Nebulization surface tension

Droplet delivery from an airblast nebulizer is governed by the surface tension, density and viscosity of the fluid, and the applied pressure, which can be passive or forced. Droplet breakup is illustrated in Fig. 6. Droplets form during this breakup at a critical Weber number (We) ... 

Chemical interferences are the result of problems with the sample matrix. For example, viscosity and surface tension affect the aspiration rate and the nebulized droplet size, which, in turn, affect the measured absorbance. The most useful solution to the problem is matrix matching, matching the matrix... 

In addition to high LC flow rates, solutions of high conductivity, and/or high surface tension are unsuitable for use with conventional ESI. An ultrasonic nebulizer can reduce such problems because it mechanically creates the spray. Unfortunately, the ultrasonically created droplets are comparatively large and this hin-... 

The most commonly used LC/MS interfaces in pharmaceutical analysis are ESI and APCI. An ESI interface on the majority of commercial mass spectrometers utilizes both heat and nebulization to achieve conditions in favor of solvent evaporation over analyte decomposition. While ionization in APCI occurs in the gas phase, ionization using ESI occurs in solution. Attributes of a mobile phase such as surface tension, conductivity, viscosity, dielectric constant, flow rate and pFi, all determine the ionization efficiency. They therefore need to be taken into consideration and controlled. 

Greenfield ef. ai.l l) observed a reduction of signal intensity that correlates with sample intake effects from the modified solution viscosity and/or surface tension of mineral acids. This, coupled with peristaltic pumping of solutions into the nebulizer, considerably reduces physical interferences. Increased salt concentration also has an effect on solution physical properties. In the experience of these authors, the high levels of salt in the matrix also increases the noise from the nebulizer system. This degradation of nebulizer performance, which is not necessarily accompanied by a proportional reduction in sensitivity, is the cause of the observed deterioration of detection limits in real samples as opposed to ideal solutions. 

High dissolved solids content in water (for example, chlorides and other salts in excess of 1500mg/l) change the viscosity and the surface tension of the digested samples and affect the nebulization and aerosol transport. 

Aspiration rate is only a small part of the overall transport process in flame spectrometry. The production of aerosol and its transport through the spray chamber are also of great importance. The size distribution of aerosol produced depends upon the surface tension, density, and viscosity of the sample solution. An empirical equation relating aerosol size distribution to these parameters and to nebulizer gas and solution flow rates was first worked out by Nukiyama and Tanasawa,5 who were interested in the size distributions in fuel sprays for rocket motors. Their equation has been extensively exploited in analytical flame spectrometry.2,6-7 Careful matrix matching is therefore essential not only for matching aspiration rates of samples and standards, but also for matching the size distributions of their respective aerosols. Samples and standards with identical size distributions will be transported to the flame with identical efficiencies, a key requirement in analytical flame spectrometry. 

The evaporative light scattering detector (ELSD) [47] is based on the ability of fine particulate matter of a solute to scatter light. To obtain suitable analyte particles, the column effluent is nebulized by an inert gas in the nebulizer and aerosol droplets are allowed to evaporate in the drift tube. Droplet size is related to mobile phase properties (surface tension, density, and viscosity). Usually, high solvent-to-gas flow ratio provides the best sensitivity because it produces the largest droplet diameters. 

The use of surfactants to modify the surface tension of an aerosol and alter its droplet size distribution has shown that their influence depends strongly on the characteristics of the solution to be aerosoled. The span, defined as 90% undersize —10% undersize/50% undersize, gives a measure of the width of the volume distribution relative to the median diameter of the droplets formed in the aerosoling process. Comparative studies performed with commercial air-jet and US nebulizers have shown that, under similar working conditions, the latter provide less heterodispersed aerosols, with span values ranging from 1.50 to 1.75, which are similar for aqueous drug solutions in the presence and absence of surfactants [156]. 

As with jet nebulizers and pMDIs, the formulation characteristics include liquid density, surface tension, viscosity, and vapor pressure. Many of these that effect nebulizer performance of formulation properties are described in the above equation. The configuration... 

Newman, S.P. Pellow, P.G.D. Clarke, S.W. Dropsizes from medical atomisers (nebulizer) for drug solution with different viscosities and surface tensions. Atomization Spray Technol. 1987, 3, 1-11. 

ESI nebulization is the result of charging a liquid at a needle tip by applying a high potential (ca. 3 kV), between the needle and a nearby counter electrode. The formation of the aerosol depends on the competition between coulomb repulsion and surface tension. Stable nebulization strongly depends on experimental parameters such as the potential difference applied, the inner and outer diameter as well as the shape of the needle, and the composition of the liquid sprayed. 

Eq. 1 predicts that the average droplet size depends on the gas and solvent flow rate. It also predicts that the average droplet size will depend on the namre of the solvent, because of the dependency on the density, surface tension, and viscosity of the nebulized liquid. The initial droplet size formed in the nebuhzer has little to do with the property of the analyte as it predominantly contains mobile phase. The final droplet size in the scattering chamber is dependent on the analyte concentration. When optimizing detector conditions, the experimental parameters that can be adjusted are nebulizer gas flow rate, mobile phase flow rate, and drift mbe temperature. 

Nonspectral interferences are either nonspecific or specific. Nonspecific interferences affect the nebulization by altering the viscosity, surface tension, or density of the analyte solution, and consequently the sample flow rate. Certain contaminants also decrease the desolvation and atomization efficiency by lowering the atomizer temperature. Specific interferences are also called chemical interferences because they are more analyte dependent. Solute volatilization inter-... 

Mobile-phase volatility is required in API LC/MS due to the need to produce gas-phase ions, whether through electrospray or chemical ionization. Atmospheric pressure chemical ionization can require higher solvent gas-phase volatility than electrospray due to its ionization mechanism. Low-surface-tension solvents also perform better due to improved nebulization properties [44-46]. Solvents such... 

Physical interferences may arise from incomplete volatilization and occur especially in the case of strongly reducing flames. In steel analysis, the depression of the Cr and Mo signals as a result of an excess of Fe is well known. It can be reduced by adding NH4C1. Further interferences are related to nebulization effects and arise from the influence of the concentration of acids and salts on the viscosity, the density and the surface tension of the analyte solutions. Changes in physical properties from one sample solution to another influence the aerosol formation efficiencies and the aerosol droplet size distribution, as discussed earlier. However, related changes of the nebulizer gas flows also influence the residence time of the particles in the flame. 

Nebulizer formulations are normally solutions, but suspensions (particle size of less than 2 (jim) are also used. Important preformulation considerations include stability, solubility, viscosity, and surface tension of the solution of suspension. 

Nebulizer formulations are normally solutions, however, suspensions are also used, e.g., the insoluble steroid budesonide has been successfully formulated for delivery by nebulization (Dahlback 1994). Some important preformulation considerations for nebulizers are stability, solubility, viscosity and surface tension (McCallion et al. 1996 Nikander 1997). In terms of solubility, the common ion effect may be important where, e.g., a hydrochloride salt is to be dissolved in saline. In addition, the temperature dependence of the solubility of the drug may... 

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