was taken into a beaker and evaporated almost to dryness, and then uranium metal was dissolved in the beaker according to the recommended procedure. The results indicate that the method provides reasonably reproducible figures and is very reliable (Table V). The standard deviation obtained (1.1%) confirmed the suitability of this method. Finally, a number of New Brunslvick Laboratory (NBL) uranium oside samples for spectrographic analysis were analyzed (Table VI). The values obtained for chromium were essentially in agreement with those furnished by NBL ( 2 ) ,with the exception of samples 65-1 and 65-5. The differences shown in the fourth and sixth columns in Table VI can be regarded as the amount of chromium originally present in the base material
(65-5), if the amounts of chromium shown in the second column were added accurately. The difference obtained by the proposed method is very consistent (2.0 to 2.9 p.p.m.), whereas that by the diphenylcarbaeide method is disparate. I n the analysis of uranium, the proposed method is more sensitive than the diphenylcarbazide method (1, 4 ) and the results are precise and accurate. This method can be used for the determination of chromium in uranium down to 1 p.p.m. It should also be useful for the determination of chromium in uranium oxides and other uranium salts. ACKNOWLEDGMENT
The authors express sincere apprecia-
tion to Kenjiro Kimura for his encouragement and Hideyo Yoshida for his assistance throughout the investigation. LITERATURE CITED
(l?(Bricker, C. E., Furman, N. H., Modified Method for the Determination of Chromium in Uranium or Its Compounds,” G. S. Atomic Energy Comm., Rept. M-4253(1943, declassified 1955). (2) Clickner, AI. R., “Semiannual Progrem Report for the Pel;iod July 1957 through December 1957, G. S.rltomic Energy Comm. Rept. NBL-143, 77 (1958). (3) Motojima, K., Hashitani, H., Bunseki Kagakza 9,151 (1?!0). (4)Rodden, C. J., Analytical Chemistry of the hlanhattan Project,” p. 447, bIcGraw-Hill, New York, 1950. RECEIVEDfor review hIay 27, 1960. Accepted September 19, 1960.
Determination of Hydrazoic Acid and Ferric ton by Spectrophotometric Measurement of the Ferric Azide Complex ERNEST K. DUKES and RICHARD
M. WALLACE
Savannah River Laboratory, E. 1. du Pont de Nemours & Co., Inc., Aiken, S. C.
)A rapid, versatile method was developed to determine, either separately or simultaneously, the concentrations of hydrazoic acid and ferric ion in solutions of nitric acid that contained hydrazine, ferrous ion, hydrazoic acid, and ferric ion. The method involves absorbance measurements of the ferric azide complex and determination of the concentration of nitric acid.
A
was sought to determine the concentration of hydrazoic acid in the presence of unknown amounts of iron, so that rates of formation of hydrazoic acid from hydrazine could be measured. The solutions of interest contained hydrazoic acid, hydrazine, ferrous sulfamate, ferric nitrate, and nitric acid. The absorption spectrum of the frrric azide comples is well known and has been used to determine the concentration of hydrazoic acid. h qualitative method was described by Feigl ( S ) , and a quantitative method involving distillation was described by Roberson and dustin ( 5 ) . .4nton, Dodd, and Harvey ( 1 ) have reported the quantitative analysis of azide a t constant acidity using ferric perchlorate. However, no 242
suitable method was found for the rapid determination of hydrazoic acid in the presence of unknown amounts of ferric ion. Ferric ion and azide ion form a 1 to 1 complex that absorbs strongly in the visible region (1, 4 ) . The molar absorptivity is 3.68 X lo3 a t the absorption band of 460 mp, and the absorption obeys Beer’s law over the range of concentrations of interest in this work. The concentration of the complex is decreased drastically as the concen-
RAPID METHOD
ANALYTICAL CHEMISTRY
tration of H + is increased, so that the reaction of formation Fe+3
I HNOJ M
Figure 1. The value of K as a function of concentration of nitric acid
(1)
