Development of a novel atmospheric pressure chemical ionization (APCI) method using palladium chloride for identification of lignin degradation products containing 3-phenylallyl alcohol

Padmaja Narra, Purdue University

Abstract

The purpose of this thesis was to develop a mass spectrometric method that allows identification of compounds containing the 3-phenylallyl alcohol in lignin degradation product mixtures because most lignin degradation products with these structural features undergo fragmentation when they are ionized in mass spectrometers by using common methods. The specific goal was to develop a mass spectrometric evaporization/ionization method that produces only one ion type per analyte without fragmentation that can be used to derive MW information The results demonstrate that when sample solutions of lignin model compounds containing the 3-phenylallyl alcohol moiety are ionized by atmospheric pressure chemical ionization (APCI) doped with PdCl2, they produce abundant (M-H)+ ion. The specificity of the method was explored by analyzing various other model compounds which do not contain the 3-phenylallyl alcohol moiety. The model compounds that contained unsaturation in the side chain but no 3-phenylallyl alcohol moiety generated ions such as (M-H+H2O) + and (M-H+CH3OH)+ upon APCI after treating the sample with PdCl2. This may have involved initial formation of (M-H)+ ions which may have rapidly reacted with water or methanol in solution. Model compounds which did not contain unsaturation in the side chain did not generate (M-H)+ ion. Experiments performed using (E)-2-methyl-4-phenylbut-3-en-2-ol suggested that the possible site of hydride loss in the formation of (M-H)+ ions is the allylic position. Sample solutions of the model compounds containing unsaturation in the alkyl chain developed significant yellowish green color upon treatment with PdCl 2. The formation of colored solutions suggests complexation between PdCl2 and the carbon-carbon double bond. The development of color was not observed in case of sample solutions which did not contain unsaturation in the alkyl chain. Finally, the method was used to explore the presence of 3-phenylallyl alcohol moiety containing compounds in real degraded lignin samples. The mass spectra collected before and after treatment of the degraded lignin sample with PdCl2 indicated the absence of compounds with the 3-phenylallyl alcohol moiety. In order to confirm this conclusion, the degraded lignin samples were doped with known amounts of model compounds containing the 3-phenylallyl alcohol moiety and the mass spectra were measured before and after treating the sample with PdCl2. The model compounds were easily identified by using this method. This method will greatly facilitate the characterization of mixtures derived from biomass. All experiments were conducted in Thermo Scientific linear quadrupole ion trap (LQIT).

Degree

M.S.

Advisors

Kenttamaa, Purdue University.

Subject Area

Analytical chemistry

COinS