ANALYTICAL CHEMISTRY
1744 Commercially available tetrachloroethylene usually already contains a preservative, often about 0.5 to 1% alcohol (f2),although advantages have been reported for pyrroles (Q), and for thymol and other compounds ( 2 ) . The purity has been satisfactory for infrared purposes when small portions were distilled as needed from a stock preserved with alcohol in brown bottles, and the first portion distilled was discarded. It seems advisable also to discard the excess remaining after use instead of attempting to preserve it. The need for such attention evidently will greatly restrict the use of tetrachloroethylene until more convenient means of maintaining its purity have been established, but for many purposes the advantages of complete supplementation warrant the extra effort. LITERATURE CITED
(1) Ard, J..S., Second Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, 1951; . 4 ~ . 4 ~CHEW, . 23, 680
(1951) (-4bstract).
(2) Bailey, K. C., J . C h e w Soc., 1939,767. ( 3 ) Bernstein, H. J., J . Chem. Phys., 18, 478 (1950).
(4) Blout, E. R., and Nellors, R. C., Science, 110, 137 (1949). (5) Dickinson, R. G., and Leermakers, J. A., J . Am. Chem. Soc., 54, 3852 (1932). (6) Fruhwirth, O., Ber., 74,1700 (1941). (7) Huntress, E. H., “Preparation, Properties, Chemical Behavior, and Identification of Organic Chlorine Compounds,” pp. 692-700, New York, John Wiley & Sons, 1948. (8) Jones, R. N., and Lauson, R., “Selection of Solvents for Infrared Spectrometry,” Bull. 3, Sational Research Council, Ottawa, Ontario, Canada, 1953. (9) Klabunde, W., U. S. Patent 2,492,048 (Dec. 20, 1949). (10) McBee, E. T., and Hatton, R. E., I n d . E n g . Chem., 41, 809 (1949). (11) Pristera, F., A p p l . Spectroscopy, 6, S o . 3, 29 (1952) (12) “United States Pharmacopeia,” 14th Revision, pp. 614-15, Easton, Pa., Alack Publishing Co., 1950. RECEIVED for review .4pril25, 1953. Accepted J u l y 29, 1953. Presented in p a r t before the Pittsburgh Conference on Analytical Chemistry and .4pplied Spectroscopy, March 5 t o 7, 1981, and before the Chemical Society of Washington, D. C., M a y 10, 1951.
Ultraviolet Spectrophotometric Determination of Antimony as lodoantimonous Acid ANITA ELKIND, K. H. GAYER, AND D. F. BOLTZ V a y n e University, Detroit, Mich. study of the solubility of antimonous oxide it became necItimonous essary to determine accurately very low concentrations of anions. A preliminary study of several colorimetric N A
methods indicated that the iodoantimonous acid method offered advantages in respect to accuracy, precision, and sensithit! . This method is based on the formation of yellow iodoantimonous acid (HSbI4) when trivalent antimony in sulfuric acid solution is treated with an excess of potassium iodide solution (I). McChesney (3) studied this colorimetric method in reference to the effect of iodide concentration, acidity, and certain diverse ions and applied the method to the determination of antimony in biological materials. He made photometric measurements in the visible region a t 425 mp. Holler (2) used the iodoantimonous acid method to determine antimony in copper-base alloys using photometric measurements in the visible region, Nikitina (4)also used the iodoantimonous acid method in determining antimony in copper and tin alloys. The purpose of this investigation was to determine the ultraviolet absorption spectrum of iodoantimonous acid and to find whether it could be used as the basis for a more sensitive spectrophotometric method for the determination of very low concentrations of antimonous ions.
Experimental Procedure. The procedure given below was followed in determining the effect of various solution variables.
