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 a purified HD gas are a key to realize a frozen-spin polarized target. However, there was an intrinsic difficulty 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 H2 and D2 molecules, respectively, and became backgrounds for the measurement of the H2 and D2 concentrations. In addition, the ortho-H2 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 a gas chromatograph and the QMS. Helium or neon gas was used as a carrier gas for the gas chromatograph which was cooled at ∼110K. The para-H2, ortho-H2, HD, and D2 are separated using the retention time of the gas chromatograph 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 ortho-H2 and D2 with good S/N ratios.