Table I. Some Limits on Detection and Selectivity Ratios Selectivity Wavelength, Limit of ratio Element nm detection, (g/sec) (w.r.t. carbon) C 247.9 1 . 9 x 10-10 I 206.2 1.0 x 10-10 1,m S 182.0 4.0 x 460 253.5 P 3.0 x 150 c1 256a 4 . 5 x 10-9 Br 292“ 2.5 x 10-9 a Band. I
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the detector tube which would particularly reduce the sulfur emission. The graph of Ps/Pcus. the theoretical ratio showed a maximum deviation from linearity of 5 %. Bromine/Carbon Ratio. The D330 monochromator was set to monitor a Br2 band emission at 292 nm. A microwave power of 70 watts was found to be optimum and a column temperature of 170 “C and a carrier gas flow rate of 3.3 L/hr were used. The compounds studied were bromoform (5.00), bromobenzene (6.45), ethyl-2-bromopropionate (6.75), dibromoethane (2.57), n-amyl bromide (2.30), ethyl bromide (0.55),and propyl bromide (1.04). The results were similar to those obtained for chlorine. All the compounds showed a linear variation when R was plotted against PC with approximately the same intercept on the R axis. When the log of the gradients of these slopes were plotted against the log of the theoretical bromine/carbon ratio, a straight line with a gradient of 1.96 was obtained. CONCLUSIONS
The present study has shown that for the limited range of sulfur, iodine, and phosphorus compounds investigated, the use of the simple expedient of simultaneously monitoring emission from two atomic lines can be used to determine the quantitative relationship between the heteroatoms and the number of carbon atoms in the compound. In each
instance the measured ratio was found to be independent of carrier gas flow rate and concentration. Hence, when these atomic emissions are used, it is unnecessary to know the exact concentration of a compound under examination and it is not essential to obtain a good peak shape in order to determine the inter-element ratios. The results obtained for chlorine- and bromine-containing compounds can be satisfactorily explained on the basis that the emitting species are diatomic (C12and Br2). The ratios of chlorine or bromine emission to atomic carbon emission were both carrier gas flow rate and concentration dependent. A series of peak ratios for a range of concentrations of the sample under investigation would be required together with a standard sample in a similar range for analytical purposes. The analytical utility of this technique is clearly limited by the sensitivities of the detectors to the elemental emissions monitored (shown in Table I) and by the relative interference of other elements at these wavelengths. Interferences with this detector may be of two types. The first occurs when a large excess of another compound gram/sec) overloads the plasma; this will affect all types of emissions and must be avoided. The second effect arises from spectral emissions from other species at the wavelength being monitored. The principal interfering element is carbon which gives rise to a large number of emitting species (e.g., Cn,CN, CH, C). The relative selectivity of each element at the atomic wavelength used is also shown in Table I. These are given as the ratio of response per gram-atom of the element to the response per gram-atom of carbon. The use of microwave-excited atomic emissions for the determination of inter-element ratios has been shown to be feasible and, providing it proves applicable to a wider range of compounds, it is considered that this will offer a valuable aid in the identification of unknown eluates in gas chromatography. RECEIVED for review February 7, 1972. Accepted June 15, 1972.
Determination of Amide, Urea, and Nitrile Compounds Using Alkali-Fusion Reaction Gas Chromatography Stanley P. Frankoski and Sidney Siggia Department of Chemistry, Uniuersity of Massachusetts, Amherst, Mass. 01002
CARBOXYLIC AMIDES have been determined by alkaline hydrolysis (1-4). While reaction is sluggish, primary amides are more reactive than secondary and tertiary. Major limitations of procedures using alkaline hydrolysis have been the dependence on concentration of caustic and attainment of high enough temperatures to force the reaction to completion. (1) S . Siggia, “Quantitative Organic Analysis via Functional
Groups,” John Wiley and Sons, New York, N.Y., 1963, Chap. 3. (2) S.Olsen, Die Chernie, 56, 202 (1943). (3) F. E. Critchfield, “Organic Functional Group Analysis,” Pergamon Press, New York, N.Y., 1963, p 52. (4) R. D. Tiwari and J. P. Sharma, “The Determination of Carboxylic Functional Groups,” Pergamon Press, New York, N.Y., 1970, Chap. 5. 2078
Other chemical and instrumental methods for amide determination have been reviewed (1-5). Some of these methods include determination by titration in nonaqueous solvents, spectrophotometric procedures, reduction with lithium aluminum hydride, gas chromatography, and reaction gas chromatography. Polymeric amides with functional groups on the polymer backbone resist alkaline hydrolysis. Polymeric nitriles are extremely difficult to determine hydrolytically. Infrared analysis can be applied to polymeric nitriles; however, diffi(5) S . Siggia, “Instrumental Methods of Organic Functional Group Analysis,” Wiley-Interscience, New York, N.Y., 1972, Chap. 3.
