Small Molecule Matrix Free Laser Desorption Ionization Mass Spectrometry

Modified Si wafers and nanoparticles (5-50 nm) have been developed and explored to assist laser desorption ionization mass spectrometry (LDI-MS) for small molecule analysis. DIOS (desorption/ionization on silicon) plates were prepared according to published protocols. DIOS was tested and compared with the optimized silicon nanoparticles derivatized by penterfluorophenylchlorosilane (PFP). SPALDI (Si nanoparticle assisted LDI) requires less laser flux than common MALDI and DIOS thus provides significant less background and higher ionization efficiency. It has higher surface homogeneity, relative salt tolerance and high selectivity which may origin from analyte dependent pre-charging. Surface characterization has been investigated. And different analytes including drugs, peptides, pesticides and acids in both biological and environmental samples have been applied by positive or negative ionization mode. Detection limits, down to the low femtomole per microliter levels have been achieved for propafenone and verapamil. SPALDI is an easily applicable practical tool at a potential low cost.