Downscaled method using glass microfiber filters for the determination of Klason lignin and structural carbohydrates

The analysis results of Klason lignin and structural carbohydrates determined by downscaled analysis methods using 50 mg and 5 mg biomass and glass microfiber filters for the filtration of acid-insoluble lignin, were compared to a conventional method using 300 mg biomass and ceramic crucibles. The usage of microfiber filters reduces space requirement in oven and furnace to a minimum and speeds up the filtration of Klason lignin about three-fold. Furthermore, tedious cleaning of crucibles is unnecessary which additionally increases the number of samples that can be analyzed in a given time frame. The analysis of 5 feedstocks comprising herbaceous, hard- and softwood, revealed no significant differences of hemicellulosic sugars between the 50 mg microfiber and the 300 mg crucible method. The 50 mg microfiber method resulted in Klason lignin values in the range of −6.1% to +4.0% (relative) and glucan values in the range of −0.8% to +3.7% (relative) of the values obtained with the 300 mg crucible method. The 50 mg microfiber method was highly reproducible with relative standard deviations (RSD%) of 0.27–0.56% (average 0.38%) for Klason lignin and 0.54%–1.46% (average 1.01%) for glucan. Compared to the 50 mg microfiber method, the 5 mg microfiber method resulted in similar deviations of Klason lignin and glucan from the 300 mg method values. However, the reproducibility was slightly lower. Overall, the 50 mg and 5 mg microfiber method reflected the actual biomass composition with sufficient accuracy and are therefore recommended as alternative methods or when downscaling of the analysis is required.