Cryogenic frozen solution matrixes for analysis of DNA by time-of-flight mass spectrometry

We present an alternative matrix system for mass analysis of high molecular weight biomolecules by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). Single-stranded DNA oligomers are embedded in thin films of frozen solutions containing photoabsorbing substituted phenols. Ultraviolet laser desorption from these cryogenically cooled matrixes generates internally colder ions than from the equivalent room-temperature crystalline matrixes containing no solvent, as evidenced by a substantial reduction in the extent of fragmentation in the corresponding mass spectra of oligonucleotides. Furthermore, the homogeneity of the frozen solution samples allows analyte signals to be obtained uniformly throughout the sample. Sensitivity and mass resolution approaching that obtained using the most effective room-temperature crystalline matrix for DNA (3-hydroxypicolinic acid) are consistently and reproducibly obtained in both positive and negative ion mass spectra. As fragmentation is a principle factor limiting the maximum attainable mass resolution in MALDI-TOF mass analysis of DNA, this improvement in generating intact DNA ions is advantageous.