Heating droplet

Nf = hqiiid-phase transfer units [Eq. (14-173)] k = hqiiid thermal conductivity p = hqiiid density Cp = hqiiid specific heat = droplet diameter t = time of contact... 

Zhang, B., McDonald, C. and Li, L. (2004) Combining liquid chromatography with MALDI mass spectrometry using a heated droplet interface. Anal. Chem. 76, 992-1001. 

The currently most frequently applied method for LC-MALDI-MS is automated post-column fractionation and on-plate collection in discrete spots of the LC colunm effluent. After the solvent is evaporated, the matrix solution can be added, and MALDI-MS analysis of the various spots can be performed. The procedure requires a liquid-handling robot, capable of disposition of effluent fractions at discrete spots on the MALDI target. A number of ways were proposed for deposition in discrete spots on the MALDI target, e.g., blotting via direct contact between droplet and target [139-140], piezoelectric flow-through microdispensing [141], pulsed electrical-mediated droplet deposition [142], and a heated droplet interface [143], Commercial LC-MALDI-MS devices were recently reviewed [144],... 

Warm droplets release the heat and the moisture into the local flowing air surrounding. The further transportation of these substances is governed by Eqs. (3.53). The problem consists now in the determination of the droplet temperature t. We start from the equation of the heat droplet balance between the change in the individual droplet thermal energy and its removal by the heat exchange and evaporation... 

The thermospray interface can be used in various modes of ionization, depending on the settings of experimental parameters and the choice of the solvent composition. The thermospray nebulization process provides for a rapid and efficient means to partially evaporate the solvent mixtures introduced into the system by means of the production of small heated droplets. For clarity of the discussion, four ionization modes are distinguished here, i.e. two electron-initiated modes and two liquid-based ionization modes. 

In a thermospray interface (Figure 3B), the column effluent is rapidly heated in a narrow bore capillary such that partial (ca. 90%) evaporation of the solvent is achieved inside the capillary. As a result, a mist of vapour and small droplets is formed in which the heated droplets further evaporate and ions are generated, either by the thermospray ionization process based on ion evaporation or by solvent-mediated chemical ionization initiated by electrons from a heated filament or a discharge electrode. The excess vapour is pumped away directly from the ion source. 

Dropping point for greases NFT 60-102 ISO 2176 ASTM D 566 Heating up to the fail of the first droplet... 

The simplest desolvation chambers consist simply of a tube heated to about 150°C through which the spray of droplets passes. During passage through this heated region, solvent evaporates rapidly from the droplets and forms vapor. The mixed vapor and residual small droplets or particulates of sample matter are swept by argon through a second cooled tube, which allows vapor to... 

A second form of desolvation chamber relies on diffusion of small vapor molecules through pores in a Teflon membrane in preference to the much larger droplets (molecular agglomerations), which are held back. These devices have proved popular with thermospray and ultrasonic nebulizers, both of which produce large quantities of solvent and droplets in a short space of time. Bundles of heated hollow polyimide or Naflon fibers have been introduced as short, high-surface-area membranes for efficient desolvation. 

The various heating methods produce a vapor that is a mixture of gas, very small droplets, and small particles of solid matter (particulates). Before droplets or particulates can coalesce, the whole vapor is swept into the plasma flame for analysis. Clearly, the closer the heating source is... 

Suffice it to say at this stage that the surfaces of most solids subjected to such laser heating will be heated rapidly to very high temperatures and will vaporize as a mix of gas, molten droplets, and small particulate matter. For ICP/MS, it is then only necessary to sweep the ablated aerosol into the plasma flame using a flow of argon gas this is the basis of an ablation cell. It is usual to include a TV monitor and small camera to view the sample and to help direct the laser beam to where it is needed on the surface of the sample. 

Having removed the larger droplets, it may remain only to encourage natural evaporation of solvent from the remaining small droplets by use of a desolvation chamber. In this chamber, the droplets are heated to temperatures up to about 150 C, often through use of infrared heaters. The extra heat causes rapid desolvation of the droplets, which frequently dry out completely to leave the analyte as small particles that are swept by the argon flow into the flame. 

Some of the droplets cany an excess of positive electric charge and others an excess of negative electric charge. The spray or stream of droplets is passed along a tube that is usually heated. 

As the name implies, thermospray uses heat to produce a spray of fine droplets. Plasmaspray does not produce the spray by using a plasma but, rather, the droplets are produced in a thermospray source and a plasma or corona is used afterward to increase the number of ions produced. 

The strong localized heating causes the liquid to vaporize very rapidly, forming a supersonic jet that leaves the end of the capillary as a mist of fine droplets mixed with vapor. 

A sample to be examined by thermospray is passed as a solution in a solvent (made up separately or issuing from a liquid chromatographic column) through a capillary tube that is strongly heated at its end, so the solution vaporizes and emerges as a spray or mist of droplets. As the droplets... 

The flow of droplets enters an evaporation chamber that is heated sufficiently to prevent condensation. 

The large quantities of solvent vapor produced from the evaporating droplets must be removed before reaching the plasma flame, which is done by having cooling tubes sited after the heated desolvation chamber to condense the vapor into liquid. This condensed liquid is run to waste. 

In a suspension polymerisation monomer is suspended in water as 0.1—5-mm droplets, stabilised by protective coUoids or suspending agents. Polymerisation is initiated by a monomer-soluble initiator and takes place within the monomer droplets. The water serves as both the dispersion medium and a heat-transfer agent. Particle sise is controlled primarily by the rate of agitation and the concentration and type of suspending aids. The polymer is obtained as small beads about 0.1—5 mm in diameter, which are isolated by filtration or centrifugation. 

If condensation requires gas stream cooling of more than 40—50°C, the rate of heat transfer may appreciably exceed the rate of mass transfer and a condensate fog may form. Fog seldom occurs in direct-contact condensers because of the close proximity of the bulk of the gas to the cold-Hquid droplets. When fog formation is unavoidable, it may be removed with a high efficiency mist collector designed for 0.5—5-p.m droplets. Collectors using Brownian diffusion are usually quite economical. If atmospheric condensation and a visible plume are to be avoided, the condenser must cool the gas sufftciendy to preclude further condensation in the atmosphere. 

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