Cross flow nebulizer

The drop in pressure when a stream of gas or liquid flows over a surface can be estimated from the given approximate formula if viscosity effects are ignored. The example calculation reveals that, with the sorts of gas flows common in a concentric-tube nebulizer, the liquid (the sample solution) at the end of the innermost tube is subjected to a partial vacuum of about 0.3 atm. This vacuum causes the liquid to lift out of the capillary, where it meets the flowing gas stream and is broken into an aerosol. For cross-flow nebulizers, the vacuum created depends critically on the alignment of the gas and liquid flows but, as a maximum, it can be estimated from the given formula. 

Using Poiseuille s formula, the calculation shows that for concentric-tube nebulizers, with dimension.s similar to those in use for ICP/MS, the reduced pressure arising from the relative linear velocity of gas and liquid causes the sample solution to be pulled from the end of the inner capillary tube. It can be estimated that the rate at which a sample passes through the inner capillary will be about 0.7 ml/min. For cross-flow nebulizers, the flows are similar once the gas and liquid stream intersection has been optimized. 

The flows of gas and liquid need not be concentric for aerosol formation and, indeed, the two flows could meet at any angle. In the cross-flow nebulizers, the flows of gas and sample solution are approximately at right angles to each other. In the simplest arrangement (Figure 19.11), a vertical capillary tube carries the sample solution. A stream of gas from a second capillary is blown across this vertical tube and creates a partial vacuum, so some sample solution lifts above the top of the capillary. There, the fast-flowing gas stream breaks down the thin film of sample... 

Nebulizers — Nebulizers of existing systems have been the object of extensive controversy. An ICP nebulizer can be the source of serious problems, if either the nebulizer or sample solutions are not treated properly, since most ICP nebulizers are fragile and easily clogged by excessive amounts of undissolved matter. However, the failure rate of the cross flow nebulizer is no greater than that of most FAA nebulizers. (This is... 

The application of the cross flow nebulizer to ICP-AES was first described by... 

The commonest form of sample introduction is by means of an aerosol generated using a pneumatic nebulizer. Several types of nebulizer can be used. All-glass concentric nebulizers (Fig. 4.7a) operate in a similar manner to those used for FAAS. Cross-flow nebulizers (Fig. 4.7b) operate by directing a high-velocity stream of gas across the mouth of a capillary... 

The principal methods of interfacing SFC with ICP-MS have been discussed by Carey and Caruso [94]. Where packed SFC columns are used, the SFC restrictor is connected to a heated cross flow nebulizer and the nebulizer gas flow carries the sample to the plasma. For the more commonly used capillary columns, the SFC restrictor is passed through a heated transfer line that is connected directly to the torch of the ICP-MS. For optimal resolution of peaks, the restrictor should be positioned so that it is level with the injector of the ICP torch. This position may be varied slightly (Fig. 10.15). Heat is applied where the transfer line and torch connect to prevent freezing of the mobile phase when it decompresses after exiting the restrictor. To transport the analyte to the plasma efficiently, a gas flow of approximately 0.8-1.0 mL/min is used. This gas flow may also be heated to improve peak resolution. 

The elements Al, Mn, and Sr were determined by means of a Perkin-Elmer Optima 4300DV inductively coupled plasma emission spectrometry (ICP-AES) instrument (axial mode), equipped with an AS-90 Plus autosampler, a cross-flow nebulizer, and a Scott-type spray chamber in Ryton. The instrumental operating parameters are listed in Table 10.1. 

To quantify the trace elements of interest plasma-based techniques were used, namely (i) ICP-AES using an Optima 3100 instrument (Perkin-Elmer, Norwalk, CT, USA) equipped with a cross-flow nebulizer and a Ryton Scott spray chamber (ii) Dynamic Reaction Cell (DRC) Q-ICP-MS using an Elan 6100 spectrometer (PerkinElmer, Norwalk, CT, USA) equipped with a quartz cross-flow Meinhard nebulizer and a cyclonic spray chamber (iii) SF-ICP-MS using an Elementl (ThermoElectron, Bremen, Germany) with a pneumatic nebulizer and a Ryton Scott spray chamber. 

Unlike some published studies [47], the authors of this chapter have found that the different As species give similar mass counts when analyzed by ICP-MS using a cross-flow nebulizer. 

B. Gammelgaard, O. Jons, Comparison of an ultrasonic nebulizer with cross-flow nebulizer for selenium speciation by ion-chromatography and inductively coupled plasma mass spectrometry, J. Anal. Atom. Spectrom., 15 (2000), 499-505. 

For many years pneumatic nebulizers of the V-groove, Meinhard and cross-flow type have been the most widely used sample insertion devices for aerosol generation. The interaction geometry between the gas and liquid sample streams allows pneumatic nebulizers to be classified into two major groups, namely (a) pneumatic concentric nebulizers, which involve concentric interaction and (b) cross-flow nebulizers, which involve perpendicular interaction between the liquid and gas streams. Pneumatic nebulizers are well established and widely used on account of their simplicity, robustness, ease of use and low cost however, they provide low transport efficiency and tend to be clogged by high salt-content solutions [4]. 

Fig. 2 (A) The concentric nebulizer (B) The cross-flow nebulizer (C) The ultrasonic nebulizer (USN) (D) The microconcentric...

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]. 

Fig. 40. Pneumatic nebulizers for plasma spectrometry. A concentric glass nebulizer, B cross-flow nebulizer, C Babington nebulizer, D fritted-disk nebulizer. (Reprinted with permission from Ref. [95].)...

A cross-flow nebulizer for dc arc solution and AAS work was described by Valente and Schrenk [113]. For ICP work the nebulizer should have capillaries with diameters < 0.2 mm and a distance of 0.05-0.5 mm between the tips. The capillaries also can be made of metal, glass or plastic and they have similar characteristics to the concentric nebulizer. Types made of Ryton for example enable the aspiration of solutions containing higher concentrations of HF. Then aerosol gas flows are around 1-2 L/min at 2-5 bar. This has been confirmed by optimization measurements described by Fujishiro et al. [114]. They found that by varying the inside and the outside diameters of the capillary from 0.15 to 0.9 mm and from 0.5 to 1.5 mm, respectively, the pressure drop across the sample tube decreases from 150 to 50 mbar. By increasing the gas flow from 0.75 to 1.75 L/min, the pressure drop across the sample tube was found to increase from 150 to 350 mbar. As shown in Fig. 43 [114], the variations in the drops in pressure considerably influence the droplet size. 

Fig. 43. Influence of pressure decrease across the sample tube of a cross-flow nebulizer on droplet size distribution. Pressure decrease ( ) 95 mm H20, (o) 250 mm H20. (Reprinted with permission from Ref. [114].)...

Fig. 49. Particle size distributions of pneumatic nebulizers for ICP. MAK, high-pressure cross-flow nebulizer CGN, concentric glass nebulizer JAB, Jarrell—Ash Babington nebulizer JAC, Jarrell—.Ash fixed cross-flow nebulizer (Reprinted with permission from Ref. [139].)...

Maximum dissolved solids nebulizers [111] are usually cross-flow nebulizers operated at a high pressure. They are often made from PTFE, including the capillaries, and thus can be used for work with HF containing solutions. In this case a nebulization chamber made of PTFE and an ICP torch with an internal tube made of AI2O3 ceramics or BN should be used. 

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