Examining chemical space coverage of solid phase extraction methods in environmental water for use with LC-MS...

Multiple solid phase extraction (SPE) methods in combination with reversed phase liquid chromatography and high-resolution mass spectrometry (LC-MS) were explored to help characterize captured chemical space and improve interpretation of non-targeted results. Reference standards for 231 surrogate chemicals were used to evaluate extraction efficiencies in spiked laboratory water, including pesticides, per- and polyfluoroalkyl substances, pharmaceuticals and personal care products, and drugs of abuse. In preliminary studies, multiple SPE cartridge chemistries and methods were examined (HLB, WAX, MCX, GCB, WCX), including combining multiple cartridge chemistries. Additional factors such as the use of a chelating agent, sample pH and acid type, and clean-up steps were also tested. The top four performing methods that covered the desired range of chemistries (HLB, HLB-WAX, HLB-MCX, and HLB-WAX-MCX) were further optimized and used for the extraction of environmental surface water. The relative extraction efficiency of the surrogate chemicals was determined in spiked surface water with 209 of the 231 surrogates being retained with all four methods, and 222 retained with HLB-WAX-MCX. The total number of chemical features observed showed 1499 chemical features detected across the four methods, with 968 chemical features detected in all four methods, and 1378 detected with the HLB sorbent alone. The types of chemicals identified, and physical/chemical properties of unidentified chemical features retained by each method were explored, showing benefits of MCX containing methods for retention of polar cations. This work provides a description of four optimized solid phase extraction methods with varying chemical coverage for use in future non-targeted analysis efforts.