many other mechanism problems are readily apparent. Comparison of the traces from the radioactivity and thermal conductivity detectors shows that increases of several orders of magnitude in specific radioactivity are obtainable in a single chromatographic pass-the compounds with olefinic tritium present are essentially carrier-free. ACKNOWLEDGMENT
Becker assisted in the preparation of the chromatographic columns.
LITERATURE CITED
( I ) Cvetanovic, R. J., Duncan, F. J., Falconer, W. E., Can. J . Chem. 41,2095 (1963). ( 2 ) Dubrin, J.7 AIacKaY, c.,Wolfgang, R., J . Am. Chem. SOc. 861 9% (1964). ( 3 ) Lee, J. K., et al., ANAL. CHEM. 34, 741 ( 1962). (4) hIuhs, A,, weis, F, T,, J , A4m. Chem. SOC.84, 4697 (1962). ( 5 ) Root, J. w., Lee, E. K. c . , Rowland, F. S., Science 143,676 (1964). (6) Rowland, F. S., Lee, J. K., Musgrave, B., White, R. M . , “Chemical Effects of Xuclear Transformations,” Inter-
national Atomic Energy Agency, 1‘01. 2, p. 67, 1961. (7) D., wolfgang, R. L., Ibid., 1-01. 2, p. 99.
E . K. C. LEE F. S.KOV,LAND Department
Of
Chemistry
Cniversity of Kansas La\%-rence,&UL RECEIVEDfor review June 10, 1964. Accepted .4ugust 6, 1964. This research has been supported by ilir Force Contract’ KO. AF 19-(604)-4053 and by U. S. Atomic Energy Commission Contract T o . AT-( 11-1)-407,
Quantitative Pyrolytic Gas Chromatography by Internal Standard SIR: Use of a n internal standard for the estimation of pyrolysis products separated by gas liquid chromatography could not be found in the literature. The primary objective of this investigation was to demonstrate the applicability of the internal standardization technique used with pyrolytic gas chromatography, for quantitative purposes, to the analysis of some coating materials. The technique and its accuracy are described and illustrated by application to the semiquantitative determination of some polymethacrylates and polystyrene in various coating systems and comparison is made to the total area method. The use of complex polymers and copolymers in coating compositions is increasingly widespread and has prompted the search for new and better methods of analysis. The combination of pyrolysis and gas liquid chromatography has greatly extended the use of gas chromatography in the field of polymer analysis
C
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IO
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Figure 1 . Acrylic automotive lacquer containing nitrocellulose A. Light ends B. Ethyl methacrylate (internal standard) C. Butyl methacrylate
and comprehensive studies for the identification of polymers from their thermal decomposition products have been described (2, 3,5, ‘7. 9 ) . Strassburger and coworkers (10) demonstrated the suitability of pyrolysis for the quantitative determination of pyrolyzates but limited their work to copolymers of methyl methacrylate. Others (4) have htudied the thermal degradation of polymers and directed their efforts a t determining the decomposition products without relating them to the quantitative character of the material from which they mere derived , Since a broad spectrum of physical and chemical properties can be incorporated into vinyl type coating materials by regulating the type and amount of monomer used in their production, search for suitable methods for their analysis is continuous. The use of pyrolytic gas chroniatography has been established as an ewellent method for identifying resins, but most methods have been found incongruous for quantitative work. Pyrolysis studies previously mentioned were conducted by researchers primarily interested in plastics, except for one dealing with the identification of coating resins ( 9 ) . Certain vinyl-type polymers, such as methacrylates and vinyl aromatics. will revert to their mononiers in high yields when subjected to optimum decomposition temperatures. Simple polymethacrylate and polystyrene systems can be determined by using the total area method of analysis which assumes that all the sample is eluted from the column and appears on the chromatogram, but this technique is inadequate and produces ambiguous results when these materials are modified with other resins or plasticizers. Two distinct types of pyrolysis systems have been used. I n one a filament is coated with resin ( I , 8, 10) or a boat
containing the sample is placed inside a spiraled filament’ (4, 6) and the sample is pyrolyzed by passing current through it. The second type utilized a micro furnace (S, 10) to decompose polymers. I n this investigation a commercial pyrolysis unit of the filament type using a platinum-rhodium ribbon was employed. Sample introduction is relatively simple and the complete analysis requires less than one hour. A solution of the polymer to be used as the internal st,andard is weighed with a known amount’ of sample and diluted with dioxane. The tip of the pyrolysis probe is dipped into t’he solution and dried. The pyrolysis is conducted in the injection port by passing a predetermined amount of current through the filament; the products of decomposition are carried onto the column as they are formed by the normal flow of helium. Separation of the pyrolysis products is accomplished
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Figure 2. Acrylic lacquer containing polyvinyl chloride A. Light ends B. Ethyl methacrylate (internal standard) C. Butyl methacrylate VOL. 36,
NO. 1 1 ,
OCTOBER 1964
21 83
Procedure. Approximately 2 grams of resin solution to be tested are weighed accurately into a stoppered 25-ml. flask. .\ solution of the internal standard is weighed accurately into the same flask; the amount of nonvolatile material in the internal standard added should approximate 5oY0 of the nonvolatile weight of the sample. The contents of the flask are thinned with dioxane to produce about a 10% resin solution. The tip of the pyrolysis probe is dipped into the solution and then dried in an oven a t 110' C. for one-half hour. With the column temperature set at 60' C. and helium flolting, the probe is inserted into the injection port and the detector current turned on. -4fter the instrument reaches equilibrium, the automated pyrolysis cycle is activated followed immediately by engagement of the temperature prograniming mechanism. The analysis is completed using the operating conditions described above.
