Matrix-assisted laser desorption time-of-flight mass spectrometry of oligonucleotides using 3-hydroxypicolinic acid as an ultraviolet-sensitive matrix.

Matrix-assisted laser desorption time-of-flight mass spectrometry has been used to produce quasi-molecular ion signals from underivatized mixed-base single-stranded DNA oligomers ranging from 10 to 67 nucleotides in length. These results were obtained with a new matrix material, 3-hydroxypicolinic acid (3-hydroxypyridine-2-carboxylic acid) which showed significant improvement over many previously reported matrices studied in terms of mass range available, signal-to-noise ratio, and the ability to analyze mixed-base oligomers. The desorption and simultaneous ionization was by pulsed laser light at 10 to 50 mJ/cm2, studied at 266, 308, and 355 nm. Spectra taken at 266 nm provided the smallest amounts of doubly charged and dimer ions--characteristics desirable for DNA sequencing by this technology. Negative-ion spectra were uniformly superior to positive-ion spectra. This new matrix also is quite effective for molecular weight determinations of peptides and proteins in both positive- and negative-ion modes.