Analysis of polyaniline oligomers by laser desorption ionization and solventless MALDI

Abstract

While direct laser desorption ionization of soluble polyaniline dried onto metal sample plates results in mass spectra that are similar to previously shown electrospray ionization data of similar samples, laser desorption of unsolubilized solid polyaniline results in major fragmentation of the phenyl rings. Solventless MALDI, a recently developed technique for insoluble or slightly soluble species, involves the use of only solid analyte and matrix during sample preparation. Solventless MALDI of solid polyaniline results in mass spectra that are similar to the direct laser desorption ionization spectra of the soluble oligomers with some larger molecular weight oligomers also being detected. Based on the matrix used, different series of polyaniline with dissimilar end groups are detected. The matrix also affects the percentages of benzenoid and quinoid units in the oligomers. Thus, solventless MALDI appears to be a promising new technique for the mass spectrometric analysis of low solubility, but industrially important, polyanilines.

Self-assembly of aniline oligomers in aqueous medium

“…The peak at m/z value of 410 may originate from oligomers with end groups containing oxygen atom [32]. The differences between GPC and MALDI-TOF analysis results can be explained as the standards used in GPC detection is very different in nature of polyaniline [33], and the MALDI-TOF method has been usually shown to be less efficient when detecting PANI with much higher molecular mass [33,34]. By referring to the literature study, we propose that OANI-B may have molecular structure containing some phenazine-like units and O0Q0N-like groups [8,12,15], as schematically shown in Scheme 1.…”

Hydrocarbon polymer analysis by external MALDI fourier transform and reflectron time of flight mass spectrometry

“…These methods are particularly advantageous for characterizing insoluble polymers [11,[13][14][15][16]20]. Although this approach may be useful in MALDI-TOF to improve the S/N, the resulting spectra do not appear to have an overwhelmingly different resolution from those obtained with solvent-based sample preparation, and in some cases the solventless method produced a more complex mass spectrum [15,20]. For example, isotopically resolved spectra of hydrocarbon polymers with m/z greater than 6000 Da have not been reported by MALDI-TOF regardless of the method used, whether it is with solvent or solventless.…”

Investigations of theoretical principles for MALDI-MS derived from solvent-free sample preparation

“…Recent studies on the implementation of the solvent-free MALDI method [14,15,[17][18][19][20][21][22][23][24][25][26][27][28][29] give rise to renewed theoretical investigations of the MALDI process. In any solvent-based sample preparation, a separation of the analyte and matrix has to be prevented.…”