Dissolved organic carbon (DOC) is one of the largest organic carbon pools in the ocean and it plays an important role in the biogeochemical cycle of water. As a unique component of terrestrial vascular plants, lignin can trace the terrestrial input of organic matter in aquatic system. Because the DOC usually exists with low concentration in high salinity water, it needs to be concentrated and extracted from the water for further chemical characterization. Solid phase extraction (SPE) enrichment is the common way to extract DOC from water. Some studies have shown that the SPE efficiency of DOC will decrease with the increase of salinity in natural water, but there is no study to show whether the SPE efficiency of lignin will change with the change of salinity in the estuary. Therefore, this study analyzes and compares the SPE efficiency of DOC and lignin under various salinity, and we also explored whether the change of lignin concentration will affect the SPE efficiency.

The results show that the SPE efficiency of DOC decreased with the increase of salinity. The variation range of the SPE efficiency for the first PPL cartridges are 37.47% ~ 49.83%. With the increase of salinity, the SPE efficiency of lignin showed minor change (less than 10%), which were all within the range of 70%~80%, indicating that the change of lignin concentration in the estuary would not be affected by the SPE. Thus, our results provided a reference and basis for subsequent biogeochemical studies of dissolved lignin in natural environments under variable salinity.