Sulfonated lignins elution with water

Elution of Lignin Sulfonates with Water. As can be seen from Figures 1, 2, 3, and 4, the fractionation of lignin sulfonates on elution with water through Sephadex G-50 and G-75 takes place in such a way that the logarithms of... 

Figure 6 shows that the proteins used for calibration elute in the same way as lignin sulfonates, which justifies the use of proteins as calibration standards. A comparison between Figures 4 and 6 shows that elution with an electrolyte solution fractionates lignin sulfonates in the range 3 000-80 000 dalton, but that elution with water fractionates those in the range 20 000-100 000 dalton. 

One disadvantage of using salt solution as eluent is that the lignin sulfonates tend to adsorb onto the gel matrix, resulting in a resolution inferior to that obtained by elution with water. On the other hand, elution behavior with water is adversely affected by the polyelectrolyte properties of the lignin sulfonates. Adsorption, which is caused by the phenolic hydroxyl... 

Non-sulfonated lignins such as those from alkaline pulping processes are insoluble in water but easily soluble in sodium hydroxide solutions. When dissolved in and eluted with a sodium hydroxide solution, they show polyelectrolyte properties, i.e., the molecular species interact. As revealed by Figure 9, the fractionation result is strongly dependent on the sodium hydroxide concentration up to a concentration of 0.4M. A 0.5M sodium hydroxide solution is thus an appropriate eluent for fractionation on Sephadex G-50 (3). 

Methods that attempt to directly measure the sulfonate content of lignin in pulps must overcome the challenge of distinguishing sulfonate from accompanying carboxylate groups. One such method (Sjostrom and Enstrom 1966, Sjostrom et al. 1965) is based on the concept that, under acidic conditions, benzidinium ions form salts only with the sulfonate groups. The pulp is saturated with an aqueous solution of benzidine hydrochloride and washed with water to remove excess reagent the benzidinium ions are eluted with hydrochloric acid and determined by UV spectrophotometry. 

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