copy before it was run through the chromatographic column and after separation both fractions were identified by their infrared spectra. The sample of diborane obtained by collecting the fraction as it came off the column $vas spectroscopically pure. This method of purification would prove convenient, especially in preparing standard samples for mass spectrographic fragmentation patterns and infrared
calibration runs, where even small amounts of impurities can lead to spurious results.
LITERATURE CITED
(1) James, A . T., IIartin,
Biochem.
(1952).
-4. J. P., J. ilondon) 50. 679
(2) Koski, W. ACKNOWLEDGMENT
The authors would like t o thank Richard J. Kokes for several stimulating and helpful discussions on the subject of vapor phase chromatography.
S., Maybury, P. C., Kaufman, J. J., .ANAL. CHEM.26, 1992 (1954).
RECEIVED for review Sovember 12, 1956. Accepted April 5, 1957. Research supported by the U. S.Air Force through the Office of Scientific Research of the Air Research and Development Command.
Determination of Small Amounts of Acrylonitrile in Aqueous Industrial Streams G. W. DAUES and W. F. HAMNER Monsanfo Chemical Co.,Texas Cify, Tex.
b A method for the determination of low concentrations of acrylonitrile in aqueous streams is based on the concentration of acrylonitrile and separation from other components by use of an azeotropic distillation with methanol coupled with a polarographic analysis. The analysis is applicable to a wide variety of water samples, regardless of the other components present. As little as 0.1 pap.m. of acrylonitrile in water has been detected.
A
for an accurate analysis for very small quantities of acrylonitrile in aqueous streams arose from studies on acrylonitrile processes and from problems in connection with waste disposal. Previously used methods, such as titration with dodecylmercaptan (1, 5 ) , modified Rjeldahl (6),direct polarographic ( 2 ) )and infrared were not suitable because of the low concentration of acrylonitrile and the presence of interfering compounds. I n order to use one of these techniques it was necessary to concentrate the acrylonitrile and t o separate it from the other components by an azeotropic distillation with methanol. The acrylonitrile was determined by a polarographic analysis of the distillate in a manner similar t o that described by Bird and Hale (8). KEED
APPARATUS
The distillation apparatus consisted of a heated glass column 60 X 1.8 cni., packed with '/*-inch glass helices, a 1-liter single-necked distillation flask, a 1-liter hemispherical Glas-Col heating mantle, and a distillation head with a holdurr of about 1 cc.
A Leetls & Sorthrup Electrochemograph, Type E, was used for the current-voltage measurements. The polarographic cell was a 15-ml. straight-type mercury-pool cell, mater-jacketed, and held a t 30" i 0.1" C. The open circuit capillary characteristics 1%-ere m2/3tl'6 = 2.683 in a solution of 0.141 tetramethylammonium iodide. MATERIALS
Tetramethylammonium iodide, polarographic grade, obtained from Southwestern Analytical Chemicals, 1107 West Gibson St., Austin, Tex. Acrylonitrile, Jionsanto commercial grade, 99.8%. Methanol. C.P. grade. Sulfuric acid, C.P. grade. Mercury, purified by oxidation and filtration through a gold filter followed by distillation. Water, equivalent of triply distilled, obtained by passing distilled water through a Deeminac ion exchange resin. Miscellaneous compounds used as "impurities" in synthetic blends were either purchased from Eastman Kodak or prepared in this laboratory. PROCEDURE
Distillation Procedure. Acrylonitrile and methanol form a n azeotrope which boils a t 61.4' C. and contains 38.7% by weight of acrylonitrile (4). Advantage was taken of this phenomenon to concentrate the acrylonitrile and to separate it from a large number of other components present in the sample. It was not necessary to isolate the azeotrope or even to carry out a close fractionation. The procedure was as foilom: Five hundred milliliters of sample, 5 ml. of concentrated sulfuric acid, and 25 ml. of methanol were added to the 1-liter distillation flask and mixed well. A few boiling chips were added and the flask was attached
t o the distillation column. The column heater voltage was then set to bring the column t o about 10" C. above room temperature and the pot teniperature was regulated to give a distillation rate of about 1 ml. per minute. The first 12 ml. overhead were collected as three equal fractions. The total time for the distillation, starting a t room temperature, was 45 5 minutes. If polarographically active aldehyde< or ketones were present, excess 2,1dinitrophenylhydrazine was added with the sulfuric acid and the mixture warefluxed for about 1 hour before the methanol was added; then the di-tillation was started Polarographic Procedure. A polarographic method was chosen for the analysis of the fractions because of its relatively high sensitivity and speed. Titration n i t h dodecylmrrcaptan has also been used successfully. The half-wave reduction potential of acrylonitrile is -1.95 volts vs. the saturated calomel electrode (8). X solution of tetramethylammonium iodide provided a suitable electrolyte fol this high negative potential region. If the concentration of acrylonitrik in the original sample was between 100 and 1000 p.p.m., the first fraction from the distillation was diluted 1 to 100 with a 0.1M solution of the electrolyte, and the second and third samplen-ere diluted 1 to 10 before the polarographic measurements were made. For samples that contained less than 100 p.p.m., only the first two fractions n-ere used and they were diluted 1 to 10. The current voltage curve from - 1.3 to -2.1 volts was obtained for each fraction, using the mercury pool as reference electrode. Oxygen caused no interference a t these potentials and. thus, its removal was not necessary. If the resulting curve was smooth and shoved a large flat plateau region, the VOL. 29, NO. 7 , JULY 1957
1035
absence of polarographically active compounds other than acrylonitrile was indicated. The diffusion current was then measured at -2.05 volts and the quantity of acrylonitrile in the original sample was read from a calibration curve relating I d of the fraction to the concentration of acrylonitrile in the original sample. Calibration. The calibration was made by carrying out t h e above procedure on synthetic samples containing known amounts of acrylonitrile. The measured diffusion currents were plotted against the parts per million of acrylonitrile in the original sample to yield the calibration curves. Each point was obtained from a single determination on an independent synthetic. The linear curves resulting from the mcasurements on each of the fractions indicated satisfactory reproducibility of the distillation step. Further proof of the reproducibility of the distillation is demonstrated by the analysis of fractions from duplicate distillations (Table I). As the acrylonitrile concentration in the original solution can 1 ) ~determined from each fraction, an internal check on the analysis is provided as well as a means of further rliniinating interferences.
