Laser ablation sample transfer for mass spectrometry
In this research, a new ambient sampling technique for mass spectrometry was developed that uses an infrared laser to ablate materials under ambient conditions that are captured in a solvent or on a surface. An infrared optical parametric oscillator (OPO) laser system at 3 μm wavelength was focused onto samples for ablation at atmospheric pressure. The ablated materials were transferred to a solvent or surface. For off-line electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) analysis, the ablated material was captured in a static solvent droplet that was deposited on a MALDI target or flow-injected into a nanoelectrospray source. The direct analysis of biological fluids for off-line MALDI and electrospray was demonstrated with untreated blood, milk, and egg. For one-line ESI, the ablated material was captured in an exposed flowing solvent stream that carried the ablated material to the ESI source. For on-line liquid chromatography ESI (LC-ESI) and on-line capillary electrophoresis ESI (CE-ESI), the ablated material was captured in the flowing solvent and injected into a LC column or a capillary with pressure driven or electrokinetic flows, respectively. The performance of the system was assessed using peptide and protein mixtures ablated from the target and analyzed with LC or CE separation. For MALDI imaging with IR laser ablation sampling, a thin tissue section placed on a microscope slide was scanned in two dimensions under a focused IR laser beam to transfer material to the target slide via ablation. After the material was transferred to the target slide, it was analyzed using MALDI imaging. Images were obtained from peptide standards for initial optimization of the system and from mouse brain tissue sections.
ablation, mass spectrometry, infrared laser, capillary electrophoresis, liquid chromatography, ambient, matrix-assisted laser desorption/ionization, electrospray ionization, tissue imaging
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