A definite amount of the standard antimony solution was transferred to a 50-ml. volumetric flask. The potassium iodide reagent solution was added, followed by the addition of the sulfuric acid reagent. I n the case of the diverse ion study, the diverse ions were added before the potassium iodide. The final volume
GENERAL EXPERIMENTAL WORK
Apparatus. A Beckman Model DU Bpectrophotometer with 1.00-cm. silica cells was used for all absorbancy measurements. A hydrogen discharge lamp was used for measurements in the 220to 400-mu region and a tungsten filament lamp was used for the 400- to 500-mp region. Solutions. A standard antimony solution was prepared by dissolving 0.2743 gram of KSbC4H,0?.’/2H,O in redistilled water, adding 160 ml. of concentrated sulfuric acid, and diluting to 1 liter with water. Each milliliter of this solution contains 0.100 mg. of antimony per ml. This concentration was checked spectrophotometrically using a standard solution prepared from pure antimony metal. Sulfuric acid reagent solutions were prepared by adding concentrated acid to distilled water and diluting to 1 liter. A potassium iodide solution was prepared by dissolving 140 grams of reagent grade potassium iodide and 10 grams of crystalline ascorbic acid in redistilled water and diluting to 1 liter. The purpose of the ascorbic acid is to reduce any trace of iodine whirh may be liberated by traces of oxidants, or by actinic rays.
Figure 1. .4bsorption Spectra for Iodoan timonous Acid 1.
2. 3. 4.
5.
3 p.p.m. antimony 2 p.p.m. antimony
1 p.p.m. antimony 24 p.p.m. antimony 12 p.p.m. antimony
V O L U M E 25, N O . 11, N O V E M B E R 1 9 5 3
1745
The ultraviolet absorption spectrum of the potassium iodide-ascorbic acid reagent was determined; i t was found to exhibit negligible abAbsorbancy Measured a t Absorbancy Measured a t sorbancy above 310 mp. 330 mp 426 mp Stability. The prepared iodoantimonous acid .4mt. Amt . Amt. Amt. added, found, a s Permissiadded, f o u n d , as Permiisisolutions are stable for a t least 5 hours. Ion Added a3 p,p.m, p.p.m. Sb bleaint.' p.p.m. p.p.rn. Sb ble a m t . * Diverse Ion Concentration. The effect of di50 0.5 500 0 1.65 1.4 0 10 2 verse ions was studied using 2 p.p.m. of antimony 20; 0 0 20d 20 20 cu++ for the ultraviolet spectrophotometric measure0 Pb++ 1 0 10 10 1: 10 3.4 H g 0 mints and 10 p.p.m. of antimony a t 425 mp. An 0 lOOd 100 100 0.15 hIoO4 - 30 lOOd 0 Xi++ 0 lOOd 100 100 eri or of less than 2.5% was considered negligible. lOOd 0 100 Snt+ 0.9 5 100 For the iiltraviolet spectrophotometric method it Turbid 100 4 wo4-0.6 500 50 wits found that 500 p.p.m. of the following ions .Isp.p.m., causing lesg t h a n +2.5% error when added t o 2 p.p.m. antlplony. did not cause interference: chloride, bromide, -1sp.p.m., causlng less t h a n +2.5% error when added t o 10 p.p.m. antlmony. See (3). nitrate, phosphate, sodium, magnesium, calcium, Larger amounts caused interference. ammonium, zinc, cadmium. aluminum, man~. ganous, ferrous, and cobaltous. It was found that 200 p.p.m. of germanium did not interfere. was adjusted to 50 ml. The reference ahsorption cell contained For the visible spectrophotometric method 500 p.p.m. of the a solution which had the same concentration in respect to sulfuric following ions did not cause interference: chloride, bromide, niacid, ascorbic acid, and potassium iodide as the solution under trate, phosphate, sodium, magnesium, calcium, ammonium, zinc, investigation. Absorbancy measurements were made every 2 cadmium, aluminum, manganous, ferrous, cobaltous, arsenite, mu from 280 to 500 mp. and mercuric. Those ions causing interference are listed in Table I. Cnless otherwise indicated, the interference was due to SOLUTION VARIABLES an increase in absorbancy, Possible methods of circumventing inAntimony Concentration. The existence of absorbancy maxterfwences were not studied. ima in the ultraviolet and visible regions a t 330 and 425 mp! respectively, permits spectrophotometric measurements to be RECOMMENDED GENERAL PROCEDURE made a t two wave lengths. The ratio of the absorbancy index Preparation of Sample. Weigh, or measure by volume, a a t 330 nip to the absorbancv index a t 425 mp is 7.50, which indisample containing sufficient antimony so that the resulting solucates that the sensitivity is increased 750% if the absorbancy tion contains 0.15 to 1.8 mg. of antimony per 100 ml. of prepared