Comparison of dynamic fast atom bombardment/liquid secondary ion mass spectrometry and electrospray mass spectrometry coupled to reversed-phase liquid chromatography for the determination of oligosaccharides in seawater

Abstract

A method has been developed for determination of non-derivatised oligosaccharides by LC–MS at low concentration levels and in complex matrices of seawater and sediment pore water. Two ionisation techniques, dynamic fast atom bombardment (FAB)/liquid secondary ion (LSI) MS and electrospray ionization (ESI), were investigated and evaluated. The electrospray using Li+ ions as adducts proved to be superior to the FAB/LSI-MS for the determination of non-derivatised oligosaccharides. The LC separation was accomplished by the use of a C18 column and the elution either by a gradient of methanol–acetonitrile–water or pure water, in which latter case the column was held at an elevated temperature. We also report results from measurements of oligosaccharides in pore waters of marine sediment cores. Oligosaccharides of a range from 2 to 6 sugar units were found in a concentration range of 2–100 nM, the smaller sugars being more abundant. The depth profiles in the sediment cores indicate a production in the redox boundary layer and from there, diffusion in both directions to the overlaying water and further down into the sediment.