lent actinides. It may be removed by extraction from 6N HNO8 by a dialkylphosphoric acid without significant loss of berkelium. Some of the elements soluble as iodates in lNHNO3 would precipitate at lower acidities. Applications. The primary application of iodate PFHS is in separating berkelium from other transplutonium elements after they have been separated from fission products and from plutonium. This appears especially attractive for final purification after process solutions have been reduced to small volumes. Assay of radioactive solutions for their berkelium content is difficult because 249Bkhas little activity except low-energy betas. Iodate PFHS gives high decontamination from interfering activities.
Another important application occurs as Z49Bk decays with a half-life of 314 days to 249Cf. The californium may be recovered periodically as a solution after coprecipitating the berkelium with cerium. The precipitate can then be prepared for a later separation by dissolving in hydrochloric acid and converting to nitrate. Thus iodate PFHS is convenient for milking 24gCf from 249Bk. When sufficient 24gBkis available, this application can be made without cerium carrier.
RECEIVED for review April 29, 1968. Accepted July 1, 1968. 155th Meeting, ACS, San Francisco, Calif., April 1968. Research sponsored by the U. S. Atomic Energy Commission under contract with Union Carbide Corp.
Indirect Spectrophotometric and Atomic Absorption Spectrometric Methods for Determination of Perchlorate W. J. Collinson and D. F. Boltz Department of Chemistry, Wayne State University, Detroit, Mich. 48202
RELATIVELY few spectrophotometric methods and no atomic absorption spectrometric methods for the determination of traces of perchlorate ion are found in the chemical literature. Methylene blue forms a very slightly soluble complex with perchlorate in aqueous solution. The methylene blue perchlorate complex can be extracted with chloroform ( I ) or 1,Zdichloroethane (2) and measured spectrophotometrically, or the excess methylene blue can be determined (3). Other dyes and extractants have been used in modification of this method (4,5). The decrease in color concomitant to the precipitation of copper(I1) tetrapyridine perchlorate has been utilized in another indirect method (6). A redox reaction in which perchlorate was reduced to chloride by vanadium(II1) to give an equivalent amount of vanadium(1V) was the basis of an indirect spectrophotometric method involving absorbance measurements at two wavelengths (7). The absorbance measurements at 400 and 750 mp were necessary in order to correct for the absorbance due to the residual vanadium(II1). A novel indirect spectrophotometric method has been proposed by Trautwein and Guyon (8). This method is based on the interference of the perchlorate ion in the development of the color due to rhenium-furildioxime complex formed when perrhenate is reduced with tin(I1) chloride in the presence (1) D. F. Boltz and W. J. Holland in “Colorimetric Determination of Nonmetals,” D. F. Boltz, Ed., Interscience, New York, 1958, p 176. (2) I. Swasaki, S. Utsumi, and C . Kang, Bull. Chem. SOC.Japan, 36, 325 (1963). (3) 31, . , G. M. Nabar and C. R. Ramachandran, ANAL.CHEM., 263 (1959). (4) V. A. Golosnitskaya and V. I. Petrashen, Xouocherk. Politekhn. Znst., 141,65 (1964). (5) S. Uchikawa, Bull. Chem. SOC.Jaoan. 40.798 (1967). (6j W. Bodenheimer and H. Weiler, ANAL.C H E M . , ‘1293 ~ ~ , (1955). (7) D. A. Zatko and B. Kratochvil, ibid., 37, 1560 (1965). (8) N. L. Trautwein and J. C. Guyon, ibid., 40,639 (1968).
