MILLIGRAMS OF CESIUM PRESENT
Figure 1 . Determination of potassium metaperiodate in the presence of cesium nitrate
metaperiodate, i t n a s shown t h a t 3.11 mg. of cesium are soluble in 6 ml. of 33y0 ethyl alcohol, 0.1111in respect to excess periodic acid. nhich are the solution conditions for the potassium determination. The concentrations of cesium selected for investigation are thus above and beloJy this solubility level. The amount of cesium coprecipitated, determined as the amount of periodate found in excess of the amount of potassium metaperiodate present, but reported as milligrams of potassium, is plotted as ordinate (Figure 1).
The results are somewhat variable, as it is difficult to maintain constant the actual conditions of precipitate formation, but it is apparent that the amount of coprecipitation is a function of the concentration of cesium present. Although 3.11 mg. of cesium should be soluble under these conditions, through coprecipitation with potassium metaperiodate less than this amount remains in solution. Five milligrams of cesium, which reported as potassium are equivalent to 1.47 mg., are completely carried down Ivith potas-
sium metaperiodate eyen when as little as 5 mg. of potassium are precipitated. When 2.5 mg. of cesium are present, which normally should be completely soluble, part or all of the cesium is precipitated, depending on amount of potassium metaperiodate precipitating. The amount of coprecipitation with potassium metaperiodate is dependent upon the rate of precipitate formation as well as the amount of cesium present. As is true of coprecipitation in general, the slower the rate of precipitation t h e lesser the amount of coprecipitation. At lower concentration levels of potassium, precipitation takes place slowly and little coprecipitation oceurs. LITERATURE CITED
(1) Jentoft, R. E., Robinson, R. ANAL. CHEM.26, 1156-8 (1954). (2) Ibid., 28, 2011-15 (1956).
J.,
(3) Snyder, E. R., "A Study of the Determination of Cesium as the Metaperiodate and the Interference of Cesium in the Determination of Potassium Metaperiodate," M. S. thesis, University of Kashington, Seattle, Wash, 1956.
ELOISESNYDER REXJ. ROBINSON Chemistry Department University of Kashington Seattle 5, Wash.
High Temperature Gas Chromatography of Aromatic Hydrocarbons SIR: A gas chromatograph capable of successful operation a t temperatures up to a t least 445" C. has been evaluated in these laboratories. The instrument used for these high temperature studies was a n especially modified design based on the Loe Engineering Co. (237 North Fairoaks -4ve.. Pasadena, Calif.) Chromat-0-Flex. A high resistance filament-type four-element detector was placed in the coluiiin oven. Other important modifications include the use of 2-inch-thick Maranite insulation, two 300-13 att strip-type base load heaters controlled b y a variable autotransformer. and one 250-matt coil-type trim heater controlled by a Hallikainen Thermotrol Model 1053A n-ith platinum resistance thermometer detector. Some exploratory studie- in high temperature gas chromatography of aromatic hydrocarbons performed n ith this instrument have led to the divoi-ery of a new type of immobile phase material with good high temperature ztahility. SCREENING OF IMMOBILE PHASES
Probably the most important single
hindrance to the development of high temperature gas chromatography has been the lack of suitable immobile phase materials. Several recent papers (1-3) have reported the suitability of silicone grease and silicone gums as high temperature-immobile phases. Ogilvie, Simmons, and Hinds (6) report the use of asphaltenes for aliphatic hydrocarbon separations. Such materials should possess both good partitioning ability and high temperature stability and preferably be readily available a t reasonable cost. K i t h these factors in mind, a number of materials n-ere selected and initially tested at 300" C. These are shomm in Table I, along with their relative ratings as partitioning agents for a test mixture consisting of biphenyl, and 0-, m-, and p-terphenyl. The partitioning ability is expressed in terms of relative peak separation, S,relative peak sharpness, &, and resolution, R, as given b y Jones and Kieselbach ( 5 ) . Because the m- and p-terphenyl isomers are the most difficult to separate, the calculations were done on this pair in all cases. Of the commercially available materials,
only the asphaltenes afford complete separation of m- and p-terphenyl. Also, in all cases, additional experimental work with higher boiling aromatic hydrocarbon samples established the loss of peak symmetry due to decomposition and/or elution of these immobile phase materials. The behavior of the asphaltenes was rather unexpected on the basis of information cited by Ogilvie, Simmons, and Hinds (6). Initially the material was an excellent partitioning agent, but it deteriorated after 48 to 50 hours. Several factors are possible explanations of the apparent differences. The origin of the asphalt may influence its performance. Ogilvie et al. make no statement as to stability for prolonged periods, and we did not observe tailing prior to 48 hours a t 300" C. We used the total asphaltene fraction and this could account for the different results. [Simmons ( 7 ) disclosed that less than 20% of the pentane-insoluble fraction was used, and that column life mas several weeks at 320' C.] When tailing developed at 300" C., we reasoned that perhaps volatiles were VOL. 3 1 , NO. 3, MARCH 1959
475
Table 1.
