On the two-domain equations for gas chromatography.

Romero, Louis A.; Parks, Michael L.

doi:10.2172/978912

Cited by 1 publication

(1 citation statement)

References 13 publications

(13 reference statements)

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“…The rate at which CH 4 moves through the trap during trapping and elution can be approximated in a similar form to the two-phase model of gas chromatography. 34 CH 4 is strongly bound to the HayeSep-D (i.e., stationary phase), and the flow of bulk gases acts as a carrier gas driving advection-diffusion. During elution, the carrier gas is changed to the slow flow of pure N 2 , and the increased temperature moves the CH 4 equilibrium into the gas phase.…”

Section: Fractionation Ofmentioning

confidence: 99%

Fractionation of Methane Isotopologues during Preparation for Analysis from Ambient Air

Safi,

Arnold,

Rennick

2024

Anal. Chem.

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Preconcentration of methane (CH 4 ) from air is a critical sampling step in the measurement of singly and doubly substituted isotopologue ratios. We demonstrate the potential for isotope fractionation during preconcentration onto and elution from the common trapping material HayeSep-D and investigate its significance in laser spectroscopy measurements. By altering the trapping temperature for adsorption, the flow direction of CH 4 through the trap and the time at which CH 4 is eluted during a desorption temperature ramp, we explain the mechanisms behind fractionation affecting δ 13 C(CH 4 ) and δ 2 H(CH 4 ). The results highlight that carbon isotope fractionation is driven by advection and diffusion, while hydrogen isotope fractionation is driven by the interaction of CH 4 with the adsorbing material (tending to smaller isotopic effects at higher temperatures). We have compared the difference between the measured isotope ratio of sample gases (compressed whole air and a synthetic mixture of CH 4 at ambient amount fraction in an N 2 matrix) and their known isotopic composition. An open-system Rayleigh model is used to quantify the magnitude of isotopic fractionation affecting measured δ 13 C(CH 4 ) and δ 2 H(CH 4 ), which can be used to calculate the possible magnitude of isotopic fractionation given the recovery percentage. These results provide a quantitative understanding of isotopic fractionation during the sample preparation of CH 4 from ambient air. The results also provide valuable insights applicable to other cryogenic preconcentration systems, such as those for measurements that probe the distribution of rarer isotopologues.

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Section: Fractionation Ofmentioning

confidence: 99%