16
ANALYTICAL CHEMISTRY
setting of 1000 counts per minute and this value, as a rule, was used as the lower limit. The iinknowns were spotted on the filter paper so that their peak heights fell within the same range as the unknownq. These conditions were established by preliminary scans. .Is with the method using a summation equation, it was found that minimum errors were obtained when the average results of two or more scans were taken.
quantitative study of carbon-14 sugars in biological fluids in connection with lactose metaholisni studies. LITERATURE CITED
Anderson, li. C.. Brookhaven Sational Laboratory. Upton, Y. Y . , private communication. Demorest, H. L., and Baskin, It., -%XAL. CHEM.26, 1531 (1954). Frierson, W.J., and Jones, ,J. IT., Ihid., 23, 1447 (1951). Jeanes, A . , Wise, C. S., and Diinler, R. J.. I h i d . , 23, 415 (1951). Jones, .1.li., Ibid., 24, 1055 (1952). l I c F a r r e n , E. F., Brand, K.. and Rutkowski, H. R . , Ibid., 23, 1146 (1951). Muller, K.H., and Wise, E. S . ,I h i d . , 23, 207 (1951). Partridge, S. 11...\'ature 164, 443 (1949). Rockland, L. B., Lieherman, J..and D u m . 11.S., AI.. CHEM. 24, i i 8 (1952). Soloway, S., Rennie, F. J., and Stetten, D., Jr. Sucleonzes 10, 52 (1952). Van Slyke, D. D., Steele, R., and Plazin, J., J . Biol. Chem. 192, i 8 1 (1951). \Tilliams, R. Ii., and Smith, R. E., Proc. SOC.Ezptl. B i d . Med. 77, 169 (1951). \Tingo, IT. J., . ~ N A L . C H E V . 26, 1527 (1954). Wiiiteringham, F. P. W.,Harrison, h.,and Bridges, R . G.. S n a l y s t 77, 19 (1952).
CONCLUSION
The .tpplication of either of the tvio methods t o the determination of the specific activity of carbon-14-labeled lactose, galactose. and glucose results in an erior no gieater than 3%. However. of iinpoi tance in these analyses is the chromatographic development to which the unknown solutions are exposed, prior to scanning. As with unlabeled sugars, the preparation of the sample, if from biological sources, is extremely critical. Interfering substances common t o carbohydrate chromatography, such a5 salts and proteins which cause distortion of sugar chromatographic patterns, should be iemoved. Relying on the extreme sensitivity of this a p p a r a t u s 4 e., 2.4 X pc. which is detectcd with ease-the techniques have been utilized t o determine the purity of lactose-carbon-14 derived from a gow: Theqe techniques now will he applied t o a
R E C E I V E for D review J u n e 8, 1955. Accepted October 11, 1955, Meetingin-Miniature, Rletropolitan Long Island Subsection, New York Section, .ICs, Brooklyn, ?;. Y . , February 25, 195.5.
(Ethylenedinitri1o)tetraacetic Acid Chelation of Platinum Group Metals Spectrophotometric Determination of Iridium WILLIAM M. MAcNEVINand OWEN H. KRIEGE The O h i o State University, Columbus, O h i o
The complex formed between iridium(1V) and (ethj 1enedinitri1o)tetraacetic acid may be used for the colorimetric determination of iridium over the range 5 to 60 p.p.m. . i n excess of (ethjlenedinitri1o)tetraacetic acid is added to the sampleof iridinm(IY), the pII is adjusted to 11.4 to 12.6, the solution is warmed on a water bath for 10 minutes, cooled to room temperature, and finally the absorbance is measured at 313 mp. The reaction between iridiiim(1F) and (ethylenedinitri1o)tetraacetic acid is complete in 10 minutes at 80" to 90' C., and the color does not fade at room temperature in 12 hours. Other platinum group metals interfere and when large amounts are present, iridium must be separated before the determination. Nitrate also interferes but may be tolerated if it is duplicated in the standards.
