International Journal of Mass Spectrometry 295 (2010) 98–102 Contents lists available at ScienceDirect International Journal of Mass Spectrometry journal homepage: www.elsevier.com/locate/ijms Short communication Advantages and limitations of laser desorption/ionization mass spectrometric techniques in the chemical characterization of complex carbonaceous materials B. Apicella a,* , M. Alfè a , A. Amoresano b , E. Galano b , A. Ciajolo a a Istituto di Ricerche sulla Combustione – C.N.R., Napoli, Italy b Dipartimento di Chimica Organica – Università Federico II, Napoli, Italy article info Article history: Received 14 April 2010 Received in revised form 21 June 2010 Accepted 21 June 2010 Available online 26 June 2010 Keywords: Mass spectrometry Time of flight Combustion Carbonaceous samples abstract Laser desorption/ionization techniques coupled with mass spectrometry analyzers have evolved rapidly in the recent years and are currently capable of providing valuable information about the chemical com- position and structure of very high molecular weight species, mainly biopolymers or synthetic polymers. In view of this rapidly increasing interest a thorough understanding of the desorption/ionization pro- cess is not only of scientific interest, but also important for a correct spectra interpretation and for further improvements of the technique. In the present paper, the effect of main experimental parameters on mass range detectable by laser desorption/ionization techniques has been investigated for standard aromatic molecules, like polycyclic aromatic hydrocarbons (PAH), fullerenes, polyacenaphthylene (PACE) and for complex carbonaceous materials like heavy fractions of fuel oils and combustion-formed particulate. In particular, it has been shown that laser power (or more specifically, the surface power density of the laser spot, named laser fluence) as well as the surface concentration of samples are crucial parameters controlling the highest detected molecular weight range. However, neither of these parameters is easily well-controlled and therefore more work is necessary for the standardization of laser/desorption techniques in the analysis of complex samples. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Laser desorption/ionization (LDI) techniques were firstly devel- oped in the early seventies [1] but only in the late eighties [2,3], with the introduction of matrix-assisted laser desorption/ionization (MALDI), they became an established method for the mass spec- trometry 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 so-called “been self-matrix” property [4,5] that means the capability of the sample (or a part of it) to act as matrix by itself. In this case, their direct photoionization takes place by laser irradiation without the necessity of an external matrix addition. The physicochemical nature of the desorption/ionization pro- cess 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 enor- * Corresponding author. E-mail address: apicella@irc.cnr.it (B. Apicella). mous 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 param- eters on the mass range detectable by LDI techniques has been investigated for standard aromatic molecules, like polycyclic aro- matic hydrocarbons (PAH), polyacenaphthylene, fullerenes and for complex carbonaceous materials like heavy fractions of fuel oils and combustion-formed particulate. The advantages and limitations of such powerful techniques in the analysis of polydisperse and chemically heterogeneous samples have been critically examined. In particular, the spectra reported in the present study, acquired in different operative conditions, put in evidence the artifacts that can lead to a misleading interpretation of the signals obtained by LDI techniques. Therefore, a critical evaluation of the LDI data, taking into account for the parameters used, has been suggested based on the analysis of standard molecules and extended to ill-structurally defined complex mixtures. 2. Experimental 2.1. Materials Standard compounds: PAH mixture is from Supelco (EPA 610). Fullerenes C60 is from Sigma Aldrich. Polyacenaphthylene (Sigma 1387-3806/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.ijms.2010.06.022