were those of o,p-quaterphenyl/l,2,4triphenylbenzene and 1,3,&triphenylbenzene/m-quaterphenyl. Very small samples were necessary for these separations. A flame ionization detector could be used t o great advantage here since even smaller sample size could then be used. Shifts in elution order of polyphenyl isomers on various salt columns mere associated with certain types of linkages in the molecule. For example, with the two compounds m-quaterphenyl/l,3,5-triphenylbenzene, the branched compound eluted ahead of the
linear one on a CsCl column, the two almost coincided on a LiCl column, and the branched compound eluted after the linear one on a CaClz column. These elution orders were found t o hold for higher molecular weight polyphenyls as well if these isomeric structures were present (6). LITERATURE CITED
( 1 ) Doss, R. C., Solomon, P. W., J . Om. Chem., in press. (2) Hanneman, W. W., Spencer, C. F., Johnson. J. F.. ANAL. CHEM.32. 1386 (1960). ’ (3) Keen, R. T., Baxter, R. A., Gercke,
R: H. J., U. S. Atomic Energy Commission Report NAA-SR-4355 (1962). (4)Moffat. A. J.. Solomon. P. W.. U. S. Atomic ’Energy Commission Report IDO-16732 (1961). (5) Normand, M. J., Geiss, F., “Progress in Analysis of Polyphenyl Mixtures,” VI1 Nuclear Congress, Rome, Italy, June 15, 1962. (6) Solomon, P. W., U. S. Atomic Energy Commission Report IDO-16912 (1964). (7) West, W. W., U. S. Atomic Energy Commission Report CRC-AEC-18 (1962).
RECEIVEDfor review August 12, 1963. Accepted December 9, 1963. This work was done under Contract AT(10-1)-1080 with the U. S. Atomic Energy Commission.
Complete Gas Chromatographic Analysis of Fixed Gases with One Detector Using Argon as Gas Carrier DAN P. MANKA Graham Research Laboratory, Jones & laughlin Steel Corp., Pittsburgh, Pa.
b A gas chromatographic method for the analysis of fixed gases containing hydrogen has been developed that requires one analysis, one detector, and argon as gas carrier. The method utilizes both sides of a sensitive microthermistor thermal conductivity cell to detect the gas components separated on silica gel and molecular sieve coltlms. A gas sample containing various concentrations of these components can be analyzed in 10 to 16 minutes, depending on the lengths of the columns.
T
HE MAJOR DIFFICULTY in the analysis of fixed gases such as Hz, 02, Nz, CHI, CO, and COz is the quantitative determination of hydrogen. The sensitivity for the detection of hydrogen with helium as carrier gas is very low because of the small difference in thermal conductivity of the two gases. Unusual responses of the detecting cell are sometimes obtained Kith the hydrogen-helium mixture. h positive and a negative peak are observed at high concentrations of hydrogen and a positive peak results with low concentrations. None of these peaks is completely reliable for quantitative determination. Thus, hydrogen must be determined with a carrier gas of considerably lower thermal conductivity such as argon. Although hydrogen can be determined with argon, the usual detector response to the other fixed gases is too low for their quantitative determination. For a complete analysis, therefore, it has been necessary to determine hydrogen using argon as gas carrier, and to
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ANALYTICAL CHEMISTRY
determine the remaining fixed gases using helium as carrier gas. This double analysis requires considerable time for the actual determinations, as well as sufficient time for the column and the detector t o reach equilibrium with each carrier gas. Fixed gases are conveniently separated on two columns in series, with a detector located at the end of each column. The retention time for all of the gases except COz is short in the silica gel column; therefore, this column serves to separate carbon dioxide. The remaining unresolved gases are separated by a molecular sieve column. Poli and Taylor (3) reported using a dual column/dual-detector for this type of analysis. Bennett, Martin, and Martinez (1) separated light gases with one column and one detector by temperature programming the molecular sieve column t o a temperature of 200” C. or higher. Madison (2) analyzed fixed and condensable gases in two columns, but with only one detector. .I cold partition column separated COz and the condensable gases while a cold adsorption column trapped the fixed gases. After separation and detection of the COZ and light hydrocarbons in the partition column, the confined fixed gases were then released by application of heat to the cold adsorption column and separated by a long activated carbon column. Thus, two analyses were required t o obtain quantitative concentrations of hydrogen and the other fixed gases. A more desirable method for rapid and complete analysis of these gases would be a procedure that requires only
one analysis and only one carrier gas without temperature programming, delaying separation of certain gases, or double analysis. This report describes the development of such a method, including selection of a detector and establishment of a separation system for complete determination of these gases in a single analysis. EXPERIMENTAL
Apparatus. A laboratory gas chromatograph was equipped with a Gow-Mac Model JDC-133 microthermal conductivity detector with the necessary bridge circuitry and power supply, a 0- to 2-mv. Bristol recorder, and a polarity switch. The detector contained two balanced 8-K microthermistors. Argon was used as carrier gas for the analysis of fixed gases. Samples were introduced through the rubber septum of a conventional injector with a Hamilton gastight syringe. Chromatographic Columns. The resolving column for fast elution of COz was a X 7-inch aluminum tube filled with 60- to 80-mesh silica gel. For elution of COz after elution of the other fixed gases, a 5-fOOt silica gel column was used. The column for resolving the remaining gases consisted of a n aluminum spacer tube inch x 23 feet filled with glass beads or firebrick in series with a l/a-inch X 15-foot aluminum tube filled with 30- to 40-mesh 13X Molecular Sieves. The spacer column prevented overlapping of peaks from the two resolving columns by giving hydrogen and the other gases a greater distance to travel before reaching the molecular sieve column. The delay could be adjusted by varying the length of the spacer column.
