Laser desorption/ionization techniques in the characterization of combustion related carbonaceous materials

Laser desorption/ionization techniques were firstly developed in the early seventieth years [1] but only in the late eighteenth [2, 3], with the introduction of matrix-assisted laser desorption/ionization, they became an established method for the mass spectrometry of macromolecular compounds. The role of matrix is to absorb UV laser radiation and to give the energy to the analyte, often not absorbing in UV region, for ionizing it in a softer way. However, many polycondensed systems, especially with aromatic moieties and, therefore, strong UV absorption, have the “been self matrix” property for which their direct photoionization takes place by laser irradiation [4, 5]. The physicochemical nature of the desorption/ionization process is still not fully understood as several parameters have a strong influence on it, such as, for example, the laser wavelength and pulse width, the laser fluence and its profile on the sample, the properties of analyte etc.. However, a thorough understanding of desorption/ionization processes is crucial for exploiting the enormous potentiality of the technique in the analysis of high molecular weight and structurally complex samples. In the present paper, the effect of the main experimental parameters on the mass range detectable by laser desorption/ionization techniques has been investigated for standard aromatic molecules, like polycyclic aromatic hydrocarbons (PAH), polyacenaphthylene, fullerenes and for complex carbonaceous materials like heavy fractions of fuel oils and combustion-formed particulate.