Ultra low-flow sheathless capillary electrophoresis-mass spectrometry for comprehensive profiling of ionogenic metabolites in body fluids

摘要

The performance of capillary electrophoresis (CE) coupled to electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS) via a novel sheathless nanospray interface is demonstrated for non-targeted profiling of ionogenic metabolites in body fluids. The intrinsically low-flow characteristics of CE are completely exploited in this set-up. This low-flow rate regime enables ESI-TOF-MS to reach its top performance, i.e. an improved sensitivity and reduced ion suppression. As a consequence, the enhanced sensitivity of the sheathless CE-TOF-MS method allows comprehensive analysis of polar and charged metabolites in body fluids. The applicability for non-targeted metabolic profiling of body fluids is especially shown for volume-restricted samples using cerebrospinal fluid (CSF), urine and plasma from mice as representative examples. These samples are often only available in small volumes, especially when using minimally invasive repeated sampling for longitudinal metabolomics studies. Sheathless interfacing of a PA 800 plus CE instrument (Beckman Coulter) and a maXis Impact UHR-TOF-MS instrument (Bruker Daltonics) was achieved through a capillary of which the outlet was etched with hydrofluoric acid, providing an outer terminus porous to the electric transport of small ions. The separation capillary with this porous tip was placed in a stainless steel ESI needle filled with static conductive liquid. The conventional ESI source was replaced by a nanoflow spray shield (Bruker Daltonics), which was positioned on the inlet of the transfer glass capillary. ESI was applied in positive ionization mode (-1.2 kV) and 10% acetic acid (pH 2.2) was used as background-electrolyte (BGE). Representative metabolite mixtures, human urine, mouse CSF, mouse urine and mouse plasma were used for method evaluation.