In terms of the number of annotated endogenous and exogenous LMWMs, the results for the two blood products are very similar (Figure ). Using the new dSPE method, 190 and 212 endogenous LMWMs and xenobiotics were annotated using C18 RPC in plasma (MARS) and serum (BioAID and Microbial Products in Infection) samples, respectively. In addition, 482 and 460 lipid species from different lipid classes were measured with a C8 RPC lipidomic assay in plasma (MARS) and serum (BioAID and Microbial Products in Infection) samples, respectively (Figure ). Except for minimal overlap of medium-and long-chain acylcarnitine species detected in both C18 and C8 RPC+, jointly the two assays yielded 661 unique annotations for both plasma and serum. By developing the reported herein dSPE-C18 RPC method, we were able to efficiently close the gap in coverage of moderately hydrophobic metabolites and enable the detection of a wide variety of chemical structures representing the blood metabolome.