Detection of carbohydrates in sea ice extracellular polymeric substances via solid-phase extraction and HPLC-ESI-MS/MS

Dissolved organic matter in sea ice is rich in extracellular polymeric substances (EPS) secreted by sea ice algae and bacteria. Carbohydrates are the most abundant component of EPS and they may contribute to the Fe-binding organic ligand pool, increasing the residence time of bioavailable Fe in the euphotic zone when sea ice melts. A new method for the determination of EPS in sea ice samples is presented, using Solid Phase Extraction (SPE) column for the extraction and the pre-concentration steps and HPLC-ESI-MS/MS for the separation and identification of the analytes. The method has been built up and optimized using composite samples obtained from pack-ice aliquots collected during the winter 2012 in the framework of the activities of Australian-led Sea Ice Physics and Ecosystem eXperiment-2 (SIPEX-2) voyage. The SPE allowed samples as small as 50 mL, also reducing sample preparation time, as well as removing the salt of the matrix. Nine EPS with a mass lower than 1500 Da were identified by HPLC-ESI-MS/MS, characterized by a different number of glucose residue units making up the polymeric chain. The total estimated concentration was 46 ppb (mu g L-1), in agreement with spectrophotometric assay results.

Automated summary

A new method for determining EPS in sea ice samples was presented, using SPE column for extraction and pre-concentration steps and HPLC-ESI-MS/MS for separation and identification. Nine EPS compounds were identified with a mass lower than 1500 Da, providing essential data for the study of the Fe-binding organic ligand pool.