Growing protein‐doped sinapic acid crystals for laser desorption: An alternative preparation method for difficult samples

This paper describes several protocols for growing large, protein‐doped 3,5‐dimethoxy‐4‐hydroxy‐trans‐cinnamic acid crystals. Examination of these crystals using laser desorption shows that the mass spectra obtained from the crystals can be useful for biochemical analysis. One particular crystal growing protocol allowed a non‐covalently bound heme group of horse muscle myoglobin to remain attached to the polypeptide following laser ablation and ionization. Crystals could be grown in solutions that contained involatile solvents that normally inhibit polypeptide ion production, such as glycerol. These crystals were protein doped and produced acceptable analytical mass spectra. The results suggest that some problems associated with the frequently used droplet‐drying method of sample preparation are caused by the changing concentration conditions present in drying solutions.