Analysis of Polyphenyls by Gas-Solid Chromatography on Inorganic Salt Columns PAUL W. SOLOMON Phillips Petroleum Co., Bartlesville, Okla. b Gas-solid chromatography in the temperature range of 200" to 500' C. has been investigated for the analysis of polyphenyls. Column packings of LiCI-, CsCI-, and CaC12-irnpregnated Chromosorb P were suitable for this analysis. Good qualitative separations of isomeric quaterphenyls and hexaphenyls were obtained. Peak shifts occurred on changing inorganic salt coatings. Quantitative applicability was demonstrated for LiCl columns.
I
THE COURSE OF RESEARCH on organic-moderator coolants for atomic reactors, analysis of the radiolysis products from biphenyl and the three individual terphenyl isomers was required. The initial radiolytic products are mainly dimers: quaterphenyls and hexaphenyls from biphenyl and terphenyl, respectively (3). The great number of possible isomeric products required the use of gas chromatographic analysis. The high boiling points (>400° C.) of the products precluded the use of organic packings for columns. Hanneman, Spencer, and Johnson (2) and West (7) have developed columns using inorganic nitrate eutectics as support coatings. These columns gave unstable baselines when used under temperature programmed conditions from 200" t o 500" C. in this laboratory. Consequently, other inorganic salts were investigated. Several alkali and alkaline earth chlorides were found t o be excellent coatings for the above high temperature range. Initial developmental work on LiCl columns and an extensive discussion of salt columns for the analysis and identification of unknown hexaphenyls have been published elsewhere (4, 6). The present paper is an abstract of the data presented in these reports. Variables associated with salt columns are discussed. Applicability to both qualitative and quantitative analytical problems associated with polyphenyl mixtures is shown. A limited amount of data is included on the analysis of nonpolyphenyl compounds.
N
EXPERIMENTAL
Reagents. Most polyphenyls used in this work were synthesized in this laboratory. Synthesis, physical prop476
ANALYTICAL CHEMISTRY
erties, and infrared spectra of all the compounds have been published (I, 6). Apparatus. An F & M Model 500 programmed temperature gas chromatograph equipped with a thermal conductivity detector was used. Chromatograph settings were as follows: detector temperature, 365-370' C.; injection port temperature, 400' C.; detector power, 150 ma.; temperature program rate, 11' C. per minute; carrier gas, helium a t a tank pressure of 80 p.s.i.g.; column material, 321 stainless steel. Column packings were prepared by slurrying the support, nonacid-washed Johns-Manville Chromosorb P unless otherwise specified, with an aqueous solution of the desired salt and oven drying the mixture a t 150" to 200' C. with occasional stirring. If lumpy, the packing was gently ground and sieved to the desired size The packings were given a final firing in a muffle furnace a t 550" to 700" C., the exact temperature depending on the salt. All samples were injected into the chromatograph as benzene solutions or suspensions. RESULTS AND DISCUSSION
LiCl was used to study some of the variables such as column size, support type, support mesh size, and carrier gas flow rate which would establish conditions for further work. Support Type. Five-foot, 0.25-inch diameter columns were packed with 20% LiC1-coated 60-80 mesh nonacidwashed Chromosorb P, 60-150 mesh alumina, 100-150 mesh silica gel, and 100-120 mesh 3-4, 4.4, and 13X Molecular Sieves. The packings were all fired a t 700" C. A sample containing all the possible terphenyl (three) and quaterphenyl (nine) isomers was run on each column starting a t 200' C. and using a helium flow rate of 60 cc. per minute. Silica gel proved oomparable to Chromosorb P in elution characteristics. Alumina and 3A Molecular Sieve raised elution temperatures 140' and 60" C., respectively, above those obtained with Chromosorb P. Molecular Sieves 4A and 13X apparently completely adsorbed the polyphenyls as nothing eluted up to 500" C. Nonacid-washed Chromosorb P was selected as the most suitable support for further work.
