Table II. Accuracy of Analysis of Synthetic Sample Containing a t Least 14 Known Impurities
cut 1 2
3
Acrylonitrile, P.P.M. Known Founa 480 490 480 460 480 570
tremely low quantities of acrylonitrile in water can be detected by this method because of t h e concentrating effect of the azeotropic distillation. T o demonstrate this, 1 liter of a n aqueous solution containing 0.1 p.p.m. of acrylonitrile was mixed with methanol and allowed to reflus for 3 hours. The first 2-nil. fraction of the overhead was diluted 1 to 10 with 0 , l M tetramethyl:inimonium iodide. The resulting solu-
tion showed a 0.5-ga. reduction wave due to acrylonitrile. Even smaller amounts of acrylonitrile may be detected by this method if a larger initial sample is used. CONCLUSIONS
This method has proved very satisfactory for the determination of low concentrations of acrylonitrile in a variety of aqueous streams. I t is reliable and ha. contributed to a successful waste disposal prograni a': well as to process studies. The analytical technique of azeotropic distillation followed by a n analysis is not unique for acrylonitrile and should have many applications in analytical n-ork. ACKNOWLEDGMENT
The authors \~-ould like to thank
Xna Hadden and Barbara Harrison for their assistance with this work. LITERATURE CITED
Beesing, D. W.,Tyler, W.R., Iiurtz, D. M., Harrison, S. A, A N ~ L . CHEV. 21, 1073 (1949). Bird, W. L., Hale, C. H., Ibid., 24, 586 (1952). Gatos, H. G., J. Chem. Educ. 31, 533 (1954). Horsley, L. H.. Britton, E. C , Nutting, H. S..Adoances in Chem. Ser., S o 6 (1952). I Jantz, G. J., Duncan, N. E ASAL. CHEX 25, 1410 (1953). (6) Peterson, G. W.,Radke, H H., IKD. ENG. CHEII, - 4 ~ 4 ED. ~ . 16, 63 ~
(1944).
(7) Yates, IT.'. F., Heider, IZ. I,., J . Am. Chem. SOC.74, 4153 (1952j. RECEIVED for review September 7, 1956. Accepted December 31, 1956. Pittsburgh Conference on Analytical Chemistry and rZpplied Spectroscopy, February 1956.
Colorimetric Method for Determining Minute Quantities of Chloroform in Carbon Tetrachloride CHARLES D. HILDEBRECHT Research Center, Diamond Alkali Co., Painesville, Ohio
b A colorimetric method for the determination of trace quantities of chloroform in the presence of carbon tetrachloride is based on the selectivity of the reaction of pyridine and sodium hydroxide with chloroform in the presence of carbon tetrachloride. The intensity of the pink to red color produced in the reaction i s measured on a photoelectric colorimeter. The method i s suitable for samples of carbon tetrachloride containing from 10 to 900 p.p.m. of chloroform.
C
is a comnion contaminant in carbon tetracliloride and its presence has a deleterious effect on many of ita applications. A method has been developed for deterniination of rliloroform in carbon tetrachloride utilizing the Fujinars ieaction. 1 I : i n ~ -halogenated compounds gil e the Fujinnra ( 6 ) color reaction. K h e n the cvxnpoiind is heated with alkali :md pj.ridine, a pink to red color is obtained depending on the concentration of the compound. This reaction h i s been the basis of many methods for determining small amounts of Idogenated compounds. Daroga and Pollard ( 4 ) adapted the Fuj ixara reaction for the determination of chloroform
or carbon tetrachloride in air and soil; however, neither component could be determined in the presence of the other. The method given here establishes the conditions whereby cliloroform may be determined in the presence of carbon tetrachloride. ildams ( I ) , Brain @), Freidnian and Calderone (j), Cole (S), Gettler and Blume (Y), and others adapted the reaction for the determination of trace aniorints of chloral hydrate, trichloroethylene, cliloroform. and the like in various media. I n all cases, high qensitivity was obtained.
