Determination of Scandium by Precipitation with Benzilic Acid Michael H. Mullin and Richard B. Hahn Department of Chemistry, Wayne State University, Detroit, Mich. 48202 MANY ORGANIC COMPOUNDS have been used for the determination of scandium (1-10). The most specific reagents are 8-hydroxyquinoline (8, 9) and mandelic acid (3). Benzilic acid has been used (7) as a reagent for the gravimetric determination of zirconium and proved to be superior to mandelic acid, owing to the lower solubility of zirconium benzilate as compared with zirconium mandelate. Since Alimarin and Han-Si (3) demonstrated that mandelic acid may be used as a reagent to determine scandium, this investigation was undertaken to determine whether benzilic acid also is suitable as a quantitative precipitant for scandium.
Table I. Effect of Diverse Ions Amount S & 0 3 Ion added recovered Error, F40. 52n -10.6 Zr02+ 78.02” +70.4 SO42c104-
~ 1 3 +
Y3+ Mgz+
Fe3+ uo22+
EXPERIMENTAL
Reagents. BENZILICACID SOLUTION.A 0.1M solution was prepared by suspending 22.8 grams of dry acid in 800 ml of water, then adding 60 ml of concentrated ammonium hydroxide and warming slightly to form the soluble ammonium benzilate. After cooling, the solution was made up to one liter with distilled water. SCANDIUM CHLORIDE SOLUTION.Scandium oxide of 99.9 purity (obtained from Alfa-Ventron, Beverly, Mass.) was dissolved in a minimum volume of concentrated hydrochloric acid and then diluted to volume with water. The solution was standardized by precipitation with mandelic acid (3). ZIRCONYL CHLORIDESOLUTION.Reagent grade zirconyl chloride octahydrate was dissolved in 2N hydrochloric acid and standardized by precipitation with benzilic acid (7). Procedure. After considerable experimentation, the following procedure was developed for the determination of scandium. A solution containing 0.03 to 1.5 millimoles of scandium is placed in a 250-ml beaker. Fifty milliliters of 0.1M benzilic acid and enough water to give a total volume of 100 ml is added and the pH adjusted to 2.5 using dilute hydrochloric acid or ammonium hydroxide. An amorphous precipitate appears immediately. This is digested at 75-80 “C for approximately 20 minutes, and during this time the precipitate becomes granular and settles out. The solution is cooled to room temperature, filtered by suction using Whatman No. 42 filter paper and the precipitate washed several times with water. The precipitate is dried and then ignited to scandium oxide for weighing. Effect of Acidity. Complete recoveries were obtained in the pH range of 1.5-5.0. Low results were obtained when the pH was less than 1.5 owing to the solubility of the precipitate in strongly acid solution. At pH greater than 5.0, (1) I. P. Alimarin, V. I. Fadeeva, and T. N. Petrova, Zh. A n d . Khim., 16, 549 (1961); Chem. Abstr., 56, 665512 (1962). (2) I. P. Alimarin and N. V. Shakhova, Zh. A n d . Khim., 16, 412 (1961); Chem. Abstr., 56, 1994d (1962). (3) I. P. Alimarin and S . Han-Si, Zh. A n d . Khim., 15, 3 1 (1960); Chem. Abstr., 54, 139771’ (1960). (4) I. P. Alimarin and S . Han-Si, Zh. Anal. Khim., 16, 279 (1961); Chem. Absrr. 56, 1994 (1962). (5) D. R. Bomberger, ANAL.CHEM., 30, 1907 (1958). (6) W. Fischer, and R. Bock, Z. Anorg. Chem., 249, 146 (1942).
(7) J. J. Klingenberg, P. N. Vlannes, and M. G. Mendel, ANAL. CHEM.,26, 754 (1954). (8) L. Pokras and P. M. Bernays, J. Amer. Chem. SOC.,75, 7 (1951). (9) L. Pokras and P. M. Bernays, ANAL.CHEM., 23, 757 (1951). (10) R. C. Vickery, “The Chemistry of Yttrium and Scandium,” Pergamon Press, London, 1960. 1878
Pb2+ Nb6+
43.38 46,97 50.48 127.65 43.26 44.06 61.75 44.38 50.60 48.56 78.57 72.42 44.27
-1.1 +3.3 +15.1 +191.1 -1.3 +0.5 $40.8 $1.2 +15.4 +10.7 +79.2 +65.1 +1 .o
Ti4+ Th4+ La3+ Te4+ These samples contained 45.78 mg of scandium oxide. All others contained 43.85 mg of scandium oxide.
