ABSTRACT
Charging of nanoparticles through electrospray has scarcely been explored. Spherical nanometer-sized amphiphilic block copolymer nanoparticles with diameters ranging from â¼65 to â¼150 nm were electrosprayed and analysed by charge detection spectrometry. Herein, we explore the charging of these micellar nano-objects by conducting a thorough study in different solvents, including pure water, and upon the addition of "supercharging" agents. The charge (z) of micellar nanoparticles electrosprayed from water solution is compared to the Rayleigh's limiting charge (z(R)) of a charged water droplet of the same dimensions. An average ratio (z/z(R)) of 0.6-0.65 is observed for the micellar macro-ions, supporting the charge residue mechanism, where the number of charges available to the micellar macro-ion is limited by the number of charges on the nanodroplet, which is a function of the surface tension of the solvent. Also we show the possibility of increasing the charging of micellar nanoparticles in the negative mode by adding organic bases (in particular piperidine) to water/methanol solutions.
ABSTRACT
We report the use of infrared multiphoton dissociation (IRMPD) for the determination of relative activation energies for unimolecular dissociation of megadalton DNA ions. Single ions with masses in the megadalton range were stored in an electrostatic ion trap for a few tens of milliseconds and the image current generated by the roundtrips of ions in the trap was recorded. While being trapped, single ions were irradiated by a CO2 laser and fragmented, owing to multiphoton IR activation. The analysis of the single-ion image current during the heating period allows us to measure changes in the charge of the trapped ion. We estimated the activation energy associated with the dissociation of megadalton-size DNA ions in the frame of an Arrhenius-like model by analyzing a large set of individual ions in order to construct a frequency histogram of the dissociation rates for a collection of ions.
