Understanding Dopant Effects on the Electrospray Ionization of Wood Bio-Oils by FT Mass Spectrometry

Bio-oils derived from lignocellulosic biomass represent an interesting alternative to fossil fuels with high volume capacity. Wood bio-oils are highly complex substances containing thousands of different compounds. Their molecular characterization is essential to optimize the upgrading processes needed to produce usable fuels. Ultrahigh-resolution mass spectrometry such as Fourier Transform Ion Cyclotron Resonance (FTICR) mass spectrometry is proving to be a highly effective technique for separating isobars and assigning thousands of molecular formulas to such complex mixtures. However, it is necessary to use appropriate ionization conditions (source type and dopant) to ionize the wide range of compound classes present in bio-oils. The effects of three dopants (formic acid, sodium acetate, and ammonium hydroxide) were evaluated with an Electrospray Ionization (ESI) source operating in positive and negative ion modes. 31 reference compounds covering a wide range of chemical families were used to rationalize the dopant effects. Some dopants promoted protonation, while others promoted sodium and polysodiated adducts, giving some structural insights. Finally, a pine bio-oil was analyzed using 18-T FTICR with quadrupolar detection (2ω) in different ionization conditions (dopant type, concentration). Strengths and weaknesses of each dopant in each polarity are discussed when used with such complex matrices.