Figure 2.
Gas chromatograms of known aromatic mixture
Biphenyl 5. Trlphenylene o-Terphenyl 6. m-Quaterphenyl 3. rn-Terphenyl 7. p-Quaterphenyl 4. p-Terphenyl 8. rn-Quinquephenyl Chromatogram at 303' C. Chromatogram from temperature programming (160" to 3 3 7 " C.)
1. 2.
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the introduction system became brittle and necessitated frequent replacement. The introduction system, the column, and the inlet to the detection system were therefore modified to eliminate these undesirable features and to provide a more extensive range of operation. Figure 1 is a schematic drawing of those parts of tho instrument in which a new stainless steel introduction system with water cooling incorporated waa in-
stalled to prolong the useful life of the septum and ball and socket joints were substituted for the rubber seals. The inclusion of Swagelok fittings (Crawford Fitting Co., Cleveland, Ohio) in the new introduction system haa permitted the use of metal columns, which heretofore waa impossible. After the completion of these modifications, the performance of ,the instrument was checked during an evalua-
tion wtudy of several silicone comlmiindq as possible high temperature stationnry phases for the separation of polyphenyls. A gas chromatographic 0.d. by &foot column packed with 5% by weight dimethyl silicone polymcr (General Elcctric SE-30 silicone gum rubber) impregnated on SO-to 100-mesh Chromosorb W was found to be a suitable liquid stationary phase for the separation of aromatic hydrocarbons a t column temperatures as high as 375" C. Recently, Vanden Heuvel et al. [J,Am. C h m . Soc. 82, 3481 (1960)l also reported excellent chromatographic separations of steroids at column temperatures as high as 260" C. using the SE-30 polymeric compound. At temperatures exceeding 375" C.,bleeding of the silicone occurred. Although a methylphenyl silicone polymer proved satisfactory at lower operating temperatures, this material was thermally unstable between 300" and 350" C. During the evaluation of thrse stationary phases, the advantages derived by temperature programming were evident, as noted in Figure 2 by the superimposed chromatograms of n complex aromatic mixture. WORKmpported in part by tbe United Stake Atomic Energy Commission under Contract No. AT(It-1)-705.
Device for Increasing Efficiency for large-Volume Gas Samples in Chromatography Fred Sicilio, James A. Knight, and
E. 1. Alexander,'
QAB chromatography, aa the size of a sample is increased, the resulting peak will broaden and eventually become flat-topped. Figure 1 compares the penks obtained from two identical samples from two columns that were operakd under similar conditions and that, wcre identical with one exception.
Radioisotopes Laboratory, Georgia Institute of Technology, Atlanta, Ga.
columns with a hypodermic syringe, through rubber septums, as ra idly m possible to simulate slug-type ckarging.
100-
IN
0 75 W VI
z
0
a
v, E W
One column consisted of 12 feet of copper tubing, of 1/4-inch uniform outside diameter, packed with 30/60 mesh acid -washed Chromosorb coated with trh-cresyl phosphate (20% by weight). The second column was identical to the first, except that a 4*/&nch length of */*-inch outside diameter copper tubing with the same packing, was connected to the forefront of the column. Retention times appear to be shortened by use of expandcd-section columns. This is not indicated in the figure. Helium at an exit flow rate of 30 ml. per minute was uscd as a carrier gas in thcse studies. The temperature of the columns and the thermal conductivit detector was maintained a t 40" All samplcs were injected into the
6
Present address, Industrial Reactor Laboratoriea, Plainaboro, N. J.
1136
ANALYTICAL CHEMISTRY
,050-
2
5 W
K
~
Z.0 -LITION TIME (MINUTES)
Figure 1. Elution curves for equalvolume samples on normal and expanded-section columns
- - -40 ml. ethane on expanded-section column __ 40 mi. ethane on normal uniform-diameter column
The effect of the expanded section iS dramatic. As yet, very little work has been performed on studying the effects of varying diameters on the efficiency of a column. The expanded section used in this work evidently acts as a sample collector, effcctively compressing the sample into a shorter plug. The increased efficiency, or enhanced peaking, is also evident when the expanded section is placed next to the detector as is the case when it is placed a t the sample-injection end. The compression of the peak width is probably due to increased lateral diffusion in the enlarged section. This type of device should be very useful for handling samples of large volume containing only small quantities of material to be analyzed and for work with preparative columns for which large-volume samples are employed. Thc device described in this paper has hem used in this laboratory to enhance the peaking of srtmples with long retention times.