ANALYTICAL CHEMISTRY, VOL. 44, NO. 12, OCTOBER 1972
culty in calibration is encountered unless a very similar polymer system is used. For polyamides composed of diamine and dibasic acids, general analysis schemes incorporating acid hydrolysis exist (6). Modifications using acid hydrolysis followed by gas chromatographic procedures have resulted in qualitative and quantitative analysis of homo- and copolymers of polyamide resins (7,8). Alkali-fusion gas chromatography has been successfully applied to difficultly saponifiable esters (9). The method employs a hot, highly concentrated caustic, Fusion applied to amide groups allows conditions drastic enough to force the reaction to completion. This method results in chromatographic resolution and quantitation of the liberated amines or ammonia. The determination is completed within one piece of apparatus. It is rapid, specific, and permits mixtures to be analyzed.
I
EXPERIMENTAL
Apparatus. Determinations were performed in essentially one piece of apparatus which has been described earlier (9). The gas chromatograph used was a Perkin-Elmer Model 990 equipped with dual thermal conductivity detector and linear temperature programmer. A Vidar Model 6300 digital integrator and an Electronik 194 potentiometric recorder (Honeywell, Fort Washington, Pa.) were used. Two stainless steel columns, 3-foot x 1/4-inch 0.d. were packed with 80- to 100-mesh Chromosorb 103 (JohnsManville, New York, N.Y.) and conditioned 18 hours at 240 "C. The gas chromatograph was operated as follows: injector temperature, 240 "C; manifold, 290 "C; detector temperature, 290 "C; detector current, 175 mA; and helium flow rate, 60 ml per minute. Columns were maintained isothermal for 3 minutes at 150 "C and then programmed 24 "C per minute to 240 "C. For samples liberating ammonia, the columns were maintained isothermal for 3 minutes at 100 "C and then programmed. Reagents. The fusion reagent was prepared by prefusing about 1 % sodium acetate with potassium hydroxide (J. T. Baker, Analytical reagent grade) in a n inert atmosphere. Preparation and storage of the fusion reagent has been described earlier (9). Benzanilide (N-phenylbenzamide, white label), acetanilide (N-phenylacetamide), carbanilide (1,3-diphenylurea, white label) and N,N'-dimethylcarbanilide (1,3-dimethyl-l,3-diphenylurea) were obtained from the Eastman Kodak Company. Benzanilide was recrystallized from ethanol-water twice. Acetanilide and N,N'-dimethylcarbanilide were sublimed at 70 "C/0.5 mm Hg for 2.0 hours and 105 0C/0.05 mm Hg for 2.0 hours, respectively. Polyacrylamide and polyacrylonitrile were obtained from K and K Laboratories and heated at 50 "C for 12 hours in uucuo to remove any residual solvent. Poly(hexamethy1ene adipamide) (Nylon 66) and poly(hexamethy1ene sebacamide) (Nylon 610) were synthesized by interfacial condensation techniques (10). The prepared nylons were qualitatively identified by their characteristic infrared spectra (6). Elemental analysis of Nylon 66 and Nylon 610 indicated 97.1 and 96.4% theoretical nitrogen, respectively. Aniline was received from the J. T. Baker Chemical Company (Baker analyzed reagent). N-Methylaniline was re(6) J. Haslam and H. A. Willis, "Identification ana Analysis of Plastics," D. Van Nostrand Co., Princeton, N.J., 1965, Chap. 4. (7) A. Anton, ANAL.CHEM., 40, 1116 (1968). (8) S. Mori, M. Furusawa, and T. Takeuchi, ibid., 42, 138 (1970). (9) S. P. Frankoski and S. Siggia, ibid., 44, 507 (1972). (10) P. W. Morgan, "Condensation Polymers: By Interfacial and Solution Methods," Interscience, New York, N.Y., 1965, p 457.
TIME-minutes
Figure 1. Gas chromatogram of Nylon 66 after alkali fusion Peak 1. Water Peak 2. 1,6-Hexanediamine
ceived from Matheson, Coleman and Bell and distilled at 74 O C j l O mm Hg. 1,6-Hexanediamine was received from the J. T. Baker Chemical Company (Baker Grade). Anhydrous ammonia was received from Matheson Gas Products. Procedure. Compounds were fused using the procedure described in the determination of carboxylic esters (9). Solid samples from 1 to 3 milligrams were weighed into platinum boats and transported in a small desiccator to a dry box containing the fusion reagent. Fusion reagent was added to totally cover the samples. The loaded boats were then transported in the small desiccator to the alkali-fusion apparatus. With the detector off, sample boats were placed in the storage area. Once all boats were in the apparatus, the apparatus was sealed and the desired flow rate was established. The detector was turned on. With the attainment of detector equilibrium and the furnace at ambient temperature, liquid nitrogen was applied to the trap loop. The first sample boat was placed in the reaction zone (furnace) and the proper temperature selected. The rate of heating was approximately 15 "C per minute. Upon completion of fusion, the products were flushed into the gas chromatograph by applying a temperature of 250 "C to the trap. With compounds processing a high melting point or thermal stability (i.e., Nylon 66), samples may be introduced into the furnace above ambient temperature, thus decreasing analysis time. Calibration was done using identical fusion conditions. The calibration materials were trapped and flushed into the gas chromatograph. Aniline, N-methylaniline, a 1,6-hexanediamine-water mixture (wjv), and ammonia (adjusted to conditions of standard temperature and pressure, 0 "C and 760 mm Hg) were used to construct calibration curves.
