MALDI-TOF Mass Spectrometry of Naturally Occurring Mixtures of Monorhamnolipids and Dirhamnolipids

MALDI-TOFMS approaches have been developed for high-throughput screening of naturally occurring mixtures of rhamnolipids from Pseudomonas spp. Monorhamnolipids and dirhamnolipids are readily distinguished by characteristic molecular adduct ions, [M+Na](+) and [M-H+Na(2)](+), with variously acylated rhamnolipids differing by 28 mu. Following proton-deuterium exchange, deuterated [M+Na-4(1)H+4(2)H](+) and [M+Na-6(1)H+6(2)H](+) ions are observed for the monorhamnolipids and dirhamnolipids, respectively, which allows rapid identification of these molecules. The described approach has been validated by compositional analysis using GC/MS, fractionation by RPHPLC, and analysis by 1D and 2D NMR spectroscopy. MALDI-TOFMS analysis allows the rapid screening of variously acylated rhamnolipids, and has potential for selective identification of new surfactants from microbial strains.