1896
ANALYTICAL CHEMISTRY
of a-furildioxime (9). The formation of an iron(I1)-1,I 0phenanthroline-perchlorate complex extractable with nbutyronitrile (10) and the iron(I1)-2,2’-bipyridine-perchlorate complex extractable with nitrobenzene (11) have been utilized as the basis of another indirect method for the spectrophotometric determination of perchlorate. The spectrophotometric method proposed as the result of this investigation is based on (1) the formation of perchloratobis(2,9-dimethyl-l,lO-phenanthroline)copper(I), (2) the extraction of this complex with ethyl acetate, and (3) measurement of the absorbance of the resulting extract (12). The atomic absorption spectrometric method involves aspiration of the extract into an acetylene-air flame an$ the copper determined using the resonance line of 3247 A. A somewhat analogous approach has been suggested for the determination of nitrate (13). EXPERIMENTAL Apparatus. The atomic absorption spectrometric measurements were made with a Beckman Model 1301 atomic absorption accessory unit, a Beckman Model DB prism spectrophotometer equipped with a Beckman potentiometric recorder, and a Techtron burner assembly. The hollow cathode tube was neon filled and supplied by Beckman (No. 180245). The spectrophotometric measurements were made in 1.000-cm cells using a Cary 14 spectrophotometer. A Thomas shaking apparatus was used for extractions. (9) V. W. Meloche, R. L. Martin, and W. H. Webb, ANAL. CHEM., 29, 527 (1957). (10) J. S. Fritz, J. E. Abbink, and C. A. Campbell, ibid., 36, 2123 (1 964). (11) Y . Yamamoto and K. Kotsuji, Bull. Chem. SOC.Japan, 37, 594 (1964). 24, 371 (12) G. F. Smith and W. H. McCurdy, Jr., ANAL.CHEM., (1 952). (13) T. Kumamuru, E. Tao, N. Okamoto, and Y. Yamamoto, BuU. Chem. SOC.Japan, 38,2204 (1965).
Table I. Effect of Diverse Ions 3 ppm C104Error Concna (spectro(PP@ photometric)
z
Ion Nos-
c1-
sod2OAc~02-
NH4+
K+
Mgz+
Fez+
~ 1 3 +
3 6 15 3 6 15 3 6 15 3 6 15 3 6 15 3 6 15 3 6 15 3 6 15 3 6 15 3 6 15
I
o’O 0.7
zError @AS)
0.5
0
1.9 5.2 0.5 1.4 1.4 0.2 0.2 1.7 0.5 0.2 0 0 0.7 1.0
1.7 4.2 0 1.3 1.5 1.1 1.7 2.5 0.3 0.8 0.6 0.9 0.6 0.9
1.0 1.5 3.2 0.7 1.2 2.2
2.0 3.3 5.8 0.7 1.4 2.6
2.2 1.2 2.9 1.0 0.2 0.5 0 1.2 3.1
2.1 1.4 5.9 1.2 1.0 1.9 0 1.7 5.1
Concentrations of perchlorate and diverse ions are in terms of volume of aqueous solution, prior to extraction. (1
Reagents. STANDARD PERCHLORATE SOLUTION.Dissolve 0.1232 gram of reagent grade “anhydrous” sodium perchlorate in distilled water and dilute to 1 liter. Dilute exactly 25 ml of this stock solution to 100 ml to obtain a standard solution containing 25.0 pg of perchlorate per ml. COPPER(II)SULFATESOLUTION.Dissolve 0.3140 gram of reagent grade anhydrous copper(I1) sulfate in distilled water and dilute to 1 liter. PHOSPHATE BUFFERSOLUTION.Dissolve 34.0 grams of potassium dihydrogen phosphate (KH2POd) in distilled water and dilute to 1 liter. HYDROXYLAMINE SULFATESOLUTION.Dissolve 50 grams of hydroxylamine sulfate, (NH~OH)zHzS04, in 950 ml of water. NEOCUPROINE REAGENT. Dissolve 0.4165 gram of neocuproine, (2,9-dimethyl-1,lo-phenanthroline), in reagent grade ethyl acetate and dilute to 1 liter with this solvent. Recommended General Procedure. Weigh or measure by volume an amount of sample containing no more than 0.6 mg of perchlorate ion. The resulting solution should be adjusted to pH 3-5 and diluted to 25 d. Transfer 6 ml of the copper(I1) sulfate solution to a 25-ml volumetric flask and add 5 ml of sample solution. Add 2 ml of the hydroxylamine sulfate solution and 5 ml of the phosphate buffer solution. Dilute to volume with distilled water and mix thoroughly. Add 10 ml of the neocuproine reagent to a 60-ml separatory funnel. Transfer solution from volumetric flask to separatory funnel. Use 1 ml of buffer solution to rinse volumetric flask. Add rinsing to separatory funnel. Place separatory funnel on shaking ap-