ANALYTICAL CHEMlSTRY, VOL. 44, NO. 12, OCTOBER 1972
2079
Table I. Determination of Amide, Urea, and Nitrile Compounds by Alkali-Fusion Gas Chromatography Conditions Analysis Standard Temp., Time, Compound theoretical deviations "C hours Acetanilide 100.5 1.5 320 0.5 Benzanilide 97.9 1.8 320 0.5 Carbanilide 98.2 1.9 340 0.5 N,N'-Dimethylcarbanilide 99.3 1.7 360 0.6 Nylon 66 98.4 2.1 360 0.5 Nylon 610 99.9 3.8 360 0.5 Polyacrylamide 98.5 3.1 300 0.3 Polyacrylonitrile 98.5 1.4 300 0.5 a Five or more determinations.
RESULTS AND DISCUSSION
Alkali-fusion results for amide, urea, and nitrile compounds are given in Table I. The temperature reported relates to the final fusion temperature. Samples were usually introduced into the furnace at ambient temperature and the final temperature was then selected. Time designates the period of fusion. Complete dissolution and fusion usually occurred within thirty minutes. A typical chromatogram of a single compound after fusion is shown in Figure 1 . The chromatogram shows two peaks, water, which is associated with the fusion reagent, and the resultant amine or ammonia. Analysis of compounds investigated by alkali-fusion gas chromatography gave results which were in excellent agreement with the theoretical amide or nitrile content based on liberated amine or ammonia. Determinations of anilides and carbanilides were within 2.1 of the theoretical predicted values with an average stan-
dard deyiation of 1.8 %. Fusion makes possible a rapid determination of amide content (primary, secondary, and tertiary) as compared to conventional alkaline hydrolysis. Polyamides, where the amide groups are links in the polymer chain were amenable to analysis by alkali-fusion. Quantitative results were obtained for Nylon 66 and Nylon 610 in less than one hour. By introducing these materials into the furnace at l 5OoC,instead of ambient temperature, reaction time can be decreased. Polymers with pendant amide groups on the polymer backbone and polymeric nitriles are also amenable to determination by fusion. Polyacrylamide and polyacrylonitrile liberated ammonia quantitatively. Fusion provided drastic enough conditions to completely react these compounds. The alkali-fusion reagent contained enough water to convert the nitrile to the amide. Upon further reaction, the reagent converts the amide to ammonia and a carboxylic acid-salt. Fusion was found to be rapid. Coupled with gas chromatographic detection, total determination and separation of mixtures are possible. It is felt that sample blends and copolymers composed of amide, nitrile, and/or ester functional groups (ix.,butadiene/acrylonitrile rubbers) may be determined without prior separation. Extension of alkali-fusion gas chromatography should result in a rapid analysis for some carbonates, polyureas, and polyurethanes. ACKNOWLEDGMENT
The authors thank Charles Meade of the University of Massachusetts who performed the elemental analyses mentioned in this paper. RECEIVED for review March 20, 1972. Accepted May 14, 1972. This work was supported by the National Science Foundation under Grant G P 28054.
Separation of Barium-140 and Lanthanum-140 by Isotopic Exchange Using Impregnated Paper Chromatography Mitchell L. Borke and Nina Y. Liang Duquesne University, Pittsburgh, Pa. 15219 MANYSPECIFIC METHODS have been developed for the separation of radioactive equilibrium mixture of 140Ba and 140La. They include the use of ion exchange resins ( I , 2 ) carboxymethyl-cellulose filter paper (3), thin layer chromatography (4), and thin layer electrophoresis (5). (1) K. B. Zaborenko, I. C . Bogatyrev, and N. L. Malgina, Radiokhimiya, 8,352 (1966). (2) K. H. Lieser and K. Baechmann, Fremenius' Z . Anal. Chem., 225, 3979(1967). (3) D. Klockow, Talunta, 15,543 (1968). (4) M. Yasuyuki, T. Kasuyuk, and M. Yukio Kanagawa-Ken Kogyo Shikensho Kenkyu Hokoku, 20, 41 (1968); Chem. Abstr., 70,16309~(1969). ( 5 ) M. Itsuhiko, T. Noriko, and S . Masaki, Yakuguku Zasski, 89, 1669(1969); Chem. Abstr., 72,62423k(1970). 2080
Until now, no application of the isotopic exchange reaction to the separation of 140Ba and 140Lahas been reported. In this investigation, the isotopic exchange reaction coupled with thin layer chromatography afforded a simple and relatively rapid separation of carrier-free I4OLa from its parent InoBa. By using an equilibrium mixture of 140Baand l40Laon barium sulfate impregnated filter paper and developing with dilute sulfuric acid-dioxane solvent system, 140Ba was retained at the point of application while 140La advanced upward almost to the solvent front, so that a clear separation was obtained. EXPERIMENTAL Chromatography paper strips, Whatman No. 1, 40 cm long, were soaked in a saturated barium chloride solution for 2 hours, then removed from the solution and dried in air.
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