LC Separation and Online MS Characterization of Saturated and Unsaturated Alginic Acid Oligomers

We report the complete separation and characterization by online high-performance liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) of fully saturated alginic acid (AA) oligosaccharides from DP1 to beyond DP23, obtained by a chemical process, and unsaturated oligomers from DP1 to DP10, produced by lyase treatment. A series of negatively charged species of different m/z ratio are seen for each oligosaccharide. Smaller AA species, from DP1 to DP4, mainly furnish M–H]^? anions whereas the DP5 to DP9-10 oligomers predominantly exist as the 2- charge state. The AA oligomers from DP10 to DP17 are mainly represented by the M–3H]^3? anions whereas species from DP18 to DP23 are characterized by the 4? charge state. Online LC-ESI-MS enabled separation and simultaneous characterization of complex saturated and unsaturated AA oligomer mixtures without previous sample treatment, in particular extensive removal of salts to obtain species compatible with ESI-MS.