl rhloride octahydrate (A. D Mackay, Inc.) was dissolved in distilled water and diluted to volume to give the concentration desired. This solution wm standardized gravimetrically by treating aliquots of the stock zirconium solution with ammonium hydroxide according to the procedure described by Scott ( 4 ) ; the precipitate was ignited and weighed as zirconium dioxide. The average of quadruplicate determinations of zirconium in this manner was 12.3 mg. per ml., with an average deviation of 3ZO.01 mg. per ml. 1-Nitroso-2-naphthol solution mas prepared after recrystallizing this reagent (Eastman Kodak Co., No. p428) twice from alcohol, and the solution was standardized amperonietrically (6). -4buffer solution mas prepared which was 2M in both acetic acid and sodium acetate. All other reagents were the same as those described by Wilson and Lovelady (6). Apparatus. d Sargent Model X X I Polarograph was used. The H-type polarographic cell contained a saturated calomel electrode and a potassium chloride-agar-fritted-glass disk salt bridge; the entire assembly was jacketed in water a t 25" =k 0.1" C. All measurements were made and are reported us. the saturated calomel electrode a t 25' C. Procedure. After a preliminary study of the zirconium-lnitroso-2-naphthol system, the following procedure was adopted for the amperometric determination of zirconium.
1199
Zirconium, Mmoles X 101 0.40 1.20 2.00 2.40 3.00 4.00 5.00
1-Nitroso2-naphthol Mmoles x io2
Mole Ratio, Zr/Titrant 1:2.00 1:2.00 1:2.03 1:2.00 1:2.01 1:2.00 1:2.00
0.80
2.40 4.05 4.81 6.03 8.00 9.99
Table 11. Amperometric Titration of Zirconium in Presence of Diverse Ion
Ion Ni(I1) Ti(1V) AI(II1) Ca(I1) Zn(I1) Cr(II1) wz(II) Au(II1)
so,-NOI F-
(0.0240 mmole of zirconium Added Mmole Form 0.02 NiCln. 6Hn0 Tic14 0.02 AlClr 0.02 CaClt. 2Hn0 0.02 ZnClr 0.02 CrCla. 8HnO 0.02 MgCls. 6HzO 0.02 AuClr . HCI. 3Hn0 0.01 0.20 KzSOb 0.20 KNOa 0.25 K F .2Hn0
taken)
Zirconium, - Mmole Found 0,0229 0.0242 0.0239 0.0237 0.0238 0.0242 0,0238 0.0241 0.0239 0,0240 0.0241
Dev. -0.001 +o. 00021 -0.0001 -0.0003 +o. - 0.0002 0002
- 0,0002
+o. 0001 -0.0001
0.0000
+O. 0001
'
1200
ANALYTICAL CHEMISTRY
thol. The volume of titrant used in each titration was determined using the extrapolation method. A typical titration curve for the ani erometric detet mination of zirconium is shown in Figure 1. The f a t a obtained from several titrations of zirconium with 1-nitroso-2-naphthol are shown in Table I ; each line in the table is the mean of two results obtained from the titration of solutions of the concentration indicated. Effect of Diverse Ions. The possible interference of several ions on the amperometric titration of zirconium in acetate buffer was studied by adding the diverse ions, individually, to solutions which were approximately 1 m M in final zirconium concentration. These solutions were made according to the adopted procedure and the volume of titrant used in each titration w a ~ determined in the usual way. The results of these titrations are shown in Table 11.
mole ratio of fluoride ion to zirconium. However, a large concentration of fluoride ion interfered-Le., the volume of titrant required to titrate zirconium in the presence of a 100-fold molar excess of fluoride ion was too large by about +4%. The analytical precision of this method is comparable to that of the cupferron procedure ( 3 ) ; the 1-nitroso-2-naphthol titrant is stable for 2 weeks as compared to 1 day for the cupferron titrant. ACKNOWLEDGMENT
The work reported in this paper was made possible by a grant from National Science Foundation. LITERATURE CITED
DISCUSSION
The average relative analytical error of this method is f0.45./;, which corresponds to about a tenfold change in concentration of zirconium. Results of the titration of zirconium in the presence of sinal1 amounts of diverse ion indicate that the ions selected for study, with the exception of nickel, did not interfere in the determination of zirconium. The interference of copper, cobalt, iron, and palladium on the titration was not studied because these elements are readily precipitated by 1-nitroso-2-naphthol. Zirconium was titrated accurately in the presence of a 10 to 1
“Organic Reagents,” vol. 4, p. 300, Interscience, New York, 1948. Kolthoff, I. M., Langer, A., J. Ana. Chem. SOC. 62, 3.172 (1940). Olson, E. C., Elving, P. J., ANAL.CHEM.26, 1747 (1954). Scott, W. W., “Standard iMethods of Chemical Analysis,” 5th ed., N. H. Furman, ed., vol. 1, p. 1103, Van Nostrand, New York, 1939. Welcher, F. J., “Organic Analytical Reagents,” vol. 3, p. 318, Van Nostrand, New York, 1949. Wilwn, R. F., Lovelady, H. G., ANAL.CHEM.27, 1231 (1956).
