Separation of hydrogen isotopic spin isomers by gas chromatography using alumina PLOT column

Abstract Background: The cryogenic properties of hydrogen isotopes are affected by ortho-para ratio of the homonuclear molecules (H₂, D₂, T₂). Purpose: It is necessary to determine the ortho-para ratio. Methods: A cryogenic elution chromatographic method for determination of the ortho-para ratio is established, in which an activated alumina porous layer open tubular (PLOT) column with 30 m × 0.53 mm × 20 μm was applied for separation of the spin isomers. Results: The isomers were well separated at base line (the resolution R_s > 1.5) at temperature of liquid nitrogen (78 K), compared with the conventional packed columns. When the Neon carrier rate is 5 mL·min^-1, the resolution of ortho-para protium R_s (o-H₂, p-H₂) and ortho-para deuterium R_s (o-D₂, p-D₂) is 6.9, 1.8, respectively. Conclusion: The resolution is affected by sample content and flow rate. According to integration of peak areas, the ortho-para rate at 300 K for protium and deuterium is 2.77:1, 1.78:1, respectively, which is in accordance with the theoretical results. Partial separation is obtained between ortho-H₂ and HD, and the resolution R_s (o-H₂, HD) reached 0.4, theoretical plates of 3.9 × 10⁵ should be required to achieve the baseline separation (R_s = 1.5). (authors)