notation cinnamic acid substitutions.
the identification of suitable matrix compounds determined extent trial , error, based on specific molecular design considerations. of low molecular weight (to allow easy vaporization), large enough (with low enough vapor pressure) not evaporate during sample preparation or while standing in mass spectrometer. acidic, therefore act proton source encourage ionization of analyte. basic matrices have been reported. have strong optical absorption in either uv or ir range, rapidly , efficiently absorb laser irradiation. efficiency commonly associated chemical structures incorporating several conjugated double bonds, seen in structure of cinnamic acid. functionalized polar groups, allowing use in aqueous solutions. typically contain chromophore.
the matrix solution mixed analyte (e.g. protein-sample). mixture of water , organic solvent allows both hydrophobic , water-soluble (hydrophilic) molecules dissolve solution. solution spotted onto maldi plate (usually metal plate designed purpose). solvents vaporize, leaving recrystallized matrix, analyte molecules embedded maldi crystals. matrix , analyte said co-crystallized. co-crystallization key issue in selecting proper matrix obtain quality mass spectrum of analyte of interest.
in analysis of biological systems, inorganic salts, part of protein extracts, interfere ionization process. salts can removed solid phase extraction or washing dried-droplet maldi spots cold water. both methods can remove other substances sample. matrix-protein mixture not homogenous because polarity difference leads separation of 2 substances during co-crystallization. spot diameter of target larger of laser, makes necessary make many laser shots @ different places of target, statistical average of substance concentration within target spot.
naphthalene , naphthalene-like compounds can used matrix ionize sample
the matrix can used tune instrument ionize sample in different ways. mentioned above, acid-base reactions utilized ionize sample, however, molecules conjugated pi systems, such naphthalene compounds, can serve electron acceptor , matrix maldi/tof. particularly useful in studying molecules possess conjugated pi systems. used application these matrices studying porphyrin compounds such chlorophyll. these matrices have been shown have better ionization patterns not result in odd fragmentation patterns or complete loss of side chains. has been suggested conjugated porphryin molecules can serve matrix , cleave eliminating need separate matrix compound.
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