as 1.1 X 10-4M Fe+3and 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.
OB
03
Table I. Standard Deviation in the Measurement of Calcium Using Glyoxal bis(2-hydroxyanil)
-
-
350
400
450
500
550
600
650
700
W A V E LENGTH, m a
Figure 1. Absorption spectra of calcium glyoxal bis(2-hydroxyanil) in chloroform I .
Llie amount of calcium that will ordinarily occur in the reagents ~ i i not l contribute to the error of measurement since the blank compensates for color from that source. The absorption maximum was determined with a Cary Model 14 recording spectrophotometer. The absorption falls off rather sharply on both sides of 535 mp, as shown in Figure 1. ,411 of the colorimctric measurements were made a t
.
that wave length. The color coniplex obeys Beer's law over the range 0 to 10 Pg Once the standard curve is plotted, i t is necessary to run only one or two points to define the curve. ACKNOWLEDGMENT
The authors are indebted t,o Glen F.
Micrograms of Calcium Per Milliliter Taken Found Found. 0.50 0.50 f 0.016 0.50 f 0.005 1 . 0 0 1.00 i 0,020 1.00 i 0.010 3 00 3.00 i 0.030 3.00 i 0.025 $5 00 + 0 048 5.00 5 00 i 0 010 7 00 7 00 =t0 000 7 00 L 0 065 10 00 10 00 zk 0 110 10 00 i 0 070 a I n a mixture of Ca, M g , Sr, and Fe.
Bailey for determining the wave length of maximum absorption. LITERATURE CITED
(1) Bayer, E., Ber. deut. chem. Ges. 90,
2325 (1957). (2) Goldstein, D., Stark-Mayer, C., Anal.
Chim.Acta. 19, 437 (1958). RECEIVEDfor review May 28, 1960. Accepted September 12, 1960. Mention of manufacturers and commercial products does not imply recommendation by the Department of Agriculture over others of a similar nature not mentioned.
Spectrophotometric Determination of Indium in Zinc and Zinc Oxide T. A. COLLINS, Jr., and J. H. KANZELMEYER Zinc Smelting Division, Si. Joseph l e a d
Co., Monaca, Pa.
b A spectrophotometric method for determining microgram quantities of indium in zinc and zinc oxide has been developed. A preliminary separation is made by extracting indium into isopropyl ether from 6M HBr and reextracting it into water. The indium, in an aqueous solution containing hydroxylamine and KCN a t pH 9, is extracted with 0.002% dithizone in CHC13. The absorbance a t 510 mp follows Beer's law to concentrations of a t least 1.5 pg. of indium per ml. A precision of 2.6y0 relative error was measured for samples containing 0.0007 to 0.0 1 % of indium.
T
HE most sensitive spectrophotometric method for the determination of trace quantities of indium is the extraction procedure employing dithizone ( 5 ) . May and Hoffman (3)outlined the optimum conditions for this determination. They used a rather lengthy separation by extraction with 8-quinolinol to eliminate the interference of zinc, lead, tin. and thallium, Kosta and Hoste ( 2 ) separated traces of indium from large quantities of zinc
by extraction of the indium into isopropyl ether from 6 M aqueous HBr solutions. Other workers ( 1 , $, 6) have found bromide extractions useful for separations of indium from a number of elements. I t appeared that the combined bromide separation and dithizone determination would give a rapid and accurate method for traces of indium in zinc-based materials. A satisfactory procedure is reported in this paper for the measurement of indium in zinc metal and zinc oxide. Interference from elements normally found in these materials is also discussed. EXPERIMENTAL
Apparatus and Reagents. A Beckman Model B spectrophotometer and l-cm. borosilicate cells were used. The p H of solutions was adjusted using a Beckman Zeromatic p H meter. Reagent grade chemicals and deionized water were used. Hydrobromic Acid, 6N. Add 600 ml. of HBr to 300 ml. of water. If appreciable bromine color is apparent, shake with 7 5 ml. of isopropyl ether for
2 minutes and discard the organic layer. Store in a brown screw-capped bottle. Hydroxylamine Hydrochloride Solution (loyo). Dissolve 50 grams of N H 2 0 H . H C l in water and dilute to 500 ml. Prepare every other day. Dithizone in Chloroform (0.002%). Prepare a stock solution by dissolving 26 mg. of dithizone in 500 ml. of CHC13 (shake vigorously!). Dilute 100 ml. of stock solution to 260 ml. to obtain the 0.00270 solution used for extraction. Store both solutions in the refrigerator. Buffer Mixture. Titrate 150 ml. of 10% hydroxylamine hydrochloride solution to p H 9.0 with 1 S iYH40H (requires about 270 ml.). Add 40 ml. of 5% KCN solution and dilute to 500 ml. with water. Shake for 2 minutes with 10 ml. of 0.0027,, dithizone in CHCI, and allow to stand 1 hour before discarding the organic layer. This quantity is sufficient for 10 samples. Procedure. Weigh samples containing 2 to 100 pg. of indium and 1.0 0.1 gram of zinc into 100-ml. beakers. Cover samples with water and dissolve by gradual addition of 10 ml. of concentrated HC1. Add 3.0 ml. of 70% HC104, cover with watch glasses, and evaporate a t moderate heat to strong fumes of HC104. Continue heating
*
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