reaction mixture and be extracted into the cyclohexane. This will show an absorbance maximum a t 305 m r instead of 298 mfi. LITERATURE CITED
(1) Anderson, D. M. W., Duncan, J. L.,
Herbich, M .A,, Zaidi, S. S. H., Analyst 88, 353 (1963).
( 2 ) Hald, J., Acta Pharm. Intern. 2 , 27
(1951). (3) Harvald, B., Valdorf-Hansen, F., Nielsen, A,, Lancet, 1960-1,p. 303. (4) Jones, R., Page, B. C., ANAL.CHEM. 36, 35 (1964). ( 5 ) Ritter, H., Mutter, K., Hofstetter, J., Pharm. Acta Helv. 36, 232 (1961). (6) Skelly, N. E., unpublished work, The Dow Chemical Co., Nov. 1962.
( 7 ) Stenger, V. A., “l$xyclopedia of Chemical Technoloev. 1st ed.. T‘ol. 11, p. 647, IntersciEce Encvclonedis. New York, 1948. (8) Stoermer, R., B e r . 41, 323 (1908). (9) United States Pharmacopeia, Third USP XVI Interim Revision Announcement, Official May 1, 1963.
RECEIVEDfor review March 30, 1964. Accepted May 8, 1964.
Ion Exchange Separation of Acetamide from Ammonium Acetate and Its Determination PERRY KING and JOSEPH R. SIMMLER Mallinckrodt Chemical Works, St. louis 47, Mo.
b An ion exchange method was developed for the deterrnination of acetamide in ammonium acetate. An aqueous solution of sample is passed through a bed of Amberlite IR-120 ion exchange resin in the hydrogen ion form. The ammonium ions are retained by the resin, but acetamide is not retained and is determined in the eluate by a semimicro Kjeldahl distillation and titration with hydrochloric acid.
T
o
CONTROL the quality of reagent grade ammonium acetate, a procedure was required which would determine the acetamide that may form because of the decompxition of the ammonium acetate during the manufacturing process. S o lil erature reference was found for the direct determination of acetamide in aminonium acetate. There are, however, many methods for determining acetamide. Several methods (1-3, 5 ) were not applicable because of the interference of the ammonium ion from the ammonium acetate. Acetamide has been determined by precipitation as the Reineckate salt ( 7 ) ) or by measuring the nitrogen gas liberated when1 acetamide is digested with concentrated hydrochloric-nitric acid mixture (8). In a study of the hydrolysis kinetics of aliphatic amides ( 6 ) , an anion exchange resin Amberlite IRA400, was used to anal!, ze the hydrolysis products. Several attempts were made to separate acetamide from ammonium acetate, A selective solubilization of acetamide with chloi*oform, followed by a micro Kjeldahl determination or spectrophotoinctric determination a t 1.46 microns, was only partially successful. Results were erratic, probably because of incomplete solubilization of the acetamide from the ammonium acetate crystzls. A (colorimetric procedure using phenol and hypochlorite ( 4 ) was tried without success. The
ammonium ion was quantitatively retained by the ion exchange resin Amberlite IR-120 AR (Mallinckrodt Chemical Works, St. Louis, !Uo.), while acetamide was not retained. The following procedure was developed on this basis. EXPERIMENTAL
Apparatus. T h e ion exchange column was a borosilicate glass tube, 35 em. long with a 15-mm. i.d. constricted a t one end to a 3-cm. length with a 4-mm. i.d. The rate of flow of the eluant was controlled b y a screw clamp on a section of rubber tubing between the 3-cm. tube of the column and a medicine dropper exit tube. Procedure. T h e column was prepared by inserting a glass wool plug, adding about 2 to 3 inches of water, and pouring a slurry of the resin into the glass tube. T h e slurry was made by mixing 11.0 grams of Amberlite IR-120 AR resin, hydrogen form, with 15 ml. of water. T h e resin was washed with two 25-ml. portions of water. After draining the water down to the surface of the resin, t,he column was ready for sample acceptance. Ammonium acetate 10 + 0.01 grams was dissolved in watcr and diluted to 100.0 ml. Ten milliliters of the solution were placed on the column and allowed to drain into the resiii bed a t a flow rate of approximately 2.5 ml. per minute. The ammonium acetate sample solution was followed by five 5.0-nil. increments of water and then with 50 ml. of water. The acetamide in the eluant was decomposed and distilled by a semimicro Kjeldahl technique. The condensate was collected in a sntui.ated solution of boric acid to which three drops of indicator were added [equal volumes of 0.25% (w./v.) methyl red and 0.16% ( W J V . ) methylene blue. tii-olvcd in 95% ethyl alcohol]. The condensate was titrated with 0.01:Y hydrochloric acid. A blank correction was determined by substituting 10 ml. of water for the sample aliquot in the above procedure.
