Quantification of mobilized copper(II) levels in micronized copper-treated wood by electron paramagnetic resonance (EPR) spectroscopy

Sapwood sawdust from southern pine was treated with micronized copper (MC) under various conditions and the mobilized copper(II) (Cumob) concentrations were determined in the treated wood by electron paramagnetic resonance (EPR) spectroscopy. The spectral parameters for the copper sulfate (CuSO4)-treated sapwood and those of the MC-treated sapwood were very similar. A linear correlation was found between the intensities of copper (Cu) EPR spectra and those of Cu energy-dispersive X-ray fluorescence spectroscopy in a series of CuSO4-treated sapwood reference samples. Thus, the EPR signal intensities could be reliably correlated to the mass of reacted Cu present using this calibration curve. The amount of the Cumob in sawdust treated by MC suspensions increased during the first 2–3 days after the initial treatment and then reached a maximum during the 7-day monitoring period. In the case of the treatment with MC alone or MC azole, an increased MC concentration led to an elevated amount of Cu (to a maximum of ∼0.23% Cu) solubilized by the sapwood. If the wood was treated with MC quat, the Cumob initially increased, but at higher concentrations the Cumob content decreased, due to the interference by the quat cobiocide on the acid reaction between the wood and the basic Cu carbonate. An examination of commercially-treated wood confirmed the laboratory observations.