The effect of processing medium on the ²H/¹H of carbon‐bound hydrogen in α‐cellulose extracted from higher plants

Abstract

Rationale: Although the 2 H/ 1 H ratio of the carbon-bound hydrogens (C-Hs) in α-cellulose extracted from higher plants has long been used successfully for climate, environmental and metabolic studies, the assumption that bleaching with acidified NaClO 2 to remove lignin before pure α-cellulose can be obtained does not alter the 2 H/ 1 H ratio of α-cellulose C-Hs has nonetheless not been tested.Methods: For reliable application of the 2 H/ 1 H ratio of α-cellulose C-H, we processed plant materials representing different phytochemistries and photosynthetic carbon assimilation modes in isotopically contrasting bleaching media (with an isotopic difference of 273 mUr). All the isotope ratios were measured by elemental analyzer/isotope ratio mass spectrometry (EA/IRMS). Results:Our results show that H from the bleaching medium does appear in the final pure α-cellulose product, although the isotopic alteration to the C-H in α-cellulose due to the incorporation of processing H from the medium is small if isotopically "natural" water is used to prepare the processing medium.However, under prolonged bleaching such an isotope effect can be significant, implying that standardizing the bleaching process is necessary for reliable 2 H/ 1 H measurement. Conclusions:The currently adopted method for removing lignin for α-cellulose extraction from higher plant materials with acidified NaClO 2 bleaching is considered acceptable in terms of preserving the isotopic fidelity if isotopically "natural" water is used to prepare the bleaching solution. | INTRODUCTIONThe natural abundance 2 H/ 1 H ratio of the carbon-bound hydrogens (C-Hs) of α-cellulose in higher plants has been shown to provide a useful record of the growth environment, 1 climate, 2-8 and plant metabolic status. 9,10 Accurate and precise isotope measurement, a must for reliable interpretation of the signal recorded in the isotopic compositions of α-cellulose, can be obtained only if (1) the α-cellulose is of an acceptable purity, (2) the original isotopic signature is retained during sample processing to α-cellulose, and (3) isotopic analysis is conducted with robust instrumentation techniques. A chemically pure α-cellulose product does not necessarily guarantee isotopic fidelity.To extract α-cellulose, solvent mixtures of various polarities are used to, first, remove the non-structural components of the cell wall preparation. It is not expected that this process will affect the H isotopic composition of α-cellulose as the solvent mixture works by pure dissolution and involves no chemical bond formation or fission on the α-cellulose. Likewise, the strong and concentrated alkaline Zhenyu Zhu, Xijie Yin, and Fengyan Lu contributed equally to this work.

Leaf transition from heterotrophy to autotrophy is recorded in the intraleaf C, H and O isotope patterns of leaf organic matter

“…Corrections were made for the absorbed water due to the hygroscopic &bond;OH groups of α‐cellulose according to Zhou et al 24 and Ma et al 6 The isotopic composition of carbon‐bound H (δ 2 H C‐H value) in the α‐cellulose was calculated using the following equation: where δ 2 H total is the isotopic compositions of all the hydrogen atoms in α‐cellulose pre‐equilibrated with air moisture of known isotopic composition (δ 2 H moisture ). A value of 0.28 rather than 0.3 (3 hydrogen atoms in the OH groups out of a total of 10 hydrogen atoms in the glucose unit of α‐cellulose) was assigned to p as not all hydrogen atoms in OH groups are exchangeable 25 . A value of 1.22 was assigned to α (fractionation factor between moisture and the hydrogen atoms in the exchangeable positions at a given equilibrium temperature) according to Feng et al 26 …”