A useful binary matrix for visible-MALDI of low molecular weight analytes.

In this work, a new absorbing candidate, rhodamine (R) 575, is described, which forms the basis of a binary matrix operating at 532 nm. Analyte ionization is found to be much more efficient when the dye is combined with a proton donor such as hydrochloric acid or alpha-cyano-4-hydroxycinnamic acid, or a proton acceptor such as sodium hydroxide. This makes the matrix more generic than many others that have been tried. Furthermore, under visible illumination R575 produces very few chemical fragments, making it useful for small molecular weight analyte detection. Spectra for a variety of analytes are shown. Insight into the MALDI mechanism was obtained by comparing the similarities and differences of visible-MALDI with the more common UV and IR-MALDI strategies.