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Determination of Sulfur and Sulfate Half-ester Content in Cellulose Nanocrystals: An Interlaboratory Comparison

Author(s)

Linda Johnston, Zygmun Jakubek, Stephanie Beck, Jun Arak, Emily Cranston, Christoph Danumah, Douglas Fox, Li Haifeng, Zoltan Mester, Audrey Moores, Savelas A. Rabb, Karen E. Murphy, Chady Stephan

Abstract

Charged functional groups on the surface of cellulose nanocrystals (CNCs) are important for controlling the colloidal stability of suspensions and the interaction of the material with its environment for most applications. Quantification of surface groups is therefore an important metric for reproducible production of this nanomaterial. Here we report the results of an interlaboratory comparison that evaluated two methods for determining the sulfur content for an NRC reference material (CNCD-1) produced from CNCs extracted by sulfuric acid hydrolysis of wood pulp. Inductively coupled plasma-optical emission spectroscopy (ICP-OES) was used to measure the total sulfur content of CNCs after microwave assisted digestion in strong acid. Conductometric titration quantified the negatively charged sulfate half ester groups on the CNC surface after dialysis and protonation using a strong acid hydrogen exchange resin to ensure full protonation. The data was analyzed using two different approaches: an ASTM/TAPPI method that uses h and k statistics to identify data sets for which the lab mean or standard deviation show excessive variation from the overall mean or standard deviation and a NIST Consensus Builder engine using the DerSimonian-Laird meta-analysis to determine a consensus estimate of the mean and its associated measurement uncertainty and evaluate unilateral and bilateral degrees of equivalence. Neither approach identified any outliers in the participating lab data sets. Both the mean of lab means and the consensus estimates were in good agreement with the values obtained for total sulfur and sulfate half ester content during certification of the reference material. The results confirmed that the difference between the sulfur content measured by conductometric titration and ICP-OES is larger than the combined 95% expanded uncertainties. The higher sulfur content measured by ICP-OES may reflect the presence of sulfur impurities that are not detected by titrat
Citation
Metrologia

Citation

Johnston, L. , Jakubek, Z. , Beck, S. , Arak, J. , Cranston, E. , Danumah, C. , Fox, D. , Haifeng, L. , Mester, Z. , Moores, A. , Rabb, S. , Murphy, K. and Stephan, C. (1970), Determination of Sulfur and Sulfate Half-ester Content in Cellulose Nanocrystals: An Interlaboratory Comparison, Metrologia (Accessed January 19, 2022)
Created September 20, 2018, Updated September 11, 2018