Determining pore size distribution in wet cellulose by measuring solute exclusion using a differential refractometer

Solute exclusion was used to determine the pore volume and micropore size distribution of wet cellulosic materials. Glucose, cellobiose, and polyethylene glycol (PEG) (8 to 130 A in diameter) were used as molecular probes. Four replicates of cellulosic samples, with each sample being analyzed 4 to 8 times, gave the concentrations of each molecular probe before and after contact with cellulose. Sugar concentrations were determined by the DNS method and PEG concentrations by a differential refractometer. Deviations arising from sample-to-sample variability result in variations of solute uptake from which the pore size distribution was determined. The need for replicate samples and a statistical approach to data analysis is indicated. Consequently, the data were fitted to an empirical logistic model function based on the minimum of the residual sum of squares using the finite-difference, Levenberg-Marquardt algorithm. A smooth increasing function resulted. We report experimental methodology employing a differential refractometer, common in many laboratories having a liquid chromato-graph instrument, combined with statistical treatment of the data. This method may also find application in determining pore size distribution in wet, hydrophilic polymers used in some types of membranes, chromatographic supports, and gel-type resins.