Mesh Size. Five-foot, 0.25-inch diameter columns were packed with 20% LiCl coated nonacid-washed Chromosorb P with mesh sizes 35-80, 60-80, and 100-140. Other conditions were the same as those given under Support Type. A sample containing selected terphenyls, quaterphenyls, and hexaphenyls was used to test these columns. Elution temperatures were only slightly different on the three columns. However, the coarser supports were superior in that adsorption and/or decomposition of the higher eluting hexaphenyls was less. Sixty-to-eighty mesh was selected as the support size for further work. Column Size and Carrier Gas Flow Rate. Using a sample containing all the isomeric terphenyls and quaterphenyls, 20% LiC1/60-80 mesh Chromosorb P/700" C.-fired packing was studied in 0.25-inch diameter columns 2, 5, 10, and 20 feet in length. Helium flow rate was 60 cc. per minute except for the 10-foot column in which rates of both 60 and 200 CC. per minute were studied. Programming was from 200' C. a t 11" C. per minute. Resolution was much improved going from a 2- to a &foot column but little advantage was noted for longer lengths. At a flow rate of 60 cc. per minute the following elution temperatures were obtained for m-quaterphenyl: 2-foot, 312" C.; 5-foot1 376" C.; and 20-f00t1 425" C. Using the higher flow rate in the 10-foot column gave an elution temperature comparable t o a 5-foot/60cc. per minute column and slightly better resolution. These elution temperatures may vary 5" to 10" C. depending on sample size, as larger samples elute a t somewhat lower temperatures than smaller ones. Apparently these columns function by an adsorption rather than solution mechanism and are quite easily overloaded. Component weights of 0.005 to 0.5 mg. have been used satisfactorily in quantitative analysis with the columns. Larger diameter columns were examined with a sample of the hexaphenyls obtained from the electron irradiation of m-terphenyl. Five-foot/O.5-inch diameter and 2-foot/l.O-inch diameter columns were studied for preparative scale work.
shown in Figure 1. Resolution with the 0.5-inch diameter &foot column compared favorably with a 0.25-inch diameter &foot column. The 2-foot, 1-inch diameter column gave considerably poorer resolution but still adequately accomplished some preparatory
Increased carrier gas flow rates were necessary with thess larger diameter columns to prevent excessive peak broadening and elevated elution temperatures. Typical chromatograms of an electron irradiated m-terphenyl sample are
COLUMN L E N G ' W - 5 F E E T H E L I U M F L O W R A T E - 6 0 CC ' M I N
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scale separations of hexaphenyl isomers (6). A &foot, 1-inch diameter column could not be examined owing to size limitations of the chromatograph oven. This column would be expected to give fairly satisfactory resolution of larger samples.
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Figure 1. Effect of column diameter and length on elution characteristics of hexaphenyls from electron-irradiated mterphenyl on 20y0 LiC1/60-80 mesh Chromosorb P columns VOL. 36, NO. 3, MARCH 1964
477
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Figure 2.
Elution characteristics of salt columns
Key to peaks (attenuation X 1 ): A, o+g; B, 0.44; C, m - 6 ; 1, o-,P+; J, 1,3,5-PhBz; K, m-44; L, m,p-44; M, p-44
478
ANALYTICAL CHEMISTRY
D, p-43; E, 1,2,3-PhsBz;
F, triphenylene;
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H, 1,2,4-PhsBs;
430
Quantitative Analyses of Polyphenyls. Typical analyses of known quaterphenyl and hcxaphenyl mixtures are shown in Table I. A 10foot, 0.25-inch diameter 20% LiC1/ 60-80 mesh Chromororb P/700° C. fired column was used for both analyses. Helium flow rate was 200 cc. per minute. Triplicate (quaterphenyl) and quadruplicate (hexaphenyl) samples mere run and percentages obtained bg planimetry of peak areas. Peaks obtained with this column were very sharp and tailed only slightly. Correction f x t o r s are necessary to obtain a high dezree of accuracy. Chromatography of Nonpolyphenyl Compounds. Limited work has shown t h a t compounds other than polyphenyls may bl? analyzed on LiCl columns. Thoi;e which have eluted in a satisfactory manner are fused ring aromatic hydrocarbons, aralkyl hydrocarbons, haloaromatics, aromatic ketones, quinones, aromatic amines, and nitroaromatics. Simple aliphatic hydrocarbons eluted very quickly and gave odd-shaped peaks. Simple aliphatic alcohols, ketones, aldehydes, and acids gave broad peaks and eluted above 200" C. Salt co umns, in general, gave better separaticlns of aromatic compounds. The elui ion temperature of a molecule appeared t o be a function of its polarity-Le., anthracene eluted 97 " C. below anthraquinone: bicyclohexyl eluted 79" C. below biphenyl. Other Inorganic Salt Columns. When conditions u n j e r which LiCl columns functioned satisfactorily in polyphenyl analyses were established, a number of other inorganic salt columns were examir ed for different types of separations iimong the various polyphenyl isomers. S o t only
NO. Salt(s)
Wt. yo Firing salt temp.