0.6
0.5
E 0.4 2 U m [r
0.3 m
a
0.2
0.1
0
0
25 50 75 100 125 MICROGRAMS OF PER C H L OR AT E
150
Figure 1. Typical calibration graphs for indirect determination of perchlorate: ( I ) atomic absorption spectrometric method; (2) spectrophotometric method The micrograms of perchlorate represent the weight present in 25 ml of aqueous solution, prior to extraction, or in 10 ml of ethylacetate,after extraction
paratus and extract for 3 minutes. Remove aqueous layer. Drain extract through cotton pledget placed in stem of funnel and collect in small bottle. SPECTROPHOTOMETRIC METHOD. Measure the absorbance at 456 mp in 1.000-cm cells using a reagent blank solution in the reference cell. Refer absorbance reading to a calibration graph obtained using standard perchlorate solutions. ATOMICABSORPTION SPECTROMETRIC METHOD. Adjust the acetylene-air burner to give a fuel-lean flame and set monochromator at 324.7 mp. Aspirate extract and record absorbance. Refer absorbance reading to a calibration graph obtained using standard perchlorate solutions. RESULTS AND DISCUSSION
Perchlorate Concentration. In the indirect spectrophotometric method, conformity to Beer’s law was observed up to 7.5 ppm in the ethyl acetate extract with a very slight negative deviation being observed up to 12.5 ppm (Figure 1, plot 2). In the atomic absorption spectrometric method, conformity to Beer’s law was obtained to approximately 4 ppm of perchlorate in the extract with moderate negative deviation to 12.5 ppm (Figure 1, plot 1). On the basis of the aqueous solution, prior to extraction, the optimum concentration range is approximately 0.5 to 5 ppm of perchlorate for both methods. Copper(I1) Concentration. Sufficient copper(I1) is required to ensure complete formation of the perchlorato-bis(2,9dimethyl-1,IO-phenanthroline) copper(1) complex. It was determined experimentally that 750 pg of copper(I1) was needed per 25 ml of solution for attaining maximum absorbance using 5 ppm of perchlorate. Hence, a copper(1) concentration of 30 ppm is recommended for the aqueous solution, prior to extraction. The hydroxylamine reduces copper(11) to copper(1). VOL. 40, NO. 12, OCTOBER 1968
1897
pH. It has been previously shown that 2,9-dimethyl-1,10phenanthroline is a specific reagent for copper(1) when the resulting complex is extractable with n-hexyl alcohol. The complex forms in pH range of 3 to 10 is very stable and is extractable within this pH range (12). Diverse Ions. The effect of 10 common diverse ions was checked. Table I summarizes the results which showed that more than about 10 ppm of nitrate, ammonium, magnesium, and aluminum should not be present and that 15 ppm of acetate chloride, sulfate, phosphate, potassium, and iron(I1) can be tolerated. In the case of magnesium and aluminum, the error assdciated with higher concentrations may be in part due to the high chloride concentration concomitant to
the use of magnesium(I1) chloride and aluminum(I1) chloride in the diverse ion study. Precision. An estimate of the precision obtainable with each method was obtained by analyzing six solutions containing 75 pg of perchlorate per 25 ml of aqueous solution. The indirect spectrophotometric method gave a mean absorbance value of 0.413,a standard deviation of 0.001 absorbance unit, or a relative standard deviation of 0.24%. The six samples analyzed by the indirect atomic absorption spectrometric method gave a mean absorbance of 0.463,a standard deviation of 0.002,or a relative standard deviation of 0.43%. RECEIVED for review May 27, 1968. Accepted July 3, 1968.