Comparison of Immobile Phases
Partitioning Ability Relative Relative peak peak Upper separation, sharpness, Resolution, Temp., Material Sm-p Q R Limit, ' C. 0.16 10.8 1.73 350 $ F % k u m silicone grease 0.086 5.10 0.44 250 C. Polyethylene 0.15 10.1 1.52 300 D. Asphaltenes 0.27 10.4 2.81 300 E. Co olymer 0.22 8.43 1.96 325 F. Pogphenyl tar I (mol. wt. 800) 0.26 10.6 2.76 400 G. Polyphenyl tar I1 (mol. wt. 2100) 0.30 10.8 3.24 450 -4. James G. Biddle Co., 1316 Arch St., Philadelphia, Pa. B. Dow Corning Corp., Midland, Mich., used as received. C. High pressure type. D. Asphaltenes precipitated from erection asphalt (Lion Oil Co., El Dorado, Ark.) by dilution of a benzene solution with 9 volumes of n-hexane. I R spectra indicated no aromatic character. M.p. 218" to 235" C. Molecular weight 6400 (freezing point depression of benzene); 7cC, 85.80; % H, 8.25. E. Prepared by method of Goldfinger ( 4 ) from reaction of equimolar amounts of odibromo- and m-dichlorobenzene in toluene with excess of potassium metal. M.p. 260' to 300" C.; molecular weight 1130 (freezing point depression of benzene); yo C, 89.73; 70 HI 6.30. F. Prepared by molecular distillation of irradiated terphenyl mixture a t 300' C. and 10-micron pressure. Residue was brittle brown resin, m.p. 121-126' C. Molecular weight 804 (freezing point depression of benzene); 70C., 94.37; % H, 5.63. G. Prepared from product described in (F) by sublimation of volatile materials at 400' C. and 0.01-micron pressure. Residue was brittle black resin, m.p. 222' to 231" C.; molecular weight 2100 (freezing point depression of benzene); 70C, 94.79, yoHI 5.20.
$:
High Temperature Runs on Polyphenyl Tar II" Conditions* Compounds A B C 3,4'-Diphenylbi henyl 0.322 0.372 lI2,4-Triphenyl!enaene 0.090 1-( 3-Xenyl)-3-phenyl-l,3-~yclohexadiene 0.186 3,3'-Diphenylbi hen 1 0.183 0.253 1-(4Xenyl)-3-p~eny~1,3-cyclohexadiene 0.244 4,4'-Bis(2-methyl-l-cyclohexenyl)biphenyl 0.135 2,2"'-Dimethyl-p-quaterphenyl 0.179 0.240 0.278 1,3-Di(2-xeny1)benzene 1,000 1.000 1.000 1,3-Di(3-xenyl)benzene 1.05 1,2,3-Triphenylazulene 0.322 0.151 1,1,4,4Tetraphenyl-l,3-butadiene 3-(3-Xenyl)-3'-phenylbiphenyl 0.940 3,3'-Di-(3-~enyl)biphenyl 3.60 0 Relative retention times, corrected for dead volume. b Condition A. 375" C., 125 ml./min., 20% immobile phase. Condition B. 430' C., 48 ml./min., 20% immobile phase. Condition C. 445" C., 48 ml./min., 20% immobile phase. Helium carrier gas, 30-60 mesh Chromosorb, and 2-meter columns used in all cases. Actual corrected retention times for 1,3-di(Zxenyl)benaene under Conditions A, B, and C were 31.2, 14.6, and 9.7 minutes, respectively. Table II.
