Yan, Qiulin, Zhao, Yu, Ma, Ran, Wang, Bo, Zhu, Zhenyu, Li, Ting, He, Ding, Hocart, Charles H., and Zhou, Youping (2023) Capping the hydroxyl groups (-OH) of α-cellulose to reduce Hy-groscopicity for accurate 18O/16O measurement by EA/Py/IRMS. Talanta, 262. 124698.

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Abstract

Obtaining an accurate measurement of 18O/16O at natural abundance level for land plants-derived α-cellulose with the currently popular EA/Py/IRMS (elemental analysis/pyrolysis/isotope ratio mass spectrometry) method is a challenge due to the hygroscopic nature of the exposed hydroxyl groups, as the 18O/16O of adsorbed moisture is usually different from that of the α-cellulose and the relative amount of adsorbed moisture is sample- and relative humidity-dependent. To minimize the hygroscopicity-related measurement error, we capped the hydroxyl groups of α-cellulose by benzylation to various degrees and found that the 18O/16O ratio of α-cellulose increased with the degree of benzyl substitution (DS), consistent with the theoretical prediction that a reduced presence of exposed hydroxyl groups should lead to a more accurate (and therefore more reliable) α-cellulose 18O/16O measurement. We propose the establishment of a moisture adsorption-degree of substitution or percentage of oxygen-18O/16O ratio equation, based on the measurement of C%, O% and δ18O of variably capped α-cellulose, so that a robust correction can be made in a plant species- and laboratory conditions-specific manner. Failure to do so will lead to an average underestimate of α-cellulose δ18O by 3.5 mUr under “average” laboratory conditions.

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