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Analysis of Pesticide Residues by Chromatographic Techniques Coupled with Mass Spectrometry
Published in José L. Tadeo, Analysis of Pesticides in Food and Environmental Samples, 2019
Wan Jing, Jin Maojun, Jae-Han Shim, A.M. Abd El-Aty
Electrospray ionization (ESI) source is an ionization mode mainly used in liquid chromatography–mass spectrometry. It serves as both an interface between the liquid chromatograph and the mass spectrometer and as an ionization device. Its main component is an electrospray nozzle consisting of a two-layer casing. The inner layer of the nozzle is the liquid chromatography effluent, while the outer layer is the atomization gas, which is usually nitrogen gas with a large flow. The liquid sample is dispersed into droplets with the aid of the atomization gas. In addition, there is an auxiliary gas nozzle at the oblique front of the nozzle. The role of the auxiliary gas is to quickly evaporate the solvent of the droplet. The charge density on the surface of droplets gradually increases during evaporation, and when it reaches a critical value, ions can evaporate from the surface. Ions pass through the sampling hole and enter the analyzer by means of the voltage between the nozzle and the cone hole. The voltage applied to the nozzle can be positive or negative. By adjusting the polarity, a positive or negative ion mass spectrum can be obtained.
Diagnosis: Nanosensors in Diagnosis and Medical Monitoring
Published in Harry F. Tibbals, Medical Nanotechnology and Nanomedicine, 2017
The manipulation of polarizable microdroplets over hydrophobic surfaces by electric fields bears some resemblances to the focusing of ions and charged macromolecules in mass spectrometer ion sources and quadrupole analyzers. The preparation of ions for mass analysis is a kind of three-dimensional gas-phase nanotechnology—for macromolecules the techniques are not purely chemical or electrophysical, but involve electronic and physical manipulations on the nanoscale. For example, the thermospray, electrospray, and nanospray ion sources prepare ions for mass analysis by creating tiny droplets of solution. As the droplets evaporate, the process is accelerated by charge, leading to loss of all of the solvent and leaving a bare macromolecule holding the charge that was on the droplet [258-262].
HPLC-Hyphenation
Published in Grinberg Nelu, Rodriguez Sonia, Ewing’s Analytical Instrumentation Handbook, Fourth Edition, 2019
R.A. Shalliker, M. J. Gray, D. Kocic, S. Pravadali-Cekic
Electrospray nebulization is a process that breaks up a fluid flow stream into a fine mist or spray by the application of an applied electric field [157]. This process differs from thermospray in that a charge is used to produce atomization rather than the atomization producing charge. In electrospray, a potential of several kilovolts is applied to a tube, through which the mobile phase eluent leaves the chromatographic column. A charge is thus imparted to the liquid as it leaves the tube. The resulting coulombic repulsion forces are sufficient to generate dispersion into a fine mist. The evaporation of the solvent molecules increases the surface charge density, which in turn, increases the particle repulsion. Hence, the radius of curvature of the liquid leaving the tube increases as the liquid undergoes further solvent evaporation. This phenomenon is referred to as a Taylor cone [164]. Stable electrospray conditions can be achieved for a number of solvents, but only at low flow rates, and hence, the technique is most suited to micro-column applications. Raynor and coworkers [164] illustrated the use of an electrospray interface for the removal of solvent and subsequent deposition of sample analyte onto a ZnSe plate. Mobile phase is transported through a capillary, which has an applied electric field of 3 kV. A sheath of nitrogen gas (1 mL/min) surrounds the capillary and serves to prevent any mobile phase being drawn back up the stainless steel tube by virtue of capillary action. The Taylor cone that results from the electrospray desolvation would appear to be inappropriate for the deposition of solute into a suitably narrow band for IR analysis. However, if the deposition substrate is an earthed semi-conductor, such as ZnSe, for example, the divergence of the spray can be limited to a large degree. The optimum distance for the location of the substrate from the outlet tip of the capillary was found to be 1.5 mm. Under these conditions, HPLC-FTIR with an electrospray interface and deposition onto ZnSe plates with subsequent IR-microscopy analysis was successful in the qualitative analysis of caffeine and barbital. However, no information was given regarding quantitation, which was in all probability poor due to the non-uniformity of the deposition of the analyte onto the substrate.
Size estimation of biopolymeric beads produced by electrospray method using artificial neural network
Published in Particulate Science and Technology, 2023
Preparation of biopolymeric beads from viscid solutions with a mono-dispersed size distribution, enough mechanical strength and a suitable size is one of the main aims of the pharmaceutical industry (Khorram et al. 2015; Samimi and Moeini 2020). In addition, the formation of droplets from high viscid solutions is a serious process in many operations such as ink-jet printing, spray drying and atomization dispersion and emulsification (Moghadam et al. 2008). The application of an electrostatic field in liquid spraying provides an external force that can effectively control the droplet size. Electrospray is a simple, reliable, and facile technique in which small size-droplets can be formed from high viscous liquids depending on their conductivity (Moghadam et al. 2009). This is the method of liquid atomization in which an electrical force is applied in the direction of gravitational force on the surface of a capillary. In electro-spraying, one subjects the surface of the liquid capillary at the outlet of a nozzle to shear stress by maintaining the nozzle at a high electric potential. This leads to elongation and, consequently, separation of the droplet from the nozzle tip (Almería and Gomez 2014).
Removing methylene blue contained in dye wastewater using a novel liquid-phase plasma discharge process
Published in Journal of Environmental Science and Health, Part A, 2020
Liquid samples were taken at the end of each experiment. An ACQUITY UPLC system coupled with a Waters Xevo TQ mass spectrometer was used to determine the residuals of MB in the treated stream. The mass spectrometer was configured in tandem with LC-MS/MS quantification applications according to the methods[18] used for single ion reaction monitoring (SIR) or multiple reaction monitoring (MRM) with slight modifications. The dimension of the column used was 1 mm (internal dia.) x 150 mm (length) and the column was packed with 5 µm phenyl hexyl packing materials from Phenomenex Inc. (Torrance, CA). The mass spectrometry system consisted of an electrospray ionization source operating in a multiple reaction monitoring mode. The detector was a photomultiplier characteristic of low-noise, off-axis, and long life. The signal received from the detector was recorded and analyzed by the MassLynx Software. Two mobile phases consisting of two solvents were used for the mass spectrometry method. Mobile phase A was water and mobile phase B was made of 20% acetonitrile and 80% 0.1 M ammonium acetate. The gradient was from 20% to 80% in 25 min with a flow rate of 0.060 mL/min and an injection volume of 4 µL. The MB removal rate (RMB) was determined using the following formula.
Review of sub-3 nm condensation particle counters, calibrations, and cluster generation methods
Published in Aerosol Science and Technology, 2019
Juha Kangasluoma, Michael Attoui
The electrospray (ES) method produces charged droplets by ripping liquid, which is at high potential, out of a thin capillary needle (Cloupeau and Prunet-Foch 1994). The electrically conductive liquid, to which the sample is dissolved, forms highly charged volatile droplets. Immediately after formation, the droplets begin to evaporate, increasing the charge-to-volume ratio until it reaches the Rayleigh limit and the droplet explodes because of Coulomb repulsion. Unipolar charged gas-phase molecules and clusters are formed as a result of ion evaporation from the droplet, or as charged residue after series of coulomb explosions and solvent evaporation (Kebarle and Verkerk 2009). The ES can be used to produce practically any liquid or solid samples that are soluble in some liquid.