Rapid solid phase extraction of dissolved organic matter

Abstract

Dissolved organic matter (DOM) is a complex mixture of organic molecules found ubiquitously in freshwater and saltwater environments. Contained within the heterogeneous mixture of DOM lies valuable information content on the source of molecules as well as the biotic mechanisms at work within an aquatic ecosystem. Recent advancements in high resolution mass spectrometry and liquid chromatography have made inroads into determinations of the molecular structures within DOM, which have been largely unknown until recently. Liquid chromatography-mass spectrometry (LC-MS) analysis, however, generally requires a prior step to concentrate/isolate DOM, and this step often limits the number of samples that can be analyzed. This study has developed a fast (<20 min) method to concentrate dissolved organic matter on commercially available online solid phase extraction (SPE) cartridges which can be directly eluted onto an LC-MS system. This method is generally faster and requires far less sample (10-100 mL) than previous SPE methods for DOM isolation. Additionally, this study tested a suite of very different SPE phases to find a combination of phases that could improve DOM recovery as compared with commonly used approaches. When a styrene divinylbenzene phase (RP1) was coupled with activated carbon, recoveries were found to be significantly higher than in previous SPE studies relying upon single phases (either C18 or styrene divinylbenzene-based). The SPE method proposed here was tested for a diverse set of salty and fresh water samples and percent recoveries ranged from 46-78% of the total dissolved organic carbon (DOC).