T
HE spectrophotometric behavior of the palladous-(ethylenedinitri1o)tetraacetate complex has been discussed ( 5 ) . In a continuation of the study of chelation of the platinum group metals with (ethy1enedinitrilo)tetraacetic acid (ethylenediaminetetraacetic acid), it has been found that the absorbance maximum characteristics of basic solutions of (ethylenedinitrilo) tetraacetic acid and quadrivalent iridium may be used for the photometric determination of the latter. Beamish and RScBryde ( 2 ) have pointed out that only one satisfactory method for the colorimetric determination of iridium has been developed-namely, that of Ayres and Quick ( I ) , who obtained a purple color through the interaction of iridium with a mixture of perchloric, nitric, and phosphoric acids. Beer's law is satisfied a t 10 to 75 p.p.m. and other platinum group
Table I. Permissible Weight of Platinum Group Metals Giving Not More than 2% Error in Detection of 1.00 Rfg. of Iridium Metal PalIadium(I1) Platinum(I1) Platinum(1V) Rhodium (111) Osniiurn(1V) Ruthenium(II1)
Milligram 0.1 0.7 0.2 0.07 0.06 0.02
metals interfere only slightly. In their evaluation of this method Beamish and RfcBryde found a large average deviation. Sulfuric acid interferes and must be controlled in standards. A heating period of 1.5 hours is needed to develop the color, and the measurements are made in strongly acid solution. When (ethylenedinitri1o)tetraacetic acid is added to acidic chloride solutions of iridium(1V) and the solution is made strongly basic, it has been found in this laboratory that there is a decided shift of the absorbance toward the ultraviolet. A more detailed study of this complex is the subject of another paper (6). In the development of the proposed method for the spectrophotometric determination of iridium there have been studied the pH of the sample, the adherence to Beer's law, the effect of time on the formation of the complex, the concentration of (ethylenedinitri1o)tetraacetic acid, and the effect of interfering ions of the platinum group metals. Figure 1 shorn s the absorbance curves of solutions 0.000264111 in iridium(IS-) added as the chloride complex, and 0.00100J~ in (ethy1enedinitrilo)tetraacetic acid added as the disodium salt.
17
V O L U M E 2 8 , NO. 1, J A N U A R Y 1 9 5 6
CURVE -
L. 12-t., 84 96 0 3 4-126
03c 02\
-
200
1
250
;;L
L-*.-300
WAVE L N G T H
Figure 1.
I
400
350
500
450
N MILLIMICRONS
Absorbance curves for iridium-(ethylenedinitri1o)tetraacetic acid complex
044 z
U 0
g!
02-
a
I 0
2
4
-
r
d ,
6
8
I
I
10
I2
I 14
PH
Figure 2. Absorhance maxima for iridium-(ethylenedinitri1o)tetraacetic acid complex as function of
PH
The solutions were adjusted to the pH values shown with potassium hydroxide and the ionic strength n-as regulated a t 0.1 with pot,assium chloride. The reaction between iridium and (ethylenedinitri1o)teti-aacetic acid proceeds slon-ly at room temperature and approximately 24 hours are needed for maximum absorption to develop. At 80" to 90" C. the reaction proceeds rapidly and is complete in less than 10 minutes, For example, the iridium concentrations found for a solution containing 65.2 p.p.m. of iridium heated at 85' to 90" C. xere for t = 0, 37.8; t = 2', 58.2; t = 4', 63.7; t = 6') 65.1; t = 8 ' ) 65.3; t = lo', 65.1; and t = 20', 65.2 p.p.m. Figure 2 shon-s that there are t8wopH regions in which the absorbance is nearly constant. The acidic range is not applicable for a spectrophotometric determination, because the absorbance is very low and there is no satisfactory peak in the visible or ultraviolet regions. In the pH range 11.4 t o 12.6 a satisfactory maximum does occur which is constant over this range. I n the pH range 8 to 10, absorbances shown in Figure 2 were difficult to measure accurately, as the solution became cloudy upon aging a t room temperature or upon being heated a t 80" t o 90" C. With absorbances measured a t 313 mp, adherence to Beer's law was tested for solutions in the pH range 11.5 to 12.6 containing 2.5 t o 75 p.p.m. of iridium(1V). All solutions contained at least 2 or 3 millimoles of (ethylenedinitri1o)tetra-
