Characterization of model compounds of processed lignin and the lignome by using atmospheric pressure ionization tandem mass spectrometry

In the search for alternatives to fossil fuel and the valuable chemicals now derived from crude oil, lignocellulosic biomass has attracted wide interest. Degradation of the cellulose and lignin components of the biomass results in complex mixtures. Hence, the ability to identify the products of processed cellulose and lignin is important. Unfortunately, mass spectrometric analysis of processed lignin (and the lignome in general) is hindered by poor ion generation and/or extensive fragmentation upon ionization. After examination of several different ionization approaches, we demonstrate here that ionization of model compounds of lignin degradation products and lignome by using positive ion mode electrospray ionization (ESI) doped with sodium chloride results in the formation of abundant adduct ions, [M + Na] ⁺, with no accompanying fragmentation. Hence, this approach allows for the determination of the molecular weights of lignin degradation products (and lignome) directly in mixtures. However, no structural information can be obtained by examining collision-activated dissociation of the sodiated molecules. Hence, a different ionization method was identified. Doping negative ion mode ESI with hydroxide ions (from NaOH) yields only one type of an ion per analyte, the deprotonated analyte, without fragmentation. Valuable structural information can be obtained for these anions by subjecting them to multiple consecutive ion isolation and collision-activated dissociation (CAD) steps (up to MS ⁷). This methodology significantly improves the information that can be obtained by mass spectrometric analysis for lignin degradation products and lignome.