Programmed Temperature Gas Chromatography SIR: Gas chromatogranis are usually obtnincd with the column maintained at a constant temperature. As a consequencc, early peaks are sharp and closely spaced, while late peaks are low, broad, and widely separated. Furthermore, it is possible for high boiling component's to go undetected because of w r y long retention time. This situation can be improved markedly by increasing the column temperature during the experiment. Greene and coworkers (4,5 ) and Evans and Killard (3) have systematically varied the column temperature for the separation of hydrocarbon mixtures and radioactive bromide mixtures, respectively. Berridge and If'atts (2) noted the improved separation of methyl ketones when column temperature was slowly increased. The excellent separation which result'ed in these cases indicates that the versatility of gas chromatography can be considerably extended by this technique. Other workers ( 1 , 6, 7 ) have increased column temperature a t intervals during a run, to shorten the time required for a n analysis. Some difficulties associated with the variable temperature technique have been reported (8, 9 ) . Our observations indicate that, with a linear column temperature rise and constant volume carrier gas flow at the exit, each solute is eluted a t a characteristic volume and temperature. By :-arying the column temperature oi-er wide limits, mixtures v i t h wide boiling point ranges can be separated rapidly. Perhaps the most important feature of this variable temperature technique is t h a t all solutes emerge as well defined peaks of nearly the same shape, even though their boiling points cover a "00" C. range. Initially, temperature adjustments \\-ere obtained in this work b y using stainless steel columns as heating elements. By passing large currents from step-down transformers through the column, temperature changes of 400" C. were obtained in 2 minutes. However, it x i s necessary to insulate the metal detector block from the column. Insulating materials with the necessary strength to permit frequent column change and gas-tight coupling without fracturing proved difficult to obtain. However, almost equivalent performance was obtained with stainless steel columns directly wound with insulated heating wire. This arrangement eliminated the need for couplings and bulky transformers associated 13-ith high-current, low-voltage n-ork.
The result of increasing the column temperature linearly with time is clearly seen in Figure 1, A . The chromatogram demonstrates the separation of a seven-component hydrocarbon mixture in a 4 f o o t b y 5-mm. (internal diameter) column packed with 25% DC-200 (viscosity grade 500) silicone oil on 3580 mesh Chromosorb. -4temperature range of 50" to 235" C. was programmed a t the rate of 6" C. per minute with a constant helium flow rate a t the exit of 35 cc. per minute. A chromatogram obtained with the same mixture, the same apparatus and flow rate, but at a constant column temperature of 168' C., is shown in Figure 1, B. Two of the three impurities associated with nhexane (peak 2 ) are not detected and peaks 1, 2, and 3 are incompletely separated. Similar results were obtained with a
mixture of nine normal alcohols, chromatographed on the same column. A chroniatogram covering the temperature range 48" to 245" C. a t a rate of 6" C. per minute and a constant flow rate of 42 cc. of helium per minute is shown in Figure 2, A. Figure 2 , B, is a chromatogram of the same mixture under identical conditions but a t a constant column temperature of 165" C. At this temperature, methanol and ethanol are not separated (peak 1 2) and propanol is only partially separated. By contrast, the loir er alcohols are resolred in the programmed temperature run (Figure 2, A ) . The sloping base line for peaks 1 and 2 is due to water, nhich yields a broad peak under these conditions.
+
The stainless steel detector block and the injection port were independently
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A
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TEMP.'(
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Figure 1.
G a s chromatograms of normal hydrocarbons
A.
Progrommed temperature Chromatogram of seven normal hydrocarbons: ( 1 ) pentone, (2) hexane, (3) heptane, (4) 1 -octene, (5) decane, (6) 1 -dodecene, and (71 1 -tetradecene E. Constant temperature chromatogram a t 168' C. of same hydrocarbon mixture
VOL. 30, NO. 6, JUNE 1958
1157
heating rate, or to operate the apparatus a t a constant temperature, a t any point in a chromatogram without altering the detector sensitivity. Carrier gas volume flow rate, measured at the column exit, was maintained constant by means of a Moore constant differential flow controller. The apparatus could equally 1%-ellbe used as a lonheat capacity, constant temperature unit. Rapid temperature adjustments were then achieved with the Pyr-OVane acting as a manually set thermostat. The effects of heating rate, flow rate, and pressure drop on retention volume are being investigated, in order to obtain an expression for the retention behavior of solutes. A more complete description of the apparatus and the observed interdependence of the above variables in programmed temperature columns is in preparation.
