Abstract
The matrix-assisted ultraviolet laser desorption/ionization time-of-flight mass spectra (UVMALDI-TOF-MS) analysis of some synthetic polymers was studied. The results obtained by using nor-harmane, gentisic acid (GA) and other UV-MALDI matrices, in positive and negative ion modes, were compared. Nor-harmane worked as an efficient matrix for the synthetic polymers belonging to the families of polyethylenglycol (PEG), polymethylmethacrylate (PMMA), polystyrene (PS) and poly(dimethyl)siloxane (PDMS). This behaviour was quite noticeable in negative ion mode for polar-protic polymers (PEG) and in both ion modes for non-polar polymers (PS). For the latter analysis the addition of Ag + salts was not necessary for the ionization process. The formation of Ag clusters when Ag + salts are used as the cationizing agent is discussed. Because the initiation of the UV-MALDI process is a photochemical reaction (matrix + hν (337 nm) → matrix*), the acid-base character of nor-harmane in the ground and the lower electronic excited singlet state, together with other photophysical properties are briefly discussed. The excellent results obtained in the analysis of commercial synthetic polymers with norharmane allow us to propose these analyte-matrix systems for UV-MALDI-TOF-MS calibration.
Highlights
Matrix-assisted ultraviolet laser desorption/ionization time-of-flight mass spectrometry (UVMALDI-TOF MS)[1,2,3] has become a versatile and important tool for the determination of molecular masses of macromolecules such as synthetic polymers[4,5,6] and bio-polymers.[7,8,9] The principal of UV-MALDI involves ionizing macromolecules for TOF-MS analysis by diluting them in a suitable matrix of small organic molecules which absorb UV-laser photons
PEG analysis Firstly, in order to compare the potential use of nor-harmane and gentisic acid (GA) as UV-MALDI matrix for synthetic commercial polymers belonging to the family of polar water-soluble polymers, several experiments were conducted
The positive ion mass spectra obtained from polyethyleneglycol 8 kDa (PEG 8000) with nor-harmane and GA as matrix are illustrated in Figures 1a and 1b respectively
Summary
Matrix-assisted ultraviolet laser desorption/ionization time-of-flight mass spectrometry (UVMALDI-TOF MS)[1,2,3] has become a versatile and important tool for the determination of molecular masses of macromolecules such as synthetic polymers[4,5,6] and bio-polymers.[7,8,9] The principal of UV-MALDI involves ionizing macromolecules for TOF-MS analysis by diluting them in a suitable matrix of small organic molecules which absorb UV-laser photons. Two parameters appear critical for effective MALDI-MS; the wavelength of the irradiating laser source and the chemical and physical properties of the matrix in which the analyte of interest is embedded. Since most of the compounds reported as useful matrices have been substituted aromatic compounds containing hydrogen donor groups, such as sinapinic acid[3] and gentisic acid,[10] some neutral and basic matrices have been reported.[2,3,4,7,8, 10,11] Pyridoindole compounds such as commercial β-carbolines (9H-pyrido[3,4b]indoles) have been reported as useful matrices for proteins,[12,13,14,15] sulfated carbohydrates[12,13,15,16,17,18] and some non-commercial synthetic polymers (polyesters, polyamides and silesquioxanes).[19,20,21,22,23,24,25] Mercaptobenzothiazoles have been reported as useful matrices for synthetic polymers.[5]
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