A blow‐by‐blow account: Extractive electrospray ionization (EESI) quadrupole TOF (QTOF) mass spectrometry has been established with a commercial instrument without hardware modification for the rapid analysis of breath without sample pretreatment (see picture). Sulfur‐containing compounds can be selectively detected by using silver cationization in the EESI source—a method of interest for in vivo metabolic studies and clinical diagnosis.

MS comes to life: A novel method to sample surfaces of biological objects uses a neutral gas beam for in vivo EESI mass spectrometric analysis without sample pretreatment (see picture; QTOF=quadropole time‐of‐flight). The sampling process results in rapid in vivo analyses with reduced ion suppression and without chemical contamination. This strategy can be used in food quality monitoring, homeland security, metabolomics, and clinical diagnosis.

We present a comparison of three different electrospray-based ionization techniques for the investigation of noncovalent complexes with mass spectrometry. The features and characteristics of standard electrospray ionization (ESI), chip-based nanoESI, and electrosonic spray ionization (ESSI) mounted onto a hybrid quadrupole time-of-flight mass spectrometer were compared in their performance to determine the dissociation constant (K D ) of the model system hen egg white lysozyme (HEWL) binding to N, N N=,

We investigated how chemical equilibria are affected by the electrospray process, using simultaneous in situ measurements by laser-induced fluorescence (LIF) and phase Doppler anemometry (PDA). The motivation for this study was the increasing number of publications in which electrospray ionization mass spectrometry is used for binding constant determination. The PDA was used to monitor droplet size and velocity, whereas LIF was used to monitor fluorescent analytes within the electrospray droplets. Using acetonitrile as solvent, we found an average initial droplet diameter of 10 m in the electrospray. The PDA allowed us to follow the evolution of these droplets down to a size of 1 m. Rhodamine B-sulfonylchloride was used as a fluorescent analyte within the electrospray. By spatially resolved LIF it was possible to probe the dimerization equilibrium of this dye. Measurements at different spray positions showed no influence of the decreasing droplet size on the monomer-dimer equilibrium. However, with the fluorescent dye pair DCM and oxazine 1 it was shown that a concentration increase does occur within electrosprayed droplets, using fluorescence resonance energy transfer as a probe for the average pair distance. ( An important aspect of the highly dynamic electrospray process concerns the shrinking droplets. After the droplet creation, solvent evaporation and Coulomb explosions lead to a decrease of droplet size until all solvent has evaporated and the final desolvated and ionized analytes are produced. A decrease of droplet size resulting from solvent evaporation will lead to a concentration increase of nonvolatile analytes within the droplets. For dissolved species that participate in a chemical equilibrium, such as free and bound states of partners that can form a noncovalent complex, the question arises whether the increasing concentrations affect the equilibrium position. Given that binding constant determination with ESI-MS usually relies on measuring the relative amounts of free and bound species, a perturbation of the equilibrium introduced by the shrinking droplets would influence the results of such an experiment. Recent studies show that the time between droplet creation and production of desolvated ions in ESI is within milliseconds [5]. In other words, if the association and dissociation reactions are fast, an equilibrium should be able to track a concentration increase within the droplets.The shrinking droplet volume also leads to Coulomb explosions/droplet fission, when the mutual repulsion of charges is high enough to overcome the surface tension of the droplet. The parent droplet ejects several smaller offspring droplets, which together carry 10 -25% of the charge, but only about 5% of the mass of the original droplet [9]. These offspring droplets then segregate within the electrospray, as shown theoretically by Wilhelm et al. [10]. Analytes will not generally be evenly distributed between the parent and offspring droplets. Partitioning processes, which have been investigated by several research g...

It is of increasing interest and practical importance to develop convenient methods based on mass spectrometry for high-throughput analyses of biological samples. This is usually difficult because of the complex matrix and ion suppression effects. Generation of ions at ambient conditions is a promising solution to these problems because the sample is easily accessible and the ion suppression effect is reduced significantly. A new method for rapid on-line detection of metabolic markers in complex biological samples is described here. It combines atmospheric pressure desorption sampling by a gentle stream of air or nitrogen with extractive electrospray ionization (EESI) and mass spectrometric analysis. The resulting mass spectral fingerprints are shown to be able to detect spoilage of meat even in the frozen (-20 degrees C) state and the contamination of spinach by E. coli, and to identify metabolites and contaminants on human skin within seconds, in an on-line and high-throughput fashion. Typical molecular markers are identified using MS/MS data and by comparison with reference compounds. Differences between closely related samples are easily visualized by using principal component analysis (PCA) of the mass spectra data. The detection limit achieved is 10 fg/cm2 (S/N = 3) for histamine on the surface of frozen meat. The technique reported here shows potential for more advanced applications in multiple disciplines, including food regulation, homeland security, in vivo metabolomics, and clinical diagnosis.