Microseparation of Lipophilic and Hydrophilic Metabolites for Single Oocyte Mass Spectrometry Analysis

Single-cell metabolic analysis has not yet achieved the coverage of bulk analysis due to the diversity of cellular metabolites and the ionization competition among species. Direct ionization methods without separation lead to the masking of low-intensity species. By designing a capillary column emitter and introducing reverse-phase chromatography principles, we achieved the microseparation of lipophilic and hydrophilic metabolites and lowered the limit of detection of hydrophilic metabolites to the level of a single oocyte. We identified 517 metabolite species in a single oocyte, achieving coverage and reproducibility comparable to those of bulk analysis. By comparing oocytes at different maturation stages, 76 metabolic features were identified with significant differences between the germinal vesicle and meiosis II stages. Metabolite level changes suggested the roles of lipid metabolism remodeling, increased amino acid synthesis, and a shift from pyrimidine metabolism to purine metabolism in the process of oocyte maturation. This microseparation mass spectrometry analysis is expected to promote single-cell metabolomics.