Nebulizer charge

Marcel Dekker, Inc. 270 Madison Avenue. New York, New York 10016 

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Nebulization ionization is the process involved in the analyte ionization in thermospray [16] and electrospray [17] interfacing. No primary ionization, i.e., a filament or a discharge electrode, is applied. The ionization mechanism is not fully understood (Ch. 6.3). The general understanding can be snmmarized as follows Upon nebulization, charged droplets of a few pm ID are generated. The fate of these droplets is determined by a nnmber of competing processes, the relative importance of which may dependent on the natnre of the analyte ... 

Figure 5 Inhaled mass of nebulized pentamidine as a percentage of the nebulizer charge for two commercially available nebulizers (AeroTech II CIS-US, Bedford, MA, and Respirgard II Marquest, Englewood, CO) plotted against time. (From Ref. 9.)...

For the same pattern of breathing, the quantity of aerosol inhaled over time is strongly dependent on the type of nebulizer utilized. As shown in Fig. 5, the AeroTech II produces aerosol at a rate approximately six times that of the Respirgard II (the difference in slopes). The plateau of each curve indicates the point at which the nebulizer runs dry and defines the amount of drug inhaled by the patient. For the AeroTech II, approximately 20% of the nebulizer charge is ultimately inhaled, versus 11% for the Respirgard II (9). 

Additional ionization is effected by including radioactive substances or plasma or glow discharges in the evaporation chamber or by electrical charging of the nebulizer. Such techniques are also discussed in Chapters 8 and 11. 

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. 

In general terms, PETN can be characterized as a sensitive , brisant, and powerful high expl. Explosive sensitivity is a rather nebulous quantity, but there can be no doubt that PETN is a much more sensitive material than TNT, but rather less sensitive than Lead Azide. In particular, PETN requires very little priming i charge (less than 1 mg LA) to initiate its detonation. This is the characteristic that makes PETN so widely used in blasting cap base charges, in detonating cord and in boosters... 

In APCI, droplets are generated by a combination of heat and a nebulizing gas. While the analytes are embedded in a droplet, and thus protected to some extent from the heat, many thermally labile materials are decomposed. In addition, ionization occurs mainly by ion-molecule reactions and yields predominantly singly charged ions. If, therefore, compounds do not undergo thermal degradation, a mass spectrometer with extended mass range would be required to detect any ions formed. 

ICP-AES was validated for the simultaneous determination of Al, B, Ba, Be, Cd, Co, Cr, Cu, Fe, Li, Mn, Ni, Pb, Se, Sr and Zn in human serum in a clinical laboratory. The samples underwent digestion and yttrium was used as an internal standard. The LOD were as follows 0.002-0.003 (xM for Ba, Cd, Mn and Sr 0.014-0.07 (xM for Be, Co, Cr, Cu, Fe, Li, Ni, Pb and Zn and 0.2-0.9 (xM for Al, B and Se. The concentrations of Al, Be and Co in human serum were found to be above the LOD, while those of Cd, Cr, Ni and Pb were below the LOQ however, in case of acute intoxication with the latter elements the method is valid . Matrix effects were evaluated for ICP-AES analysis using solution nebulization and laser ablation (LA) techniques. The main matrix-related interferences stem from elements with a low second ionization potential however, these are drastically reduced when pure He is used as carrier gas. This points to Ar (the usual carrier) participation in the interference mechanism, probably by interacting with doubly charged species. ... 

In IC-MS systems, the core of the equipment is the interface. In fact, inside the interface evaporation of the liquid, ionization of neutral species to charged species and removal of a huge amount of mobile phase to keep the vacuum conditions required from the mass analyzer take place. Two main interfaces are used coupled to IC, namely electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI). In the ESI mode, ions are produced by evaporation of charged droplets obtained through spraying and an electrical field, whilst in the APCI mode the spray created by a pneumatic nebulizer is directed towards a heated region (400°C-550°C) in which desolvation and vaporization take place. The eluent vapors are ionized by the corona effect (the partial discharge... 

A promising detection principle utilizes similar nebulization procedure as applied in ELS, namely the corona-charged aerosol detectors, CAD. In CAD, the aerosol particles interact with an ionized gas (usually nitrogen). The particles become charged and electrically detected [294]. It has been shown that the response of CAD does not depend on the nature of analyte. On the other hand, the size of the aerosol depends on the mobile phase composition and it has to be calibrated. 

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