proceeds only to a small extent a t concentrations of H + in excess of 0.1M. Under these conditions only an insignificant amount of either hydrazoic acid or ferric ion is consumed in the complex and the absorbance, A , due to the ferric azide complex is A = K(Fe+3)(HNs) (2) where k‘ is a parameter that involves the equilibrium constant of Equation 1 and depends on the concentration of H+. The relation between K and the nitric acid concentration was determined a l 23’ C. mith known solutions of ferric nitrate and sodium azide in nitric acid. The results are shown in Figure 1. These data were treated by the method of least squares to obtain the equation
log K
0+O0~
+ HE3 + Fe?\’s+2+ H +
=
3.283
-
1.361 log (BSOa) ( 3 )
Equation 3 was verified using three spectrophotometers and is assumed t o be universally applicable. If only one of the components, either ferric ion or hydrazoic acid, is present, its concentration can be determined by measuring the absorbancr after the addition of a known amount of the other
component. -4 determination of the free nitric acid concentration is also necessary in order t o determine from Equation 3 the appropriate value of K t o use in Equation 2. This same technique may be applied if both components are present but not in sufficient concentration to produce a measurable absorbance. The concentration of the added component would be large compared to the concentration of either component already present. However. at high concentrations of acid, relatively high concentrations of HN3 and Fe+3 produce no measurable absorbance. In this cas? the conccntration of the added coniponcnt muit be very high or the acidity must be reduced. If both componciits are present in unknown amounts. but in sufficient quantities to produce a nicmuralde absorbance, the concentration of each component can be determinrd simultaneously by a dilution twhniquc. The original solution is diluted and the absorbance, A,, of the ferric azide complm is measured. -4 known amount of ferric ion or hydrazoic acid is then addcad to a similar dilution and the absorbance, A , of the resulting complex is measured. The addition of one of the components, for instance ferric ion, sufficient to increase the concentration by an amount (Fe+3), increases the absorbance from the original value A , to n new value A. Since the total concentration of ferric ion is the sum of the concentration of the ferric ion originally present, (Fe+3)0, and that due to the added ferric ion, the quantity (Fe+9, can be calculated from the equation
provided that the concentrations of hydrazoic acid and nitric arid are the same in both dilutions. Finally, the concentration of hydrazoic acid can be calculated from Equation 2 by substituting the values for A , and (Fe+3),. EXPERIMENTAL
Apparatus. A Beckman DU spectrophotometer with matched 1.0-cm. Corex cells was used for absorbance measurements. Reagents. Hydrazine was from a 35% aqueous solution produced b y Betz laboratories under t h e name Hyzeen. A 2.OM solution of ferrous sulfamate was prepared from reagent grade iron powder a n d sulfamic acid. Standard solutions of oxalic acid, nitric acid, ferrous ammonium sulfate, sodium hydroxide, ferric nitrate, and sodium azide were prepared from reagent grade chemicals and were analyzed before use. Procedure I. Procedure I was used for solutions t h a t contained hydrazoic acid or ferric ion, but that showed no measurable absorbance because of the ferric azide complex. An aliquot of a
Procedure I I I T
11 I1 I1 I1 I1 I1
Table I. Analysis for HN3 and Fe+3 ComComAv. Found for 10 HSO3, ponent(s) ponent Added, Detn , Std. Dev., Molarity Present Analyzed Molarity Molarity Molarity 0 0021 0 098 0 095 HSj 1 01 HS, 0 0027 0 293 HNj 0.294 4 72 HS3 0.0013 Fe+3 0.102 0.102 1 00 Fe"3 0.0021 0 306 0 305 Fpi-3 Fe+3 4 66 0.0095 G 0003 0.99 HNs 0.0098 Hh3-Fe+3 0.0005 0.0077 1.02 HNI 0.0078 HN3-Fe+3 0.0044 0.0352 4.72 HNa 0.0392 HNZ-Fe+a 0.0075 0.0004 Fe+3 0.0084 0.99 Fe+3-HXa 0.0009 0.0102 0,0106 Fe+3 1.02 Fe+tHS3 0.0253 0.0011 Fe+s 0.0245 4 i2 Fe+3-HX;
:
standard solution of 0.klI ferric nitrate or 0.5d1 sodium azide was added t o a 2-ml. aliquot of the sample. This solution was diluted \I ith u-ater to 25 ml. and the concentration of HS03 was determined by titration with a standard solution of S a O H . I n the presence of ferric ion, the acid was titrated after the iron was complexed with ovalate (6). The absorbance of the solution a t 460 nip was measured at 23' C. against a reagent blank. The concentration of HN03 \vas substituted in Equation 3 to calculate the correct value for K , and the concentration of HS3or Fe+3 was calculated from Equation 2. Procedure 11. T h e following procedure mas used for samples t h a t contained ferric ion and hydrazoic acid in sufficient concentrations t o produce a measurable absorbance by the ferric azide complex. A 4-ml. aliquot of the sample was diluted to 5 ml. with 0.5M HS03. An aliquot of 0.531 ferric nitrate n-as added t o a second aliquot of the same size; this solution was then diluted with nitric acid to give a final acid concentration equal to that in the dilution of the first aliquot. The absorbance was measured for each solution. Only one acid determination was required to calculate from Equation 2 , the value of K , since the final solutions were a t the same acid concentration. The concentration of ferric ion was calculated from Equation 4 and the concentration of hydrazoic acid was calculated from Equation 2 . This procedure was also used by substituting H X 3 for Fe+3. RESULTS
Precision. Each variation of Procedures I a n d I1 was used t o determine the concentration of hydrazoic acid and/or ferric ion in solutions of nitric acid. T h e results are shown in Table I. T h e standard deviations were larger for t h e simultaneous determination of hydrazoic acid and ferric ion by Procedure TI. The precision was essentially the same a t 1.0 and 4.72M nitric acid. Interferences. Procedure I was used t o test interference from reagents that were expected to be present in samples t o be analyzed. Results in
Table I1 show t h a t low concentrations of hydrazine did not interfere with the analysis of 13x3or Fe+3. h'o interference by ferrous sulfamxte was found in the analysis for Fe+3 or HN3, as shown in Table 11. Sensitivity. Maximum sensitivity is obtained at low concentrations of "03; ho\yever, below a b o u t 0.1M HKO1 t h e precision of the analyses is decreased because large quantities of HNI and Fe+3 are consumed in the formation of the complex and Equation 2 is no longer valid. The minimum detectable concentration of H S 3 or F e t 3 may be calculated for any concentration of H + from Equations 1 and 2 by assuming an absorbance of 0.05 and a given concentration of H N 3or Fef3. I n this study maximum concentrations of 0.25M Fe+3 and 0.12hf "3 were used. These concentrations permitted the determination of concentrations as low
Table It. Analysis for HNI and Fe+3 in t h e Presence of Interferences (Using Procedure I, I . O M HSO,) Interference, Component Added, Found, Molarit>- Analj-zed Molarity Molarity Hydrazine Contamination 0.00
0.01 0.03 0.05 0.10 0.00
0.01 0.03 0.05 0.10
0.0098 0.0098 0.0098 0.0098 0.0098
P P_+ 3 -
0 0102
0 ,0096 0 ,0095 0 ,0098 0 .0008 0 ,0098
Fe+3 Fe+3 Fe+8 Fe+3
0.0102
0 ,0103 0 ,0104 0 ,0106 0 ,0105
HN3 HNI HN:, HN; HN?
0.0102 0.0102 0,0102
0 ,0102
Ferrous Sulfamate Contamination HX3 0,0098 0.0096 0.00 0.0098 0.0095 HS, 0.01 HN3 0.0098 0.0100 0.03 HN, 0,0098 0.0101 0.05 0.00 Fe+3 0.0196 0.0193 0.0196 0.0193 0.01 Fe+S 0.0196 0.0193 0.02 Fe+S 0.0196 0.0194 0.03 Fe+3 Fe+3 0.0196 0.0195 0.04
VOL. 33, NO. 2, FEBRUARY 1961
0
243
as 1.1 X 10-4M Fe+3 and 2.3 X 10-4M HN3 in 1.OM H?rT03. DISCUSSION
These procedures were used successfully to follow the rate of formation of hydrazoic acid from hydrazine and the simultaneous oxidation of ferrous ion to ferric ion. The procedures are applicable to solutions containing perchloric and sulfuric acids; however, the constants shown in Equation 3 should be
determined for each acid. The values for the constants also change a t high concentrations of hydrazine. It is advisable to perform analyses in a hood because of the toxicity of hydrazoic acid ( 2 ) .
(3) Feigl, F., “Inorganic .Ipplications,” 4th ed., Vol. 1, Elsevier, New York,
LITERATURE CITED
Idaho Falls, Idaho, October 1957 RECEIVEDfor review July 11, 1960. Accepted October 10, 1960. Kork performed under contract ,4T(07-2)-1 ryith the C S. .4toniic Energy Commission.
(1) Anton, .I.,Dodd, J. G., Harvey, A.
E., ANAL. CHEX.32, 1209 (1960). (2) Audrieth, L. F., Chem. Revs. 15, 169 (1934).
1954.
(4) Ricca, B., Gam. chzm. i t a [ . 75, 71
(1945).
