4.2. Protein layer formation and localization on PE-UHMW
PE-UHMW has a very hydrophobic surface and sample preparation for MALDI profiling and MSI experiments are critical because of polymer hydrolysis.The balance between quickly evaporating solvents, neutral pH, good analyte incorporation into the matrix and sufficient protein desorption/ionization for MS analysisis important to be kept. Especially large proteins at very low concentrations are difficult to be finally detected. The chosen compromise for MALDI matrix concentration, solvent type and application method produced rather thick matrix layers, but ensured efficient extraction and analyte incorporation.The time span of matrix application was observed to be the most critical point during the application process. Enough time for matrix crystallization between droplet depositions of each matrix layer is mandatory to ensure fine matrix crystallization also on folded or rough surface regions