Determination of lignin in herbaceous plants by an improved acetyl bromide procedure

Abstract A modified acetyl bromide procedure is proposed for the spectrophotometric determination of lignin in herbaceous plants. The digestion with 25 % acetyl bromide (AcBr) in acetic acid at 70°C is improved by including 4 % perchloric acid in the digesting solutions. This allows for more rapid, complete digestion and the use of coarser samples. On the basis of infrared spectra and nitrobenzene oxidation data for milled sample lignins, the value of 20.0 g −1 litre cm −1 for the specific absorption coeficient of AcBr‐treated lignins of herbaceous plant samples gave lignin values which were consistent with nitrobenzene oxidation data, but were higher than those obtained by the acid detergent lignin method and the earlier AcBr method proposed for grasses. The lower lignin values obtained in the latter methods are considered to be due to partial lignin solubilisation in the sulphuric acid digestion.