Improved Separation of Isotopic Hydrogens by Gas Chromatography Michael E. Gersh,' Sterling Chemistry Laboratory, Yale University, New Haven, Conn. TOTAL COUNTS
of separating the isoT topic hydrogens Hz, H D , HT, Dz, DT, and Tz by gas chromatography has HE PROBLEM
been examined in a number of different studies. Several fairly effective methods have been developed, all based on adsorption on solid substrates such as Fe203, A1203 Cr203, -41203, A1203 molecular sieves, and silica gel (1). These methods, however, suffer from the fact that separation factors are relatively small and that there is often considerable tailing. For effective separations, long columns and correspondingly large amounts of gas and time are required. We have found that addition of a small amount of Hz to the H e carrier gas obviates the problem of tailing and improves the separation factors when used in conjunction with very highly activated columns. This appears to be due to a displacement (flushing) action of the H P . (The use of Hz in the carrier gas obviously precludes the observation of a mass peak for H2. If it is necessary to observe a mass peak for Hz, one may use Dz in the carrier gas.) The method was applied to the separation of HT and DT. The isotopic hydrogens were counted in an internal flow proportional counter (3) where it was found that the presence of Hz caused no deterioration of counting characteristics. Typical results are shown in Figure 1. It is evident that tailing i s essentially eliminated. d separation factor of 1.44 is obtained with a retention volume of HT of 1000 cc. and at a flow rate of 75 cc. per minute. This means t h a t the time of analysis is only 23 minutes. The problem of tailing is relatively common in adsorption chromatography
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Present address, Chemistry Department, University of Wisconsin, Madison, Wis.
1786
ANALYTICAL CHEMISTRY
T I M E AFTER INJECTION
Figure 1.
OF
SAMPLE (MINUTES)
Typical chromatogram
of isotopic mixtures of trace gases on highly activated columns. It is possible that the principle of adding a specific displacement agent to the carrier gas may have some general usefulness. EXPERIMENTAL
The column is 150- to 200-mesh alumina coated with Fez03 ( 2 ) , in a 4 foot x */*inch (0.d.) stainless steel coil (which follows an empty 6 foot X inch (0.d.) stainless steel capillary cooling coil). The column is activated for 12-14 hours at 475" C., during which time i t is purged with a slow flow of Nz. The column is operated at a temperature of 77" K., with a flow rate of 75 cc. per minute and a n elution gas that is 97% H e and 3% Hz. The detector volume is 30 cc., and the counting gas is 50y0 elution gas and 50% methane.
ACKNOWLEDGMENT
The assistance of James Dubrin, John Todd, and John Xcholas is gratefully acknowledged. Special thanks must be given to Richard Wolfgang both for his suggesting the problem and for his constant encouragement. LITERATURE CITED
., Chem. Rev. R., J . Phys.
F. S.,ANAL. WORKperformed in partial fulfillment of requirements for B. S. degree a t Yale University, under auspices of AEC contract SAR/AT (30-1) 1957 and National Science Foundation undergraduate fellowships.
