Analytical in source pyrolytic methylation electron impact mass spectrometry of phenolic acids in biological matrices

Abstract

Phenolic acids in complex biological matrices are easily decarboxylated under pyrolysis electron impact (EI) conditions depending on their binding to other plant cell wall compounds. Pyrolysis gas chromatography/mass spectrometry (Py‐GC/MS) of phenolic acids reveals only the decarboxylated compound but this product may also be derived from the alcoholic lignin monomers. Discrimination between the acidic and alcoholic phenol can be obtained by stabilization of the molecular ion of the two compounds. Samples of p‐coumaric acid, of sporopollenin from Pinus pollen wings, of bamboo milled wood lignin (MWL) and of tobacco leaf nerve MWL were analysed by analytical Py‐EIMS. Mass peaks for the molecular ion of p‐coumaric acid and of the decarboxylated product may be observed. Results are compared with Py‐MS data of samples treated with tetramethylammonium hydroxide (TMAH), a compound used to methylate the phenolic hydroxyl group and the carboxyl group of the phenolic acid in the ion source of the mass spectrometer. Mass spectra of samples treated with this agent show a high content of double methylated p‐coumaric acid (m/z 192). TMAH treatment allows discrimination between phenolic acids and alcohols under Py‐MS and Py‐GC/MS conditions by producing more stable molecular ions.

Studies on the cell wall of dinoflagellate resting cysts : morphological development, ultrastructure, and chemical composition

“…On the basis of Py-GC/MS analysis, therefore, pollens can be clearly distinguished from the dinoflagellate resting cyst material. The aromatic character of the Juniper and Oak pollen residues is consistent with the results of several recent investigations of sporopollenin of Pinus mugo (a gymnosperm) and Corylus avellana (an angiosperm) (Schulze Osthoff and Wiermann, 1987;Herminghaus et al, 1987;and Mulder et al, 1992). Using a variety of methods (IR analysis, chemolysis, and "in-source" Py-MS), these studies each report that phenolic compounds (e.g.…”

“…To allow comparison of our results to these studies, we adopted the above treatments, basing details on the scheme provided by Tegelaar (1990). It should be noted, however, that an alternative isolation strategy, the use of enzymes to remove unwanted cellular materials, has been applied by some pollen investigators (Schulze Osthoff and Wiermann, 1987;Mulder et al, 1992) and shows great potential for obtaining pure cell wall fractions while avoiding aggressive acid/base treatments altogether.…”

“…In two investigations and Mulder et al, 1992), some attention was focused on the identification and potential structural role of p-coumaric acid as elucidated by "in-source" Py-MS techniques. In Py-MS (16 eV) spectra of Pinus pollen wing material, this compound showed a molecular ion at m/z 164 and a major fragment ion (M + -C02) at m/z 120.…”

“…examined the chemical structure of sporopollenin from diverse sources using high resolution solid state 13C NMR spectroscopy and concluded that precursors to sporopollenin biosynthesis consisted largely of saturated compounds such as fatty acids. Finally, several investigators Mulder et al, 1992) found that degradation of pollen sporopollenins by various means tended to yield significant amounts of phenolic compounds, products which are inconsistent with a parent structure composed entirely of carotenoid precursors.…”

Getting to the root of the problem: litter decomposition and peat formation in lowland Neotropical peatlands

“…Additionally, it is important to consider that TMAH-Py-GC/MS produces the methyl esters of carboxylic acids and methyl ether of alcohols (Challinor 1989). Thus, this method allows to identify the fatty acids and lignin monomers as their corresponding fatty acid methyl esters (FAME) and methylated lignin unit derivatives respectively (Mulder et al 1992). Considering this, each TMAH-Py-GC/MS product was assigned a chemical class based on their molecular similarity to their probable molecular origin (ESM_2) (Schellekens 2013).…”