Matrix/sample interactions in ultraviolet laser‐desorption of proteins

Examination, by optical microscopy, of the matrix/analyte morphology of a sample propared from a droplet in matrix‐assisted UV laser‐desorption mass spectrometry (MUVLDMS) reveals that the matrix crystallizes to a large extent, thus altering the concentration of the material in regions on the surface from that of the bulk applied solution. Microscopy reveals that vanillic acid and to a lesser extent nicotinic acid matrices form prominent crystalline rings around the dried sample spot while sinapic acid forms a more uniform dispersion of the crystallized matrix. Insulin analyte investigated in this report tendss to form a thin isotropic phase in the center of the drops. The first reported use of a KrF excimer laser (249 nm) in MUVLDMS is also discussed.