2
5:
7 n
n
w
X
t-
6
go
GO
I
I
gO x
I
I
0 (u
>
X
I
cu
z w
fn
z
0 L fn
Figure 1. Flow diagram for analysis of fixed gases with one detector and argon as gas carrier 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.
X I
Sourci: of carrier gas Regulnting valve Samp e injector Silica gel column Side No. 1 of detector Spacer and molecular sieve columns Side No. 2 of detector Heated compartment Detector circuits Recorder
K
0 IO
w
I-
kl
n
v)
X
x
ll
0 O
Procedure. The detector sensitivity of lov9 gram p:r ml. suggested the probable analysis of all fixed gases using argon as gas car-ier. Tests with mixtures of gases containing various concentrations of the components indicated sufficient sensiivity to analyze all these gases with argon using a sample size of 0.1 to 0.2 cc. Maximum thermistor response to these gases in argon carrier gas was obtained a t a current of 5.6 ma.; therefore, this cell current was uscd in all analyses. Flow Design for Complete Analysis
with One Detector. The gases were separated by two methods with the flow diagram in Figure 1. I n one method, C O z was sepiirated from the other gases on a short silica gel column and detected iii one side of the cell; the remaining uiiresolved gases, after passing through this side of the cell, were separated in the molecular sieve column and detected in the other side of the cell. The injected gas sample flowed into the 7-inch silica gel column. -411 the gases except C 0 2 eluted rapidly and were detected in side 1 as one peak. The C 0 2 eluted 11/2 minutes later. The polarity was then switched. The H2, O ! , N2, CHI, and CO, after elution through side 1, flowed through the spacer column into the molecular sieve column where they were separated and detected in side 2 of the cell. After elution of CO, the polarity switch was returned to its original position. Usually only minor base line adjustments were necessary when the polarity was switched. The second methoi consisted of lengthening the silica gel column to 5 feet so that C02 eluted after CO. The operating conditions were similar to the first method. After all the gases except COZ were eluted from the silica gel column and detected as a composite
0
(u
0 0
A-
-
Figure 2. Chromatogram illustrating analysis of fixed gases where COzelutes after the composite peak
peak in side 1, the polarity switch was reversed to record these gases separated on the molecular sieves and detected in side 2. iifter elution of CO, the polarity switch was returned to its normal position to record COZwhich was eluted from the silica gel column and detected in side 1. Operating conditions consisted of a cell and column temperature of 30' C., a 15 cc. per minute argon flow, and a 0.1 cc. sample of the gas. The thermal conductivity detector was calibrated with a standard gas mixture of known concentration. The areas under the gas component peaks of a sample were measured and the concentration of each component was calculated by comparing its peak area with the peak area of the same component in the standard gas.