RESULTS AND DISCUSSION
The quantitative retention of ammonium ions by the cation resin was demonstrated by the following experiments. Several 25-ml. portions of water were passed through the resin bed onto which 10.0 ml. of a 10% solution of ammonium acetate has been placed. The 25-ml. portions were collected separately and analyzed by the Kjeldahl procedure. Results are given in Table I. After the third eluate, the titer was less than the blank (0.25 ml.), indicating complete removal of acetamide and complete retention of the ammonium ion by the resin. If all of the ammonium ion were eluted, 1300 ml. of the acid would be required. KO doubt the retention of ammonium ion, as expressed by the following equation
R-H’
+ S H 4 + + CHSCOO- e R-NH4+ + CHSCOOH
where R - equals the ion exchange resin, is enhanced by the formation of acetic acid. In another experiment, 10 ml. of a 10% ammonium acetate solution was analyzed by the above procedure. Ten milliliters of 7.770/, (UT., v.) acetic acid, the amount of acetic acid which is generated in the column mhen 10 ml. of 10% ammonium acetate exchanges with the cation resin, was then put through the same column. The eluate from the ammonium acetate solution
Table I.
Titers of Successive Eluates (0.01 N Hydrochloric acid)
Eluate, 25-ml.
Titer, ml 5.30 2.35 0.42
0.08
VOL. 36, NO. 9, AUGUST 1964
1837
Table II. Recovery of Acetamide Added to Ammonium Acetate
Amount added, mg.
Amount recovered, mg.
Recovered, %
2.0 5.0 10.0
2.18 4.98 9.74
109,o 99.6 97.4
and from the acetic acid solution was analyzed by the Kjeldahl method and the amount of nitrogen found, expressed as acetamide, was 9.4 mg. and 0.3 mg., respectively. Further verification that the ammonium ion was quantitatively retained by the resin was obtained by passing 10 nil. of the 10% ammonium acetate solution through a resin bed twice the height of that in the procedure. The acetamide content was found to be 9.5 mg., compared with 9.4 mg. found using the shorter column. Subsequent applications of the procedure to several different manufactured lots of ammonium acetate revealed one lot which contained less than 0.01% acetamide, again indicating quantitative
retention of ammonium ion by the cation resin. The recovery of known amounts of acetamide added to 10.0-ml. portions of 10% ammonium acetate solutions is shown in Table 11. The amount of acetamide originally found in the 10% solution of ammonium acetate was taken into account in calculating the recovery of the added acetamide. The average nitrogen content expressed as acetamide for three 10.0-ml. aliquots of the 10% ammonium acetate prior to adding acetamide was 4.74 =t0.05 mg. Other nitrogen compounds not retained on the resin column and capable of being converted to ammonia by the Kjeldahl procedure naturally would interfere with the determination of the acetamide. However, the presence of amides other than acetamide in ammonium acetate is not expected. The procedure could be readily adapted for the determination of ammonium ions in acetamide or in other nonionizable water- (or alcohol-) soluble nitrogen compounds. After retaining the ammonium ion on the ion exchange resin, thus separating it from the other nitrogen compounds, the ammonium ion could be eluted from the resin with
Determination of Fluorine in
a strong acid such as hydrochloric acid. The ammonium ion in the acid eluant could then be determined by the usual Kjeldahl procedure. ACKNOWLEDGMENT
The authors express their gratitude for suggestions from coworkers in the Analytical Research Group, Department of Quality Control, hlallinckrodt Chemical U70rks. LITERATURE CITED
