FTIR spectroscopic prediction of Klason and acid soluble lignin
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351 www.metla.fi/silvafennica · ISSN 0037-5330 The Finnish Society of Forest Science · The Finnish Forest Research Institute FTIR Spectroscopic Prediction of Klason and Acid Soluble Lignin Variation in Norway Spruce Cutting Clones Sanni Raiskila, Minna Pulkkinen, Tapio Laakso, Kurt Fagerstedt, Mia Löija, Riitta Mahlberg, Leena Paajanen, Anne-Christine Ritschkoff and Pekka Saranpää Raiskila, S., Pulkkinen, M., Laakso, T., Fagerstedt, K., Löija, M., Mahlberg, R., Paajanen, L., Ritschkoff, A.-C. & Saranpää, P. 2007. FTIR spectroscopic prediction of Klason and acid soluble lignin variation in Norway spruce cutting clones. Silva Fennica 41(2): 351–371. Our purpose was to develop a FTIR spectroscopic method to be used to determine the lignin content in a large number of samples and to apply this method studying variation in sapwood and heartwood lignin content between three fast-growing cutting clones grown in three sites. Models were estimated with 18 samples and tested with 6 samples for which the Klason lignin + acid soluble lignin content had been determined. Altogether 272 candidate models were built with all-subset regressions from the principal components estimated from differ- ently treated transmission spectra of the samples; the spectra were recorded on KBr pellets of sieved and unsieved unextracted wood powder and subjected to four different preprocessings and two different wavenumber selection schemes. The final model showed an adequate fit in the estimation data (R 2 = 0.74) as well as a good prediction performance in the test data (R 2 P = 0.90). This model was based on the wavenumber range of 1850–500 cm –1 of the line- subtraction-normalised spectra recorded from sieved samples. The model was used to predict lignin content in 64 samples of the same material. One of the clones had a slightly lower sapwood lignin content than the two other clones. The fertile growing site with fast growing trees showed slightly higher sapwood lignin content compared with the other two sites. The model was also used to predict the lignin content in the earlywood of 45 individual annual rings. Variation between individual stems and between annual rings was found to be large. No correlation was found between the lignin content and density of earlywood. Keywords FTIR, lignin, Norway spruce, PCR, principal component regression Authors’ addresses Saranpää, Raiskila and Laakso, Finnish Forest Research Institute, Vantaa Research Unit, P.O. Box 18, FI-01301 Vantaa, Finland; Pulkkinen, Department of Forest Ecology, P.O. Box 27, FI-00014 University of Helsinki, Finland; Fagerstedt, Department of Biological and Environmental Sciences, Plant Biology, P.O. Box 65, FI-00014 University of Helsinki, Finland; Ritschkoff, Löija, Mahlberg and Paajanen, VTT Building and Transport, P.O. Box 1806, FI-02044 VTT, Finland E-mail pekka.saranpaa@metla.fi Received 26 July 2006 Revised 22 January 2007 Accepted 13 March 2007 Available at http://www.metla.fi/silvafennica/full/sf41/sf412351.pdf Silva Fennica 41(2) research articles
FTIR spectroscopic prediction of Klason and acid soluble lignin
