LC-Swan Probe: An Integrated In Situ Sampling Interface for Liquid Chromatography Separation and Mass Spectrometry Analysis

In situ sampling mass spectrometry (MS) systems can achieve rapid analysis of samples, while most of them do not have the pretreatment capability of chromatographic separation. This Article describes the design, fabrication, and application of a swan-shaped in situ sampling MS probe with liquid chromatography (LC) separation capacity. The LC-Swan probe was fabricated based on a single capillary with a micrometer-sized hole at its U-shaped bottom for sampling, a monolithic column for separation, and a tapered tip for electrospray. Four functions including in situ sampling, sample injection, chromatographic separation, and MS electrospray were integrated in the LC-Swan probe. Direct sampling and contacting–dissolution–injection sampling modes were developed to perform in situ sampling and injection of liquid samples and dry spot samples, respectively, in the high flow-resistance LC system. A pressing–sealing method was also developed using a polydimethylsiloxane (PDMS) sealer to achieve the sealing of the probe sampling hole during the high-pressure chromatographic separation process. The LC-Swan probe-based system exhibited effective desalting capacity in the analysis of angiotensin II with similar relative standard deviations (RSDs) of retention time and peak area below 3% and 19% (n = 3) for both salt-containing and salt-free samples. The present system was applied for analyzing cytochrome C digest to test its separation capability for samples with complex compositions, and 19 peptides were detected in 13 min with an amino acid coverage of 85%. We also applied the system in metabolite analysis of mouse organ sections of brain, liver, and kidney to preliminarily demonstrate its application potential in MS imaging analysis.