( 1 ) Archibald, R. M., Bzol. Chem. 1 5 1 , 141 (1943). ( 2 ) Bergman, F., AKAL. CHEM.24, 1367 (1952). ( 3 ) Brauniger, H., Spangenberg, K., Pharmazze 12,411 (1957). ( 4 ) Domnas, A,, J. Bzochem. ( T o k y o ) 50, 46 11961). ( 5 ) I&e, B’. V., Sergeeva, Z. I., Zh. Analit. Kham. 12, 540 (1957). ( 6 ) Kesdy, F., Bruylants, A., Bull. Soc. Chim. Belges 66,565 (1957). (. 7.) Kum-Taff. Kum-Taff,, L.,, Anal. Chim. Acta 24, 397 (1961). 18’1 Renard. 11..Me’dart. J.. Bull. SOC. 18’1 Roy. Scz. i i e g e 18,409 (1949). \
,
RECEIVEDfor review March 20, 1964. Accepted April 20, 1964. Presented a t the Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, March 1964.
FIuorine-Oxygen
Mixtures
SAMUEL KAYE and J. E. KOENCY General Dynarnics/Astronautics, San Diego 12, Calif.
b A method has been developed for determining the quantity of fluorine in fluorine-oxygen mixtures. A liquid sample is vaporized completely and allowed to expand into a Tefloncoated cell with sapphire windows. The per cent absorption is read directly from the recorder of a spectrophotometer and converted to volume or weight concentration from previously prepared calibration curves.
R
ADVANCES in propellant technology have pointed to the utilization of fluorine-enriched oxygen as an oxidant system. Enrichment of liquid oxygen by 30y0 of fluorine will increase specific impulse, provide for higher payload, result in propellant hypergolicity, and simplify the propulsion system of space vehicles. One of the problems arising from the use of fluorine-oxygen (flox) mixtures is the determination of the concentration of each component in the mixture. h rapid, accurate analytical method is required so that flos composition can be adjusted while the mixture is being ECEXT
1838
ANALYTICAL CHEMISTRY
prepared. In addition, composition must be accurately monitored while in the storage tank and composition on loaded vehicles must be known so that reliable calculations may be made regarding engine performance and operation. The present investigation was done to develop a method for determining rapidly the amount of fluorine in oxygen used in this oxidant system. Fluorine may be determined in many ways. One way is by gravimetric precipitation as lead chlorofluoride or as calcium fluoride, each of which has its particular advantages ( 2 ) . Small quantities can be determined titrimetrically with thorium nitrate, colorimetrically by peroxytitanic acid or by ferric ion, fluorometrically by aluminum-morin reagent, and potentiometrically with a ferrous-ferric ion concentration cell. Larger quantities may be determined gasometrically by direct reaction with mercury, or indirectly by measurement of the amount of bromine, chlorine, or iodine the fluorine displaces from the corresponding sodium salts. All the above methods require considerable time to perform. -1 rapid method is de-
scribed here which requires no highly trained personnel. It employs an ultraviolet spectrograph and a Teflon-coated stainless steel cell with sapphire window to measure the amount of absorption a t the peak of the broad absorption band of fluorine displayed by the system at 278.0 mp. The intensity of the absorption a t this wavelength is a function of the fluorine concentration. Unknown concentrations can be determined immediately by a reading of the intensity and comparison with calibration curves prepared from known concentrations. EXPERIMENTAL
Apparatus. The apparatus is shown in Figure 1. Tanks containing pure fluorine and various mixtures of fluorine/oxygen are attached to the inlet valve of a 10-cm. stainless steel absorption cell. The windows of the cell are of sapphire. They seat on the polished edges of the cell which are coated with a thin film of Kel-F 90 grease. The windows may then be cemented to the steel tube with any appropriate chemical cement. The cell itself is Tefloncoated on the inside to resist fluorine