B
C A
B
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MINUTES Figure 3. Acrylic resin plasticized with butyl benzyl phthalate A. Light ends B. Methyl methacrylate C. Ethyl methacrylate (internal standard)
by programmed temperature gas chromatography using a 10-foot silicone grease column. EXPERIMENTAL
Apparatus. The equipment used to obtain the chromat'ograms was a Model 500 Linear Programmed Temperature Gas Chromatograph (F & 11 Scient,ific Corp.) equipped with a Broivn Electroriik recorder (Minneapolis-Honeywell) and an integrator (Disc Instruments, Inc.). T h e pyrolysis was performed with a Model 80 Pyrolyzer ( F & A I Scient,ific Corp.). A IO-ft. length of '/,-inch copper tubing was packed with 20y0 by weight, of silicone grease on 60- to 80-mesh acid mashed Chromosorb Jf7 and conditioned at' 250' C. Operating Conditions. Injection port temperature,ooC. 75 Detector cell temperature, C. 300 Detector cell current, ma. 160 Helium flow at exit, cc./minute 75 Pyrolyzer electrode current, amps. 11 Duration of filament current, seconds 12 Programmed temperature analysis: Starting column temperature, "C. 60 Column heating rate, "C. /minute 5.6 Finishing column temperature "C. 225 21 84
ANALYTICAL CHEMISTRY
polymer used as the internal standard, when pyrolyzed alone, yielded 98% ethyl methacrylate and 2% methyl methacrylate. Calibration correction factors obtained by pyrolyzing poly(ethyl methacrylate) with known amounts of polyimethyl methacrylate), polyibutyl methacrylate), and polystyrene were 1.0, 0.98, and 1.25, respectively. Compensation was made for impurities. Figures 1 and 2 show the chromatograms obtained from acrylic nitrocellulose and acrylic vinyl lacquers. ?;either the plasticizers nor modifying resins interfered with the analysis. The only extraneous peaks observed of any significance were the gaseous products from the nitrocellulose. Poly (methyl met hacrylate) modified rvith butyl benzyl phthalate was pyrolyzed and produced the chromatogram in Figure 3. A blend of polybtyrene, rosin ester, and tricresyl phosphate was examined and is shown in Figure 4. When a styrenated alkyd mas pyrolyzed, two peaks emerged; one was styrene monomer and the other phthalic anhydride. These peak. along with that of the internal standard are shown in Figure 5. The analytical results were tabulated and are shown in Table I. The same chromatograms were used to compute the results shown in the total area column and illustrates the erroneous results obtained using this method. DISCUSSION
The method described was applied t o polyniers which are frequently used in organic coatings and interference from modifying resins and plasticizers was not encountered. Acrylate resins do not produce as high yields of monomer as do the methacrylates and some difficulty may be encountered in their analysis. iiny of the polymers which produce high yields of monomer could be used satiqfactorily in place of poly(ethy1 methacrylate) as internal standard.
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Figure 4. Polystyrene modified with ester gum and tricresyl phosphate A. light ends B. Ethyl methacrylate (internal standard) C. Styrene
Calculation.
Polymer,
=
A x B C where,
A
Corrected area of peak being determined B = Per cent internal standard C = Area of internal standard =
RESULTS
Five different coating systems were subjected to the method to establish the applicability. The ethyl methacrylate
I 0
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10
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Figure 5 . Chromatogram from a styrenated alkyd
obtained
A. Light ends 8. Ethyl methacrylate (internal standard) C. Styrene D. Phthalic anhydride
providing the necessary calibration is carried out. Different ratios of internal standard to material being measured were tested but the correction factors did not change. The last peak to emerge on the chromatograms obtained from styrenated alkyds was established as phthalic anhydride by injecting phthalic anhydride onto the column and observing the retention time. Attempts to estimate the phthalate content of resins by pyrolysis were not successful. The total area method was used for comparison because it is the simplest and one of the most widely used methods for quantitative estimates. Another technique (IO), utilizing a calibration curve obtained from a series of samples of known composition would be more accurate than the total area method but its general application to organic coating systems has not been illustrated. Injection port temperature was found to be a critical variable and erratic results were produced by higher settings. The pyrolysis probes used were calibrated by the manufacturer and the maximum temperature used in this study exceeded 1000° C. A thermal degradation study (6) of poly(methy1 methacrylate) and polystyrene has shown that temperatures as high as 1000" C. produce low monomer yields. The high yields of monomer obtained in this investigation have been credited to the geometry of the filament used, with the transition temperatures during degradation being near optimum. The proposed method is rapid, relatively simple, and should be applicable
Table I.
