Differentiation of walnut wood species and steam treatment using ATR-FTIR and partial least squares discriminant analysis (PLS-DA).

Wood is a ubiquitous material used in everyday life. Accurate identification of species can be of importance in a historical context enabling appropriate conservation treatment and adequate choice of material to be applied to historic wooden objects, and in a more modern context, in the identification of forgeries. Wood is also often treated to improve certain physical characteristics, often strength and durability. However, determination of whether or not a piece of wood has been treated can be very difficult. Infrared spectroscopy has previously been applied to differentiate between different wood species or between treated and untreated wood, often in conjunction with chemometric analysis techniques. Here, we report the use of mid-IR spectroscopy, coupled with partial least squares discriminant analysis for the discrimination between two walnut wood species and to differentiate between steam-treated and untreated samples of each of these wood species. We show that the discrimination between species and between steam-treated and non-steam-treated wood from Juglans nigra is very clear and, while analysis of the quality of the discrimination between steam-treated and non-steam-treated J. regia samples is not as good, it is, nevertheless, sufficient for discrimination between the two groups with a statistical significance of P < 0.0001.