Influence of sample preparation method and silver salt types on MALDI-TOFMS analysis of polybutadiene

Abstract

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) analysis of nonpolar polymeric materials is affected by the sample preparation as well as the matrix and cationizing agent. This study examined the influence of silver salt types on the MALDI analysis of polybutadiene (PB). Silver trifluoroacetate (AgTFA), silver benzoate (AgBz), silver nitrate (AgNO₃), and silverp-toluenesulfonate (AgTS) were used as the silver salts to compare the MALDI mass spectra of PB. The mixture solution of PB and 2,5-dihydroxybenzoic acid (DHB), as a matrix dissolved in THF, was spotted on the sample plate and dried. A droplet of the aqueous silver salt solution was placed onto the mixture. The mass spectrum with AgBz showed the clear [M + Ag]⁺ ion distribution of PB while the mass spectrum with AgTFA did not show [M + Ag]⁺ ions but only silver cluster ions. The mass spectra with AgNO₃ and AgTS did not show a clear [M + Ag]⁺ ion distribution. The difference in the formation of [M + Ag]⁺ ions of PB depending on the silver salts was attributed to the silver cation transfer reaction between the silver salt and the matrix (DHB). The mass spectrum showed a clear [M + Ag]⁺ ion distribution of PB when the conjugate acid of the silver salt was less acidic than the matrix.