A rapid and precise method for determination of D/H ratios of plant methoxyl groups

Abstract

Stable hydrogen isotope ratio measurements of specific plant components are increasingly used in numerous fields of research, including sample origin verification and climate research. A recently suggested method with considerable potential in this context is the D/H isotope ratio (delta(2)H value) analysis of plant matter methoxyl groups. The method entails ether or ester cleavage with hydriodic acid (HI) to form the gaseous compound methyl iodide (CH(3)I) and measurement of the delta(2)H value of this gas. Here we describe a method for the rapid and precise delta(2)H analysis of plant matter methoxyl groups using gas chromatography/pyrolysis/isotope ratio mass spectrometry (GC/P/IRMS). The conditions for sample preparation were investigated for isotope discrimination effects, the GC conditions were optimized, the reproducibility of the measurement of standards was studied, and the precision of the method was defined. The reproducibility of delta(2)H values determined for a CH(3)I standard on 20 consecutive measurements was found to be 2 per thousand. The method was also tested on four methoxyl-rich plant components: vanillin, lignin, wood and pectin. The analytical precision obtained, when expressed as the average standard deviation for these compounds, was better than 1.6 per thousand. The described method is rapid, allowing preparation and analysis of a sample within 1 h, and produces accurate and reproducible isotopic measurements.

Water drives the deuterium content of the methane emitted from plants

“…Messenger et al (2009) showed that reactive oxygen species (ROS) are involved in the formation of CH 4 . Although the relevance for the global CH 4 budget is less than initially thought, the existence of CH 4 formation from plants has been confirmed by several isotope studies (Greule et al, 2008(Greule et al, , 2009Keppler et al, 2008;Bruggemann et al, 2009;Vigano et al, 2009). Vigano et al (2009) showed that the CH 4 emitted from plant matter upon irradiation with UV light is very depleted in both 13 C and D. For 13 C, that study clearly identified isotope discrimination between the plant biomass, the methoxyl groups and the CH 4 emitted.…”

“…The second reservoir, which does not form CH 4 and is fully exchanged, has a constant isotope signal. However, prior research has shown that OCH 3 groups contain only non-exchangeable hydrogen (Keppler et al, 2007;Greule et al, 2008;Vigano et al, 2009). In a recent study where we analyzed dD of OCH 3 of numerous wood samples from various regions (Rö ckmann et al, in press), the isotope variability in the OCH 3 groups was more strongly linked to the variability in the (in this case model predicted) dD of the source water.…”

“…The D/H isotope ratios of the plant methoxyl groups were analyzed according to (Greule et al, 2008(Greule et al, , 2009). In brief, methoxyl groups of plant material are cleaved off with hydroiodic acid (HI) at 130°C in closed reaction vials.…”

D/H ratios of methoxyl groups of the sedimentary organic matter of Lake Holzmaar (Eifel, Germany): A potential palaeoclimate/-hydrology proxy

“…Methoxyl groups of SHM were converted to methyl iodide (CH 3 I) by the 'HI-Method' (for detailed description see Greule et al, 2008). Briefly, HI (0.5 mL, 55-58%) was added to the sample material in crimp glass vials (1.5 mL) which were sealed with crimp caps containing polytetrafluoroethylene (PTFE) -lined butyl rubber septa.…”

“…The dD methoxyl signatures of lignin and pectin of the same plant sample are known to be similar (Greule and Keppler, 2011). dD methoxyl values can be measured by cleavage of the ether or ester moieties with hydroiodic acid (HI) to form the gaseous compound methyl iodide (CH 3 I) whose dD value is measurable by gas chromatography pyrolysis isotope ratio mass spectrometry (GC-P-IRMS) (Greule et al, 2008;Feakins et al, 2013b). For the purposes of brevity this procedure is hereafter referred to as the 'HImethod'.…”