2-
0 0 N x
W
!= ln 0
a
2
z
0 8
W
N
I
RESULTS
A typical chromatogram is shown in Figure 2 for the flow design with a short silica gel column that elutes COa ahead of the remaining gases. The complete analysis is accomplished in 10 to 11 minutes. The chromatogram in Figure 3 illustrates the second flow design with a long silica gel column that elutes CO1
~~
18
12 T I M E , MIN
6
0
Figure 3. Chromatogram illustrating analysis of fixed gases where COZ elutes after the C O peak VOL. 36, NO. 3, MARCH 1964
481
after elution of the other fixed gases. The analysis time is 11 to 16 minutes, depending on the lengths of the columns. Calibration tests showed that the detector response to the fixed gases was in volume per cent. Each method, based on a sensitive, fast-response detector and the ability to interchange both sides of the cell for reference and sensing, provides a rapid, one-sample analysis of fixed gases. Blast furnace top gases; combustion
gases; fuel mixtures of blast furnace, coke oven, and natural gases; and hydrogen generator gases with hydrogen concentrations varying from 0.05 to 95.0 volume % are ideally analyzed by these methods. Other fixed gases may be determined accurately in concentrations as low as 0.05 volume %. LITERATURE CITED
(1) Bennett, C. E., Martin, A. J., Martinez, F. W., Jr., report, “Linear Programmed
Temperature Gas Chromatography,” F&M Scientific Corp., 1960. (2) Madison, John J., ANAL. CHEM.30, 1859 (1958). (3) Poli, A. A., Taylor, B. W., Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Pittsburgh, Pa. (March 2-6, 1959). RECEIVEDfor review August 16, 1963. Acce ted November 18, 1963. Pittsburg[ Conference on Analytica.1Chemistry and Applied Spectroscopy, March 1963, Pittsburgh, Pa.
Analysis of Polyester Resins by Gas Chromatography C. C. LUCE and E. F. HUMPHREY Molded Fiber Glass Research Co., Ashtabula, Ohio
L. V. GUILD* and H. H. NORRISH2 Burrell Corp., Pittsburgh, Pa.
JAMES COULL University of Pittsburgh, Pittsburgh, Pa.
W. W. CASTOR Forbes laboratory, Pittsburgh, Pa.
b A method has been developed for comparing polyesters in cured laminates by means of pyrolysis and gas chromatography. The pyrolysis furnace which can be attached to a conventional GC unit is described. The temperature used in the series was 760” C. Chromatographic data and chromatograms of several resins are given.
T
BROAD APPLICATION of gas chromatography to the analysis of volatile materials has resulted in many workers extending this method to less volatile compounds, and finally to materials which would normally not exert sufficient vapor pressure for an analysis. Where there is insufficient vapor pressure, the worker must resort to pyrolysis techniques. The earliest work of the application of pyrolysis in combination with gas chromatography was carried on by Davison, Slaney, and Wragg (1). They collected pyrolysis products of natural and synthetic rubber and subjected them to gas chromatographic analysis. The method was considerably simplified when the pyrolysis system was directly connected to a chromatographic column and continuously swept with carrier, first described by Radell and Struta (7). HE
1 Present address, University of Pittsburgh, Pittsburgh, Pa. 2 Present address, Ace Scientific Co., Linden, N. J.
482
0
ANALYTICAL CHEMISTRY
They indirectly heated a metal loop containing the sample. Two methods of pyrolysis have since been used. The sample is pyrolyzed on a metal filament heated directly by an electric current; or in a small furnace. A number of workers have used the filament method. Janak (4) pyrolyzed a nonvolatile sample on a heated platinum spiral and analyzed the pyrolysis products by gas chromatography. He carefully controlled the current and time of heating, and studied the pyrolysis products of barbiturates, protein derivatives, and other materials. Lehmann and Brauer (6) applied the filament method to the analysis of poly (methyl methacrylate). The pyrolysis furnace method was used by such workers as Hewitt and Whithan (3) and Legate and Burnham (6). More recently Ettre and Veradi (2) have used the furnace method for studying the breakdown products of poly-(n-butyl methacrylate) and nitrocellulose by both pyrolysis techniques. They compared the chromatograms by flash pyrolysis to those done a t a constant temperature. They showed the importance of holding the instrument and pyrolysis parameters constant. The present work confirms that of Ettre and Veradi, and the instrumentation is along similar lines, except the work was done with polyesters. The present study was undertaken with three objectives in mind. The first was to determine the applicability of the pyrolysis technique to the characterization of thermosetting poly-
esters. Of interest was the effect on B pyrolysis chromatogram of changing any given component in a polyester, as well as the effect of changing the ratio of the various components. This information would allow the fingerprinting of a particular polyester composition. A second objective was to study more subtle effects in an effort to relate physical properties of a given polyester to the pyrolysis chromatogram. Such physical properties are usually affected by curing temperature, inhibitor, catalyst, etc. The third objective was to evaluate various instruments and techniques which have been developed, as well as to explore new ones that might be more suited to this problem. EXPERIMENTAL
Instrument. All the present studies were made on a Burrell Model KD instrument using a flame detector. The flame detector was chosen in preference to a thermal conductivity detector for two reasons. First, a smaller sample size could be employed with the flame detector because of its higher inherent sensitivity. The smaller samples were believed to be advantageous in pyrolysis studies, giving more rapid and uniform breakdown. Second, since the flow was interrupted to introduce the sample, the time required for stabilization after sample introduction is much longer with thermal conductivity. With the flame detector, only the pressure drop across the column needs to be reestablished.