acetic acid for each millimole of iridium, and solutions were heated for 10 minutes on ii Tvater bath to ensure equilibrium eonditions prior to the measui,ements. Agreement with Beer's lanis excellent except for a slight deviation beloxv 3 p.p.ni. The molar absorptivity for the iridium complex is equal t,o 3.2 X 103. The effect of time upon the absorbance of a solution containing iridium(1T') and the complexing agent is shown in Figure 3 . =It room temperature a slow reaction occurred n-hich did not reach equilibrium within 24 hours. The solution \Those behavior is reported in Figure 3 was 0.000264.ll in iridium and 0.00100.11 in the disodium salt of (ethylenedinitri1o)tetraaeetic acid. Its pH v-as 12.0. When a similar solut,ion was heated at 80" t o 90' C. equilibrium !vas reached in 10 minutes. .Us0 studied was the effect of the concentration of the (rthylenedinitri1o)tetraacetic acid on the rate of formation of the stable species having a maximum a t 313 mp. It was found that the ],ate of establishment of equilibrium conditions varied directly xith the concentration of the complesing agent. However, because a 10-minute heating period at 80" to 90" C. produced equilibrium, it seemed unnecessary to provide more than 2 or 3 millimoles of (ethylenedinitri1o)tetraacetic acid for each millimole of iridium(1V) present. The complexing agent does not absorb appreciably a t t,hc wave length used for this determination. Therefore, an excess of this reagent does not interfere m-ith the determination and need not be avoided. The precision of the determination of iridium was determined at 10 and 75 p.p.m. of iridium. Ten determinations of the iridium in a solution containing 10.12 p.p.m. of iridium gave 10.02, 10.16, 10.18, 10.08, 10.21, 10.03, 10.09, 10.26, 10.04, and 10.19 p,p.m. Similarly 10 determinations of the iridium in a sample containing 75.6 p.p.m. of iridium gave '75.2, 75.1, 75.7, 75.8, 75,G, 75.9>75.1, T5.Sl 75.2, and 75.5 p.p.m. The interference of other plittinum group metals was studied by adding known amounts of hydrochloric acid solutions of osmium(IT'), rutheniuni(IIIj, platinum(II), platinum(IV), rhodium(III), and palladium(I1) to standard hydrochloric acid solutions of iridium(1T'). Sufficient (ethylenedinitri1o)tetraacetic acid was added to provide 2 or 3 millimoles for each millimole of platinum group metal present. The pH x a s regulated to 11.4 to 12.6, the solution heated for 10 minutes, cooled to room temperature, and finall!. its ltbsorbance measured a t 313 mp. The procedure follo~vcd xith samples containing iridium a n d other platinum metals was identical with that for solutions containing only iridium. Table I s h o w the amount of other platinum group metals that cause a 2y0 variation in the Rhsorhanee in the spectrophotomctric measurement of iridium. 111 the
10 I
2 0 7-
3 4 5
6 7
S 9 10
200
250
300 350 IO WAVE LENGTH I N MILLIMICRONS
TIME I N HOUPS 0 2 05 10 17 35 55 85 /I 5 24 0
480
450
500
Figure 3. Variation in absorbance of iridium-(ethylenedinitri1o)tetraacetic acid complex upon aging
18
ANALYTICAL CHEMISTRY
presence of larger amounts of other impurities, it may be necessary to separate the iridium prior to the final determination of the iridium photometrically. Sulfuric acid causes no noticeable change in the optical properties of these solutions. However, the presence of nitric acid interferes. There is an increase in absorbance in the region 260 to 330 mp, which may be because of a reaction between chloride and nitrate ions, since this interference appears to be independent of the iridium concentration. Recommended Procedure. If a significant quantity of trivalent iridium is present, warm the solution, containing the chloride, on the water bath for 1 hour, and pass chlorine gas slom-ly through it. Remove the excess chlorine by boiling the solution for 5 minutes. Add enough disodium salt of (ethylenedinitri1o)tetraacetic acid to provide 2 or 3 millimoles for each inillimole of iridium, to the solution containing iridium(1V) in chloride solution. Adjust the pH to 11 4 to 12.6 with potassium hydyoxide. Adjust the volume so that the concentration of iridium is 5 to 60 p.p.m. Heat for 10 minutes on a water bath a t 80' to 90" C. Cool to room temperature and measure the absorbance in 1-cm. cells at 313 mp. EXPERIMENTAL
Apparatus. Absorbance measurements were made with a Beckman quartz spectrophotometer, Model DU, with 1.000-em. matched silica cells. A constant sensitivity was maintained by use of variable slit widths. pH measurements were made with a Beckman, Model H, battery-operated meter. A Beckman blue-tipped glass electrode was used in alkaline solutions. Reagents. Iridium chloride was obtained from the American Platinum Korks. Spectrographic investigation shoiyed traces of rhodium present. Reagent grade perosmic acid, ruthenium chloride, platinous chloride, platinic chloride, rhodium chloride, and palladium chloride were used for the study of interferences. Spectrographic analyses indicated less than significant amounts of impurities. Solutions were analyzed and standardized by procedures from the Gilchrist-Wchers (4)scheme. (Ethylenedinitri1o)tetraacetic acid \vas obtained as the disodium salt in analytical reagent grade from the F. W. Bereworth Co. Preparation of Standard Solution. One-half gram of iridium chloride was dissolved in 500 ml. of 0.1M hydrochloric acid. The iridium was converted to the quadrivalent state by heating the solution on a water bath for 1 hour, while chlorine was bubbled into the solution. Excess chlorine was removed by boiling for 5 minutes. The total iridium in the standard solution was determined by a modified procedure of the Gilchrist-Wichers scheme (4)., I n a mildly alkaline aliquot the iridium was oxidized with sodium bromate, precipitated as the hydroxide, coagulated by heating, filtered, and the residue ignited first in air and then in a stream of hydrogen using a Rose crucible. The amount of iridium( IV) in the standard sample was determined by the iodometric procedure of Delepine ( 3 ) . An excess of potassium iodide was added to an acidic aliquot of the standard solution, which
reduced iridium(1V) to the trivalent state with the formation of an equivalent amount of iodine. The liberated iodine was titrated with a standard thiosulfate solution. Results of these two determinations indicated that the treatment with chlorine had resulted in the complete conversion of iridium to the quadrivalent state. DISCUSSIOn-
The use of (ethylenedinitri1o)tetraacetic acid in the photometric determination of iridium has several distinct advantages.
It is applicable over a concentration range (5 to 10 p.p.m.) in which other methods are lese sensitive. There is an almost linear relationship betreen concentration of iridium and absorbance over the range from 2.5 to 75 p.p.m. The reaction is rapid and equilibrium is reached within 10 minutes a t 80' to 90" C. The color does not fade a t room temperature in 12 hours. Only one developing reagent is needed after the pH is regulated with potassium hydroxide. An excess of (ethylenedinitri1o)tetraacetic acid causes no interference and need not be destroyed. Sulfate ion is not detrimental, This determination is performed in strongly basic solutions where no other method is applicable. On the other hand, the chief limitation to the use of (ethylenedinitri1o)tetraacetic acid as a developing agent is the interference of the other platinum metals. The extent of interference is shown in Table I. I n the presence of large quantities of interfering metals, it is necessary to separate the iridium first. .4 second limitation to the method is the interference caused by the presence of nitrate ion. If more than a trace of nitrate is present in the sample it is necessary to add an amount of nitrate ion to each of the standards, equal to that in the unknown. This method is primarily suggested for the rapid, accurate determination of chloride solutions of iridium( IV) containing only traces of other platinum metals. LITERATURE CITED (1) Ayres, G. H., and Quick, Q., AXAL.CHEY.22, 1403 (1950). (2) Beamish, F. E., and XcBryde, W. A. E., Anal. Chim. Acta 9, 349 (1953). , (3) Delkpine, M., Ann. chim. 7, 277 (1917). \ - - -
(4) Hillebrand, W. F., Lundell, G. E. F., Bright, H. A., and Hoffman, S. I., "Applied Inorganic Analysis," 2nd ed., pp. 339-83, Wiley, Sew York, 1953. (5) MacKevin, W. >I., and Kriege, 0. H., ANAL. CHEW 27, 535 (1955).
(6) IllacNevin, W.AI., and Kriege, 0. H., unpublished data. RECEIVED for review July 6, 1954. Accepted September 26, 1955.
Emission Spectrometric Determination of l o w Percentages of Zirconium in Hafnium LINSLEY S. GRAY, JR.,
and
VELMER A. FASSEL
lnstitute for Atomic Research and Department of Chemistry, lowa State College, Amos, Iowa
The unique similarity in the chemical properties of zirconium and hafnium precludes the use of classical chemical methods for the determination of small amounts of zirconium in hafnium. In this paper, emission spectrometric procedures are described for the determination of zirconium in hafnium in the ranges 0.001 to 0.2% using conventional direct current carbon arc excitation and 0.01 to 0.5% using the conducting briquet excitation technique.
T
HE chemical properties of zirconium and hafnium are so
strikingly similar that chemical analyses of mixtures of these elements can be made only by indirect methods, such as atomic weight (4, 7 , 1 4 ) or density determinations (11). These procedures not only involve time-consuming operations and careful attention to experimental details, but they become increasingly inaccurate as the purity of the zirconium or hafnium increases. Moreover, pure binary mixtures are required in order to obtain reliable results,
