A novel methodological approach for δ¹⁸O analysis of sugars using gas chromatography-pyrolysis-isotope ratio mass spectrometry

Abstract

Although the instrumental coupling of gas chromatography-pyrolysis-isotope ratio mass spectrometry (GC-Py-IRMS) for compound-specific δ(18)O analysis has been commercially available for more than a decade, this method has been hardly applied so far. Here we present the first GC-Py-IRMS δ(18)O results for trimethylsilyl-derivatives of plant sap-relevant sugars and a polyalcohol (glucose, fructose, sucrose, raffinose and pinitol). Particularly, we focus on sucrose, which is assimilated in leaves and which is the most important transport sugar in plants and hence of utmost relevance in plant physiology and paleoclimate studies. Replication measurements of sucrose standards and concentration series indicate that the GC-Py-IRMS δ(18)O measurements are not stable over time and that they are amount (area) dependent. We, therefore, suggest running sample batch replication measurements in alternation with standard concentration series of reference material. This allows for carrying out (i) a drift correction, (ii) a calibration against reference material and (iii) an amount (area) correction. Tests with (18)O-enriched water do not provide any evidence for oxygen isotope exchange reactions affecting sucrose and raffinose. We present the first application of GC-Py-IRMS δ(18)O analysis for sucrose from needle extract (soluble carbohydrate) samples. The obtained δ(18)Osucrose/ Vienna Standard Mean Ocean Water (VSMOW) values are more positive and vary in a wider range (32.1-40.1 ‰) than the δ(18)Obulk/ VSMOW values (24.6-27.2 ‰). Furthermore, they are shown to depend on the climate parameters maximum day temperature, relative air humidity and cloud cover. These findings suggest that δ(18)Osucrose of the investigated needles very sensitively reflects the climatically controlled evaporative (18)O enrichment of leaf water and thus highlights the great potential of GC-Py-IRMS δ(18)Osucrose analysis for plant physiology and paleoclimate studies.

A novel methylation derivatization method for δ18O analysis of individual carbohydrates by gas chromatography/pyrolysis–isotope ratio mass spectrometry

“…The chromatograms of the methylated carbohydrates were clearly different from those in a recent study using a trimethylsilylation derivatization method . While the peak shapes for the methylated and silylated carbohydrates were similar in the FID trace (i.e.…”

“…Raw data obtained from Isodat were offset corrected relative to the reference values determined by TC/EA‐IRMS. If applicable, data were corrected for instrument drift and analyte amount effects using the δ 18 O values and peak areas of the interspersed standard measurements as described by Zech et al . For drift corrections, equations of logarithmic trend lines were generally used, derived from the δ 18 O values of several triplets plotted against the running number.…”

“…This method is recommended for the pentoses, arabinose and xylose, and for the deoxysugars, fucose and rhamnose, but it is not applicable to hexoses. A further study based on trimethylsilylation as the derivatization method of individual plant carbohydrates yielded good results especially for sucrose, with precision ranging from 0.5 to 1.1‰ . By contrast, this method was not satisfactory for the analysis of fructose, glucose, and pinitol.…”

Multi-isotope labelling of organic matter by diffusion of <sup>2</sup>H/<sup>18</sup>O-H<sub>2</sub>O vapour and <sup>13</sup>C-CO<sub>2</sub> into the leaves and its distribution within the plant

“…This could indicate the synthesis of different compounds in the particular tissues and thus a change in OM characteristics, but it could also be the result of exchange and fractionation processes during transport and biosynthesis. To further test these two possibilities, a better estimation of the maximum label strength by compound-specific sugar analysis would be needed, which has been further developed for δ 13 C (Rinne et al, 2012) and for δ 18 O (Zech et al, 2013) recently but does not yet exist for δ 2 H analysis.…”

Quality control of sweet medicines based on gas chromatography-mass spectrometry

“…Derivatizations including methylation and silylation are also necessary of Py-GC for improving the behavior of analytes during separation in the column, modifying the thermal degradation pathway or enhancing detectability (98). The derivative reagent including TMCS (103), BSTFA (103,104) and HMDS (105,106) are most commonly used. Recently, on-line analysis of thermally assisted hydrolysis and methylation (THM) gas chromatography commonly used tetramethylammonium hydroxide (TMAH) (107)(108)(109) as base reagents, made the analysis simpler and faster (99).…”