The effect of solvent on matrix-assisted laser desorption ionization mass spectrometry

Abstract

Since its introduction in 1988, matrix-assisted laser desorption/ionization mass spectrometry (MALDI) has developed into a useful analytical tool in the biological field. The work presented here focuses on the effect of solvent on MALDI ion yields. We found that factors other than the crystallization of the analyte and matrix affect the ion yields. It was previously thought that solvents with physical characteristics such as low surface tension, low viscosity, high density, and high vapor pressure would lead to smaller crystal formation, resulting in higher MALDI ion yields. Our results do not support this. Instead, we propose that the interactions of the matrix and analyte in solution stabilized or destabilized by the solvent are carried through the crystallization process of MALDI. To further explore the solvent induced interactions between the matrix and analyte, studies using the addition of water to an aprotic solvent are presented. It appears the addition of water to acetone increases the abundance of protonated analyte ions and decreases the amount of cation adducts found in the mass spectrum. Thus, water stabilizes the interaction between the matrix and analyte in solution. In addition, a study using hydrogen/deuterium exchange using MALDI is demonstrated and discussed. It was found that as the solvent polarity decreased the amount of exchange was increased in the case of bovine insulin. Yet, the amount of hydrogen/deuterium exchange for bradykinin was decreased as the solvent polarity was decreased.