the precipitate undergoes hydrolysis and basic salts are precipitated. A pH of 2.5 was chosen as optimum since the precipitation of scandium is complete at this acidity and there is a minimum of interference from foreign ions. Quantitative precipitation of scandium was obtained in the range of 1.75 to 105.24 mg of Sc20,. Larger amounts of scandium could be determined by increasing the amount of benzilic acid used for precipitation. The large volume of precipitate, however, would be inconvenient in filtration and ignition. Composition and Solubility of the Precipitate. A known amount of scandium was precipitated with benzilic acid and dried at 120 “C for 24 hours. This dried precipitate was weighed, ignited to scandium oxide, and weighed again. From these data, the precipitate composition was determined to be a hydrated scandium tribenzilate and is not suitable for direct weighing owing to variations in the degree of hydration. This varied between 0.5-3 moles of H20 per mole of scandium tribenzilate depending on the temperature and length of drying. Using scandium-46 as a tracer, the solubility of scandium tribenzilate was found to be 8.4 X 10-8 mole/liter. Interference of Foreign Ions. The possible interference of other ions was determined by precipitating known amounts of scandium with benzilic acid from solutions containing known quantities of impurities. The results of these determinations are given in Table I. Separation of Scandium from Zirconium. Since zirconium is a serious interference in most of the analytical methods for determining scandium, it was decided to investigate the possibility of separating scandium from zirconium using benzilic acid. Scandium does not precipitate with zirconium at high acid concentrations (1-3 normal), but zirconium does accompany scandium in precipitation from weakly acid (pH 2-3) solutions. Therefore, an initial separation of zirconium from a scandium-zirconium mixture is required prior to the determination of scandium. The following procedure was employed : A solution containing 5 mg to 100 mg each of scandium oxide and zirconium oxide was made 4N in hydrochloric acid, then heated to near boiling. Zirconium benzilate was
ANALYTICAL CHEMISTRY, VOL. 44, NO. 11, SEPTEMBER 1972
Table 11. Separation of Scandium and Zirconium Using Benzilic Acid SC203 sc203 sczo3 ZrOz ZrOz Sample added, mg found, mg recovered, % added, mg found, mg 29.05 98.7 26.31 25.45 I 29.44 27.87 94.7 26.31 29.78 I1 29.44 1.11 18.8 91.55 101.49 111 5.89 100.2 27.7 28.1 118.0 IV 117.7 101.1 9.2 8.5 119.0 V 117.7 99.7 91.55 96.07 17.61 VI 17.66 VIIQ 58.87 59.81 99.7 27.47 26.15 Mandelic acid used in place of benzilic acid.
precipitated by the addition of 100 ml of hot, 0.1M benzilic acid solution. The precipitate was filtered through filter paper, washed several times with hot water, then dried and ignited to the oxide for weighing. The p H of the filtrate was adjusted to 2.5 and scandium determined by precipitation with benzilic acid using the procedure given previously. Several different mixtures of scandium and zirconium were analyzed and the results are listed in Table 11. One sample was analyzed using mandelic acid in place of benzilic acid and the results were comparable. The efficiency of the separation was determined using scandium-46 tracer and the study showed that the separation of scandium from zirconium using benzilic acid is quantitative.
ZrOp recovered, 96.8 113.2 110.9 101.4 92.4 104.9 95.2
DISCUSSION
The volume of the scandium benzilate precipitate is larger than that of scandium mandelate and therefore is less subject to loss during transfer. The solubility of scandium tribenzilate is about one-tenth that of scandium trimandelate ( 4 ) . This property, along with the relative ease of handling the scandium benzilate precipitate, makes benzilic acid the preferred reagent over mandelic acid for the gravimetric determination of scandium.
RECEIVED for review February 9, 1972. Accepted May 12, 1972.
Simultaneous Microestimation of Choline and Acetylcholine by Gas Chromatography D. J. Jenden, R. A. Booth, and Margaret Roch Department of Pharmacology, UCLA School of Medicine, Los Angeles, Gal$ 90024
AN ADEQUATE STUDY of acetylcholine turnover must involve concomitant measurements of both choline and acetylcholine, since the former is generally believed t o be one of the major precursors of acetylcholine and its availability under some circumstances is probably rate limiting. Many biological and chemical methods have been described for the microestimation of acetylcholine ( I ) with broad agreement regarding the tissue levels obtained. On the other hand, results obtained by different procedures for the measurement of brain levels of choline have given widely disparate results (2-4). Gas chromatographic methods have been described for the microanalysis of choline esters in tissues and perfusates (5-9). (1) D. J. Jenden and L. B. Campbell, in “Analysis of Biogenic Amines and Their Related Enzymes,” Vol. 19, D. Glick, Ed.,
Interscience, New York, N.Y., 1971. (2) J. Schuberth, B. Sparf, and A. Sundwall, in “Drugs and Cholinergic Mechanisms in the CNS,” E. Heilbronn and A. Winter, Ed., Research Institute for National Defense, Stockholm, 1970. (3) I. Hanin, R. Masserelli, and E. Costa, in “Drugs and Cholinergic Mechanisms in the CNS,” E. Heilbronn and A. Winter, Ed., Research Institute for National Defense, Stockholm, 1970. (4) D. J. Jenden, in “Drugs and Cholinergic Mechanisms in the CNS,” E. Heilbronn and A. Winter, Ed., Research Institute for National Defense, Stockholm, 1970. (5) D. E. Schmidt, P. I. A. Szilyagi, D. L. Alkon: and J. P. Green, J. Pltarmacol., 174, 337 (1970). (6) D. J. Jenden, I. Hanin, and S. I. Lamb, ANAL.CHEM.,40, 125 (1968).
One of these may be simply modified t o measure free choline ( I , 3, 4). However, the original procedure cannot be employed for the simultaneous estimation of both, because the choline modification requires conditions under which its acetate ester is unstable. In this report a procedure is described for the derivatization of choline and acetylcholine, which allows their simultaneous measurement without mutual interference. EXPERIMENTAL
The basic procedure is similar to that described earlier (7, 8) except that: a) silver p-toluenesulfonate in acetonitrile is used in place of a suspension of Biorex 9 ion exchange resin t o remove Reineckate ion; b) choline is converted to propionylcholine by reaction with propionyl chloride in acetonitrile solution; Ag+ serves as a catalyst for the acylation; c) dimethylaminoethanol may be removed from the sample if necessary by extraction of the dry residue with pentane containing trimethylamine ; and d) pivaloylcholine is used as a n internal standard in place of hexyltrimethylammonium. (7) I. Hanin and D. J. Jenden, Biochem. Pharmacol., 18, 837 (1969). (8) D. J. Jenden, L. B. Campbell, and M. Roch, Afial. Biochem., 35, 209 (1970). (9) W. B. Stavinoha and L. C. Ryan, J. Pharmacol., 150, 231 (1965).
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