( 5 , Roberson, C. E., Austin, C. X., ANAL.CHEY.29, 854 (1957). (6) Sikes, J. H., Rein, J. E , “Manual of the Analytical Methods,” Yuppl. S o . 3, IDO-14316,Phillips Petroleum Co.,
Colorimetric Determination of Ultramicro Quantities of Calcium Using GIyoxaI bis(Zhydroxyani1) KENNETH T. WILLIAMS and JOHN R. WILSON Western Regional Research laboratory, Western Utilization Research and Development Division, Agriculturcl Research Service,
U. S. Department o f Agriculture, Albany, Calif. b A colorimetric method for the determination of ultramicro quantities of calcium in the presence of other common cations is presented. This new procedure does not require a preliminary separation of calcium. The complex formed with glyoxal bis(2-hydroxyanil) obeys Beer’s law over the range 0 to 10 pg. Colorimetric measurements were made at 535 mp.
s m c m c SPOT TEST for calcium observed by Goldstein and StarkXayer (2) has been used as the basis for a quantitative determination in ultramicro quantities. The calcium complex of glyoxal bis(2-hydroxyanil) permitted the colorimetric measurement of calcium in the presence of other common cations, including magnesium, strontium, and iron. Only 2 ml. of sample are required and the range is from 0.5 to 10.0 pg. per nil. The complete determination is made in a test tube. EXPERIMENTAL
Apparatus. N a k e colorimetric measurements with a colorimeterspectrometer (Bausch and Lomb Spectronic 20 used here) using 1/2-inch matched test tubes. Reagents. Prepare glyoxal bis(2hydroxyanil) according t o Bayer ( I ) , by dissolving 4.4 grams of freshly sublimed o-aminophenol in 1 liter of water at 80’ C. and adding 4.0 grams of a 30% solution of glyoxal in water. Maintain the mixture at 80’ C. for 30 minutes, then store overnight in the refrigerator. Filter the precipitate, wash with water, and repeatedly recrystallize from methanol until i t gives a colorless solution. The reagent solution is a 0.4% w./v. solution of glyoxal bis(2-hydroxyanil) 244
ANALYTICAL CHEMISTRY
in absolute ethyl alcohol. Prepare this solution fresh daily. Commercially available o-aniinophenol is difficult to sublime without entrapping impurities. Sublime using a 100-mm. diameter Petri culture dish, a 95-mm. filter paper disk, a 41,’2-inch Precision Scientific Co. Xo. 61725 electric hot plate set a t 700, and a 0to 130-volt voltage control set a t about 40. The control on the hot plate without the voltage control allows too a i d e a variation between maximum and minimum temperatures. Spread 3 grams of o-aminophenol in cover section of the culture dish so as to corer a 50-mm. diameter in the center. Place the filter paper circle over the o-aminophenol and insert the bottom section of the culture dish to hold the filter paper in place and to complete the sublimation vessel. (The vessel is in an inverted position as compared to the manner in which it is used as a culture dish.) P u t the vessel on the hot plate and heat just belon- the fusion temperature of the o-aminophenol for 3 hours; some adjustment of the voltage control may be necessary. About 1 gram of o-aminophenol in thin clear crystals will gather on the upper surface of the filter paper. Prepare the color-developing solution by dissolving 10.0 grams of sodium hydroxide and 0.5 gram of sodium carbonate in 100 ml. of water. Use chloroform, reagent grade, for color extraction. Prepare a standard calcium solution by dissolving a weighed amount of calcium carbonate, Iceland Spar or primary standard grade (Mallinckrodt Chemical Works), in a slight excess of hydrochloric acid and dilute to a definite volume. Make solutions to contain 0.5, 0.7, 1.0, 3.0, 5.0, 7.0, and 10.0 pg, of calcium per ml. by dilution. Procedure. Transfer 2.00 ml. of t h e sample solution into the test tube,
add 1.00 ml. of the reagent solution, and mix thoroughly. Add 0.20 ml. of the color-developing solution, mix thoroughly, and centrifuge (take centrifuge u p to about 3000 r.p.m. and immediately turn i t off) to coagulate a n y precipitate t h a t forms. Add 5.00 ml. of chloroform, stopper (rubber), and shake the test tube well while inverting it 10 times. Clarify the chloroform layer by centrifugation. Water will adhere to the wall of the test tube below the surface of the chloroform unless the tube is centrifuged. This should be done rapidly by taking the centrifuge up to about 3000 r.p.m. and immediately turning i t off. Excess centrifugation will coat the wall of the tube, below the chloroform level, with any precipitate that may be present. Read the color a t 535 mp against a reagent blank containing 2.00 ml. of water and the same amount of the reagents as the sample. The color is stable for 15 minutes after the addition of the color-developing solution. The color is very unstable if the water and chloroform phases are remixed after separation by centrifugation. Prepare a standard curve using 2.00ml. aliquots of the solutions containing from 0.5 to 10.0 pg. per ml. of calcium. Plot calcium in micrograms against per cent transmission on semilog graph paper. DISCUSSION
This new procedure does not require a preliminary separation of the calcium. The data in Table I show that 10 times as much magnesium, one tenth as much strontium, and one tenth as much iron as calcium do not interfere. Strontium gives a color with the reagent solution, but the presence of carbonate ion in the color-developing solution depresses this color formation.