being eluted from the asphaltenes, hence raising the melting point. However, a n increase of column temperature to 350" C. gave no reduction in tailing but rather a n increase in this undesirable behavior. A melting point increase is thus apparently not the ansn-er, but rather decomposition must take place after a short exposure to temperatures of 300' C. Clearly a more stable material is required to attain satisfactory performance at temperatures above 350" C. Satisfactory performance includes ability to operate for several days at the elevated temperature while retaining separation power, good peak symmetry, and a low elution rate. A high elution rate complicates spectral identification of collected fractions.
476
ANALYTICAL CHEMISTRY
Having exhausted the supply of commercial materials which appeared promising, we turned to two polyphenyl tars isolated in the course of work on characterization of irradiated terphenyl mixtures. The method of isolation and properties of these tars are also summarized in Table I. Polyphenyl tar I1 is preferred because of its higher molecular weight, which gives increased temperature stability and negligible elution rate. This material is a complex system not readily identified. Its spectra showed peaks a t 3.2 (m), 3.4 (w),6.2 (m), 6.75 (m), 6.9 (w), 9.3 (w), 9.9 (w),11.2 (m), 11.9 (m), 12.1 (w), 12.6 (m), 12.9 (w), 13.3 (s), 13.5 (m), 14.3 (s) microns. Inasmuch as the polyphenyl tars are somewhat tedious to isolate and are not
a n item of commerce, we made preliminary attempts to synthesize a comparable material from readily available starting materials such as dihalobenzenes. Several polymers prepared by a Miurtz reaction (4) decomposed rapidly above 359'. The best of these is listed as E in Table I. The decomposition was probably promoted b y the stainless steel reacting with residual halogen in the copolymer. It is probable that a pure polyphenyl of molecular weight above 1000 would be a very satisfactory though costly immobile phase. H I G H TEMPERATURE RUNS
Our operational experience at temperatures above 350" C. has been limited by a lack of pure hydrocarbons. I n Table I1 are summarized retention time data for a series of hydrocarbons under three sets of conditions. These preliminary data demonstrate the possibilities for analysis of very high boiling aromatic hydrocarbons. No evidence for decomposition was noted during these runs a t elevated temperatures. ITe are continuing to evaluate the polyphenyl t a r immobile phase using a series of high molecular xeight hydrocarbons prepared in a synthesis program. A description of the instrument and a complete treatment of this exploratory work are in preparation. The finished paper will include retention time data for polyphenyls, fused ring aromatics, aromatic olefins, and arylated alkanes a t several temperatures, densities of the recommended immobile phases, and chromatograms to indicate the resolving power of the various immobile phases. LITERATURE CITED
(1) Cropper, F. R., Heywood, A., in
"Vapour Phase Chromatography," D. H. Desty, ed., p. 316, Academic Press, New York, 1957. (2) Dal Nogare, S., Safranski, L. W., ANAL.CHEM.30,894 (1958). (3) Felton, H. R., in "Gas Chromatography," V. J. Coates, H. J. Noebels, I. S.Fagerson, eds., p. 131, Academic Press, New York, 1958. (4) Goldfinger, G., J. Polymer Sn'. 4 , 93 (1949). (5) Jones, W. K., Kieselbach, R., ANAL. CHEW30,1590 (1958). ( 6 ) Ogilvie, J. L., Simmons, M. C., Hinds, G. P., Jr., Ibid., 30,25 (1958). (7) Simmons, M. C., personal communication.
Atomics International A Division of North American Aviation, Inc. P. 0. Box 309 Canoga Park, Calif.
R. A. BAXTER R. T. KEEN
RECEIVED for review September 11, 1958. Accepted January 7, 1959.
