Ultrasonic nebulizer designs

To accommodate smaller liquid flows of about 10 pl/min, micro-ultrasonic nebulizers have been designed. Although basically similar in operation to standard ultrasonic nebulizers, in these micro varieties, the end of a very-small-diameter capillary, through which is pumped the sample solution, is in contact with the surface of the transducer. This arrangement produces a thin stream of solution that runs down and across the center of the face of the transducer. The stream of sample... 

Five basic nebulizer designs, known to be used on ICP systems are cross flow, concentric, flow shear, ultrasonic, and FAA. The cross flow and concentric designs are most commonly supplied with commercial systems. FAA nebulizers were supplied with early multi-element systems and there are some commercial suppliers who provide ultrasonic nebulizers. 

Nebulizers are designed primarily for the atomization of aqueous formulations either as solutions or suspensions, and typically contain additional excipients. These systems are nonpressurized formulations and do not contain propellants. Traditionally, nebulizers operated using one of two basic mechanisms jet nebulization or ultrasonic nebulization. Jet nebulizers (Fig. 3) function using the Venturi effect to... 

Ra determination in environmental samples (highly saline thermal waters) by ICP-QMS with ultrasonic nebulization has been described by several working groups. Radium was preconcentrated and isolated from the matrix elements by selective extraction using a radium specific solid phase extraction membrane disk designed for radioactive counting methods as proposed by... 

Except for a few laboratory-made units and some devices marketed by other firms, most applications of ultrasonic nebulization (USNn) in atomic spectrometry have been developed with two commeroial devioes from CETAC Technologies viz. the U-5000AT+ and U-6000AT+). It should be noted that these two commercial ultrasonic devices were originally designed for ICP instruments but have been used with other types of detectors [20]. 

Table 1 Design features of ultrasonic nebulizers determining particle size distribution and mass output...

A basic understanding of the nebulizer function and the types of nebulizers is necessary to successfully interface CE to the ICP-MS. Nebulization, as previously described, is the process to form an aerosol, i.e., to suspend a liquid sample into a gas in the form of a cloud of droplets. The quality of any nebulizer is based on many different parameters including mean droplet diameter, droplet size distribution, span of droplet size distribution, droplet number density, and droplet mean velocity. There are numerous nebulizers commercially available for the use with ICP-MS systems, and their detailed description can be found elsewhere.Pneumatic designs, both concentric and cross flow, are the most popular for CE interfaces with the occasional use of the ultrasonic nebulizer (USN). Figure 2 shows some typical nebulizers. The pneumatic nebulizer is either a concentric design (Fig. 2A), where both the gas stream and the liquid flow in... 

An ultrasonic nebulizer has been designed and used for inductively coupled plasma atomic emission spectrometry [60] and microwave induced plasma-atomic emission spectrometry [61]. The apparatus is inexpensive and can be operated conveniently. Using this nebulizer, the detection limits of many elements, such as phosphorus, aluminum, and silver, were much reduced compared with the limits obtained using an aerodynamic nebulizer [62-64], The ultrasonic nebulizer was found to be suitable for samples which have a high salt concentration. 

Dennis JH. Drug nebulizer design and performance breath-enhanced jet vs constant output jet vs ultrasonic. J Aerosol Med 1995 8(3) 277-280. 

The most commonly used nebulizer designs are pneumatic and ultrasonic, although other types (electrostatic, jet impact, and mono-dispersive generators) have been described. The selection of the appropriate nebulizer depends upon the characteristics of the... 

Many designs of nebulizer are commonly used in ICP/MS, but their construction and mode of operation can be collated into a small number of groups pneumatic, ultrasonic, thermospray, APCI, and electrospray. These different types are discussed in the following sections, which are followed by further sections on spray and desolvation chambers. 

Nebulizers are used to introduce analyte solutions as an aerosol spray into a mass spectrometer. For use with plasma torches, it is necessary to produce a fine spray and to remove as much solvent as possible before the aerosol reaches the flame of the torch. Various designs of nebulizer are available, but most work on the principle of interacting gas and liquid streams or the use of ultrasonic devices to cause droplet formation. For nebulization applications in thermospray, APCI, and electrospray, see Chapters 8 and 11. 

There is a very wide range of designs for nebulizers, but most are based on some form of gas/liquid sprayer or on ultrasonics. 

This may be either a continuous process, used when the sample size is relatively large (1 ml or more), or a discrete process, used with samples of less than 20 /il. Continuous-flow systems are simpler to use and more precise, but they are less sensitive. They employ a nebulizer in association with a flame or gas plasma, and either a rotating electrode (Rotrode) or drip-feed to the electrode with the arc or spark. The pneumatic nebulizer has an efficiency of 5-10% and generates an inhomogeneous aerosol. Efiiciency can be improved by proper design of the nebulizer and spray chamber (N4), by use of heated nebulizer gas (R6) or ultrasonic devices (S23). The maximum improvement is a 5- to 10-fold increase in sensitivity. There is also an increase in the complexity and cost of the instrument which usually offsets these benefits. The effect... 

The specific design of the various sample introduction devices or spray probes depends to a large extent on the technique applied, i.e., ESI, APCI, or other. With respect to ESI, systems have been described for conventional pure ESI, pneumatically-assisted ESI or ionspray, ultrasonically-assisted ESI, thermally-assisted ESI, and micro- and nano-ESI (Ch. 5.5). The heated-nebulizer system (Ch. 5.6.2) is used in APCI and atmospheric-pressure photoionization (APPI). 

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