Gas Chromatography

To prepare frozen-spin HD targets for photonuclear physics at JLab, high purity HD is required. Commercially available gas is only $\sim$98\% HD. To reach the purity required to make nuclear targets, the gas is distilled at low temperature to remove the H$_2$ and D$_2$ impurities. To monitor the distillation process and correlate the gas purity with the spin relaxation times, a low temperature gas chromatograph system has been developed that produces good separation of H$_2$, HD and D$_2$. The system uses a PLOT 5A column in a mixture of LN$_2$ and i-pentane at temperatures between 110K and 135K. With this system, the relative concentrations can be determined with uncertainties of $\sim$10\%. The chromatography process and the resulting chromatograms will be discussed.