Semiquantitative Analysis of Methacrylate and Styrene Polymers in Organic Coatings
Bystem Poly(butyl methacrylate) Poly(viny1 chloride) Dioctyl phthalate Poly( butyl methacrylate) Nitrocellulose Butyl phthalate Poly( methyl methacrylate) Butyl benzyl phthalate
Present 45.8%
Found Internal standard 43.0; 44.8; 43.3
Total area 76.9
64.3
62 7 ; 5 9 . 7 ; 6 2 . 9
74.1
68.8
69.6; 69.2
95.7
Polystyrene 33.8 36.0; 36.3 Rosin ester Tricresyl phosphate Styrenated alkyd 44. Oa 44.8; 43.2; 43.7 Styrenated alkyd 35.14 33.1; 31.0; 33.9 Polystyrene content determined by chemical method (11).
to a broad range of vinyl-type coating materials currently in use. ACKNOWLEDGMENT
The advisory assistance of C. F. Pickett, director of the laboratory, and M. H. Swann of the analytical section is acknowledged and appreciated. LITERATURE CITED
(1) Barlow, A,, Lehrle, R. S., Robb, J. C., "Techniques of Polymer Science," Plastics and Polymer Group, Society of
Chemical Industry, London, September 1962. (2) Cobler, J . G.7 SamSel, E. p., SOC. Plastics Engrs. Trans. 2 , 145 (1962). (3) Cox, B. C., Ellis, B., ANAL.CHEM.36, 90 (1964).
85.7 61.3 59.7
(4) Ettre, K., Varadi, P. F., Ibid., 34, 752 (1962). (5) Hewitt, G. C., Whitham, B. T., Analyst 86, 643 (1961). (6) Lehmann. F. A,. Brauer. G. hf.. ANAL. CHEM.33, 673 (1961). ' (7) Nelson, D. F., Yee, J. L., Kirk, P. L., Microchem. J . 6 , 225 (1962). (8) Pariss, W. H., Holland, P. I)., Brit. PZastics 33, 372 (1960). (9) Sadowski, F., Kuhn, E., Farbe u. Luck 69, 267 (1963). ( l o ) .Strassburger, J., Brauer, G. M., Tryon, M.,Forziati, A. F., ANAL. CHEM.32, 454 (1960). (11) Swann, M. H., Ibid., 25, 1735 (1953). G. G. ESPOSITO Coating and Chemical Laboratory Aberdeen Proving Ground, Md. RECEIVEDfor review June 8, 1964. Accepted July 14, 1964.
Column Chromatography with a Polynitrostyrene Resin Stationary Phase SIR: This is a report of the preliminary evaluation of a polynitrostyrene resin as a chromatographic adsorbent for electron donor molecules such as polycyclic aromatic hydrocarbons, aromatic amines, and phenols. The stationary phase, which has the structure
I
will be referred to as tetranitrobenzylpolystyrene (TXI3P) resin. T K B P resin was prepared by conventional Friedel-Crafts benzylation of 2%
divinylbenzene-polystyrene resin using benzyl chloride in nitrobenzene solvent, followed by nitration with a mixture of fuming nitric and fuming sulfuric acids. T N 3 P is thermally stable to a t least 160" C. and displays the chemical inertness typical of nitroaromatics. The structure was assigned from infrared and NMR spectra and from elemental analysis. The resin was converted to the desired chromatographic form by grinding, screening to a suitable mesh range, and washing with acetone. I t was stored overnight in the eluting solvent to ensure equilibration, after which the column was wet-packed in the conventional manner. Samples were introduced to the column in half-milliter volumes of solvent; elution was carried out by gravity
flow. For the experiment shown in Figure 1 the positions of the bands on the column were followed by observing the fluorescence of the sorbates. Fractions of elutriant were collected automatically and were analyzed for anthracene and pyrene by measuring absorbances a t 377 and 273 mM, respectively. The number of theoretical plates were calculated by the method of James and Martin ( 2 ) ; the Rs value was obtained according to the suggestion of De Ligny et al. ( I ) . Pi charge-transfer complexation is proposed as the mode of chromatographic adsorption, with the resin acting as the acceptor and the sorbate as the donor. This is based on the known complexation between polynitroaromatics and electron donors, on the spectra of the charge-transfer complexes of VOL. 36, N O . 1 1 , OCTOBER 1964
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