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282
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Table 1.
Analysis of Quaterphenyl and Hexaphenyl Mixtures Correction % % Quaterphenyl Added Found Std. dev. factor" 0,o4.13 4.05 10.13 1.020 o,m18.99 19.75 f O .94 0.962 0,P13.32 14.03 0.949 fO. 28 m.m22.51 22.99 0.979 1 0 .47 33.70 32.48 f O .57 1.038 m,P1.095 7.35 6.71 f0.06 PJPHexaphenyls 2,4-Diphenyl-2 '-( 3-xeny1)biphenyl 8.77 6.94 10.26 1.264 m,o,m,m-Hexaphenyl 15.03 13.44 f0.30 1.118 3,5,2',4'-Tetraphenylbiphenyl f0.45 13.48 13.71b 0.910 m,o,p,.m-Hexaphenyl 2,4-Diphenyl-3 '-( 3-xeny1)biphenyl f0.09 10.65 11.05 0.964 f0.09 2,4-Diphenyl-4'-( 3-xeny1)biphenyl 4.71 4.94 0.953 m-Hexaphenyl 18.94 20.06 f 0 . 10 0.944 3,5-Diphenyl-4'-(3-xenyl)biphenyl} m,p,m,m-Hexaphenyl 23. 22 24.86* f O . 68 0.934 m,p,p,m-Hexaphenyl 5.19 4.99 f0.21 1.040 (correction Factor) ( % Found) = % Added. h o t separated chromatographically on LiCl column.
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were salts varied b u t their concentration on Chromosorb P and firing temperatures used. h complete listing of all the salts examined is available (6). The most promising salts found were the following: LiCl, CsCl, CaC12. A sample containing all the terphenyl and quaterphenyl isomers plus triphenylene was used to evaluate columns containing these salts as coatings. Varying salt concentrations from 20 t o 50% and firing temperatures from 550" t o 700" C. had only slight effects on elution characteristics of LiCl and CsCl columns, CaC12 column elution characteristics were altered considerably by changing either variable. Table I1 shows typical elution data for these columns. Also included are data from one column coated with a CaCl2/CsC1 mixture which
Table II. Elution Characteristics of Salt Columnsa Elution temperature, " C. Tri1,2,3- phenyl1,2,40,p0-$4 m-93 p-$3 PhaBz ene 0 ~ m - 4Ph3Bz ~ $4 313 315 __ 328 283 287 300 307 S N 355 A355 313 320 340 329 345 N 330 326 351-A-355 375 378 P 340 S P 310 315 325 330 344 342 355 A
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was particularly useful. Programming was begun a t 200" C. Ten-foot, 0.25inch diameter columns and 200-cc.per-minute helium flow were used. Figure 2 shows typical chromatograms obtained on these columns. Sharp peaks, little tailing, and good baseline stability are characteristic of all of the columns. No single column gave a complete separation of all the components present. However, by using two columns, for example 2 and 7 (see Table 11), a complete analysis was possible. Numerous alterations in the order of peak elution on different salt columns were noted. Changing salt concentration or firing temperature with CaClz columns exerted a pronounced effect on elution characteristics of several polyphenyls. The most difficult separations to obtain with these columns
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6 CaCI2 50 700 260 303 309 S S 7 50/50 T-N-1 CaC12/CsCl 20 700 278 323 313 328 347 337 347 a Letters refer to resolution: A, almost; P, partial; S, slight; N,none. Investigated a t Eurhtom also (6).
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VOL. 36, NO. 3, MARCH 1964
479
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
480
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.
