Comparison of sample preparation methods for NIR analysis of carbohydrate content of unbleached eucalyptus pulps.

Near-infrared (NIR) spectroscopy provides a rapid method for estimating pulp carbohydrate content. Previous studies have used a variety of sample preparation methods; however, the influence of preparation method on calibration performance has not been examined. This study compares carbohydrate content calibrations for four sample preparation methods (coarse, fine, and milled pulp, and handsheets). Fifty-nine unbleached pulps (52 single-tree, 7 mill composite) with known carbohydrate composition (arabinose, fructose, galactose, glucose, rhamnose, and xylose) were prepared using the four methods. NIR spectra were collected from the samples, which were divided into calibration (40 samples) and prediction sets (19 samples). Calibrations were created for each combination of preparation method and carbohydrate, and tested on the prediction set. Calibration statistics were good for rhamnose and xylose but weaker for other carbohydrates. Coarse and fine pulp produced the best calibrations, but they were not significantly different from calibrations for handsheets; milled pulp provided the weakest calibrations.