Adsorption behavior of optical brightening agent on microfibrillated cellulose studied through inverse liquid chromatography: The need to correct for axial dispersion effect

Abstract Inverseliquid chromatography is a technique for studying solid/liquid interaction and most specifically for the determination of solute adsorption isotherm. For the first time, the adsorption behaviour of microfibrillatedcellulose was assessed using inverse liquid chromatography. We showed that microfibrillatedcellulose could adsorb 17 mg/g of tetrasulfonated optical brighteningagent in typical papermakingconditions. The adsorbed amount of hexasulfonated optical brighteningagent was lower (7 mg/g). The packing of the column with microfibrillatedcellulose caused important axial dispersion ( D a  = 5e-7 m²/s). Simulation of transport phenomenain the column showed that neglecting axial dispersion in the analysis of the chromatogram caused significant error (8%) in the determination of maximum adsorbed amount. We showed that conventional chromatogram analysis technique such as elution by characteristic point could not be used to fit our data. Using a bi-Langmuir isotherm model improved the fitting, but did not take into account axial dispersion, thus provided adsorption parameters which may have no physical significance. Using an inverse method with a single Langmuir isotherm, and fitting the transport equation to the chromatogram was shown to provide a satisfactory fitting to the chromatogram data. In general, the inverse method could be recommended to analyse inverse liquid chromatography data for column packing with significant axial dispersion ( D a > 1e-7 m²/s).