measurements are made at the ultraviolet absorbancy maximum. solution. This prepared solution should be slightly acidic with Conformity to Beer's law was observed at 425 mp for 0 to 25 sulfuric acid. Measurement of Desired Constituent. Transfer a 10-ml. alip.p.m. of antimony and a t 330 mp for 0 to 4 p.p.m. of antimony. quot to a 50-ml. volumetric flask. Add 25 ml. of the potassium The optimum concentration range is 0.3 to 3.5 p.p.m. of antimony iodide-ascorbic acid reagent. Dilute to the mark with a sulfuric when measurements are made a t 330 m p and approximately 3 to acid solution containing 250 ml. of concentrated sulfuric acid per 25 p.p.m. of antimony a t 425 mp. JVhen concentrations are liter. Mix thoroughly and measure the absorbancy at 330 mu using 1-cm. silica cells and a reagent blank solution in the referlarger than 25 p.p.m. of antimony, it is advisahlp to prepare a ence cell. calibration graph. Figure 1 shows t,he effect of antimony concentration of the ult,raviolet absorbancy maximum and a comparison DISCUSSION of the magnitude of absorbancy masimum in the visible and ultraviolet regions. The spectral slit, widt.h \vas maintained a t 5.5 The coesistence of an absorbancy maximum in the ultraviolet mp for measurements at 330 mp and a t 1.25 mp for 425 mfi. region with the previously known absorbancy maximum in the Acid Concentration. The effect of sulfuric acid concentration visible region JTas established for the iodoantimonous acid system. was studied using 2 p.p.m. of antimony when spectrophotometric Spectrophotometric measurement in the ultraviolet region remeasurements were made a t 330 mp and using 14 p.p.m. of antisults in greatly increased sensitivity. The recommended general mony at 425 mp. Variable amount,s of an 18 .Y sulfuric acid were procedure using 2 p.p.m. of antimony gave a standard deviation of added to give various acidities. The acidity due to the sulfurir 3.3% when the absorbancy was measured at 330 m p . The same arid in the standard solution was taken into consideration in procedure using 10 p.p.m. of antimony gave a standard deviation computing the final acidity. The final acidity should be 2.4 to of 1.1% when the atisorhancy was measured at 425 mp, Mer3.8 -Y in respect to sulfuric acid, regardless of whether measurecuric, plumbous, and bismuthyl ions are the main interfering subments were made at 330 or 425 mp. The final acidity of approsistances in the ultraviolet method, while bismuthyl is the main niately 2.8 .\- was used in subsequent investigat,ions. This acidoffender in the visible method. ity corresponds to that recommended by AIcChesney ( 3 ) . Iodide Concentration. The effect of iodide concentration was ACKNOWLEDGMENT also studied using 2 p,p.m. of antimony in spectrophotometric One of the authors (hnita Elkind) wishes to express appreciameasuremenbe a t 330 mp and 14 p.p.m. of antimony a t 425 m p . tion to the Wayne Chapter of Sigma Xi for financial assistance The absorbancy as measured a t 330 mp increased until 3 grams of given in the course of this study. the potassium iodide had been used per 50-mI. final volume. When nieasurements were made at. 425 mp it was found that 3.5 LITERATURE CITED grams of potassium iodide per 50 ml. were needed to ensure attainment of maximum absorbancy. There is a negligible change (1) Fauchon, AT. L., J . Pharm. Chem., 25, 537 (1937). in absorbancy when measurements are made a t 330 m p if t,he (2) Holler, A. C . , ; ~ N . L L . CHEM.,19, 353 (1947). (3) McChesney, E. w., IND.ENG.CHEM., A N A L . ED.,18, 146 (1946). final iodide concentration corresponds to 3 grams of potassium ( 4 ) Nikitina, E. I . , Zanodskaya Lab., 14, 933 (1948). iodide per 50 ml. of solution. The recommended iodide concentration is 3.5 grams of potassium iodide per 50 ml. of solution, RECEIVED for review March 2 5 , 1953. Accepted July 22, 1953. Presented which corresponds to the use of 25 ml. of the iodide-ascorbic acid RIarch 3, 1953, at t h e Pittsburgh Conference on hnalytical Chemistry a n d reagent. This also results in an ascorbic acid concentration of Applied Spectroscopy, cosponsored b y t h e Pittsburgh Section of the AMERI0.25 gram per 50 ml. of solution. C A CHEMICAL ~ SOCIETY and Spectroscopy Soriety of Pittsburgh. Talde I. Interference of Diverse Ions with Determination of Antimony as Iodoantimonous Acid
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