(1) Flagg, 3. F.,
(2)
(3) (4) (5) (6)
HEchIvRD
for review August 8, 1955.
Accepted Maroh 30, 1956.
Separation and Purification of Milligram Amounts of Cesium from large Amounts of Other Alkali Salts S. A. RING’ Chemical Technology Division,
U.
S. N a v a l
Radiological Defense Laboratory, San Francisco, Calif.
A procedure is presented for the separation of milligrani q u a n t i t i e s of cesium f r o m approximately ten t h o u s a n d times as m u c h sodium and five t i m e s a s m u c h rubidium). At the s a m e time the method reduces the r u b i d i u m i m p u r i t y in the final cesium s a m p l e to less t h a n 2 p a r t s per t h c u s a n d . This separation is accomplished by means of an ion exchange step employing s o d i u m h j droxide elution f r o m a phenolic methylene sulfonictype resin, followed b y one or more precipitation steps for final purification of t h e cesium f r o m sodiurn a n d 110tassium.
c
’1IASSICAL precipitation methods were not found satisfa(:-
tory for the isolation and purifiration of small amounts of cesium from large excesses of the other alkali metals. There methods involve separation of the heavy a.lkali group-potassirim, rubidium, and cesium-from sodium, provided sodium is not present in overwhelming abundarice, followed by separation of cesium, rubidium, and potassium from each other. Cesium and rubidium are especially difficult t o separate, although some success has been achieved with paper rhroniatogmphy (8) and solvent extraction (IO). I n the past few years great suc(!esti has also been achieved by chromatographic elutiori of the alkalies with hydrochloric acid from cation exchange resins ( I , 9 , 4 , 6, 7 ) . However, the ion exchange methods involve approximately equal amounts of the alkalies in the starting product for a good separation of cesium from rubidium. Any large excess of one or more of the alkdies would involve the use of large equipment and long elution times, becaui3e the procedures require adsorption of the entire starting product on the exchange medium and consequetit 1 Present addresa, National Carbon Research I,aboratories, Cleveland 1, Ohio.
separation from that point. These requirements become prohibitive in the case of separation of a few milligrams of cesium from a pound of other alkali metals. Miller and Kline (9) have reported an exceptional ability of Amberlite IR-100 cation resin to adsorb cesium out of a concentrated sodium solution a t pH 13, as well as good retention of cesium when this same solution is eluted through P column of the resin. The special selectivity for cesium may be ascribed to the phenolic structure of the resin, because the nuclear sulfonic resiris under the same conditions do not show this property. The following experiments describe the conditions for adsorption of cesium from a highly concentrated alkali salt solution onto a phenolic methylene sulfonic resin column, as well as the method for the removal of rubidium and the bulk of the potassium by eluting with a 0.5N sodium hydrovide solution. EXPERIMENTAL
Because the similar Amberlite types are no longer being manufactured, phenolic methylene sulfonic resin, Duolite C-3 (Chemical Process Go., Redwood City, Calif.), waa used in these experiments. Duolite C-3 is produced in a single coarse grade, two thirds of which is 20 to 50 mesh and the remaindFr larger than 20 mesh. In ail the experiments except one the resm was used unaltered. After exploratory runs had been made with radioactive cesium and rubidium tracer to determine roughly the conditions by which cesium would be adsorbed on the resin column and rubidium would be eluted, the experimental runs were made without tracer and the samples analyzed for alkali content by a flame photometric method (6). I n each experiment the cesium and rubidium were contained initially in from 1 to 2 liters of saturated sodium chloride solution (roughly 1 pound of salt). This solution was made 0.5N in hydroxide ion with sodium hydroxide pellets and added to a resin column 1.2 cm. in diameter and either 80 or 120 cm. long. The resin was then eluted with reagent grade 0.5N sodium hydroxide
