HD gas analysis with Gas Chromatography and Quadrupole Mass Spectrometer

A gas analyzer system has been developed to analyze Hydrogen-Deuteride (HD) gas for producing frozen-spin polarized HD targets, which are used for hadron photoproduction experiments at SPring-8. Small amounts of ortho-H2 and para-D2 gas mixtures (�0.01%) in the purified HD gas are a key to realize a frozen-spin polarized target. However, there was an intrinsic diffi culty to measure these small mixtures in the HD gas with a quadrupole mass spectrometer (QMS) because D + and [H2D] + produced from the ionization of HD molecules were misidentified as H 2 and D2 molecules, respectively, and became backgrounds for the measurement of the H2 and D2 concentrations. In addition, the ortho-H 2 and para-D2 are not distinguished from the para-H2 and ortho-D2, respectively, with the QMS. In order to obtain reliable concentrations of these gas mixtures in the HD gas, we produced a new gas analyzer system combining two independent measurements with the gas chromatography and the QMS. Helium or neon gas was used as a carrier gas for the gas chromatography which was cooled at�110 K. The para-H2, ortho-H2, HD, and D2 are separated using the retention time of the gas chromatography and the mass/charge ratio. Although the para-D2 is not separated from the ortho-D2, the total amount of the D2 is measured without the [H2D] + background. The ortho-H2 concentration is also measured separately from the D + background. It is found that the new gas analyzer system can measure small concentrations of�0.01% for the otho-H2 and D2 with good S/N ratios.