Determination of Lignin in Wood and Pulp by the Acetyl Bromide Method

2 Determination of Lignin in Wood and Pulp by the Acetyl Bromide Method 

The reagents used for the analysis are ultra pure (EP) grade acetyl bromide (Tokyo Chemical Industries), 2M sodium hydroxide, acetic acid (BDH Analar grade or equivalent) and analytical grade 70% perchloric acid. The acetyl bromide should be stored under nitrogen when not being used (Wu and Wilson 1967). 

Using a Wiley mill, wood samples are ground and the 40-60 mesh fraction is Soxhlet-extracted with ethanol benzene (1 2, v/v). Pulp samples are used without size reduction and are solvent exchanged with acetone before drying at 60 °C at 20 mm (Note 1). 

Note 1. Pulp samples dried directly from the water-wet state require Wiley-milling to insure their dissolution in the acetyl bromide reagent. 

Note 2. Samples ranging in size from 2 to 105 mg and containing from 0.6 to 21.3 mg of lignin have been successfully examined (Johnson et al. 1961). According to these authors, sample size is not necessarily restricted to these limits and hence, in theory, the method should be applicable to materials containing even smaller amounts of lignin. In practice, however, sample size may affect the analytical result (see Discussion section below). 

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