B
LITERATURE CITED
MINUTES
Figure 2.
G a s chromatograms of alcohols
A.
Programmed temperature chromatogram of nine alcohols. ( 1 ) methanol, ( 2 ) ethanol, (3) 1 -propanol, (4)1 -butanol, ( 5 ) 1 -pentanol, (6) cyclohexanol, (7) 1 -octanol, (8)1 -decanol, and ( 9 ) 1 -dodecanol E. Constant temperature chromatogram a t 165" C. of same alcohol mixture
maintained a t a temperature of 203" C. The detectors were Fenwal lOs-ohm matched, mounted thermistors; the reference thermistor %vasisolated in a helium atmosphere in the detector block. The thermistor detectors could be operated at a rated maximum ambient temperature of 250" C. (bead temperature 300' C.). Variations in column temperature did not significantly affect the detectors until the column temperature approached that of the detector block (Figures 1, A , and 2, A ) . Peak areas for individual solutes were reproducible to rt3% over a sixfold change in heating rate. The stainless steel columns were uni-
formly wrapped ivith Glasohm insulated resistance wire. Po\ver vias supplied from a Pyr-OVane temperature controller (Minneapolis-Honeyn-ell) , whose set point was linearly driven up-scale by means of a 5000 r.p.m. motor and gear reduction train (about 3 X 105 to 1). A thermocouple attached to the column provided the temperature measurement on the Pyr-0-Vane. Variable rates were achieved over the range 3" to 17' C. per minute by means of a Netron variable ratio speed changer. Varying the heating rate corresponds to varying the flow rate during a constant temperature run. It was possible to vary the
(1) Ashbury, G. K., Davies, A. I., Drinkwater, J. W.,ANAL.CHEM.29, 918 (1957). (2) Berridge, N. J., Watts, J. D., J. Sei. Food Agr. 5 , 417 (1954). (3) Evans, J. B., Willard, J. E., J. Am. Chem. SOC.78,2908 (1956). (4) Greene, S. A,, Moberg, hl. L., Wilson, E. >I., .4~'.4~.CHEM. 28, 1369 (1956). ( 5 ) Greene, S. A,, Pust, H., Ibid., 29, I055 (1957). Kamer,' J. H., van de, Gerritsma, K. W., Wansink, E. J., Biochem. J. 61, 174 (1955). Keulemans, A. I. V., Verver, C. G., "Gas Chromatography," pp. 60-1, Reinhold, New Tork, 1957. Lichtenfels, D. H., Fleck, S. A., Burom, F. H., As.&. CHEM. 27, 1510 (1955).
Patton, H. W.,LeKis, J. S., Kaye, W.I., Ibid., 27, 170 (1955). STEPHEN DALNOGARE C. EUGEXEBENNETT Polychemicals Department E. I. du Pont de Nemours & Co., Inc. Wilmington, Del. RECEIVEDfor review April 28, 1968. .-iccepted -4pril 30, 1958.
Benzene Extraction of Antimony Iodide SIR: The solubility of antimony iodide in benzene was first reported by MacIvor (4). Fauchon (1) found that antimony iodide dissolves in potassium iodide solution to give a yellow color of unknown composition, which AlcChesney ( 3 ) used to develop a method for the colorimetric determination of microgram quantities of antimony. The isolation of antimony by benzene extraction from acid iodide solution was used by V e s t and Hamilton ('7) prepara1 158
ANALYTICAL CHEMISTRY
tory to a spot test. I n another paper, West (6) reported that bismuth is the only other element extracted in significant amount. Because of this high selectivity it seemed desirable to make a quantitative study of the extraction to see how efficiently the antimony may be removed. It was hoped that the dependence of the extraction on the iodide concentration in the aqueous phase would throw some light on the inorganic
chemistry of antimony in iodide solutions. EXPERIMENTAL
Reagents. Antimony trioxide (Baker) was purified as directed by Schumann (5). A stock solution of antimony was prepared by dissolving a weighed quantity of the purified oxide in 5M sulfuric acid. Rfallinckrodt analytical reagent grade benzene was redistilled in an all-glass still. For the
