Using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for the characterization of functionalized carbon nanotubes

Abstract: RATIONALE Functionalization of carbon nanotubes (CNTs) generates complex systems that require the development of suitable characterization protocols. New techniques have been explored, and existing analytical and spectroscopic methods to characterize functionalized CNTs have been adapted. Presently, chemical characterization of functionalized CNTs (f-CNTs) remains a difficult task. METHODS Matrix-assisted laser desorption/ionization (MALDI) analysis is performed on f-MWCNT samples prepared via grafting or absorption of anti-oxidant (AO) molecules on both MWCNT-COOH and MWCNT-OH. Covalently functionalized MWCNTs were subjected to thermal degradation and/or hydrolysis reaction before analysis, whereas MWCNTs with a physical adsorption of the functionalizing molecules were directly spotted in the target sample. Noteworthy, in our approach f-MWCNTs constitute at the same time analyte and MALDI matrix. RESULTS The identification of functionalizing AO molecules is ascertained after degradation or hydrolysis reactions in both MWCNT-COOH and MWCNT-OH grafted samples. Absorbed AO molecules, as well as organic impurities derived from grafting reactions, are also revealed by MALDI MS without any preliminary cleavage reaction. CONCLUSIONS A simple MALDI-TOF mass spectrometry method permits to obtain the unambiguous discrimination between grafted or adsorbed functionalized molecules onto the surface of MWCNTs.