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In this study, a fast and efficient method for the separation and analysis of the products in the acid-catalyzed depolymerization of commercially available sodium lignosulfonate has been developed. The depolymerized lignosulfonate products were well separated and characterized by advanced polymer chromatography (APC) employing four ACQUITY APC XT columns in series and a ultraviolet detector. The developed method enabled the detection of relative-low-molecular-mass lignin degradation products with peak molecular weights ( M p ) of 720, 490, and 260 Da, and an extremely low polydispersity index (PDI) of 1, indicating almost complete conversion of lignosulfonate to smaller molecules. The effects of reaction temperature, time, and catalyst/lignin ratio on the reaction products were systematically investigated. High yields of depolymerization (>80%) could be obtained under the mild acid-catalyzed conditions at 130℃ for 60 min using a catalyst/lignin ratio of 2.334:1. Preliminary studies also indicated that the mild acid-catalytic mechanism is unaffected by the reaction time, temperature, or catalyst concentration, thus suggesting the specificity of the catalytic procedure employed.

The effects of testing conditions, such as pH and ionic strength of the mobile phase, on the relative molecular mass obtained by advanced polymer chromatography (APC) were investigated systematically. The non-size exclusion effects were discussed for lignosulfonate and its ultrafiltration fractionation product. The relative molecular mass distribution of lignosulfo-nate was well-characterized by an APC system using three columns in series, with a 10 μ L injection volume and 0.1 mol/L NaNO 3 as the aqueous mobile phase, at a flow rate of 0.5 mL/min. The relative molecular mass distribution is in the eight molecular mass ranges. Optimized test conditions were used to characterize the ultrafiltration fractionation product of lignosulfonate. The obtained number average relative molecular masses ( M n ) of the three components were 40410, 12208, and 1516 Da, indicating that lignosulfonate was well separated into three fractions by ultrafiltration membrane separation. The APC technique presented herein provides the basis for further application of the fractional separation products of lignosulfonate.

Advanced polymer chromatography (APC) is a newly developed high resolution polymer characterization technique. Within 10 min, it can separate polymers with high resolution and obtain the average relative molecular mass distribution parameters of the polymers. The Mr distribution of the depolymerized lignin product was well characterized with low relative standard deviation (RSD less than 1%) by APC system using ACQUITY AQ 450 Å, 200 Å, and 45 Å columns in series, with 10 µL injection volume, and weak alkaline phosphate buffer solution as the aqueous mobile phase at a flow rate of 0.5 mL/min. Compared with traditional gel permeation chromatography (GPC), the APC system had the advantages of high sensitivity and good reproducibility. The technique to determine the average relative molecular mass distribution of depolymerized lignin oligomers in aqueous phase described in this paper will pave the way for new methods to separate and analyze high performance natural materials, and the feasible method for the investigation of the mechanism of depolymerization and the regulation for liquefied lignin would also be established.