Droplet charging electrospray

The electrospraying of biomaterials into cells is used in gene therapy and gene transfection. The biomaterial penetrates the cell by means of the intrinsic droplet charge that develops during electrospraying. ... 

Spraying capillaries for ESI (a) Nebulization and droplet charging by the electric field only, (b) Pneumatically assisted electrospray or ionspray and (c) Tri-coaxial probe with sheath flow. 

The minimum ion concentration for an electrospray has been experimentally determined as 10 mol [9]. When this minimum concentration is met, on the basis of theoretical reasoning and experimental measurements [10], the following relationships for spray current I, drop radius R and droplet charge q have been proposed ... 

The charged droplets produced by an electrospray shrink due to solvent evaporation as long as the droplet charge remains constant. The energy required for the solvent evaporation is provided by the thermal energy of the ambient air. The charge on the droplets is assumed to remain constant because the emissions of ions from solution to gas phase are highly endothermic [26]. 

Fig. 32.19 The charged residue model (CRM) and ion evaporation model (lEM) of gas phase ion generation from charged electrospray droplets...

Tang, Gomez, A., Keqi. (1994). Charge and hssion of droplets in electrosprays. Physics of Fluids, Vol. 6, 404. 

The other recent approach to use of LC-MS for analysis of PSP toxins (Dell Aversano 2005) exploits the unique properties of hydrophilic interaction chromatography (HILIC, Section 4.4.2c) that are ideally suited to these highly polar analytes. Moreover, the high organic content of the mobile phase leads to ready evaporation of the charged electrosprayed droplets and thus high ionization efficiency. 

Tang, K. Smith, R. D. Physical/chemical separations in the break-up of highly charged droplets from electrosprays. J. Am. Chem. Soc. 2001, 72, 343-347. 

Considering the requirements for charge balance in such a continuous electric current device and the fact that only electrons can flow through the metal wire supplying the electric potential to the electrodes, one comes to the conclusion that the electrophoretic charge separation mechanism [of droplet charging and formation] requires that the [positive-ion] electrospray process should involve an electrochemical conversion of ions to electrons [within the metal ES capillary[. 

The assistance of a high-velocity gas flow or ultrasonic vibration is used in electrospray mass spectrometry. In a simple approximation, the pneumatic or ultrasonic nebulizer takes care of aerosol formation, while the electric field does the droplet charging. When... 

Apparent concentration sensitivity of electrospray can be attributed to a decrease in droplet charging efficiency and a shift toward larger diameters in the droplet size distribution if the liquid flow rate is increased, according to the scaling laws in Eqs. (4.1) and (4.2) ... 

A solution of an analyte in a solvent can be sprayed (nebulized) from an electrically charged narrow tube to give small electrically charged droplets that desorb solvent molecules to leave ions of the analyte. This atmospheric-pressure ionization is known in various forms, the one most relevant to this section being called electrospray. For additional detail, see Chapters 8, 9, and 11. 

Electrospray ionization mass spectrometry (ESI-MS) is an analytical method for mass determination of ionized molecules. It is a commonly used method for soft ionization of peptides and proteins in quadmpole, ion-trap, or time-of-flight mass spectrometers. The ionization is performed by application of a high voltage to a stream of liquid emitted from a capillaty. The highly charged droplets are shrunk and the resulting peptide or protein ions are sampled and separated by the mass spectrometer. 

The flow rate of liquid in the HPLC-electrospray system is paramount in determining performance both from chromatographic and mass spectrometric perspectives. The flow rate affects both the size and size distribution of the droplets formed during the electrospray process (not all droplets are the same size) and, consequently, the number of charges on each droplet. This, as we will see later, has an effect on the appearance of the mass spectrum which is generated. It should also be noted that the smaller the diameter of the spraying capillary, then... 

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