Complementary Analytical Liquid Chromatography Methods for the Characterization of Aqueous Phase from Pyrolysis of Lignocellulosic Biomasses

In this work, two analytical liquid chromatography methods were developed and compared for the characterization of aqueous phases from pyrolysis of lignocellulosic biomasses. NanoLC electron ionization-mass spectrometry (EI-MS) represents a novel and useful tool for both separation and identification of semi/nonvolatile and thermolabile molecules. The use of nanoscale flow rates, the highly reproducibility, and high detailed information on EI spectra are the principal advantages of this technique. On the other hand, comprehensive 2D-LC, providing a two-dimensional separation, increases the overall peak capacity lowering the occurrence of peak coelutions. Despite the use of reversed phase modes in both dimensions, a satisfactory degree of orthogonality was achieved by the employment of a smart design of gradient elution strategies in the second dimension in combination with photodiode array detection (PDA) and atmospheric pressure chemical ionization-mass spectrometry (APCI-MS). Because of the absence of the preliminary extraction procedure, the fingerprint obtained for these samples results is independent of the extraction yield or contamination contrary to the gas chromatography-mass spectrometry (GC-MS) approach where a liquid–liquid extraction of the water phase is necessary. The main classes of identified compounds were phenols, ketones, furans, and alcohols. The synergistic information on the two powerful analytical approaches, e.g., NanoLC EI-MS and LC × LC, in the identification of such complex samples has never been investigated and fully benefit on the one hand from the superior degree of mass spectral information from EI-MS and on the other hand from enhanced LC × LC compound separation.