Frit nebulizers

The aim of breaking up a thin film of liquid into an aerosol by a cross flow of gas has been developed with frits, which are essentially a means of supporting a film of liquid on a porous surface. As the liquid flows onto one surface of the frit (frequently made from glass), argon gas is forced through from the undersurface (Figure 19.16). Where the gas meets the liquid film, the latter is dispersed into an aerosol and is carried as usual toward the plasma flame. There have been several designs of frit nebulizers, but all work in a similar fashion. Mean droplet diameters are approximately 100 nm, and over 90% of the liquid sample can be transported to the flame. 

There are problems in use of the frit nebulizer. Memory effects tend to be severe, and each sample needs to be followed by several wash-outs with clean solvent before the pores of the frit become free of residual sample. Biological samples frequently contain detergent-like materials, and... 

Flow injection techniques can be used to inject sample volumes as small as 10 jiL into a flowing stream of water with little degradation of detection limits. Frit nebulizers have efficiencies as high as 94% and can be operated with as litde as 2 jiL of sample solution. 

The introduction of liquid samples into the LP-ICP-MS has been shown to be feasible [115]. A glass frit nebulizer may be used along with desolvation to improve analyte signal stability. To date, however, no speciation studies using such a system have been performed. 

Fig. 46. Demountable thimble frit nebulizer and its spray chamber (not drawn to scale). (Reprinted with permission from Ref. [120].)...

Layman L. R. and Lichte F. E. (1982) Glass frit nebulizer for atomic spectrometry, Anal Chem 54 638-642. 

Liu H., Clifford R. H., Dolan S. P. and Montaser A. (1996) Investigation of a high-efficiency nebulizer and a thimble glass frit nebulizer for elemental analysis of biological materials by inductively coupled... 

Frit-type nebulizer The concentric and cross-flow nebulizers are inefficient at the 1 mL min i flow rate at which they usually operate, producing only about 1% of droplets of the correct size to pass into the plasma. An alternative design is the frit nebulizer, which produces droplets with a mean size of 1 Xm. The glass frit nebulizer is depicted schematically in Figure 6. The sample flows over the fritted glass disc as the nebulizing gas is passed through the frit. This... 

Figure 6 Glass frit nebulizer schematic. Reprint permission from Ingle JD and Crouch SR (1988) Spectrochemical Analysis. p. 193, Figure 7-5. Englewood Cliffs, NJ Prentice Hall.

M. Ibrahim, W Nisamaneepong, and J. Caruso. Microcolumn high pressure liquid chromatography with a glass-frit nebulizer interface for plasma emission detection. J. Chrom. Sd., 23, 144 (1985). 

Pneumatic nebulization of liquids is based on the viscous drag forces of a gas flow passing over a liquid surface and entraining parts of the liquid, by which small independent droplets are produced. This may occur when the liquid is forced through a capillary tube and at the exit the gas then flows concentrically around the tube or perpendicularly with respect to the liquid stream. A frit can also be used, which is continuously wetted and through which the gas passes. 

In the pneumatic nebulizers used in atomic spectrometry, the liquid flow is usually of the order of 1 to a few mL/min and the full efficiency of the nebulizer (a few %) can actually be realized at gas flows of 2 L/min. However, even with gas flows below 2 L/min, droplet diameters as low as about 10 pm and injection velocities below about 10 m/ s are obtained. Pneumatic nebulization can be realized with a number of types of nebulizers. For flame emission and atomic absorption as well as for plasma spectrometry, they include concentric nebulizers, so-called cross-flow nebulizers, Babington nebulizers and fritted-disk nebulizers (Fig. 40) [95]. 

FIGURE 8-11 Types of pneumatic nebulizers (a) concentric tube, (b) cross-flow, (c) fritted disk, (d) Babington. 

A) Concentric glass nebulizer [741 B) Cross-flow nebulizer C) Babinglon nebulizer D) Fritted-disk nebulizer... 

Fritted-disk nebulizers have high nebulization efficiencies and low sample consumption (down to 0,1-0.5 mL/min). They are especially useful for plasma spectrometry of organic solutions, or for coupling with liquid chromatography [77]. However, in comparison with other typtes of nebulizer they suffer from memory effects rinsing times are much higher than the 10-20 s required for the other pneumatic nebulizers. 

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