Carbohydrate Polymers 130 (2015) 77–86 Contents lists available at ScienceDirect Carbohydrate Polymers j ourna l ho me page: www.elsevier.com/locate/carbpol Characterization of sodium carboxymethyl cellulose by comprehensive two-dimensional liquid chromatography Maria Shakun a , Thomas Heinze b , Wolfgang Radke c,∗ a Fraunhofer Institute for Structural Durability and System Reliability LBF, Division Plastics, Schlossgartenstraße 6, D-64289 Darmstadt, Germany b Friedrich-Schiller-Universität Jena, Humboldtstrasse 10, D-07743 Jena, Germany c PSS Polymer Standards Service, In der Dalheimer Wiese 5, D-55120 Mainz, Germany a r t i c l e i n f o Article history: Received 27 February 2015 Received in revised form 29 March 2015 Accepted 13 April 2015 Available online 28 April 2015 Keywords: Sodium carboxymethyl cellulose Degree of substitution Size exclusion chromatography Gradient liquid adsorption chromatography Two-dimensional chromatography a b s t r a c t Two series of sodium carboxymethyl celluloses (NaCMC) with average degrees of substitution (DS) ran- ging from 0.45 to 1.55 were synthesized from low molecular mass Avicel cellulose (Avicel samples) and from high molecular mass cotton linters (BWL samples). The samples were characterized by online two- dimensional liquid chromatography using gradient liquid adsorption chromatography in the first and size exclusion chromatography (SEC) in the second dimension. This method allows the simultaneous determination of the chemical composition (DS) and the molar mass distribution within the individual samples. Moreover information was obtained on the dependence of the elution volume in gradient chro- matography on molar mass. As expected, evidence for a stronger influence of molar mass on gradient elution volume was found for the low molecular mass NaCMC as compared to the high molecular mass BWL samples. Finally the applicability of the method for the simultaneous separation of blends heteroge- neous with respect to chemical composition (DS) and molar mass was demonstrated. Such blends cannot be efficiently separated by either SEC or gradient chromatography alone, nor by simply combining the results of both methods. Only the complete two-dimensional chromatogram can reveal the complexity of such blends, since it reveals the correlations between molar mass and chemical composition. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Sodium carboxymethyl cellulose (NaCMC) is one of the most important cellulose derivates in terms of sales (approx. 230 000 t per annum (Thielking & Schmidt, 2006) up to now). NaCMCs are produced commercially by polymer-analogous reaction of alkali cellulose with monochloracetic acid or its sodium salt (slurry pro- cess) in aqueous NaOH and an organic liquid (Heinze, 2005). Due to the molar mass distribution of the parent celluloses and the sta- tistical nature inherent in the substitution reactions, the products obtained are supposed to be heterogeneous in terms of chemi- cal composition on different structural levels and in molar mass. These heterogeneities and also the correlation between molar mass and chemical composition can influence application properties of NaCMC products. Evidence on the influence of chemical hetero- geneity of NaCMC on the monomer (AGU, anhydroglucose unit) level on application properties like the solubility in water, the gel formation in salt containing solutions etc. are given in the following ∗ Corresponding author. Tel.: +49 6131 96239 37. E-mail address: WRadke@pss-polymer.com (W. Radke). articles (Heinze, 2005; Ramos, Frollini, & Heinze, 2005; Saake et al., 2000; Stigsson, Kloow, & Germgard, 2006). It is highly probably that also the heterogeneity on the polymer level/s influences the properties of the products. It should be mentioned that the term homogeneous is often used in the field of cellulose derivatives to describe a random distribu- tion pattern of the AGUs which is in agreement with the random distribution of the Spurlin model, while the term heterogeneous indicates a deviation from this model. However, a sample yielding a random substitution pattern of the AGUs is not really homoge- neous, as the different AGUs will differ in their distributions along and among the different chains. In the following, the term narrowly distributed denotes a fraction or material in which all chains have the nearly same ratio of substituents to AGUs, irrespective of the placement of the substituents within the AGUs or along the chains. Due to their impact on application properties knowledge on the above mentioned heterogeneities and their correlations is essential for establishing and understanding structure-property relation- ships. The molar mass distribution of NaCMCs can be obtained by SEC (Eremeeva & Bykova, 1998; Hoogendam, Keizer, Stuart, & Bijsterbosch, 1998; Kath, Lange, & Kulicke, 1999; Kulicke, Kull, Kull, & Thielking, 1996; Rinaudo, Danhelka, & Milas, 1993; Shakun http://dx.doi.org/10.1016/j.carbpol.2015.04.011 0144-8617/© 2015 Elsevier Ltd. All rights reserved.