Gas chromatography flow rates for determining deuterium/hydrogen ratios of natural gas by gas chromatography/high‐temperature conversion/isotope ratio mass spectrometry

Abstract

The effects of the gas chromatography flow rate on the determination of the deuterium/hydrogen (D/H) ratios of natural gas utilising gas chromatography/high-temperature conversion/isotope ratio mass spectrometry (GC/TC/IRMS) have been evaluated. In general, the measured deltaD values of methane, ethane and propane decrease with increase in column flow rate. When the column flow rate is 1 mL/min or higher, which is commonly used for the determination of D/H ratios of natural gas, the organic H in gas compounds may not be completely converted into hydrogen gas. Based on the results of experiments conducted on a GC column with an i.d. of 0.32 mm, a GC flow rate of 0.6 mL/min is proposed for determining the D/H ratios of natural gas by GC/TC/IRMS. Although this value may be dependent on the instrument conditions used in this work, we believe that correct deltaD values of organic compounds with a few carbon atoms are obtained only when relatively low GC flow rates are used for D/H analysis by GC/TC/IRMS. Moreover, as the presence of trace water could significantly affect the determination of D/H ratios, a newly designed inlet liner was used to remove trace water contained in some gas samples.

New on‐line methods for determining the deuterium/hydrogen composition of water and hydrocarbon gases using O2– ion‐conducting solid electrolyte reactor

“…Gas chromatography/thermal conversion isotope ratio mass spectrometry (GC/TC-IRMS) is more suitable for determining the D/H composition of natural gas than off-line methods. [1][2][3] The pyrolysis reactor converts H-bearing organic compounds into hydrogen gas for IRMS measurements in a flow of helium carrier gas. Quantitative pyrolysis by GC/TC-IRMS requires a ceramic tube (Al 2 O 3 ) inserted into the TC heater and set to a temperature of 1430 C. The high-temperature furnace is made of silicon carbide (SiC) heating elements.…”

“…The inner surface of the small ceramic tube (320 mm  0.5 mm i.d.) must be conditioned with methane at the working temperature of 1430 C. [3] Gucciardi et al [4] described a modified gas chromatograph that contained a deactivated column connecting the split injector to a high-temperature conversion reactor. The gas chromatograph was interfaced to an IRMS instrument for the analysis of D/H in water and urine samples with reproducibility varying from 0.9 to 5% and accuracy from 1 to 2.6%.…”