HLOROFOIW
METHOD
Reagents. All t h e chemicals used n e r e of C.P. quality. Pyridine, water white. Methanol. Sodium hydro\ide, lOy0solution. Chloroform. Carbon tetrachloride. Procedure. Pipet 5.0 ml. of distilled water and 1.0 ml. of carbon tetrachloride (sample or standard) into a clean, d r y 100-id. graduated cylinder a n d add 5 drops of 10% sodium hydroxide. Pipet 15.0 ml. of pyridine into t h e graduate, mix well, and ininiersc' in a boiling n a t e r b a t h for 3 minutes ( r 5 seconds). Remove the graduate and place it into a cold
water 1,)atli (15' to 20" C.) for 7 minutes. R e m o w from the b a t h , dilute to 100 nil. \Tit11 methanol, and mix the contents thoroughly. Allow the sample to stand for 10 minutes, then measure the absorbance using a 525-mp (green) filter and a reference of distilled water. Determine the chloroform content of the sample from a standard curvc. The elapsed t'imes stated here must be adhered to as closely as possible. -4s many as six samples can conveniently be run simultaneously if each sample is started at the point of immersing the prcvious one in the boiling n-ater bath and if they are spaced 1 minute apart. Calibration Curve. Prepare a standard solution of chloroform in carbon tetrachloride by breaking a glass ampoule containing a weighed quantity of chloroform (about 1.6 grams) in a 1-liter flask nearly filled with C.P. carbon trt'rachloride. Dilute to the mark and mix thoroughl>-. Deliver aliquots of this solution r:inging froin 1 to 75 nil. from a buret' into 1001111. volumetric flasks, t,lien ninkc up to volume with C.P. carbon t'etracliloride. This gives a series of standards ranging from about 10 t o 750 p . p m Use the procedure given aliove to determine the absorbance of each standard plus a sample of the carbon tetrachloride used for preparing th(t standard solutions. Plot a curve of absorbance us. chloroform concentration. Thc curve will be a straight line but n1:ty riot VOL. 29, NO. 7, JULY 1957
1037
pass through the point of origin if there is a trace of chloroform in the carbon tetrachloride. If any absorbance is found for the blank carbon tetrachloride sample, it must be subtracted from the absorbances measured on the standards. When the corrected data are plotted, the curve will pass through the origin. The data in Table I were obtained using a sample of carbon tetrachloride that contained about 25 p.p.m. of chloroform.
Table I.
Sodium Hydroxide Concentration. Several samples were prepared using the O.O2O1, chloroform standard, and the concentration of 10% sodium hydroxide mas varied from 0 to 20 drops. The data obtained are plotted in Figure 2. Three drops of 10% sodium hydroxide are necessary to develop the full color. However, there is no significant difference when sodium hydroxide concentration is varied from 3 io 20 drops.
Water-Pyridine Ratio. Several samples were prepared using the 0.029& standard. I n all cases the total volume of pyridine and water was 20 ml. The volume of pyridine was varied from 5 to 19 ml. and conversely, the volume of water was varied from 15 to 1 ml. The data obtained (Figure 3) shows that in this procedure, as in that of Daroga and Pollard, the pyridine-water ratio is the most critical part of the method.
Typical Data for Calibration Curve
(Carbon tetrachloride contained about 25 p.p.m. of chloroform) Chloroform -4 -4 Scale Scale Reading Added, 7 0 Reading Blank 0.000 3.0 0.010 13.5 1015 0,020 23.5 20.5 0.030 35.0 32.0 0,040 42.5 39.5 0.050 59.0 56.0 0.060
67.0
MINUTES
64.0
Figure 1.
OF
HEATING
Effect of variation in heating time
In all the data presented here the A scale reading is equal to the logarithmic scale reading (absorbance) times 100. The cells employed were cylindrical, 23 nim. in inside diameter. The original carbon tetrachloride and the O.O.I1Y0and 0.06% chloroform standards were analyzed by infrared methods. The following results were obtained: Chloroform .4dded,
96
Chloroform Found, % (Infrared)
0.000 0.040 0 060
