Analysis of Ethanol‐Soluble Extractives in Southern Pine Wood by Low‐Field Proton NMR

Abstract

Low‐field proton NMR was evaluated as a nondestructive and rapid technique for measuring ethanol‐soluble extractives in southern pine wood. Matchstick‐sized wood specimens were steeped in extractive‐containing solutions to generate extractive‐enriched samples for analysis. Decay curves obtained by the Carr‐Purcell‐Meiboom‐Gill (CPMG) pulse sequence were analyzed with Contin, a constrained regularization program used to generate continuous distributions of transverse (spin‐spin) relaxation times. Air‐dry wood samples gave maximum signal amplitudes that did not clearly reflect differences in extractives content. Oven drying removed signals for bound water that were superposed with those for the extractives. Relaxation times and the corresponding amplitudes were then positively correlated with the added extractives. Treatment of air‐dry samples with dichloromethane‐d ₂ prior to analysis increased the mobility of the extractives, thereby resulting in a shift of the corresponding signals to longer relaxation times. This provided the opportunity to quantify the added extractives in the presence of bound water.

Keywords:

• Extractives
• low‐field proton NMR
• relaxation time
• southern pine
• wood

Karen Reed is acknowledged for her skillful assistance with the preparation of the extracts and FTIR spectroscopic analyses.