Use of Sodium Cerium EDTA for Titrimetric Determination of Metallic Elements with Ethylenediaminetetraacetic Acid Stanley S. Yamamura Idaho Nuclear Corporation, Idaho Falls, Idaho
THEuse of EDTA in chemical analyses has been studied and reported very extensively in the last 25 years. This popularity has led to the generation of much useful information and many useful methods of analysis. Unfortunately, it also has created a dilemma for the analytical chemist. Table I, based on information presented in one table in the “Handbook of Analytical Chemistry” edited by Meites ( I ) , shows the abundance of available methods for some common metals. It is easy to see that an analyst, especially one unaccustomed to EDTA methodology, is inclined to ask the question, “Which of this bewildering array of methods should I try first?” The purpose of the present study was to establish one procedure which could be used to determine reliably a large number of metals without special procedural adaptations for different metals. The titrimetric procedure based on the use of sodium cerium(II1) EDTA octahydrate (NaCeEDTA 8Hz0) salt ( 2 ) satisfied these requirements. This method has been found to be applicable to 33 metals including Am, Bi, Cd, Co, Cu, Fe, Ga, Hg, In, the lanthanides, Mn, Ni, Pb, Sc, T1, V, Y ,Zn, and Zr. It probably i s applicable to Bk, Cf, Cm, and Hf as well. EXPERIMENTAL
Apparatus and Reagents. All titrations were performed with a standard 10-mI buret calibrated in 0.05-ml divisions. Analytical Reagent and spectrographically-analyzed chemicals were used throughout without purification. The 0.05M EDTA titrant was prepared from the disodium salt, filtered through a 0.45-micron membrane filter, and standardized against standard hydrochloric acid solutions of zinc metal and zinc oxide by direct titration at pH 5.5 to a xylenol orange, 3 ’,3"-his( bis(carboxymethy1)amino methyl}5 ’,5 ”-dimethylphenolsulfonaphthalein,end point and against (1) L. Meites, “Handbook of Analytical Chemistry,” McGrawHill, New York, 1963, pp 3-164 to 3-200. (2) S. S. Yamamura, ANAL.CHEM., 36, 1858 (1964). 1898
ANALYTICAL CHEMISTRY
Table I. Availability of Visual EDTA Titration Methods Different modes Number of Metal ion of titrationo references 36 43 Bi 3+ 56 53 Cd2+ 63 69 cuz+ 63 50 Fe3+ 61 67 Ni2+ 58 66 PbZ+ 68 59 Zn2+ 0 In a number of cases, several variations are listed for a given mode of titration, hence the number of available methods exceeds the indicated number of modes of titration.
standard nitric acid solutions of bismuth metal, mercury metal, indium metal, nickel metal, and lead nitrate salt by the proposed method. The seven standardization values with a relative standard deviation of 0.08% were averaged. The nature and compositions of the metal solutions used in this study are summarized in Tables I1 and 111. Xylenol orange was used as a 0.2z (w/v) solution in water while arsenazo, o-( 1,8-dihydroxy-3,6-disulfo-2-naphthylazo) benzenearsonic acid, was used as a 1 (w/w) mixture with solid sodium chloride. Sodium cerium(II1) EDTA was prepared as described in a previous paper (2) and used as the solid. Recommended Titration Procedure. Pipet a sample aliquot containing 0.05 to 0.45 mmole of titratable metal into a 150-ml beaker. Add 0.5 ml of concentrated perchloric acid and dilute to about 120 ml with water. Add 0.50 gram of NaCeEDTA.8H20, stir for about 2 minutes, then add 5 drops of 0.2z (w/v) xylenol orange or, if copper is being determined, sufficient arsenazo-sodium chloride mixture to give a rich red-orange coloration. Noting the number of drops, add pyridine dropwise to the appearance of a red or violet coloration, then add two times as much additional pyridine. If the red or violet coloration does not appear
z
