Abstract
Electrospray ionization (ESI) generates bare analyte ions from charged droplets, which result from spraying a liquid in a strong electric field. Experimental observations available in the literature suggest that at least a significant fraction of the initially generated droplets remain large, have long lifetimes, and can thus aspirate into the inlet system of an atmospheric pressure ionization mass spectrometer (API-MS). We report on the observation of fragment signatures from charged droplets penetrating deeply the vacuum stages of three commercial mass spectrometer systems with largely different ion source and spray configurations. Charged droplets can pass through the ion source and pressure reduction stages and even into the mass analyzer region. Since droplet signatures were found in all investigated instruments, the incorporation of charged droplets is considered a general phenomenon occurring with common spray conditions in ESI sources.
Highlights
Electrospray ionization (ESI) [1,2,3] is one of the most frequently applied ionization methods in mass spectrometry (MS) [4,5,6,7]
The main focus was on a SCIEX Triple Quad 6500 System with an IonDrive Turbo V ion source, which was operated with a TurbolonSpray ESI probe (SCIEX, Ontario, Canada)
Additional unassigned signals below the low mass cutoff (LMCO) are present with low intensities
Summary
Electrospray ionization (ESI) [1,2,3] is one of the most frequently applied ionization methods in mass spectrometry (MS) [4,5,6,7]. An electrospray ion source consists of a glass or metal capillary in a strong electric field gradient. Liquid analyte solution is pumped or aspirated into the capillary. Charge separation processes in the liquid driven by the present electric field lead to the formation of a spray of charged droplets from the ESI capillary [6]. These charged droplets undergo a temporal evolution: Evaporation of neutral molecules, primarily solvents, leads to droplet shrinkage. The charge density due to the ions present in the droplet increases. If the resulting electric field in the droplet is high
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