Table
I.
Precision of Duplicate Anal-
ysis of Actual Plant Streams Acrylonitrile Found, P.P.31 Sample Cut Used 1 1 2 2 2 2 :3 3 -4 4 0
5
1 1 1 1 2 2 1 1 2 2 2 2
150 1'io 12 12 13 14 42 4.3 37 44
205 215
Purification and Storage of Mercury. Mercury, cleansed by oxidation and filtration follos ed by distillation, was used for t h e dropping mercury electrode and the pool electrode. Mercury which had been stored in polyethylene bottles for any length of time was generally not suitable because of large residual currents rvhich developed before -2.1 volts us. mercury pool with O.1M tetramethylammonium iodide electrolyte. Freshly distilled mercury and that stored in glass or ceramic containers did not show this effect. 9storage test was made on a sample of mercury which showed no large residual current at 2.1 volts vs. mercury pool with 0.1M tetramethylammonium iodide electrolyte. Half of the mercury mas stored in a polyethylene bottle and half in a glass bottle. After storage of 4 and 9 months, each sample was used as a pool electrode and a polarogram was obtained under the same conditions. The resulting current-voltage curves
1036
ANALYTICAL CHEMISTRY
I -1 4
-I
e
-2
e
VOLTS v&Hq P O O L
Figure 1. Effect of polyethylene storage on mercury for polarographic use
Current-voltage curves obtained at a dropping mercury cathode using as reference electrode a pool of mercury -4. Freshly distilled 8 . Stored in polyethylene bottle for 4 months C. Stored in polyethylene bottle for 9 months
are shown in Figure 1. The appearances of the polarogranis suggest that they may be due to hydrogen discharge a t the dropping mercury electrode. Gatos ( 3 ) has reported that mercury stored in polyethylene bottles had a supressing effect on polarographic waves indicating the solution or niechanical removal of surface-active agents from the polyethylene. DISCUSSION
Analysis of Industrial Streams. The analysis has been used successfully on several plant streams, particularly n aste streams, \!-hich contained many impurities that were not known. Inspection of the shape of the current-voltage nave gave a good indication of whether or not polarographically active interfering coinpounds n ere present in the distilled samples. If no interference was noted. the average of the values derived from the three fractions was reported. Khen interfering compounds nere present, only the fractions showing no interferences were used. Lactonitrile, a conimon impurity in these streams, deconipoqes ( 7 ) readily to acetaldehyde and hydrogen cyanide when heated. I n the analysis of such streams, acetaldehyde and hydrogen cyanide were found in the overhead fractions. S o interference n a s encountered from hydrogen cyanide; honever, acetaldehyde is polarographically active in this region and interferes nith the analysis. This interference was minimized by addition of acid to retard the decomposition of lactonitrile. If acetaldehyde, per se, were present in low concentrations (< 100 p.p.m.), interference from this compound with the analysis was usually present only in the first fraction. The analysis was then made on the second or third fraction and no
special effort was necessary to eliniiiinte acetaldehyde interference. When acetaldehyde and other polarographically active aldehydes and ketones n-ere present in large quantities, 2,i-dinitrophenylhydrazine was added with the sulfuric acid and the solution \vas allowed to reflux prior to the addition of methanol. The 2,4-dinitrophenylhydrazones remained in the flask upon distillation. ' Precision and Accuracy. Calibration dat,a shori- a linear relationship between concentration of acrylonitrile in the original solution and the diffusion current measured on a given fract,ion. In using this method it is assumed that the distillation is reproducible for any aqueous sample-Le., for a given concentration of acrylonitrile and regardless of the other coniponents present, the amount of acrylonitrile in the various fractions d l be the same. That thip is reasonably true is shown by the analysis of a synthetic mixture containing a large number and variety of impurities in addition to a known concentration of acrylonitrile. An amount equivalent to 500 p.p.ni. of each of the following compounds as added to tap Tvater: cyanobutadiene, lactonitrile, propionitrile, acetonitrile, hydrocyanic acid, acetone, methyl ethyl ketone, crotonaldehyde. paraldehyde, acetic acid, acrylic acid, benzene. styrene. ethylbenzene, and 480 p.p.m. of acrylonitrile. The distillation >vas performed as described. Addition of 2,i-dinitrophenylhydrazine and reflus were used because of the high concentration of aldehydes in this sample. The results of this analysis are shown in Tahle 11. An estimate of the precision of the analysis can be made from the data in Table I, which shows the reproducibility of duplicate distillations and a p l y s e s of actual plant samples. Detection Limit of Analysis. Es-
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
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