Aqueous samples were co-crystallized with 2,5-dihydrobenzoic acid matrix (10 mg ml21 in acetonitrile) on a Bruker-Daltonics 49-place target. The laser output was at 337.1 nm, typically at 60 % of 150 ́ıJ maximum output, and 80 shots were accumulated. A 200 ns pulsed ion extraction was used with matrix suppression up to 200 Da. The instrument was calibrated externally on a dp series of malto-oligosaccharides.